key: cord-0044593-rdhuc2n2
authors: Anderson, Nancy L.
title: Pet Rodents
date: 2009-05-15
journal: Saunders Manual of Small Animal Practice
DOI: 10.1016/b0-72-160422-6/50179-0
sha: 2e712958409321618cd47155982fceb5b51eb808
doc_id: 44593
cord_uid: rdhuc2n2

nan

Many small rodents are commonly kept for companionship and enjoyment. This chapter provides information needed to diagnose and treat the most frequently encountered problems of mice, rats, gerbils, hamsters, guinea pigs, and chinchillas.

• Cages should be made of stainless steel, hard plastic, or glass. These materials are cleaned and sanitized easily and are resistant to gnawing or corrosion from urine and fecal matter. Minimum floor space and height requirements are listed for each species in • Guinea pigs can be housed in open-topped enclosures with walls higher than 10 inches. Ensure that dogs, cats, wild animals, and small children do not have unsupervised access to these cages.

• Clean cages as needed, usually 1 to 3 times per week for most rodents. A scrub brush, dish soap, and water work well. If cages are not kept clean, ammonia, other irritants, moisture, and bacteria concentrations rise to harmful levels, predisposing animals to disease.

• Disinfect the cage twice a month with 1 part sodium hypochlorite (household bleach) mixed in 30 parts water. Let the bleach solution stand for at least 15 minutes. Rinse the cage well afterward.

• All solid-floored cages need to be covered in bedding.

Shredded paper, non-resinous wood shavings, wood wool, and corn cobs are all acceptable. Provide at least 2 inches of bedding. Most rodents enjoy burrowing in deeper bedding when it is provided in one corner of a cage. Do not, however, fill the entire cage with deeper bedding. This usually leads to poor sanitation as a result of owners' failure to recognize buildup of hidden wastes such as moisture from leaking water bottles, cached foods, urine, and feces.

• Wire mesh floors can be used successfully only if the dimension of the mesh is correct. Size the openings to be just large enough for an adult to retract a tarsal joint back through the mesh. Larger holes make it difficult for the animals to walk and cause pressure sores. Smaller openings may cause injuries such as tibial fractures and self-mutilation while struggling to free trapped appendages. Bedding above the wire keeps waste from dropping through the wire and therefore is not recommended. Wire bottom cages do not work well for breeding animals because neonatal rodents must be surrounded by nesting material to maintain moisture in the nest and prevent dehydration. Young rodents often cannot walk correctly on mesh sized for adult feet.

• All pet rodents require visual security. Tubes, jars, or cans made of nontoxic, nonabrasive substances work well for this purpose. Also provide objects for gnawing. Rodents possess open-rooted teeth, and constant wear is necessary to maintain normal dentition. Mice, rats, gerbils, and hamsters enjoy and benefit from exercise wheels.

• A good room temperature range for most pocket pets is 70°F to 75°F. Keep rodents with disease at 85°F to 90°F unless hyperthermia is of concern (some chinchillas).

• Provide 10 to 12 hours of darkness to 12 to 14 hours of light. This light cycle is essential if breeding is desired.

• Hamsters, guinea pigs, and chinchillas that are exposed to temperatures below 65°F may hibernate for a few days or until the ambient temperature rises. Heart rates may be less than 5 bpm during hibernation.

M Key Point Feed pet rodents laboratory animal chow appropriate for their species (Table 177 -2). Seed diets are deficient in protein and contain excessive fat.

• Seeds, as well as vegetables and other foods, may be fed as treats but not to provide more than 15% of calories. Intermittent exposure to vegetables and seeds causes mild, transient diarrhea.

• Supplementation of vitamin C is recommended for all guinea pigs.

• Adult chinchillas that are not obese should be fed high quality, fresh grass hay ad libitum. Obese animals may need to have the hay rationed. Chinchillas require 1 / 8 to 1 / 4 -cup of fresh pellets per animal each day. Feeding pellets free choice leads to obesity, and the high protein and calcium levels in these diets may predispose animals to urinary tract disease. Most pellets also do not provide sufficient fiber to maintain normal gastrointestinal (GI) motility.

• Store food in tightly sealed containers at less than 60°F; keep food refrigerated if possible.

• Feed all diets within 90 days of milling to ensure the highest nutritional value. Encourage owners to check dates on packages and ask pet store managers about providing dates on bulk items.

• If possible, feed pet rodents except guinea pigs from overhead racks. These devices reduce wastage and eliminate fecal contamination of food. Covered hoppers, heavy crocks, or stainless steel bowls that are attached to the side of the cage to eliminate spillage are acceptable and recommended for guinea pigs.

• Feed breeding females and their litters from the floor of their cages until the young are large enough to reach overhead feeders or crawl in and out of crocks.

• Cannibalism of neonates commonly occurs as the result of stress associated with cage cleaning. To minimize cannibalism, clean the cage and provide a 10to 13-day food supply 1 to 2 days before parturition.

M Key Point Provide fresh water in clean containers daily.

• Do not provide water in open crocks. These are contaminated or spilled easily and are a common cause of dehydration and poor sanitation. • Sipper tubes and water bottles work well. Clean with dish soap and water daily and disinfect them weekly. Guinea pigs expel food from their mouths into their sipper tubes, so more frequent cleaning is needed.

• Some water bottles have special valves to minimize backflow. Supplement guinea pigs' water daily with 200 mg vitamin C/L. If the water is not dechlorinated, it will inactivate the vitamin C.

Quarantine all newly acquired animals in a different room from current pets for a minimum of 30 days. Feed and handle quarantined animals last. Recommend that caretakers wash their hands and change clothes before handling current pets. Avoid the introduction of adult animals because this frequently results in fighting. Instead, place animals together while young and allow them to mature together. Avoid keeping more than one male per cage because this also usually leads to fighting.

A systematic history and physical examination are mandatory. Many disease syndromes are caused by poor husbandry. Pets that have been kept isolated from other rodents or acquired from a private breeder are less likely to harbor infectious disease than animals obtained from a pet store, laboratory, or wholesaler. See Table 177 -3 for normal physiologic data.

Obtain the following information: • Observe the pet in its cage for mentation, activity, locomotion, dyspnea, head posture, haircoat, and any grossly observable abnormalities.

• Note respiratory and heart rates before restraint when possible. Observe the condition of cagemates.

M Key Point If dyspnea or severe depression is detected, warn the owner that the animal is critically ill and could die of stress brought on by an examination.

• Handle such animals as little as possible. Initially, treat severely ill animals symptomatically, then 

• Note the type of diet and bedding as well as the level of sanitation and compare these with what was described in the history.

• Observe quantity and quality of feces and urine. Diarrhea, soft stools, absence of stools, copious urine, and discolored urine all can be signs of illness.

• Coprophagy is a normal behavior in rodents.

• Check the diet and water supply for freshness, quantity, source, and accessibility.

• Evaluate the presence and suitability of cage furniture. Adequate visual security and the ability to exercise and gnaw are extremely important.

• An accurate weight in grams is extremely important for evaluating an animal's body condition, calculating drug dosages, and monitoring treatment. The easiest method of weighing a pet rodent is to place it in a box and then subtract the weight of the container.

• Restraint of pet rodents is easy with experience. Pets that have been handled frequently and gently by the owners require only minimal restraint. Gentle pressure directs the animal as needed. Grasp less cooperative patients (except chinchillas and guinea pigs) by the scruff over the back of the neck with thumb and forefinger ( Fig. 177-1) . Take care to pinch enough skin to prevent the animal from turning around, yet leave enough slack for respiration. On smaller specimens, hold the base of the tail, if present, between the fourth and fifth fingers to provide additional restraint.

• Hold docile guinea pigs with the palm of one hand supporting the chest while the other hand supports the hind quarters ( Fig. 177 -2). Place the thumb and forefinger of the first hand in the axillas for additional control.

• Take care to minimize damage to the fur when handling chinchillas because they lose hair easily. Grasp the animal by the tail and scoop it up into the palm of the same hand ( Fig. 177-3 ). If necessary, grasp the thorax just behind the axillas.

• Calm uncooperative rodents by placing an appropriately sized towel over the head. Complete the physical examination by wrapping the patient in a towel and exposing only needed areas. Even oral, ophthalmic, and aural examinations can be performed with minimal effort if the animal is given the chance to relax in the towel "burrow."

• Remove particularly aggressive patients from their cages by scooping them up in a can or bucket; then slide them out onto a slick surface and pick them up or transfer them to a holding area or scale. M Key Point Lift the hind quarters of mice and rats by the base of their tails to facilitate scruffing. Never use the tip of the tail for restraint, or the skin of the tail may slough.

Once the animal is restrained properly, examine the head. Assess the cranial nerves. Check the nose for presence and character of discharge. Examine the mouth for ptyalism, swelling, overgrown incisors, or discharges. To inspect the oral cavity, place an avian speculum across the mouth just caudal to the incisors. Use a light source and a pair of hemostats as retractors to improve access. Alternatively, use an otoscope with a pediatric head to examine the premolars and molars of guinea pigs and chinchillas for overgrowth. Examine the cheek pouches of hamsters for swelling, impaction, or discharge. An ophthalmic examination, including a fundic examination, is important.

• Use a slit lamp to identify superficial pathology, especially corneal ulcers or foreign bodies.

• If indicated, perform fluorescein stain and conjunctival scrapings or cultures.

• Note the presence of conditions such as discharge, asymmetry, and exophthalmos.

M Key Point Gerbils, rats, and mice produce red tears (chromodacryorrhea) with stress or disease. Do not confuse them with hemorrhage.

• Guinea pigs suffering from hypovitaminosis C often produce dry, white tears.

• Check ears for discharge, foreign bodies, and mites.

Bluish discoloration of the ears is a sign of cyanosis. Bright red injected coloration is associated with septicemia. Sores behind the ears and on the neck are often a sequela of aural disease.

• Evaluate submandibular, axillary, inguinal, and popliteal lymph nodes for size and consistency. Enlargements usually indicate infectious or neoplastic disease.

• Reevaluate respirations and heart rate after the stress of handling and compare them with the resting rate noted when the animal was in the cage. Note dyspnea or respiratory sounds. Auscultate animals weighing more than 200 g. Counting every third or fourth beat and multiplying by the appropriate factor allows recording of heart rates up to 500 bpm.

• Palpate the abdomen. Pay special attention to differentiating pregnancy from the bladder, kidneys, abdominal masses, enlarged cecum, and fecal balls in the colon. While palpating the abdomen, examine the mammary chain of all female rodents for signs of mastitis, lactation, or neoplasia. Also check male mice and rats for mammary neoplasia. Mammary tissue extends from the base of the neck to the base of the tail. Gerbils typically have an elliptical sebaceous gland on their ventral midline. Do not confuse this with neoplasia or infection. Check the rectum and perineal area for signs of diarrhea, prolapse, irritation, parasites, and bite wounds. Note that coprophagy is normal in rodents.

