key: cord-021413-1ht1xm88 authors: Kraft, Lisbeth M. title: Viral Diseases of the Digestive System date: 2013-10-21 journal: Diseases DOI: 10.1016/b978-0-12-262502-2.50016-x sha: doc_id: 21413 cord_uid: 1ht1xm88 This chapter discusses three virus infections affecting the digestive system of mice and their properties: (1) epizootic diarrhea of infant mice (EDIM), (2) reovirus 3 infection, and (3) murine hepatitis virus infection (MHV). All three infections may cause serious, debilitating, and sometimes fatal diarrheal disease in nursling and weanling mice. Mice of all ages can be infected by the EDIM virus but overt disease is restricted to animals up to about 12–13 days of age at the time of first exposure. The EDIM virus is worldwide in distribution. Its prevalence is difficult to estimate because serologic tests have not been readily available, and it is not customary to sacrifice animals for the purpose of examining the appearance of their intestinal tract or for electron microscopic visualization of fecal contents. The acute disease of reovirus 3 infection affects mainly sucklings and weanlings, whereas the chronic disease is encountered in animals over 28 days of age. The MHV virus, on the other hand, has been found to affect cotton rats, rats, and hamsters. epidemic diarrhea of infant mice, it is common knowledge that virtually every colony of conventional mice suffered that infec tion to a greater or lesser extent. In recent years, with the advent of measures such as cesa rean derivation, barrier-sustained breeding and maintenance procedures, routine serologic surveillance, laminar flow hoods or rooms, and filter-top cages, the problems associated with these diseases have become somewhat less critical. Neverthe less, they are at times and under certain circumstances still troublesome. All three infections may cause serious, debilitating, and sometimes fatal diarrheal disease in nursling and weanling mice. Thus, the economic impact on commercial mouse col onies can be severe. Furthermore, newborn mice, pooled from many dams and then redistributed to them at random, are used for the isolation and identification of certain viruses in diagnos tic and epidemiological studies, for example arboviruses (Shope, 1980) , coronaviruses , and reoviruses (Stanley, 1977) . Clearly, indigenous infection with related or identical agents in only a few such infants could confound and compromise the validity of observations follow ing the inoculation of test materials. It should be pointed out, too, that Collins and Parker (1972) demonstrated both reovirus 3 and murine hepatitis virus as contaminants in some murine leukemia and transplantable tumor specimens. Whereas it is mainly from these standpoints that the diseases in question derive importance, they should not be dismissed without considering their intrinsic value as models for elucidat ing the pathogenesis and control of related infections in man and other animals as well as their utility for the molecular biologist. Cheever and Mueller (1947, 1948) , Pappenheimer and En ders (1947) , and Pappenheimer and Cheever (1948) were the first to describe the pathological changes and epidemiology of EDIM. Runner and Palm (1953) and Cheever (1956) also con tributed to knowledge concerning the epidemiology and etiol ogy of the disease. Thereafter Kraft (1957 Kraft ( , 1958 Kraft ( ,1961 Kraft ( ,1962b Kraft ( , 1966 reported on studies regarding the etiology, mode of transmission, carrier state, immune response, pathogenesis, and control of the disease. Serologic studies were also under taken by Blackwell et aL (1966) . Kraft (1963, 1967) first demonstrated the agent in electron micrographs of infected infant mouse intestinal epithelium. Banfield et aL (1968) enlarged on those findings, comparing the virions to those of the reoviruses. Particles of similar morphology were subsequently observed in the diarrheal feces of many species, primarily in the young: cattle (Mebus et aL, 1969) , man (Flewett et aL, 191 A) , horse (Flewett et aL, 1975) , pig (Rodger et aL, 1975) , sheep , rabbit , deer (Tzipori et aL, 1976) , goat (Scott et aL, 1978) , and dog (England and Poston, 1980) . In addition, one virus, SA-11, was isolated from a nondiarrheal monkey, and another, OA (offal agent), was recovered from intestinal washings of sheep in an abattoir (Els and Lecatsas, 1972) . Much and Zajac (1972) purified EDIM virus from diarrheal infant mice and further characterized it. Based on its moφhology and other known characters, EDIM virus has been placed into the genus Rotavirus in the family Reoviridae (Matthews, 1979) . During the past decade, knowl edge of the rotaviruses as agents of diarrheal disease of young mammals has burgeoned, especially with regard to those af fecting children, calves, and piglets. Reviews concerning the genus have been published by Wyatt et aL (1978 ), McNulty (1978 , Flewett and Woode (1978) , Andrewes et aL (1978) , and Holmes (1979) . Additional comments may be found in the American Veterinary Medical Association Panel the Young (Anonymous, 1978) . The