• Evaluate the urogenital tract for signs of inflammation, foreign bodies, urine scalding, and vaginal discharge. Locate and palpate the testicles in males. The easiest method of determining sex in pet rodents is to compare the anogenital distance, which is twice as long in males as in females. Other characteristics that allow the determination of sex are as follows:

• Visualization or palpation of testicles or extrusion of the penis from the prepuce indicates a male. • The presence of two external openings (i.e., anus and urethra) indicates a male. • The presence of three openings (i.e., anus, vagina, and urethra) indicates a female.

• Examine the skin and fur for conditions such as crusts, alopecia, masses, herniations, and wounds. • Check tail and feet for swellings, coloration, sores, length of toenails, and condition of footpads.

• Evaluate the extremities for trauma or other abnormalities.

Apply cellophane tape to crusted areas of the skin and view under a microscope as an aid in diagnosing ectoparasites such as lice, mites, and fleas. Skin scrapings are beneficial in detecting mites and dermatophytes. Dermatophytes are diagnosed best through culture of broken hairs or crust on dermatophyte test medium. Use small, cotton-tipped swabs to obtain ear swabs from animals weighing more than 25 g. Mix debris with mineral oil and view under low magnification to test for ear mites, or roll onto a glass slide and Gram stain to look for bacterial or yeast infections.

Collect urine by placing the rodent in a clean meshbottomed cage with a plastic liner. After enough urine has been produced, collect it off the bottom of the cage with hematocrit tubes or a syringe and a 25-gauge needle. Perform cystocentesis on non-pregnant animals weighing more than 100 g with a 25-to 27-gauge needle.

Collect feces over several hours to provide a volume sufficient for fecal flotation. Flotation allows the detection of nematodes and some trematodes and cestodes. Cellophane tape applied to the perineal area and then viewed under a microscope often reveals oxyurid eggs. Use a fresh saline smear or fecal sedimentation to diagnose protozoal parasites. Fecal cultures are useful in diagnosing bacterial diarrhea.

Radiology is an extremely useful tool. Machines capable of exposures as low as 40 kvp and 3 to 10 MAS effectively image mice. Most radiograph machines are capable of generating diagnostic radiographs of guinea pigs, chinchillas, and mature rats at settings used for kittens. Positioning is accomplished with masking tape or Velcro straps. Sedate unruly animals. Techniques used in cats for contrast studies of both urinary and GI systems are modified easily for use in pocket pets.

• Use lateral or medial saphenous veins to obtain samples in animals heavier than 100 g. Liberally clip the area to allow exposure of the vessel before attempting venipuncture. Place a 25-to 27-gauge needle in the vein and collect blood into microtainers or hematocrit tubes as it drips from the hub of the needle (Fig. 177-4) . Take extreme care not to col-lapse and lacerate the vein with overzealous aspiration if a syringe is attached to the needle.

• It is also possible to use the cephalic vein in guinea pigs.

• Jugular veins are good alternatives in thin individuals under sedation.

• An alternative technique that is useful in smaller animals is to coat the skin over the vein with a thin layer of petroleum jelly and then to puncture the vessel. Blood is collected with a hematocrit tube as it exits the wound. Samples up to 1% of the animal's weight are considered safe, even in stressed animals.

M Key Point Attempt tail bleeding only as a last resort in mice, rats, gerbils, and hamsters. These techniques often are not acceptable to owners.

To bleed the tail, warm the tail with water or compresses to dilate the tail vessels. In large rats, perform venipuncture with a needle and obtain blood in the usual fashion. In smaller animals, lacerate the tip of the tail. Blood from the wound is collected as described previously. See Tables 177-5 and 177-6 for hematology and chemistry values.

Incorporate oral medications into a treat, or administer them in liquid form. If the medication is palatable, administer it by placing the tip of a dosing syringe into the diastema.

M Key Point Take care not to place the tip into the contralateral cheek pouch, or the patient may store the medication and expel it later.

Administer medication in small amounts. Ensure that the animal swallows the medication in its mouth before more is administered. This technique is useful for force-feeding pellet gruels to anorexic pets if the caregiver is patient. Medication or food that is administered too quickly will be spit out or aspirated.

For rodents that are intractable or for administration of unpalatable substances, pass a stomach tube per os.

• Metal feeding needles, red rubber urinary catheters, or infant feeding tubes work well. Selection is based on the size of the animal and individual preference. Metal feeding needles with ball tips frequently are used in patients weighing less than 100 g . The metal provides the necessary stiffness to pass a tube of small diameter. The ball at the end of the needle makes it difficult (but not impossible) to pass the tube into the trachea. These tubes have the potential to create esophageal tears with improper restraint or when excessive force is applied.

• Measure the length from the tip of the nose to the last rib. Ventroflex the head slightly, and place the tip of the tube through the diastema and over the tongue. If the tube does not pass easily down the esophagus to the premeasured distance, check the tube size and/or reposition the tube before attempting further advancement. The needle is easily palpable percutaneously if it is placed correctly. It is usually safe to administer up to 3 ml/100 g body weight.

• A flexible catheter is ideal for use as a stomach tube in larger rodents ( Fig. 177-6 ). Use a speculum to prevent chewing on the tube. An otoscope head, avian speculum, or piece of wood or plastic with a hole drilled in the center works well. Measure and mark the tube for the distance from the tip of the nose to the last rib. Place the speculum in the mouth and over the tongue. Pass the tube while holding the speculum in place and slightly ventroflexing the head. Resistance is encountered if the tube is malpositioned or is an inappropriate size. The tube must pass over the tongue before it can be advanced down the esophagus. This is difficult in some animals. Palpate the throat to confirm the presence of the feeding tube in the esophagus.

M Key Point Because the placement of a stomach tube is a blind procedure, administer a small volume of sterile saline into the tube before administering the medication to ensure that the tube is not in the trachea. Misplaced medications are fatal.

• This method is also useful for administration of nutrition to anorexic patients. Place a pharyngostomy tube if repeated dosing is necessary, using the technique for cats. Flush pharyngostomy tubes with water at least every 4 to 6 hours. Nasogastric tubes are not recommended because they are difficult to place and maintain patency because of their small size. Securely suture all tubes to the skin. Place a tube collar made of radiographic film or use rear leg hobbles to prevent removal of tubes.

• Nutritional support is critical in rodents because of their high metabolic rate. Provide supplements in animals that are anorexic for longer than 12 hours. If the GI tract is capable of digestion, use a slurry of pellets mixed with a high-calorie supplement. If the tube diameter is too small for this mixture, use avian hand-feeding formula or a mixture of vegetable and cereal baby foods in place of the pellets. If the ability of the GI tract to tolerate enteral feeding is questionable, first try isotonic electrolyte or dextrose solutions. Parenteral nutrition is used successfully in research animals and may be feasible in select pet cases.

Administer SC injectable medications or fluids over the shoulder blades or in folds of skin on the flank.

• Avoid irritating substances in rats and mice because their mammary tissue extends into these areas. The resulting inflammatory response is thought to increase the occurrence of mammary neoplasia.

M Key Point In general, avoid streptomycin and the carrier procaine in all pet rodents because of a high incidence of toxicity and hypersensitivity reaction.

Give IM injections in the semimembranous and semitendinous muscles. Inject only small volumes of nonirritating substances, or tissue damage with resulting self-mutilation may occur. Use the epaxial or triceps muscles if repeated injections are necessary.

M Key Point Use intraperitoneal (IP) injections only as a last resort for large volumes of fluids or for irritating injections that cannot be administered via an IV or IO route.

Express the bladder and aseptically prepare the abdomen.

Restrain the rodent with its head down to move the abdominal organs cranially. Give the injection 0.5 to 2 cm lateral to the midline in the caudal abdomen. Aspirate before injecting to ensure that the injection is not being given into the bladder or bowel. Never use this technique in pregnant animals.

Give IV injections into any of the veins as previously described. In addition, the penile vein may be used in hamsters and guinea pigs. Placement of IV catheters is possible in animals heavier than 100 g.

For small rodents, give a bolus of fluids every 2-4 hours, followed by a diluted heparin flush. A pediatric IV pump is used for continuous infusion of fluids to Mark distance from nose to last rib larger animals. Maintenance of catheters in active animals is extremely difficult.

For IO injections, place a spinal needle into the proximal tibia or femur following the technique used for placing an intramedullary pin. Once the needle is seated, remove the stylet. Aspirate and check the hub of the needle for bone marrow. The tip of the needle should be in the bone marrow cavity that directly drains into the central venous system in normal bones (i.e., the cortex must be intact). Administer drugs, blood, or fluids at a rate similar to that used for IV catheters.

• In chinchillas and guinea pigs, withhold food for 6 hours before anesthesia. Withhold food from smaller, mature rodents for 2 hours. Withhold food from immature animals for up to 1 / 2 hour depending on age and condition.

• Use heat lamps and heating pads to prevent hypothermia. Have a prewarmed incubator available for recovery. Preoperative or intra-operative warmed SC or IV fluids are strongly recommended. Place IV or IO catheters whenever possible.

• Administer atropine preoperatively to reduce airway secretions. Acepromazine, diazepam, or midazolam work well as premedications for other anesthetics. Avoid acepromazine in gerbils because it potentiates seizures. See Table 177 -7 for anesthetic drugs and dosages.

Surgical anesthesia is reached when toe, tail, and ear pinch fail to generate a withdrawal reaction.

Depth of anesthesia is best monitored by pulse and respiratory rate and character. Pulses drop to within normal ranges after induction. Further reduction, especially to less than 80% of the original stabilized value, is an indication to lighten the plane of anesthesia. Monitor the electrocardiogram (ECG) of small patients by clamping the alligator clips onto the hubs of all-metal 27-gauge needles or steel sutures placed through the skin at the usual sites. Tape cables to the table to maintain placement. Doppler units taped over the chest also provide accurate heart rates. Pulse oximeters are easier to use, more sensitive, and more expensive than the instruments mentioned previously. These instruments are easily taped to the patient's ear, foot, or tail and provide heart rates as well as information regarding oxygenation.

Respirations are often shallow and rapid during induction. They become deep and regular as a surgical plane of anesthesia is reached.

The corneal reflex varies markedly between individuals and anesthetic agents. If the animal has a corneal reflex after induction and then loses it, reduce the anesthetic.

Induce gas anesthesia using small face masks purchased from laboratory supply houses or make them from syringe cases and latex gloves ( Fig. 177-7) . Induction in an anesthetic chamber is also possible.

All rodents induced and maintained on gas anesthesia require some form of non-rebreathing system. Usual induction is achieved between 2% and 3% for isoflurane and 2% and 4% for halothane. Maintenance for isoflurane and halothane varies from 0.25% to 2%. There is marked individual variation in the amount of anesthetic required for induction and maintenance. Use of 50% nitrous oxide in oxygen reduces anesthetic concentration requirements for other gases.

M Key Point Some chinchillas and guinea pigs hold their breath while being induced with gas anesthetics and then take deep rapid breaths. If the concentration of anesthetic gases is high enough, this behavior results in death.

The risk of this behavior is reduced by premedication with tranquilizers, initial induction with nitrous oxide with later addition of primary anesthetic gas after relaxation, and low induction settings. Changes in respirations, especially erratic or apneustic patterns and decreased respiratory rates, indicate deepening anesthesia.

Most pet rodents are not intubated for anesthesia because of their small size. When necessary, as in prolonged oral and other procedures, endotracheal intubation is accomplished with the animal in dorsal or ventral recumbency, depending on the clinician's preference. Small non-cuffed or Cole endotracheal tubes work well. A stylet usually is required to provide enough stiffness for the tube to pass the larynx. Extend the animal's head and neck. Grasp the tongue with forceps and use gentle traction. The tip of the tube then is advanced above the tongue and just past its base. The hard palate is used to deflect the tip of the tube ventrally into the glottis. This is a blind procedure that is difficult to master. Use of a laryngoscope is helpful in larger rodents. Another technique is to place an over-the-needle catheter in the trachea and move it up retrograde through the larynx to act as a guide. The catheter is removed after the endotracheal tube is in place.

it is extremely important that the tube be checked for patency. Rodents produce copious respiratory secretions, which frequently clog endotracheal tubes.

The small diameter allows these tubes to collapse or kink, resulting in asphyxiation of the patient. Check patency at least every 2 minutes by applying positive pressure ventilation at 10 to 15 cm water and watching for excursion of the chest wall. If extending the head and neck does not result in air flow, suction the tube. If this is either not successful or impossible, remove the tube and continue anesthesia with a mask or reintubate the animal with a new tube. Because of the small diameter of the trachea, endotracheal tube-induced tracheitis and subsequent swelling of the trachea may become a life-threatening situation.

Doses and routes for injectable anesthetics are listed in Table 177 -7. Needed doses for injectable anesthetics are tremendously variable among species and individuals. Most injectable anesthetics provide safe sedation for minor procedures, but very few induce a safe surgical plane of anesthesia on a consistent basis.

• Ketamine in combination with diazepam is easily obtainable, is given intramuscularly, and has a wide margin of safety, but it does not provide good analgesia.

• Intraperitoneal injections of barbiturates provide surgical anesthesia but have a low margin of safety and a significant mortality rate. Barbiturate anesthesia can result in fatal ileus.

Euthanasia is performed easily by induction of inhalant anesthetic through a mask or chamber followed by an overdose of barbiturates given intraperitoneally, IV, or intracranially. Euthanasia by IP injection of barbiturates alone causes pain in some animals.

• Surgical techniques for pet rodents are similar to those used in cats and birds.

• Hemostasis is critical because of small blood volumes. • Electrosurgery for incisions and cautery is highly recommended.

• If necessary, give fresh blood transfusions drawn from a donor of the same species and mixed with sodium heparin (1000 IU/ml) at a rate of 0.005 ml/1 ml of blood directly into an IV or IO line.

• The lack of a filter creates a potential for thrombosis.

• Transfusion reactions are possible.

Administer postoperative analgesics to all rodents undergoing surgical or dental procedures. Common analgesics include buprenorphine, butorphanol, ketoprofen, carprofen and meloxicam. See Table 177 -7 for dosages.

The most common surgeries are laceration repair and removal of dermal or SC masses.

• Most rodents will not gnaw on skin sutures. • If this occurs, use steel sutures, subcuticular sutures, or tissue glue.

• If an animal still chews at its suture line, physical restraint, such as a tube or an Elizabethan collar, is required.

Castration is a common procedure in guinea pigs. This usually is performed when owners want to house more than one male together or do not wish to breed their female any longer. 

Common abdominal surgeries include cystotomy for urolith removal in guinea pigs and rats, and cesarean section (C-section) in guinea pigs and chinchillas because of dystocia.

Use a technique similar to those described for dogs and cats. Preplaced stay sutures are recommended to define incision edges for closure. Use 4-0 polyglactin 910 or polydioxanone (PDS) on a taper needle and suture in a simple continuous pattern to close the body wall. Close the skin with a subcuticular suture (absorbable) or interrupted skin monofilament, nonabsorbable suture.

Fracture fixation is accomplished best with intramedullary pinning or Kirschner apparatus. Rodents gnaw on bandages until they remove them. If they are unable to remove a splint, self-mutilation often results in self-amputation. If a cast or splint is necessary, physical restraint often is required. Healing usually takes 3 to 6 weeks.

Incisors can be trimmed with nail trimmers, but this technique often fractures the tooth, causing abscesses of the root. Instead, use a high-speed dental burr or a flat cutting disk on a Dremel hand tool. Trim molars with a high-speed drill or pediatric rongeurs. A mouth speculum that deflects the tongue and other soft tissues is essential to prevent lacerations and provide working space ( Fig. 177-8) . Intubate the trachea to prevent aspiration pneumonia when working on molars.

If a tooth is abscessed, extract both it and the occlusal tooth.

• If necessary, approach cheek teeth via an incision through the cheek.

• Use a fine dental elevator to loosen the teeth. • Patience and firm but gentle pressure are needed, or the root or surrounding bone may fracture.

• The roots of the maxillary incisors curve dramatically back into the head. Take care to follow the curve of the tooth.

• Packing an infected tooth socket with a calcium hydroxide paste may decrease the occurrence of persistent infection. Remove the paste in 3 to 4 days.

• Administer meloxicam, carprofen or ketoprofen postoperatively to control pain. See Table 177 -7 for dosages.

In chinchillas with dental malocclusion, the roots of the molars can become impacted, causing swelling of the mandible or exophthalmos and epiphora. These teeth are extremely difficult to extract without causing extensive bony and soft-tissue damage. Discourage breeding of animals with malocclusion, unless it was acquired as a result of trauma or infection, because this trait is hereditary.

Most pet and laboratory mice are derived from Mus musculus, which is the common house mouse. Mice sold in the pet trade are randomly bred and less likely to suffer from the genetic problems associated with inbred laboratory rodents. Mice possess brown fat tissues between their scapulae that also are known as hibernating glands; these are thought to provide an energy store. The spleen in male mice is 50% larger than that of females.

Ectoparasites usually are found in new acquisitions.

• Alopecia and pruritus, especially on the back of the head and dorsal midline, usually are associated with lice (Polyplax serrata), mites, or fleas. • Mite infestation (e.g., Mycoptes musculinus, Myobia musculini, Radfordia affinis) often causes a greasy haircoat and folliculitis.

Transmission of lice and mites occurs via direct contact. Fleas are transmitted by other household pets, such as cats and dogs.

• Diagnosis is based on clinical signs, history, visualization of parasite, skin scrape, and cellophane tape test.

• Treatment of fleas and lice is with Pyrethrin powder.

Ivermectin is recommended for treatment of mites (see Table 177 -8).

• Change the bedding and thoroughly clean the cage between treatments to prevent reinfestation. Occasionally, the surrounding environment needs to be treated with a premises spray used for killing fleas.

• Alopecia also may be the result of dermatophytes (see Chapter 42). Lesions are often hyperkeratotic.

• Diagnosis is made by skin scrape or isolation on culture. Most dermatophytes found in pet rodents do not fluoresce under a Wood's lamp.

• Treatment is with lime-sulfur dip or griseofulvin (Table   177 -9).

• Ulcerative dermatitis is a common syndrome caused by Staphylococcus aureus characterized by pododermatitis, mastitis, and abscesses in other areas.

• Administer antibiotics based on culture and sensitivity tests. Chloramphenicol is recommended pending culture results (see Table 177 -9). The application of hot packs, local drainage, and topical medications are also beneficial in selected cases.

• Mastitis also may be caused by Escheria coli or Pasteurella, Klebsiella, Pseudomonas, or Streptococcus species. Mastitis usually is caused by poor sanitation, abrasive bedding, or overly aggressive young.

• Preputial gland abscesses are fairly common in males and are usually caused by E. coli or S. aureus. Local flushing and topical treatment are usually adequate.

• SC abscesses can be the result of the aforementioned bacteria or Actinobacillus spp. or Corynebacterium kutscheri. Corynebacteria is associated with widespread abscesses, septic arthritis, gangrene, and ulcerated draining tracts. Diagnosis is based on finding grampositive pleomorphic rods on Gram stain and isolation on culture.

• The bacteria are usually sensitive to ampicillin, chloramphenicol, and tetracycline (see Table 177 -9).

• Lymphoma and mammary neoplasia are common causes of SC masses. Mammary neoplasia is usually malignant in mice, and metastasis to the lungs is common. (Mice have five pairs of mammary glandsthree thoracic and two abdominal.)

• Obtain thoracic radiographs before surgery.

• Give a guarded prognosis for long-term survival.

• Other possibilities for SC masses are fungal granulomas, nodules from the Psorergates simplex mite, hematoma, hernia, non-neoplastic lymphadenopathy, or emphysema.

• Otitis externa usually is caused by ear mites, although bacteria or fungi also may cause primary or secondary otitis.

• Clinical signs include erythema, pruritus, waxy debris, and excoriations behind the ears. • Mites may be diagnosed by identification on otoscopic examination or microscopic examination of ear swabs (see "Techniques"). • Treatment requires cleaning debris from ears with a commercial ear cleanser followed by administration of three doses of ivermectin at 2-week intervals or topical acaricides used daily for 3 to 4 weeks (see Table 177 -9).

• Bacterial and fungal otitis is diagnosed by identification of organisms or Gram-stained specimens and isolation on culture.

• Treatment is similar to that used in cats.

• Otitis media/interna usually are caused by hematogenous spread or local invasion of bacteria from a primary abscess.

• Clinical signs include head tilt, circling, facial nerve paralysis, and otitis externa. • Rule out mouse hepatitis virus as the cause of the head tilt (see "Gastroenterology"). • If treatment of the primary disease is successful, the otitis media usually resolves, although a residual head tilt may persist. • If a cluster of Pseudomonas infections occurs in a population, evaluate the water source and produce for contamination. Use sodium hypochlorite in the drinking water at 10 ppm to control an outbreak while water quality is being restored.

• Damage to the pinnae can be associated with trauma, dermatitis, pox virus, hypersensitivity reactions, and vasculitis. Dry gangrene is a common sequela and is usually self-limiting.

I have observed a steroid-responsive pruritus in pet mice. The pruritus is severe enough to result in significant self-mutilation. This condition has been nonresponsive to treatment with ivermectin, lime-sulfur dips, griseofulvin, multiple antibiotics, oral prednisolone, and antihistamines. Attempts at bacterial and fungal culture have failed to identify a pathogen. An inflammatory response is observed on histologic examination. Mice with this condition respond to repository methylprednisolone injections every 2 to 4 weeks (1.0 mg/kg IM). Most owners have not elected to continue injections for longer than a few months. Once the injections are stopped, the pruritus returns, often requiring euthanasia of the affected mouse.

• Bilateral alopecia found around the muzzle associated with no other abnormalities usually is caused by friction from overhead feeders.

• Alopecia occurring in smaller, weaker individuals is often the result of barbering. Removal of the mice in best condition from the cage results in normal appearance of barbered mice in 2 to 3 weeks.