classification of EDIM virus in the genus Rotavirus, family Roeviridae, derives from its moφhology and mode of replication as seen in electron micrographs (Adams and Kraft, 1967; Banfield et aL, 1968) , which were later shown to re semble those observed in ultrathin sections in human intestinal material containing ''reovirus-like" particles (Bishop et aL, 1973) . The term rotavirus (L. rota, wheel) was proposed by Flewett et aL (1974) because of its moφhology as viewed in negative-contrast electron micrographs. It has become widely used in preference to duovirus, which is synonymous (David son et aL, 1975) . There is no evidence that antigenic or pathogenetic variants of EDIM virus exist. Analysis of RNA segment and struc tural polypeptide variation, however, as has been accom plished for other rotaviruses Derbyshire and Woode, 1978; Rodger and Holmes, 1979) , may reveal differences among strains. Further, several serotypes have been described a m o n g the h u m a n rotaviruses by m e a n s of the serum neutralization test (Beards et al., 1980) . This technique may also prove useful in future studies of E D I M virus strains. a. Morphology, Size, and Composition. Kraft (1962b) , using Millipore filters, determined the size of the infective E D I M virion to be between 33 and 100 n m . In electron micro graphs, A d a m s and Kraft (1967) mined the m e a n diameter of 100 virions of purified E D I M virus to be 5 4 . 4 ± 2 n m . O n the other h a n d , Melnick (1979) gives about 50% is lost at 4X for 24 hr or at 37T for 1 hr. Although some infectivity (>0.05%) remains at either 56°C or 60°C for 30 min, it is abolished at 70T for 15 min (Cheever and Muel ler, 1947; Kraft, 1957 Kraft, , 1962b . Much and Zajac (1972) found that the purified virus is unstable at both 4° and -24''C for 2 weeks but found that at -70°C infectivity is retained for at least 4 weeks. c. Ejfect of Chemicals. In an intestinal filtrate, EDIM virus titer is not significantly reduced when held in ether or 0.1% sodium deoxycholate at 4°C for 24 hr (Kraft, 1962b) . According to Much and Zajac (1972) , the purified virus is stable in 20% ether, 5% chloroform, or 0.1% sodium deoxycholate at 4°C for 1 hr and, as is true for other rotaviruses, is resistant to pancreatin. Ward and Ashley (1980a,b) examined the effects of the anionic detergent sodium dodecyl sulfate and of the chelating agent ethylenediaminetetraacetate on purified simian virus and determined that low concentrations and mild temper ature conditions readily inactivated the agent. Both chemicals modified the viral capsid to prevent adsoφtion of the inacti vated virions to cells. Indeed, this study was the outgrowth of a need to determine the survival of enteric viruses in wastewater. It had been determined that wastewater sludge reduced the heat necessary for simian rotavirus inactivation. Ionic detergents in the sludge were identified as the active components. Nonionic detergents did not destabilize the virus; further, these com pounds protected the virus from the destabilizing effect of sodium dodecyl sulfate. Destabilization by both cationic and anionic detergents was found to be dependent on the pH of the medium. A systematic study of the stability of EDIM virus to extremes of pH has not been reported. Much and Zajac (1972) Kraft (1966) Replication of EDIM virus occurs in epithelial cells of the villi of the small intestine. In electron micrographs, Kraft (1967), Banfield etal. (1968) , and Holmes etal. (1975) demonstrated replication by budding in distended cistemae of the endoplasmic reticulum. The significance of intracytoplas mic and intranuclear tubular structures encountered is not clear. Using direct immunofluorescence, Wilsnack et al. (1969) found that EDIM virus antigen in infant mice is limited to the cytoplasm of the villous epithelium from the duodenum to the colon and is detectable within 48 hr after peroral inoculation. Stainable virus was also seen in the intestines of contact infant mice without necessarily causing clinical signs to appear. The virus could not be stained in the stomach or liver of mice infected either naturally or experimentally. Kraft (1958) studied the distribution of infectious EDIM virus in 3-day-old mice following peroral inoculation. At 3 hr, virus was detected in the stomach and small and large intes tines (the cecum was not tested) and could not be recovered from the lungs, liver, spleen, kidney, or blood. At 22 hr, all those tissues were positive except for the kidney. The bladder and urine, as well as the brain, were also devoid of the agent, but at 30 hr, these too were positive. At 72 hr, the liver, spleen, kidney, and intestines yielded virus, but the brain was negative. The blood, stomach, lungs, bladder, and urine were not tested at that interval. At 6 days, blood, liver, and intestines, the only tissues examined, still contained virus. Ingested virus from a diarrheal litter brings about an active infection in the nursing dam that previously had been nondiarrheal herself and had had only nondiarrheal litters (Kraft, 