• Tailhead alopecia and scabbing are usually the result of aggression. Separate affected animals, or additional trauma may occur.

• Other rare causes of alopecia are endocrinopathies, leprosy, and hereditary alopecia in nude mice.

• Epiphora is a common condition of pet mice. The most common causes in pets owned for longer than 2 months are ammonia fumes and overgrown incisors.

• Ammonia causing contact irritation is diagnosed by examining an uncleaned cage and checking for odor.

• Treatment is improved sanitation.

• Overgrown incisors are diagnosed easily by oral examination. Treat by trimming the affected teeth and providing opportunities for gnawing.

• Foreign bodies and the resultant corneal ulcers can cause epiphora. An eye examination, including fluorescein stain, is indicated. Treat by removing the foreign body and administering an ophthalmic antibiotic (gentamicin, tetracycline, or chloramphenicol in affected eye, q8h-q6h).

• In newly acquired pets, epiphora is often the first clinical sign of an upper respiratory infection. Pasteurella pneumotropica is the most common pathogen, although Salmonella spp., mycoplasma, Sendai virus, lymphocytic choriomeningitis, and mouse pox also may cause epiphoria. The ocular discharge later appears mucopurulent (see "Respiratory").

Retinal degeneration can be either hereditary or (in albino mice) may be caused by exposure to highintensity lighting. The resulting blindness often goes undetected because patients adapt well and behave normally in their cages. • Clinical signs include dyspnea (often described as chattering), mucopurulent oculonasal discharge, hunched posture, and anorexia. Animals with a chronic history of this disease are often cachexic.

• Radiology aids in determination of the extent and severity of the pneumonia and the absence or presence of distant foci of infection.

• Treatment with tylosin is successful in controlling the disease if it is not too advanced. Tetracycline, enrofloxacin, and chloramphenicol also have been used (see Table 177 -8).

• Many patients need nutritional support. • Mice with pyometra or other abscesses require surgical debridement.

• Recovered animals are carriers and stress elicits clinical signs. Strictly quarantine these animals.

A common cause of pneumonia in newly acquired mice is Sendai virus. Acute fatalities are seen in suckling or weanling mice.

• Transmission is by aerosol or direct contact.

• Clinical signs in adults are caused by secondary bacterial infections and are similar to those in MRM.

• Diagnosis is based on clinical signs and serologic testing.

• Treat with antibiotics to control the secondary bacterial infection and provide supportive care as needed.

• Prohibit breeding for 4 to 6 weeks. • A killed vaccine is available.

• Recovered animals are resistant to new infection.

Common primary or secondary pathogens causing respiratory signs in mice are Streptococcus pneumoniae, Corynebacterium kutscheri, Pasteurella pneumontropica, Pseudomonas aeruginosa, and Klebsiella pneumoniae. Treatment is empiric or based on culture and sensitivity of a tracheal swab sample.

Dyspnea often is caused by metastasis to the lungs from mammary adenocarcinomas. Primary lung tumors, especially pulmonary adenomas, also occur frequently.

Although not frequently diagnosed, cardiac disease can result in signs of respiratory disease. Diagnosis is based on radiographic evidence of cardiomegaly and pulmonary edema.

• Tapeworms usually do not cause clinical signs. Occasionally, heavy burdens may cause diarrhea or weight loss. The chief concern is the zoonotic potential of one species, Hymenolepis nana, which is directly transmissible to humans.

• Diagnosis is made from visualization of eggs in the feces. Treat with praziquantel or niclosamide (see Table 177 -8). Improve sanitation, and remove indirect hosts (e.g., fleas, beetles, roaches).

• Pinworms (Syphacia obvelata, Aspiculuris tetraptera) may cause anal pruritus and, in severe cases, rectal prolapse.

• Diagnosis is based on clinical signs and observation of eggs on cellophane tape after application to the perineal region. Treat with piperazine or mebendazole every 7 to 10 days for three treatments or with fenbendazole once daily for 5 days (see Table  177 -8) and provide improved sanitation.

• The protozoal parasite Spironucleus muris causes diarrhea and slow growth associated with a pot-bellied appearance in young mice.

• Diagnosis is by fecal wet mount, although falsenegative findings are common. • Treat with oxytetracycline (see Table 177 -9). Supportive care to combat dehydration and hypothermia is extremely important. • Control is achieved with improved sanitation.

• Giardia spp. and, rarely, Eimeria falciformis show signs similar to Spironucleus. Giardiasis is zoonotic. Treat with metronidazole. Treat Eimeria with sulfadiazine/trimethoprim (see Table 177 -9). Most other protozoa are considered nonpathogenic.

• Cysticercus fasciolarus causes nonpathologic cysts of the liver. These cysts are the infective form of Taenia taeniaformis in carnivores.

Viral Diseases • Diagnosis is based on clinical presentation, serology, and presence of syncytial giant cells in the epithelium of the small intestine. • Treat supportively, and quarantine affected individuals. The prognosis is grave.

• Although less commonly seen in pet mice, reovirus occurs in older suckling mice. It is characterized by an oily diarrhea, which results in a greasy haircoat. Other signs are conjunctivitis, stunted growth, and tremors. Transmission is by ingestion.

• Diagnosis is based on clinical signs, histology, and serology. • Treat supportively. The long-term prognosis is grave. Initial survivors are weak and jaundiced, suffer from alopecia, and eventually die.

• Transmissible murine colonic hyperplasia (MCH) caused by Citrobacter freundii is characterized by diarrhea followed by rectal prolapse and stunted growth. Transmission is feco-oral.

• Diagnosis is made by clinical signs and fecal culture.

• Treat with neomycin, tetracycline, or sulfamethazine until sensitivity results are available (see Table  177 -9). Severe thickening of the distal half of the colon is observed at necropsy.

• Salmonellosis, also known as mouse typhoid, is transmitted by latent carriers or contaminated feed or bedding. Incubation lasts for 3 to 6 days.

• Clinical signs are lethargy, anorexia, purulent conjunctivitis, arthritis, and diarrhea. • Diagnosis is based on clinical signs and fecal culture. Treat supportively. Use of antibiotics is controversial. • Quarantine survivors. • Sanitation is extremely important because Salmonella spp. are zoonotic. On gross postmortem examination, erythema of distal ileum and congestion of the spleen and liver are seen. With more chronic infections, necrotic foci are seen in the liver, spleen, and lymph nodes. Prevent infection by feeding a fresh laboratory chow from a reputable source. Thoroughly wash all produce and then dip it in a diluted bleach solution. Rinse completely before feeding.

• Tyzzer disease is caused by Bacillus piliformis. Transmission is feco-oral.

• Clinical signs are precipitated by stress and consist of anorexia, diarrhea, and high mortality in weanlings. • Diagnosis is made by clinical signs or isolation on culture. Enteritis and multiple gray-yellow necrotic foci in the liver are seen on gross postmortem examination. • Administer tetracycline for 4 to 5 days (see Table  177 -9) and reduce stress to control the disease.

Breeding systems vary; from one to six females may be placed with one male. All animals are housed together, and the young are removed after weaning. Females in proestrus have swollen vulvas. Vaginal plugs are present post-copulation. Female mice that have been bred within 4 days abort if a new male is placed in the cage. Inappropriate light cycle, inappropriate age, crowding, and poor nutrition are the most common causes of infertility in pet mice. Pyometra due to Pasteurella pneumontropica, Mycoplasma spp., or other bacteria is also common.

Desertion of litters is usually a result of stress, lack of nesting materials, agalactia, or mastitis.

• Urethral obstruction from proteinaceous plugs of inspissated ejaculum may develop in aged male mice. Pseudomonas, E. coli, or Proteus are the most frequently cultured pathogens. Before complete obstruction, chronic hematuria may be noticed by the owner.

• Antibiotics, which are chosen based on the results of urine culture, are often curative with early presentation. Complete obstruction requires surgical removal.

• Glomerulonephritis is very common in geriatric mice. It frequently is secondary to chronic viral infection. Clinical signs are anorexia, lethargy, dehydration, and cachexia. Urinalysis demonstrates proteinuria. As the disease progresses, the urine becomes isosthenuric, the blood urea nitrogen (BUN) and creatinine levels rise, and other electrolyte abnormalities typical of chronic renal failure occur. Treat supportively. Prognosis for long-term survival is grave.

• Coccidia (e.g., Klosseilla muris) occasionally is found in the urine. The clinical significance of its presence is unknown.

• Mice can be asymptomatic carriers of leptospirosis; however, this is rarely seen in pet mice.

• Diagnosis is based on darkfield microscopy of urine, serology, or histopathology. Euthanasia of carriers is recommended.

• Infectious polyarthritis or mouse rheumatism is caused by Streptobacillus moniliformis. In humans, it is known as rat bite or Havernill fever. Transmission is by direct contact. Clinical signs are cachexia, keratitis, edema and ulceration of the appendages, and ankylosing arthritis.

• Diagnosis is based on the bacterial culture findings or the presence of caseous pericarditis and arthritis on necropsy. • Treat with antibiotics chosen through the results of culture and sensitivity tests. Use penicillin while awaiting results. Supportive care is important. Animals that recover remain arthritic. Control is achieved through quarantine and sanitation.

• The most frequently diagnosed neurologic disease in pet mice is head tilt resulting from bacterial otitis media (see "Otitis"). The second most common cause of neurologic signs is trauma.

• Diagnosis is based on history and clinical signs. Consider neoplasia in aged mice with slowly progressive signs.

• Lymphocytic choriomeningitis is a zoonotic arenavirus. Transmission is airborne, transplacental, or by direct contact, fomites, or insect vectors. Acute signs usually occur in mice that are 3 to 6 weeks old. Approximately 20% of infected individuals show acute clinical signs, which include lethargy and photophobia followed by convulsions and paralysis. In animals that are latently infected, glomerulonephritis develops later. Mice infected after weaning and before 1 year in age lose weight, appear arthritic, and show signs of conjunctivitis and photophobia. The virus runs its course in several weeks. Animals that recover show no residual signs.

• Diagnosis is based on clinical signs and the presence of immunofluorescent antibody (IFA). Pleural effusion, splenomegaly, and hepatic lipidosis are found on necropsy. Treat supportively. House survivors separately. • Prevent the disease by improving sanitation, providing pest control, and cleaning produce. Consider euthanasia because of the zoonotic potential of the virus.

• Mouse poliomyelitis/encephalomyelitis, also known as Theiler disease, causes clinical signs in 1 in 10,000 infected mice. Two-thirds of healthy mice are carriers. Transmission is by oral or respiratory routes. Mice younger than 4 weeks of age show signs of encephalitis. Animals that are 6 to 10 weeks old are weak in the rear legs and progress to paralysis. The tail may remain mobile. Affected mice continue to eat and be alert. Albino mice are predisposed to show clinical signs.

• Diagnosis is based on clinical signs, serology, or histopathology that shows necrosis of the ganglionic cells of the anterior horn of the spinal cord. • Treat supportively. Consider euthanasia because of poor prognosis.

• Seizures in mice commonly result from otitis media, trauma, liver or kidney failure, toxin, bacterial meningitis, neoplasia, or viral encephalitis.

• Leukemia in mice is usually viral in origin. Transmission is trans-mammary or trans-placental.

• Clinical signs are anemia, dyspnea (with thymic involvement), and those signs that are compatible with chronic disease. • Diagnosis is based on complete blood count (CBC), bone marrow aspirate, or histopathology. Prognosis is grave.

• Eperythrozoon coccoides is a rickettsial red blood cell (RBC) parasite of mice. Affected mice are usually asymptomatic. Occasionally, fever, anemia, and splenomegaly develop in infected animals. Transmission is through the louse Polyplax serrata. Control is by extermination of the louse.

• Treat with tetracyclines.

Pet rats are derived from the Norwegian or brown rat (Rattus norvegicus), which did not originate from Norway, but from Asia. Breeds of rats are called strains when they are inbred extensively and stocks when strains are hybridized. Rats have brown fat, as discussed in the section on mice. They do not possess a gallbladder. Their mandibular symphysis is articulated normally.

Rats are neophobic; therefore, make gradual changes in food or environment when possible.

• Fleas, mites (e.g., Radfordia ensifera, Ornithonyssus bacoti), lice (i.e., Polyplax spinulosa), ear mites (i.e., Notoedres muris), and dermatophytes cause similar signs in both mice and rats. Treatment also is similar (see "Mouse").

• SC masses in rats are similar to mice. Pasteurella pneumotropica is a very common pathogen in mastitis and SC abscesses.

• Treat with chloramphenicol until culture results are available (see Table 177 -9).

• Mammary cancer develops in 50% to 90% of adult female rats and in approximately 15% of male rats. Always submit biopsy specimens for histologic examination. Most, but not all, of these tumors are fibroadenomas, which are benign. Prognosis for longterm survival after surgical removal is good. Other common neoplasms include interstitial cell tumors of the testes, which cause SC swellings in the inguinal region, and squamous cell carcinomas of the Zymbals gland of the external ear canal.

• Ulcerative dermatitis occurs in rats as well as mice.

Staphylococcus aureus is the causative agent. C. kutscheri follows a similar course in rats and mice (see "Mouse").

• Ringtail is the formation of constrictive bands of fibrous tissue around the tail in nestling rats. These bands result in gangrene of the distal tail. This disease occurs when environmental humidity is less than 40%.

• Treat by making a longitudinal incision of the ring to release the stricture and apply topical dimethyl sulfoxide (DMSO), steroid, and antibiotic solution (10 ml DMSO, 6 ml 50 mg/ml amikacin, 4 ml 2 mg/ml dexamethasone) four times daily. • To prevent ringtail, keep humidity above 50%, use solid-bottom cages and provide ample nesting material. Prognosis for life is excellent. Prognosis for retention of the distal tail is guarded.

• Epiphora and blepharospasm are caused mostly by ammonia fumes, overgrown incisors, or foreign bodies (see "Mouse").

• Sialodacryoadenitis virus is a coronavirus that is endemic in many rat populations.

• Clinical signs vary from mild keratoconjunctivitis to blepharospasm, chromodacryorrhea, severe uveitis, hyphema, buphthalmos, periorbital swelling, and pneumonia. The clinical course of the disease lasts 10 to 14 days. Rats maintain normal activity levels and appetite.

• Treatment is not necessary for mild infections. Place rats showing marked ocular disease or discomfort on the appropriate ophthalmic ointments (e.g., atropine, antibiotic, steroid) based on presentation.

Administer parenteral antibiotics to animals that show signs of respiratory problems. Recovery is usually complete unless the eye ruptures or selfmutilation occurs. • Control is achieved by not introducing new animals for 4 weeks.

• In contrast to mice, Sendai virus rarely causes clinical signs in rats.

• Mucopurulent ocular discharge also may be caused by infection with mycoplasmosis, Streptococcus pneumoniae, Pseudomonas spp., and other less common bacterial or viral agents that cause pneumonia.

• Cataracts are primary hereditary defects or occur secondary to severe uveitis or diabetes mellitus.

Retinal dystrophy and colobomas are also inheritable traits in rats. Retinal degeneration occurs in rats housed under intense lighting.

• MRM is extremely common in pet rats. Its presentation is similar to the disease in mice (see "Mouse").

• Streptococcus pneumoniae is normal flora for rats.

However, during stressful situations, bacteremia may occur, resulting in pneumonia. Clinical signs are similar to MRM. Differentiation is based on culture and the presence of extensive fibrinopurulent pleural effusion on necropsy.

• Ampicillin controls clinical signs if treated early in the course of disease (see Table 177 -9). Prevent the condition by minimizing stress.

• Corynebacterium kutscheri and Pasteurella pneumotropica cause signs similar to MRM (see "Mouse"). There is a serologic test for C. kutscheri. See the Mouse section for a discussion of Pseudomonas aeruginosa.

• Pneumocystosis carinii is an uncommon protozoa that infects the lung. Cysts and trophozoites live in the alveoli. Clinical signs occur only in immunocompromised or geriatric individuals. Signs are cachexia, cyanosis, and dyspnea.

• Diagnosis is based on clinical signs, tracheal wash, response to therapy, or histologic examination. • Treat with sulfadiazine/pyrinrethamine (see Table  177 -9).

• Myocardial degeneration and subsequent congestive heart failure are fairly common in geriatric rats. Diagnosis is based on radiographs of the thorax and clinical signs. Treat supportively, and use furosemide and digitalis at cat dosages to alleviate pulmonary edema.

• Polyarteritis nodosa is an idiopathic condition of geriatric rats that results in thickening and tortuosity of arteries, especially in the mesentery, pancreas, and testicles. Affected areas are predisposed to clot formation and aneurysms.

• Nematode (Syphacia muris), cestode, and intestinal protozoal parasite infestations are similar to those in mice.

• Capillaria hepatica has no clinical significance. Yellow streaks on the liver are an incidental finding at necropsy.

The causes and treatment of malocclusion are similar to those for mice.

• Epizootic diarrhea of suckling rats is a viral disorder found in rats 7 to 14 days old. The infection causes a mild diarrhea. Most animals recover. Occasionally, stunting occurs. Treat supportively.

• Salmonellosis in rats is similar to that in mice.

• If breeding is desired, take females showing signs of estrus (e.g., lordosis, hyperactivity, quivering ears, and swollen vulva) to a male rat's cage for 24 hours, or keep one male in a cage with up to six females. Check females for a post-copulatory plug to confirm breeding. Remove females just before parturition, and house females individually while raising the young. A vaginal discharge is seen 1.5 to 4 hours before labor. Parturition is accompanied by stretching and extension of the rear legs. All neonates usually are delivered within 1 to 2 hours. • Two extremely common conditions in geriatric rats are nephrocalcinosis and chronic progressive nephropathy. Clinical signs are compatible with those of chronic renal failure. Enlarged or small irregular kidneys may be found on physical or radiographic examination. Isosthenuria and marked proteinuria are found in urinalysis.

• Definitive diagnosis is based on renal biopsy.

• Treat supportively. Prognosis for long-term survival is grave.

• Trichasomoides crassicauda is an uncommon parasite of the urogenital tract. The adult worms usually reside in the kidney, but they occasionally may wander into the genital tract. The ova are passed in the urine.

• Clinical signs are hematuria and stranguria. Proliferative mucosa of the bladder occasionally may be palpated as an abdominal mass. • Treatment is somewhat successful with methyridene (see Table 177 -8). Sanitation is critical in control of this disease.

• Klossiella muris is an incidental coccidia of the urinary tract.

• Many geriatric pet rats have chronic progressive radiculoneuropathy.

• Clinical signs are compatible with cauda equina syndrome, including posterior paresis progressing to paralysis, urine retention, and incontinence. Prognosis is grave. • Treat supportively or euthanize.

• Streptobacillus moniliformis, a normal bacteria found in the oral, nasal, and pharyngeal cavities of rodents, is isolated from 43% of middle ear infections and 35% of chronic pneumonias in rats. The bacteria is nonpathogenic for gerbils and guinea pigs.

• Clinical signs vary with the site of infection. Head tilt and circling, septic arthritis, and respiratory disease commonly are seen. • Diagnosis is based on isolation on culture. The clinical signs mimic many other diseases, especially MRM and Pseudomonas infection (see "Mouse").

• Head tilt in rats also may be the result of trauma or neoplasia, especially pituitary adenomas.

• Hemobartonella muris is an RBC parasite of rats that is nonpathogenic unless the rat is immunocompromised or splenectomized. Transmission is through the louse Polyplax spinulosa.

• Clinical signs result from hemolytic anemia and hemoglobinuria.

• Treat with tetracyclines (see Table 177 -9).

Mesocricetus auratus, better known as the golden or Syrian hamster, is a primarily nocturnal rodent that originated in the Middle East. Almost all hamsters in the United States are the offspring of three siblings imported in the 1930s. Many color variations are available. Long-haired hamsters are called "teddy bear" hamsters. The stomach has two compartments, a non-glandular forestomach, which functions like a rumen, and a glandular stomach. Hamsters are very territorial. They possess flank glands, which are larger in males, that are rubbed against objects to mark their territory. Females are larger than males. Except during estrus, they use this size advantage to attack males. Do not allow groups to estivate together or recently awakened animals may cannibalize sleeping hamsters.

M Key Point Hamsters are extremely sensitive to antibiotics.

Penicillins, clindamycin, lincomycin, streptomycin, tylosin, erythromycin, and cephalosporins eliminate the normal intestinal flora, allowing overgrowth of pathogenic bacteria, particularly Clostridium difficile. Diarrhea, which is almost always fatal within 3 to 7 days, subsequently occurs. Even antibiotics considered to be safe can have this effect. Treat by discontinuing antibiotics, providing a Lactobacillus supplement, and giving supportive therapy.

• Hamsters are susceptible to Demodex criceti and D.

aurati mites. D. criceti is limited to skin folds. D. aurati causes hyperpigmentation, alopecia, and seborrhea sicca affecting the dorsal midline. Demodex is carried by many normal-appearing hamsters.

• Clinical signs occur in immunosuppressed animals, as would occur with stress, chronic infection, pregnancy, or malnutrition. • Diagnosis is based on clinical signs and deep-skin scrapings. • Treat with amitraz every 2 weeks for two treatments past two consecutive negative skin scrapings. Use the manufacturer's recommended dilution for dogs.

• Sarcoptes mites infrequently cause facial alopecia.

Diagnosis is based on skin scraping. Treat with ivermectin (see Table 177 -8). Do not confuse this condition with alopecia caused by contact with feeders or barbering.

• Notoedres mites affect only the external ear canal in female hamsters but may affect the ears, feet, geni-talia, and tail in males. Diagnosis is made by observation of mites on samples from ear swabs, skin scrapings, or both. Treat with ivermectin (see Table 177 -8).

• Other less common causes of alopecia in hamsters are dermatophytosis, endocrinopathies, and genetic defects.