1958) . Blood, liver, spleen, and feces all contain infectious virus in the dam 1 week after her litter is given virus perorally as an intestinal filtrate. Later, Kraft (1961) determined that adult male mice can also be intestinal carriers for at least 17 days after a single peroral exposure. With regard to the mechanism of cell penetration. Holmes et al. (1976) proposed that lactase of the villous brush border of the intestine may be the receptor that uncoats the rotavirus virion by attacking the glycolysated polypeptides of the outer capsid. In addition, pancreatic enzymes within the lumen may also be instrumental in the infectious process (see Section II,B,6). The question of cofactors that might enhance pathogenicity or of interfering substances, in addition to antibodies, that might inhibit EDIM virus replication is open. Kraft (1958) found increased numbers of Clostridium tertium in the intes tine of diarrheal animals, and Pappenheimer and Enders (1947) remarked on the persistent presence of ''coccoid bodies" in the intestines of diarrheal animals as seen by light microscopy. In both instances, these may be considered opportunistic or ganisms. Their effect on the severity of the clinical disease is unknown, however. One report (LaBonnardiere and deVaurieux, 1979) The use of standard methods to grow EDIM virus in tissue culture has resulted for the most part in failure. Habermann (1959) (Thiel et al., 1978) . Further, Babiuk et al. (1977) and Al meida et al. (1978) state that calf rotavirus production is mark edly enhanced when passaged in the presence of trypsin. Clark et al. (1979) produced high-titer calf rotavirus in a variety of continuous cell lines, also by utilizing trypsin, and Matsuno et al. (1977) were successful in producing plaques with bovine rotavirus in monkey kidney cell monolayers when trypsin was incorporated in the overlay medium. Estes and Graham (1979) found that simian virus titers were enhanced by both trypsin and elastase in Vero as well as MA 104 cells. Ramia and Sattar (1980) studied additional proteolytic enzymes utilizing plaque formation by simian virus SA-11 in MA 104 cells as the endpoint. Elastase, a-chymotrypsin, subtilase, pronase, and pan creatin were as effective as trypsin, whereas pepsin, papain, and thermolysin were ineffective. Another approach with human rotavirus has been to incoφorate the agent into cells by means of low-speed centrifugation of the two together (Banatvala et al., 1975; Bryden et al., 1977; Schoub et al., 1979; Wyatt et al., 1980) . It remains to be seen if similar treatments will lead to suc cessful cultivation of EDIM virus in tissue culture. Chick embryos appeared unaffected when the chorioallantois was inoculated. The agent did survive up to 5 days, but an increase in infectious titer could not be demonstrated (Kraft, 1958) . Moon (1978) of each disease appears to be reflected not only in the particular group of cells but also in the numbers of host cells involved. Lucid descriptions of the natural clinical disease are given by Cheever and Mueller(1947) , Seamer (1967) , and McClure et al. (1978) . The experimental disease does not differ signifi cantly (Kraft, 1957 (Kraft, , 1962b . Overt illness is confined to pre- Typical appearance of infant mice infected with enterotropic MHV (pair of mice at left) or rotavirus (pair at right) compared with normal mice of the same age (center pair). Note the evidence of inanition and dehydration in the MHV-infected animals, whereas those infected with rotavirus show mainly a somewhat prominent abdomen and only a slightly smaller size than the normal control mice. weanling mice. T h e first signs usually appear at 7 -8 days of age. In mild cases diarrhea is manifested by a minimal amount of pasty fecal material about the perineum. In severe cases the amount is copious, the entire infant becoming soiled. Rectal impaction may occur at about 1 2 -1 6 days of a g e , and death can ensue if the impacted mass is not removed spontaneously or deliberately. Death does not seem to be the result of the virus infection per se, but rather as a consequence of protracted obstipation. In pure E D I M virus infections, mice continue to nurse throughout their illness (in the absence of impaction). They may be slightly stunted (Fig. 2 ), but those with mild cases soon attain the weight of their nondiarrheal peers. Especially when diarrhea is mild, morbidity in the natural disease m a y be difficult to ascertain, but one could quite cor rectly assume that, if diarrheal signs are observed in a few litters, it is likely that all infants in a colony will sooner or later be affected. Concerning mortality, Cheever and Mueller (1947) state that there was both 100% recovery and 100% lethality in their outbreaks. Based on present k n o w l e d g e , the first is suggestive of E D I M virus infection and the latter of another disease, perhaps murine (mouse) hepatitis. At no time do a d u h mice exhibit signs of illness ascribable to E D I M virus infection. In the experimentally induced dis ease, the absence of external clinical signs cannot