• Dermal SC masses are usually abscesses caused by Pasteurella pneumotropica, S. aureus, or Streptococcus spp. Treatment is based on results of culture and susceptibility testing. Use chloramphenicol until culture results are available. Other frequent causes of SC swellings are distended cheek pouches and testicles, mastitis, hernias, neoplasia, and lymphadenopathy.

• Epiphora and conjunctivitis are caused most frequently by increased environmental ammonia concentrations, incisor overgrowth, foreign body, or lymphocytic choriomeningitis (see "Rat"; "Mouse").

• Mucopurulent discharge is caused by secondary infection by Pasteurella or Streptococcus spp.

• Hamsters are predisposed to rupture of the eye following trauma or infection. Surgical enucleation is advised. Electrosurgery is extremely helpful in controlling bleeding but do not apply heat to the stump of the optic nerve or vessels, or thermal injury to the brain may result. Place gelfoam in the socket to enhance clot formation.

• Hamsters are susceptible to viral respiratory infections of humans.

• Clinical signs include nasal discharge, sneezing, otitis media, fever, and pneumonia. Uncomplicated cases last 5 to 7 days. Complications are usually the result of secondary bacterial infections. • Treat supportively. Use of antibiotics is indicated if copious nasal discharge, dyspnea, anorexia, or marked lethargy is observed. Overuse of antibiotics may cause diarrhea-related death in hamsters that might have recovered uneventfully if left untreated.

• Most dyspnea in hamsters is caused by blunt thoracic trauma. Hamsters often bite when startled. Reflex actions on the part of humans, especially children, cause hamsters to be flung against hard objects.

• Diagnosis is by history and presence of fresh epistaxis. • Treat supportively. Emergency shock therapy, consisting of supplemental heat, oxygen administration, parenteral fluids, and glucocorticoids, frequently is required.

• Sendai virus can cause death in suckling hamsters housed with mice. Adults show no clinical signs (see "Mouse").

• Primary bacterial pneumonia most frequently is caused by Yersinia pseudotuberculosis, Pasteurella pneumotropica, or Streptococcus. Clinical signs are compati-ble with those of pneumonia seen in other species, as well as weight loss and conjunctivitis. All three agents have a tendency to form distant abscesses, especially in the uterus.

• Diagnosis is based on clinical signs and isolation on culture. • Treat with chloramphenicol until antibiotic susceptibility results are available. Abscesses require surgical debridement; however, anesthesia in affected animals is very risky. Recovered hamsters are carriers and must be quarantined from other rodents. Prognosis is guarded.

• Cardiac thrombosis is seen in 73% of geriatric hamsters. Most thromboses occur in the left atrium and are secondary to degenerative cardiomyopathy, cardiac amyloidosis, sepsis, or calcification of the great vessels. Congenital myocardial necrosis also occurs.

• Clinical signs include cyanosis, dyspnea, and acute death. Enlargement of the cardiac silhouette and pulmonary edema sometimes can be seen on thoracic radiographs.

• Furosemide and digitalis (using standard cat doses) may temporarily alleviate clinical signs.

• Hamsters can carry the zoonotic tapeworm H. nana (see "Mouse").

• Treat with niclosamide or praziquantel (see Table  177 -8) and provide improved sanitation.

• Pinworms (Aspicularis tetraptera, Syphacia muris, S. obvelata) occur in hamsters as well as in mice.

• Treat with fenbendazole (see Table 177 -8).

• Hamsters are predisposed to dental caries. A large percentage of affected teeth become abscessed, causing facial swelling, ptyalism, and anorexia.

• Diagnosis is based on clinical signs, oral examination, skull radiographs, and isolation on culture. • Extract the tooth and administer antibiotic therapy based on results of susceptibility testing. Prognosis is variable depending on the condition of the animal, tooth affected, and extent of the abscess (see "Mouse").

• Overgrown incisors also occur, as in mice.

• The cheek pouches are very distensible. Impaction of the pouches occurs on occasion.

• Clinical signs vary from ptyalism to swelling from abscess. In simple cases, removal of the material from the pouch with fine forceps is sufficient. Sedation usually is not required.

• If a fungal or bacterial infection of the pouch is present, remove the exudate, submit samples for Gram staining and bacterial or fungal culture, and flush the pouch with diluted iodine solution. If cellulitis is present, administer systemic antibiotics as well. Fistulas often heal spontaneously.

• Proliferative ileitis (i.e., wet-tail disease) is thought to be caused by a Campylobacter-like organism with or without concurrent bacterial or viral infections. More than 90% of animals with clinical signs die. The highest morbidity and mortality rates occur in hamsters 3 to 8 weeks of age. Teddy bear hamsters may be more susceptible to infection than shorter-haired varieties. Transmission is feco-oral.

• Clinical signs include diarrhea, which mats on the ventrum and perineum, and results in anorexia, dehydration, and a hunched posture. The abdomen frequently seems painful on palpation. Bowel loops often are distended on palpation because of ileal obstruction or intussusception. Rectal prolapse usually occurs.

• Administer neomycin, gentamicin, metronidazole, or tetracycline (see Table 177 -9). Supportive care is critical. Prognosis is grave, even with treatment. Gross postmortem findings include gas and yellow diarrhea in the distal intestinal tract, mucosal thickening in the ileum and distal jejunum, peritonitis, and liver abscesses.

• Other common causes of bacterial diarrhea include E.

coli, Tyzzer disease, or Salmonella spp. (see "Mouse").

In hamsters older than 1 year of age, liver cysts that are derived from the biliary duct often develop. Less frequently, similar cysts arise from the pancreas, epididymis, and seminal vesicles. This syndrome is called polycystic disease. No clinical signs are associated with cysts in these structures, which are an incidental finding on abdominal palpation. No treatment is recommended.

• Timing is critical to prevent injury to the male when breeding hamsters. Transfer the female to the male's cage in the early evening 3 days after a creamy, viscous vaginal discharge is noticed. Monitor the pair carefully. Remove the male immediately if the female is aggressive. Remove the male after mating or after 1 to 2 hours even if mating has not occurred. Two days after successful copulation, a gray malodorous vaginal discharge is observed. Pregnancy is highly likely if there is no translucent vaginal discharge 5 to 9 days post-breeding. Pseudopregnancies last 8 to 12 days. Normal gestation is 15 to 16 days. Before par-turition, a hemorrhagic vaginal discharge appears, and the female may pant. Hamsters rarely suffer from pregnancy toxemia (see "Guinea Pig").

• Infertility may be caused by pyometra (see P. pneumotropica and lymphocytic choriomeningitis).

• Cannibalism is most frequently a result of stress or mastitis.

• In almost 90% of geriatric hamsters, renal amyloidosis develops. The disease tends to develop more rapidly in females.

• Clinical signs include edema and ascites due to protein loss in the urine, as well as the typical signs of chronic renal failure.

• Treat supportively. Prognosis for long-term survival is grave.

• Head tilt is usually secondary to otitis media. Also consider lymphocytic choriomeningitis or neoplasia as differential diagnosis (see "Rat").

• In hamsters fed all-seed diets and deprived of exercise, cage paralysis syndrome often develops. Usually pets are presented for acute posterior paresis which, in reality, was slowly progressive. The distinction is important in ruling out trauma. In mild cases, the hamster is able to move its hind limbs but unable to support weight. Vitamin D and E supplementation, along with nutritional improvement and providing exercise, is curative in 1 to 2 weeks. In severe cases, recovery is negligible or incomplete.

Lymphoma and lymphosarcoma may be viral in origin. Diagnosis is made by biopsy or fine-needle aspiration of affected lymph nodes. Rule out lymphadenopathy caused by lymphadenitis from infection with Streptobacillus moniliformis (see "Rat"). Although many hamsters initially respond well to chemotherapy protocols established for cats and dogs, prognosis for long-term survival is grave. 

• Rarely, Demodex spp. mites cause alopecia in gerbils.

• Diagnosis is based on skin scraping.

• Treat with rotenone ointment or amitraz dips every 2 weeks for three to six treatments. Use manufacturer's recommended dilution for dogs.

• Acute moist dermatitis usually is caused by S. aureus infection. Infection on the face often begins with the harderian glands. The gland secretion is viscous and causes matting, with secondary staphylococcal infection occurring under the mats. Attempts at grooming spread the infection to the feet and abdomen.

• Diagnosis is based on clinical signs and isolation on culture. • Administer enrofloxacin, tetracycline, or chloramphenicol and apply warm, moist compresses to remove dried debris. Remove possible irritants from cage (e.g., pine or cedar shavings, ammonia). Occasionally, surgical removal of a chronically infected or inflamed gland is needed.

• Alopecia of the facial area, especially when it is symmetric, is usually the result of self-trauma from feeders, cage bars, or overzealous burrowing.

• Treat by changing cage construction or providing better visual security.

• Gerbils that catch their tails in crevices or are restrained inappropriately by their tails often are presented for avulsion of the skin from their tails.

• Treat initially by controlling hemorrhage and hypovolemic shock. • Amputate the tail after patient stabilization to prevent ascending infection. In some animals, the infection is localized to the distal tail, which is sloughed in approximately 3 to 4 weeks.

• Generalized alopecia is normal in some weanling gerbils. The hair grows in as the animals mature.

• Melanomas are found most frequently on the ears, feet, or base of the tail.

• Diagnosis is based on biopsy.

• Treat by surgical removal.

• Sebaceous gland disease is usually the result of bacterial infections or neoplasia.

• Diagnosis is based on cytologic examination, culture, histologic examination, and response to antibiotic therapy. • Treat bacterial infections with parenteral or topical antibiotics based on the severity of signs.

• Sebaceous gland adenomas, basal cell tumors, and squamous cell carcinomas are the most frequently encountered neoplasms.

• Take a radiograph of the thorax to diagnose metastases. Prognosis for long-term survival is based on tumor type, stage, and character. • Treat by surgical excision.

Chromodacryorrhea and epiphora occur as in mice. Tapeworms (i.e., H. nana and H. diminuta) and pinworms (i.e., Syphacia obvelata, Dentostomella translucida, and Aspicularis tetraptera) occur as in mice.

Incisor overgrowth occurs as in mice.

• Salmonella spp. cause transient diarrheas in gerbils.

The source of infection is usually unwashed greens, contaminated feed, or carrier rodents of another species. Most recover. Animals that die have a fibrinosuppurative peritonitis.

• Treat supportively. Use antibiotics in severe cases based on results of culture and susceptibility testing.

• Tyzzer disease, caused by Bacillus piliformis, is seen most often in weanlings at 3 to 7 weeks of age and in post-partum females.

• Clinical signs include anorexia, lethargy, rough haircoat, and sometimes diarrhea. Gross postmortem findings include yellow-gray nodules in the liver and hemorrhage at the ileocecal junction. • Diagnosis is based on postmortem examination or response to therapy. • Treat with oxytetracycline (see Table 177 -9) and supportive care.

Hepatic lipidosis and gallstones are frequent sequela to lipemia in gerbils fed diets with excessive fat.