be relied upon for a negative diagnosis (Kraft, 1957) . Necropsy of each animal is essential. In this w a y , the appearance of the colonic contents can be observed, which in normal infant mice are burnt orange in color and semisolid but formed in consistency. T h e colon is not distended. In diarrheal m i c e , however, even in those with no external soiling, the colonic contents are fluid or m u c o i d , bright lemon yellow to amber, or gray-green, with no formed feces in evi dence. G a s is often seen in the colon and c e c u m , which are distended. T h e stomach, t o o , is distended with curdled milk (except in terminal cases with anal impaction). All other or gans appear normal. Gross change is not seen in the intestines of adults exposed perorally. It is noteworthy that in germ-free infant m i c e , ex perimental E D I M virus infection appears in the gross as it does in conventional mice (Kraft, 1966) . The histologic picture has been confirmed by others (Adams and Kraft, 1967; McClure et aL, 1978) . There is no inflam matory reaction in the intestines. Inclusions may indeed be found in enterocytes near the tips of villi, especially in the jejunum, and infrequently in the sloughed cells seen in the lumen. Epithelial cells near and at the tips of villi are fre quently vacuolated. Acres and Babiuk (1978) have pointed out that in all species studied, the rotaviruses cause diarrhea by attacking and de stroying the columnar epithelium of the small intestine. Middleton (1978) considers that cell migration from the crypts is speeded in response to diarrhea and that the infected cells are relatively immature. Enzyme levels, high thymidine kinase and low sucrase, are similar in such cells to those of normal crypt cells and thus support this view. The microscopic appearance belies the severity of the gross and clinical findings of EDIM. In this regard, D-xylose absorp tion has been studied in calves in which 60-90% reduction occurred during the acute illness with the calf rotavirus . Aberrations in sodium transport have also been investigated in other animals and in humans (Middleton, 1978) , but such studies have not been carried out in mice using the mouse agent. Cheever and Mueller (1947) and Kraft (1957) demonstrated that the agent is transmissible perorally. Kraft (1957) showed further that dissemination in a mouse colony is mediated prin cipally by the airborne route. Kraft (1961) examined the neutralization test in EDIM and found that antibodies were not always formed following infec tion, and when they were present, they tended to be low in titer. Sera from adult mice having had lifelong contact with the agent (in the form of consistently diarrheal litters) were more apt to neutralize the virus than those of mice exposed for the first time as adults. On the other hand, hyperimmunization of mice has resulted in the production of significant serum titers of both complement-fixing and neutralizing antibodies (Blackwell etaL, 1966) . Antibody response measured by other serologic tests has not been investigated for EDIM, nor have immune substances in lacteal secretions been measured directly. Suggestive of their presence, however, are data showing that infants of primiparae who themselves had been diarrheal in infancy resisted about 10 ID50 more of EDIM virus than did offspring of previously nondiarrheal dams (Kraft, 1961) . Antirotaviral immunoglobu lins have been found in both colostrum and milk in man (Yolken et aL, 1978c; Simhon and Mata, 1978; Thouless et aL, 1977a) , bovines (Acres and Babiuk, 1978) , and lambs (Snodgrass and Wells, 1976) . Indeed, local immunity afforded by lacteal immune substances is regarded as crucial for protection against any intestinal infection in the young (Welliver and Ogra, 1978; Snodgrass and Wells, 1976 As indicated, mice of all ages can be infected, but overt disease is restricted to animals up to about 12-13 days of age at the time of first exposure. There seems to be no predilection for a particular sex. The observation that first litters are more apt to show copious and protracted soiling than those of later parity has been reported by Cheever and Mueller (1947, 1948) and by Runner and Palm (1953 EDIM Virus is probably worldwide in distribution. Whether it occurs in wild mouse populations is unknown. Its prevalence is difficult to estimate, since serologic tests have not been readily available, and it is not customary to sacrifice animals for the purpose of examining the appearance of their intestinal tract or for electron microscopic visualization of fecal contents. As has been shown experimentally, latent carriers can exist. The carrier rate in a diarrheal colony is not known, nor is the frequency of viral shedding under colony conditions. Cheever and Mueller (1948) examined seasonal variations in the weaning percentage in their mouse strains and found that there was a significant effect in only the CFW mice. They experienced the lowest weaning rate in the late fall and winter. Runner and Palm (1953) , studying C3H mice, indicated that there was a higher