• Breeding is most successful if animals are paired at weaning and kept in these pairs. Male gerbils aid in raising the young. Pairing older animals causes fighting. An average of 20% of neonates fail to survive to weaning. This is usually the result of agalactia and crushing.

• Chronic hemorrhagic discharge from the vulva is usually the result of cystic ovaries or ovarian tumors. Most tumors occur in animals older than 2 years of age and consist of granulosa cell tumors or theca cell tumors. Leiomyomas of the uterus also cause similar clinical signs.

• Rule out urinary tract disease by performing a urinalysis via cystocentesis. Large masses may be visualized on abdominal ultrasound. Definitive diagnosis is based on vaginal cytology followed by exploratory laparotomy.

• Ovariohysterectomy is curative for cystic ovaries and tumors if they have not metastasized.

• Chronic renal failure develops in most gerbils older than 2.5 years of age.

• Clinical signs are polyuria, polydipsia, weight loss, and anorexia. Urinalysis demonstrates proteinuria, hematuria, casts, and an increase in white and red blood cells.

• Treat supportively. Prognosis for long-term survival is grave.

• Up to 50% of gerbils in certain family lines suffer spontaneous epileptiform seizures. The seizures are induced by stress and are self-limiting. Seizures usually start as the gerbil reaches 2 months of age.

• Treatment is unnecessary.

Chinchilla laniger and C. brevicaudata are nocturnal rodents from the Andes mountains in South America. Most animals kept in the United States are the descendants of 11 animals. Aside from pets, chinchillas are raised commercially for their pelts. The most common coat color is gray; the most valuable coat color is black.

M Key Point Chinchillas are sensitive to antibiotics (see "Hamster"); therefore, avoid use of penicillins, lincomycin, erythromycin, and cephalosporins.

House chinchillas in a cool environment because they are prone to overheating. If heat stroke occurs, treat with tepid water baths and supportive therapy.

• Chinchillas require dust baths to keep their skin in condition. Use commercially available chinchilla dust only. Sand substitutions do not condition the coat and occasionally cause conjunctivitis. Offer dust at least once a week.

• Dermatophytosis occurs as in guinea pigs. • Fur chewing is a serious problem in chinchillas that are farmed for pelts and often is seen in pet chinchillas that are recent culls from a ranch. The etiology of fur chewing is unknown. Some cases seem to be related to chronic disease, malnutrition, poor caging, or stress. Theories for undiagnosed cases include genetic abnormality; undiagnosed dermatophytosis; or adrenal, pituitary, or thyroid gland abnormalities.

• Diagnostics such as skin scraping, fungal culture, fecal, CBC, history profile, and biopsy are recommended. In general, if changes in diet and husbandry do not elicit a response or an underlying treatable disease condition is not discovered, prognosis for cure is grave.

• One source advocates plucking all remaining underfur in chewed areas in an attempt to stimulate new hair growth. Place collars after this procedure until the fur has grown in completely.

• Cystic SC masses may be caused by the intermediate stage of Multiceps serialis. Transmission is by ingestion of feed contaminated with canine feces.

• Diagnosis is made by histopathologic or cytologic examination of tissue samples. Treat by surgical removal of the masses.

• Otitis caused by Pseudomonas spp. occurs as in rats.

• Conjunctivitis occurs as in mice. • Cataracts are congenital or developmental. • Asteroid hyalosis occurs as a degenerative change.

Pneumonia occurs as in guinea pigs.

Parasites Tapeworms (i.e., H. nana) occur as in mice.

Malocclusion of incisors and cheek teeth occurs as in guinea pigs.

• Diarrhea is caused most often by Coccidia or Giardia spp. or a bacterium.

• Clinical signs range from soft stools and weight loss to fluid diarrhea, dehydration, bloating, septicemia, and sudden death. • The protozoal parasites are best diagnosed on fresh saline smear or necropsy.

• Bacterial diarrhea is most often caused by contaminated feed and is diagnosed by isolation on culture. Clostridium spp., Pseudomonas aeruginosa, E. coli, Salmonella enteritidis, and Pasteurella spp. are the most common isolates.

• Treat supportively and use appropriate antiprotozoal or antibiotic drugs.

• Pasteurella pseudotuberculosis causes acute death from septicemia or a chronic weight loss with intermittent diarrhea. Enlarged mesenteric lymph nodes are a hallmark of this disease.

• Diagnosis is based on clinical signs, histopathologic examination of tissue samples, and isolation on culture. • Treat with sulfa drugs until sensitivity results are available. Prognosis for recovery is poor. Gross postmortem examination reveals yellow to white necrotic foci in the liver.

• Check male chinchillas four times per year for penile hair rings. Roll back the prepuce and expose the penis. Roll hair rings off the penis after application of a water-soluble lubricant. Treat ulcerations topically or systemically as needed.

• Dystocia is fairly common in chinchillas (see "Guinea

Pig").

• Metritis is suspected when post-partum vaginal discharge, failure to return to a normal estrus cycle, anorexia, weight loss, polydipsia, polyuria, and chewing at flank and abdomen are present.

• Diagnosis is based on history, physical examination, abdominal radiographs, culture, ultrasound, and CBC. It usually is caused by bacteria introduced by the male or spread from an internal abscess. Retained placentas, macerated fetuses, and dystocia are predisposing factors toward metritis. • Treat with ovariohysterectomy after stabilization.

Females used only for breeding purposes may be treated with antibiotics alone, but the prognosis is poor.

• Female chinchillas are aggressive toward male chinchillas when not in estrus. Breeding operations usually have separate cages for females and an interconnecting run for the male. Females are kept out of the male's run by their larger size or collars. The young are precocious and do not need a nest. Chinchillas only produce two litters per year.

• Clinical signs include hot, swollen mammary glands.

Suspect mastitis if previously healthy neonates become restless, then lethargic.

• Perform bacterial cultures on milk samples, and treat with antibiotics based on susceptibility testing. Administer sulfa drugs until susceptibility results are available. Local hot packing is also beneficial. Occasionally, surgical drainage is required. Foster neonates to another female if possible, or use puppy or kitten milk replacers to hand-raise babies.

• Chinchillas seem to be particularly sensitive to Listeria monocytogenes. Clinical signs can mimic P. pseudotuberculosis and include anorexia, lethargy, abortion, generalized central nervous system (CNS) signs, hepatitis, mild enteritis, and mild emphysematous pneumonia. Necropsy shows yellow foci in the liver.

• Diagnosis is based on isolation on culture.

• Treat with sulfa drugs (see Table 177 -9) until sensitivity results are available. The prognosis is poor.

• Other less common causes of neurologic disease in chinchillas include lymphocytic choriomeningitis, Streptococcus spp., Balisascaris procyonis (i.e., aberrant migration of raccoon roundworm), lead poisoning, and thiamine deficiency.

Guinea pigs (Caviae porcellus) are nocturnal rodents that originated in the Andes mountains. They are known for their dietary need for vitamin C. They are used as a food source in their native lands. There are three basic types: English, which have short hair; Abyssinian, which have short, cowlicked hair; and Peruvian, which have long hair. Male guinea pigs are known as boars and the females as sows. Guinea pigs become neophobic as they mature. Offer a variety of foods early in life and make changes in diet or environment gradually. Guinea pigs stampede when excited. Square cages and strategically placed barriers on external walls prevent the trampling of small or weak animals.

The smooth muscle of the bronchial tree is quite developed in guinea pigs. This places them at high risk for asthmatic-type anaphylactic reactions.

Both male and female guinea pigs have one pair of inguinal mammary glands; however, only the female's are well developed.

M Key Point Antibiotic toxicity (see "Hamster"): guinea pigs also may be sensitive to tetracyclines.

• Fleas occur as in mice.

• Lice (i.e., Gliricola porcelli, Gynopus ovalis) usually cause no clinical signs except occasional alopecia, seborrhea, and trauma secondary to pruritus. • Diagnosis is made by observation of lice on skin scraping. • Treat with ivermectin, 5% malathion dust, or pyrethrin shampoo (see Table 177 -8).

• The mite Trixacarus caviae causes severe pruritus and is zoonotic. It mainly affects the dorsal midline and is difficult to find on skin scraping. It occurs most frequently in recently post-partum females, in which alopecia is the predominant clinical sign. Treat with excellent sanitation and ivermectin (see Table 177 -8).

• Chirodiscoides caviae lives on the hair shaft of the perineal regions. It does not cause clinical signs.

• Treat with 5% carbaryl or lime-sulfur dip (1:40) (see Table 177 -8). Sanitation is critical in preventing reinfestation.

• About 6% to 13% of guinea pigs are carriers of Trichophyton mentagrophytes.

• Clinical signs are alopecia and seborrhea sicca, usually starting on the face and spreading along the dorsum. • Treat with lime-sulfur dips or griseofulvin (see Table  177 -9) combined with topical povidone iodine or chlorhexadine shampoos.

• Other causes for alopecia are barbering, alopecia of the flanks in late-gestation females, and generalized alopecia of young at weaning. Subclinical hypovitaminosis C causes a poor hair coat and seborrhea sicca, as well as anorexia and large, malodorous stools.

• "Lumps" is the lay terminology for cervical lymphadenitis, which is characterized by lymphadenopathy in the ventral neck region. • Pododermatitis and sore hocks are very common in guinea pigs. Predisposing factors are untrimmed toe nails, poor sanitation, and wire flooring. S. aureus is the most commonly cultured pathogen.

• Clinical signs range from small ulcers on the soles of the feet to abscesses and gangrene. Radiography is essential in determining whether bony involvement is present. Untreated pododermatitis usually develops into osteomyelitis, which is very difficult to cure. • Treat mild cases by improving sanitation and grooming. Place affected individuals in solidfloored cages with paper bedding. Use sulfa drugs (see Table 177 -9) until results of susceptibility testing are available. Surgically remove or curette abscesses, and apply topical therapy and hot packing. Amputation may be necessary when severe osteomyelitis exists.

• Conjunctivitis and epiphora occur as in mice.

• Inclusion body conjunctivitis is caused by Chlamydia psittaci and is self-limiting in 3 to 4 weeks. • Perform a conjunctival scraping to differentiate inflammatory conjunctivitis secondary to infection from allergy. I have observed an idiopathic, topical steroid-responsive lymphoplasmacytic conjunctivitis in guinea pigs.

• White, dry ocular discharge is an early sign of hypovitaminosis C.

• "Pea-eyes" is the lay terminology for subscleral fatty deposits or protrusion of the lacrimal gland through the lower conjunctiva. The condition is thought to be hereditary. Treatment is not required.

• Cataracts occur and are either congenital or developmental.

• Diabetes mellitus in guinea pigs also may cause cataracts. Usually, no other clinical signs are present and urine glucose is greater than 100 mg/dl whereas blood glucose remains within normal limits.

• Corneal or scleral calcification is usually an incidental finding. A thorough workup, including serum chemistry profile and radiographs, is recommended to ensure that generalized metastatic calcification is not present.