incidence of diarrhea in December/January (Kraft, 1961; Blackwell et al., 1966) , complement fixation (Wilsnack et al., 1969; Kapikian et al, 1976; Thouless et al., 1977b) , direct immunofluorescent staining or precipitin (Wilsnack et al., 1969; Spence et al., 1975; Foster α/., 1975; Peterson α/., 1976) , immune electron microscopy (Kapikian et al., 1974; Bridger and Woode, 1975) , immunoelectroosmophoresis (Tufvesson and Johnsson, 1976; Middleton et al., 1976) , enzyme-linked im munosorbent assay (ELISA) (Scherrer and Bernard, 1977; El lens etal., 1978; Yolken etal., 1978a,b,c) , radioimmunoas say (Acres and Babiuk, 1978; Kalica et al., 1977; Middleton et al., 1977) , immunodiffusion (Woode et al., 1976) , hemagglutination inhibition (Fauvel et al., 1978) , enzymelinked fluorescence assay (ELISA) (Yolken and Stopa, 1979) , an unlabeled soluble enzyme peroxidase-antiperoxidase method , plaque reduction test (Estes and Graham, 1980) , serologic trapping on antibody-coated electron microscope grids (Nicolaieff et al., 1980) , a solid phase system (SPACE, solid phase aggregation of coupled erythrocytes) for detection of rotaviruses in feces (Bradbume et al., 1979) , and immune electron microscopy with serum in agar diffusion (Lamontagne et al., 1980) . More recently, Sheridan and Aurelian (1981) have described an ELISA test for EDIM virus which should prove beneficial for both practical (serologic) purposes and for investigations of the antigenic structure of the virion. In the absence of a reliable tissue culture system, EDIM virus isolation is generally impractical. Bacteria-free filtrates of intestinal suspensions can, of course, be given to diarrheafree animals (gnotobiotes or axenics), but this is expensive and inefficient. On the other hand, such filtrates may be concen trated by ultracentrifugation and examined in the electron mi croscope for characteristic virus particles Flewett, 1978) . The particles may also be identified by immune electron microscopy. A practical approach to a presumptive diagnosis would be to kill selected animals in order to examine the appearance of the colonic contents. The inclusion of sentinel dams with litters in a breeding colony should be considered. These might be sac rificed at intervals to determine the presence of EDIM in the colony. Together with the clinical history of the mouse colony, this practice may provide a fairly reliable, although not pathognomonic, indication of the presence of EDIM. His topathologic examination could also be of value. Based on experimental results, Kraft et al. (1964) proposed the use of air-filter devices, essentially dust caps for each cage, for the practical control of airborne transmission of EDIM in a commercial mouse colony. It was subsequently shown (Kraft, 1966 ) that 43% of first litters and 79% of all other litter parities were weaned from cages without filters, whereas in cages pro vided with filters, weaning percentages were 96 and 99%, respectively, during the same observation period. It should be pointed out that both EDIM and mouse hepatitis virus (LIVIM) were present simultaneously in that colony. Although the filter devices did not eliminate the disease(s), they probably reduced the pathogenic microbial load in the immediate environment of the susceptible animals, but the precise mechanism by which this control method succeeds to the extent that it does is obscure. Since that time (1964), various devices based on a filter cage or filter-top design have been utilized. Some of these are de scribed by Simmons and Brick (1970) . Woods et al. (1974) evaluated them from the viewpoint of environmental factors within the cages. They found that dry bulb temperature dif ferentials, comparing environments inside and outside the cage, were not significantly different (about 2°C) between fil tered and unfiltered cages, but that dew point differentials were significantly greater in the filtered cages (about 5°C) than in unfiltered cages (about 3°C). However, they concluded that a suitable cage size for a particular species and number of ani mals could compensate for the higher wet bulb readings under filters to maintain acceptable conditions for the animals. Cur rently, several types of filter covers or bonnets are available commercially. Vaccination as a method of control has not been attempted. Judging from the lack of reports to the contrary, caesarian derivation together with barrier maintenance apparently elimi nates and controls the infection. Kunstyf (1962) attempted to control EDIM by decontamina tion of air by the use of triethylene glycol but was unable to do so. The use of antibiotics, too, is without value, although there seems to be amelioration of signs for a short period as secon dary organisms are temporarily reduced in number. As indicated by Kraft (1966) , it may be relatively easy to establish a colony of mice free from EDIM virus infection. This may be accomplished by eliminating those breeding pairs whose first litter is diarrheal. Filter devices are required for this, and they and the animals must be handled with the aid of a transfer or laminar flow hood using sterile techniques during observation and handling of the animals. The method is suita ble for small colonies, but it is impractical for commerce where caesarian derivation and barrier maintenance are the methods of choice. Reovirus 3 was first isolated from the feces of an Australian child manifesting a cough, fever, vomiting, hypertrophic tonsils, and bilateral bronchopneumonia. It was named hepatoencephalomyelitis virus by Stanley et al. (1953) , who originally recovered the agent. Sabin (1959) proposed the name reovirus for a group of agents associated with the respi ratory and enteric tracts of humans. They were found to be ether resistant, about 70 nm in size by membrane filtration but of unknown shape, and caused distinctive cytopathic effects in monkey kidney tissue cultures. One of the ECHO group of viruses, ECHO 10, now synonymous with reovirus, became a member of the new group on that basis. (ECHO is the acronym for enteric cytopathic /zuman 6>φhan, agents isolated in tissue culture from asymptomatic humans-so-called viruses in search of disease.) Stanley (1961) then demonstrated that the hepatoencephalomyelitis virus was serologically identical to reovirus 3. Additional strains have since been recovered from humans, other mammals, marsupials, birds, insects, and reptiles (for review, see Stanley, 1974) , and from moUusks (Meyers, 1979; Meyers and Hirai, 1980) . Reoviruses have been divided into three serotypes on the basis of hemagglutination inhibition and neutralization tests (Sabin, 1959; Rosen, 1960) . Reovirus 3 was established as an indigenous murine virus by Hartley et al. (1961) and by Cook (1963) . Reviews concerning the biological and clinical aspects of disease caused by this agent have been prepared (Stanley, 1974 (Stanley, , 1977 . When Gomatos et al. (1962) and discovered that reoviruses possess double-stranded RNA, a unique characteristic among viruses, molecular biologists were inspired to study them in minute detail. Currently, knowledge of reovirus replication on biochemical and biophysical planes is as extensive as that available for any other virus and is, for the most part, outside the scope of this chapter. Interested readers are therefore referred to reviews by Shatkin (1969) and Joklik (1974) for extended literature coverage and detailed dis cussion and to Andrewes et al. (1978) for a condensed over view. or Reovirus, in the family Reoviridae (Melnick, 1979) . Wild-type strains of reovirus 3 include: Dearing, the pro totype strain (Sabin, 1959) , isolated from a child with diarrhea; Abney (Rosen, 1960) , isolated from a child with a febrile upper respiratory infection; CAN 230, from a case of Burkitt's lymphoma (Bell et al., 1964) ; and several strains obtained from naturally infected cattle (Rosen, 1960) . Mutant, temperature-sensitive (ts) strains have been developed in the laboratory (Fields and Joklik, 1969) and have been used for studying the synthesis of viral RNA and peptides (Cross and Fields, 1972; as well as for examining problems of pathogenesis. A neurotropic strain was also de-rived from the m o r e hepatotropic original isolate (Stanley et aL, 1954) . T h e reovirus 3 virion (Fig. 3) has a m e a n diameter of about 6 0 -7 6 n m and is icosahedral in shape, with 5:3:2 symmetry. Particles have a core, an inner layer or shell containing a n u m b e r of capsomers formalin at 56°C. Ether treatment was ineffective. Rozee and Leers (1967) determined that although cholorform does not affect infectivity, it does destroy the hemagglutinin. Wallis et al. (1964) found that Mg^^ enhances the titer of reovirus at 50°C. The infective titer increased four to eight times by heat ing for 5-15 min in 2 Μ MgCl2. Other divalent cations and NaCl were ineffective. Hemagglutinin was not affected. It is thought that the high temperature and Mg^+ caused activation of reovirus particles that were inactive in the original prepa rations. As with rotavirus. Ward and Ashley (1978) found that reovirus was sensitive to anionic detergents in wastewater sludge, i.e., these chemicals decreased the temperature needed to inactivate the virus. Cationic detergents were more active than anionic, and nonionic detergents were inactive in decreas ing reovirus thermal stability. Mutagens (nitrous acid, nitrosoguanidine, and proflavine) have been applied to reovirus 3 (Fields and Joklik, 1969) . The resulting mutants are of interest not only to the molecular biologist but to the clinical virologist as well, since some of them produce altered disease pictures (Fields and Raine, 1972) . For example, when inoculated into rats, wild-type virus produced a necrotizing encephalitis, whereas a mutant gave rise to a slowly progressive communicating hydrocephalus. The effects of enzymes are described below (see Section III,B,5). In phosphate-citrate buffers, Stanley et al. (1953) ascertained that the virus is stable between pH 2.2 and 8.0. e. Antigenic Determinants. Sabin (1959) demonstrated that the mammalian reoviruses known at that time could be divided