• Pneumonia in guinea pigs usually is caused by infection with S. pneumoniae, S. zooepidemicus, or Bordetella bronchiseptica. S. aureus, P. aeruginosa, Klebsiella pneumoniae, and Pasteurella multocida also are cultured frequently. Transmission is by direct contact, fomites, or aerosol. Hypovitaminosis C and stress often predisposes guinea pigs to bacterial respiratory infections. Weanlings are particularly susceptible. Clinical signs and diagnosis are similar to other small mammals (see "Mouse").

• Take radiographs to rule out abscesses, pleural effusion, or pericardial effusion in refractory cases. • Treat with chloramphenicol, sulfa drugs, or enrofloxacin (see Table 177 -9) and vitamin C (Table 177 -10) until results of culture and susceptibility testing are available. Cats, dogs, rabbits, and rats are reservoirs for Bordetella spp. As in other rodents, respiratory infections may lead to otitis interna/media. Bordetella spp. also cause pyometra and abortions.

• Nasal discharge is most frequently a sign of upper respiratory tract infection but also may be associated with allergies or volatile irritants.

• The diagnosis of allergic rhinitis is made by exclusion and through response to antihistamines or environmental changes.

• Bronchogenic papillary adenoma develops in approximately 30% of guinea pigs older than 3 years of age.

• Diagnosis is often an incidental finding when thoracic radiography is performed for another problem. • Occasionally, clinical signs are seen as a result of pressure on the heart or great vessels.

• Dyspnea most frequently is caused by heat stress or trauma. Other causes are pregnancy toxemia, gastric bloat, volatile irritants, pleural effusion, pneumonia, or pulmonary edema.

Rhabdomyomatosis is a common necropsy finding. Gross lesions appear as pale foci located on the endomyocardium and valves. Histologic examination reveals myocardial cells that have stored excessive glycogen. Do not confuse these areas with thrombi, abscesses, or neoplasia. Their clinical significance is unknown.

• Paraspidodera ucinata is the cecal pinworm of guinea pigs. They are generally asymptomatic, but heavy infestations can cause diarrhea and weight loss.

• Diagnosis is based on fecal examination or cellophane tape test. • Treat with piperazine or fenbendazole (see Table  177 -8).

• Coccidiosis caused by Eimeria caviae is a fairly common cause of diarrhea in guinea pigs recently purchased from pet stores.

• Clinical signs are tenesmus, diarrhea, dehydration, and death. • Diagnosis is based on fecal examination. On gross postmortem examination, petechiation and thickening of the colon are seen. • Treat supportively and administer sulfa drugs (see Table 177 -9).

• Cryptosporidium wrairi and Giardia spp. are found rarely. They cause a chronic enteritis. Balantidium spp. are thought to be nonpathogenic.

• Malocclusion in guinea pigs is diagnosed on oral examination.

• Clinical signs are ptyalism and anorexia. The premolars are the most commonly affected teeth. • Long-standing hypovitaminosis C predisposes guinea pigs to malocclusion.

• Treat malocclusion as in other rodents (see "Dental Procedures").

• Hypovitaminosis C (i.e., scurvy) is associated with soft, malodorous feces. Degeneration of the epithelium of the intestinal tract adversely affects digestion and absorption and allows secondary bacterial infections.

• Diagnosis of scurvy is based on clinical signs, the exclusion of other causes of diarrhea, and response to vitamin C therapy (see Table 177 -10).

• Salmonellosis usually is contracted through contaminated feed.

• Clinical signs range from sudden death to diarrhea and anorexia. The diarrhea is frequently light colored. Sepsis is common and may cause conjunctivitis, shock, pneumonia, abortion, and neurologic symptoms. • Diagnosis is based on isolation on culture of feces or other appropriate tissue samples. • Treatment is controversial because recovered individuals remain carriers. Use sulfa antibiotics or enrofloxacin (see Table 177 -9) until sensitivity testing results are available. Supportive care is essential.

• E. coli, Arizona, and Clostridium are other commonly cultured diarrhea-causing organisms. Clostridium are diagnosed most easily by finding large numbers of spores on a Gram stain fecal specimen. Treat with metronidazole (see Table 177 -9).

• Yersinia pseudotuberculosis either causes an acutely fatal diarrhea or localizes into regional lymph nodes.

• Diagnosis is based on culture.

• Treat by surgical removal or drainage of abscessed lymph nodes. Mesenteric lymph node involvement necessitates abdominal surgery. Treat with sulfa drugs or enrofloxacin until susceptibility testing results are available (see Table 177 -9).

• One male usually is housed with four to six females for breeding purposes. Signs of estrus are vulvar swelling, lordosis, and opening of the vaginal closure membrane. Fetuses are palpable at 4 to 5 weeks of gestation. Parturition occurs within 48 hours after the pubic symphysis has reached 15 mm. Neonates weighing less than 60 g have a grave prognosis for survival even with intensive care. Neonates normally do not nurse for the first 12 to 24 hours. Litters with five or more fetuses usually result in abortion.

• Dystocia commonly occurs in females bred after the age of 6 to 9 months. After this age, the symphysis fuses and is unable to open the 2 to 3 cm required to allow passage of a fetus. Dystocia in younger guinea pigs may be caused by obesity, large fetal size, fetal malpresentation, subclinical ketosis, or uterine inertia. On presentation, check the pelvic symphysis. If active contractions are present and the symphyseal gap is less than 2 cm, perform a C-section. Normal parturition is very rapid, with a rest of only 3 to 7 minutes between fetuses.

• Perform a C-section if active straining does not produce a fetus within 15 to 20 minutes. Radiograph sows with a history of weak contractions to determine the stage of pregnancy and evaluate the size of the fetuses. If well-developed skeletons of appropriate size are seen and the pubis has not yet fused, give oxytocin and calcium (see Table 177 -10). If no fetuses are produced within 15 to 20 minutes, perform a C-section.

• If poorly developed fetuses are seen radiographically, consider fetal death, ketosis, or a nonreproductive disorder as possible causes of dystocia.

M Key Point Pregnancy toxemia usually is seen in obese sows with large litters in late pregnancy.

Other risk factors include systemic disease or diet change causing anorexia, genetics, stress, and first litter.

• Clinical signs are tachypnea, depression, malodorous breath, seizures, and icterus. A urine pH of less than 6 with marked proteinuria is compatible with pregnancy toxemia. A marked hyperkalemia and elevation of liver enzymes often occurs. Thrombocytopenia may be present. • Treat with IV or IO saline, dextrose, glucocorticoids, and calcium. Surgical abortion of the fetuses may be attempted, but the anesthesia risk is quite high. Prognosis for survival is grave. Do not rebreed affected females. Do not breed sows heavier than 900 g.

• Large litters can cause a hemorrhagic syndrome.

Compression of the portal vein and liver causes hepatic dysfunction, which results in vitamin K and clotting factor deficiency.

• Treat with vitamin K supplementation (see Table  177 -10). Response is poor in severely compromised patients. Affected individuals are at risk of ketosis developing. Prognosis is guarded.

• Vaginitis in guinea pigs frequently is caused by foreign bodies, usually bedding.

• Diagnosis is made on vaginal examination.

• Treat by flushing the vagina to remove the foreign material.

• Vaginal discharge also can be caused by pyometra, uterine torsion, urinary tract infection, or urogenital neoplasia.

• Diagnosis is based on findings on abdominal palpation, vaginal cytology and culture, urinalysis, abdominal radiographs, ultrasound, and exploratory. • Treatment varies with the condition and is similar to that used in cats.

• Ovarian teratomas and uterine tumors occasionally are diagnosed and usually resolve with ovariohysterectomy.

• A symmetric alopecia with concurrent abdominal enlargement may be seen in female guinea pigs with cystic ovaries.

• Diagnosis is based on abdominal palpation, cytology, and ultrasound. • Treat by performing an ovariohysterectomy. If the guinea pig is not a good candidate for surgery, human chorionic gonadotropin (hCG, 1000 USP units IM, repeat in 1 week) may temporarily resolve clinical signs.

• Male guinea pigs are prone to preputial foreign bodies. A preputial discharge is the usual presenting complaint.

• Diagnosis is based on physical examination.

• Treat by removing foreign bodies and performing local flushing. Chronic problems require a change in bedding.

• Male guinea pigs produce sebaceous secretions in the folds around their perineal area. Clean these areas with soap and water semiannually to prevent localized pyoderma.

• If pyoderma occurs, treat with topical therapy and oral antibiotics.

Bacterial cystitis and urolithiasis are relatively common in guinea pigs. Diagnosis is based on a history of stranguria, hematuria, painful abdomen, and anorexia, in addition to abdominal palpation, urinalysis, urine culture, abdominal radiographs, and ultrasonography. Treatment consists of antibiotics based on results of culture and susceptibility testing and surgical removal of calculi, if present. Prevention of recurrence is difficult if the calculi are not caused by a bacterial infection. Addition of vitamin C to the drinking water as well as changing the brand of diet are sometimes helpful in preventing recurrence of metabolic stones.

Klossiella cobayae is a coccidia that lives in the renal tubules. It has no clinical significance.

The most common orthopedic problem seen in guinea pigs is overgrown toenails. This leads to pododermatitis and sore hocks as well as to degenerative joint disease and a predisposition to tibial fractures.

Tibial fractures are the most common fracture seen in guinea pigs. They most frequently occur after foot entanglement. Internal fixation with an IM pin or application of a Kirschner apparatus is the repair of choice.

M Key Point Signs of hypovitaminosis C or scurvy start to develop in guinea pigs as early as 10-15 days if they are placed on diets 100% deficient in vitamin C.

Early signs are soft, malodorous stools, weight loss, poor hair coat, and anorexia. Later, petechia, gingivitis, cutaneous and oral sores, swollen costochondral junctions, joint pain and hemorrhage resulting in lameness, and conjunctivitis become apparent. Treat supportively and administer parenteral vitamin C (25 mg/day).

• Lymphocytic choriomeningitis occurs as in mice. • Guinea pig paralysis syndrome starts with mild pyrexia and urinary incontinence, followed by weight loss and posterior paresis that progresses to paralysis. Currently, the etiology is unknown, but it does not appear to be contagious.

• Treat with supportive care. Prognosis for long-term survival is grave.

• Head tilt is usually the result of otitis or trauma (see "Mouse").

Cavian leukemia has a viral etiology. The liver, spleen, and lymph nodes are the primary organs involved. There is no current treatment. Quarantine exposed individuals. Death usually occurs within 5 days after discovery of lymphoblasts in the peripheral blood.

Neutrophils normally have red granules. Kurloff bodies are normally occurring eosinophilic intracytoplasmic inclusion bodies that are found in mononuclear cells. They are seen most frequently in females and appear to correspond positively with estrogen levels.

Metastatic calcification occurs in most guinea pigs older than 1 year of age. It is more severe in females than in males. The stomach is one of the first organs affected. Dysfunction in motility causes obstruction. The tendency appears to be exacerbated by high calcium and low phosphorus diets.

Exotic Animal Formulary

The Biology and Medicine of Rabbits and Rodents

Veterinary Clinics of North America