into three serologic groups by neutralization tests. They could also be differentiated by hemagglutination inhibi tion (Rosen, 1960 ), Hull et al. (1956 having discovered that ECHO 10 virus possessed a hemagglutinin for human O eryth rocytes. Later, reported that reovirus 3, but not reovirus 1 or 2, agglutinated ox erythro cytes. The reovirus 3 hemagglutinin was inhibited by nonspecific substances such as normal mouse, rabbit, or rat serum, and by Vibrio cholerae filtrate. Weiner et al. (1978) were able to show that the 57 RNA segment, which is associated with type specificity, encodes the polypeptide that determines the hemagglutinating properties of the virion. Complement-fixing antigens were prepared by Stanley et al. (1953, 1954) and by J. C. Parker et al. (1965, 1966) . These are group specific. Leers et al. (1968) determined that reovirions display at least one type-specific and one to two group-specific antigens when studied by immunodiffusion. With the more sensitive Im munoelectrophoresis technique, however, these authors en countered two type-specific and four group-specific precipitin lines. The agent is regarded as pantropic in mice. In neonates, Stanley et al. (1953) (Wolf et al., 1981) . Papadimitriou (1965 Papadimitriou ( , 1966 Papadimitriou ( , 1968 also studied viral replica tion by electron microscopy in the mucosa of the common bile duct and in the liver. Reovirus 3 has been reported to be oncolytic for a mouse ascites tumor by Bennette (1960) , Bennette et al. (1967,a,b) , and Nelson and Tamowski (1960) . Most of the studies dealing with replication of the reoviruses have been accomplished in tissue culture, frequently in plaque assays in L-cell monolayers. Other cells that have been suc cessfully employed are primary kidney monolayers of rhesus, patas, and capuchin monkeys, as well as those of pigs, cats, and dogs. Continuous lines, such as FL human amnion, BS-C-1, and KB, have also been used (Hsiung, 1958; Cook, 1963; McClain etal., 1967; Rhim and Melnick, 1961; Harford et al., 1962) . Harford et al. (1962) (1973a,b,c, 1974, 1979) . Stanley et al. (1953, 1954) reported the development of pocks on the chorioallantois of 12-day-old chick embryos in oculated with infectious brain and liver. The embryos appeared unaffected, and with succeeding passages, the pocks could no longer be observed, although oral inoculation of suckling mice with chorioallantoic suspensions resulted in active disease. Essentially the same results were found following amniotic inoculation. The experimental and natural diseases appear identical ex cept for variations in intensity of signs, perhaps due to dif ferences in infectious dose. Up to 16 days after intraperitoneal inoculation, the mice appear emaciated and uncoordinated. The hair is oily and matted-the so-called oily hair effect (OHE)-an effect that can be demonstrated in contact animáis as well. However, in these mice it disappears as soon as the diseased animal is removed from the healthy ones. The effect was ultimately traced to a high proportion of fat in the intesti nal contents (steatorrhea): 12.9% in infected animals as com pared with 4.6% in normal mice. Feces may contain as much as 29% fat in infected mice (Stanley et al., 1953 (Stanley et al., , 1954 . The thymus and other organs appeared normal. In the central nervous system, neuronal degeneration began about the ninth day and was most prominent in the brain stem and cerebral hemispheres. By the tenth day, perivascular cuf fing as well as neuronal satellitosis was evident. The meninges were infiltrated with round cells and netrophilic leukocytes. By the fourteenth day encephalitis was severe and widespread, with small hemorrhages occurring in necrotic regions. In suckling rats inoculated intracerebrally with reovirus types 1, 2, or 3, viral cytoplasmic inclusions and intranuclear bodies corresponding to Cowdry type Β inclusions have been ob served (Margolis et al., 1975) . The latter were seen in cells that were free from intracytoplasmic inclusions; they were readily found in weanlings, were unassociated with inflam and their microvilli swollen. The common bile duct is dilated, and the ampullary region becomes obstructed with debris. It is this obstruction that leads to both hepatic and pancreatic dys function, for after studying the pancreatic lesions further, Papadimitriou and Walters (1967) concluded that, even though virions were seen in pancreatic acinar cells, the principal cause of acinar degeneration is ductal obstruction. Based on the neutralization test, determined that the SI genome segment is linked to type speci ficity, and Finberg et aL (1979) found that the same genome segment is also responsible for the production of cytolytic Τ lymphocytes after reovirus infection. Tytell et aL (1967) , working with reovirus 3 RNA, found that it was highly active in inducing interferon in rabbits and tissue culture, and Lai and Joklik (1973) showed that coreless virions as well as those lacking the outer capsid shell induce no interferon. The question of the role of interferon in protection of mice from either the acute or chronic infection remains an intriguing problem. In an effort to permit a precise definition of the host cellular immune response to viral antigens, Weiner et aL (1980b) and Greene and Weiner (1980) which also determined serotype-specific humoral (neutraliz ing) and cytolytic T-cell responses. It is clear that the agent can be transmitted by the oral route as well as by parenteral inoculation. Mice respond to the natural infection with neutralizing, hemagglutination-inhibiting, and complement-fixing an tibodies. As indicated earlier (Section III,B,3,^), precipitating antibodies can also be demonstrated. There is no evi dence that any mouse strain is more or less susceptible to reovirus 3 infection than any other, provided the animals come from a colony that is free of the infection. The host range is broad. Stanley (1974) cited at least 60 species that may be infected with reoviruses, and, as men tioned above, it is thought that the prevalence of antibodies in otherwise normal mammals is related to this fact and that mosquitoes or other insects may be operational in the spread of the infection. The acute disease affects mainly sucklings and weanlings, whereas the chronic disease is encountered in animals over 28 days of age. There is no indica tion that either sex is more or less susceptible than the other. In an epizootic described by Cook (1963) , 130 of 800 first litters were affected. Later-parity litters were involved hardly at all. In view of the absent or low complement-fixing antibody titers in the presence of significant hemagglutination-inhibiting titers that follow natural infection, prevalence estimation by immunologic means may be difficult to assess. The data cited by Parker et al. (1966) , 82% of 34 colonies positive, and by Descoteaux et al. (1977) , 100% of five colonies posifive, may be typical incidences for conventional mouse colonies. As already indicated, reovirus 3 infection is regarded as worldwide in distribution. This aspect of reovirus 3 infection has been covered above (Section III,B,l,2a,¿?). munoperoxidase method (enzyme-labeled antibody) has been employed for reovirus 1 (Ubertini et al., 1971 ) and may find application for reovirus 3 diagnosis as well. Although OHE may not be absolutely pathognomonic for reovirus 3 infection, it seems distinctive enough so that a provisional diagnosis may be made when it is seen. Stronger evidence is afforded if the animals are also jaundiced and wasted. Necropsy coupled with histopathologic examination is never a mistake and is to be encouraged. The placement of sentinel animals at strategic locations in an animal colony should be considered. Such animals may be regarded as expendable for sacrific, necropsy, and virus isolation as well as for the acquisition of serum for antibody determinations. There is no evidence that epizootics occur preferentially at a particular time of the year. J. C. Parker et al. (1965, 1966) discussed the serologic diagnosis of reovirus 3 infection, concluding that for these puφoses the hemagglutination inhibition test was the most reliable. In preparing type-specific antisera for standardizafion and controls, Behbehani et al. (1966) found that the ubiquity of inhibitory substances (antibodies included) in most mamma lian species precluded accurate work. They therefore used domestic geese, in which virtually no hemagglutinafion inhibi tion or neutralizing antibodies could be detected prior to im munization. In any event, for routine surveillance, the hemagglutination inhibition test is currently utilized. Comments similar to those expressed for EDIM virus recov ery and visualization apply. Although it is possible to perform these procedures, they are inefficient for routine diagnostic puφoses. Stanley (1977) has outlined methods for this pur pose. In brief, infectious material can be inoculated into tissue cultures (primary rhesus monkey or human kidney) or newbom mice (from reovirus 3 free colonies!), or the material may be subjected to immunofluorescent methods. An im- Cesarean derivation and barrier maintenance are believed to be suitable techniques for control and prevention of reovirus 3 infection. Although no experimental evidence has been found, it is possible that the use of filter devices in conventional colonies might also be helpful in preventing the spread of infection. In the absence of information on the vertical trans mission of the agent, it is impossible to evaluate the influence of that route on successful control of the endemic disease. Although therapy is impractical from the standpoint of con trolling epizootics of reovirus infection, it is nonetheless of considerable interest that Willey and Ushijima (1980) found that thymosin given intraperitoneally to 7-day-old mice that had been neonatally infected with reovirus 2 (2 LD50) signifi cantly increased their mean survival time, provided it was ad ministered at 2200 hr. When given at 0800 hr, significantly increased survival time was not observed, but when inoculated at 1200 hr, there was an apparent decrease in mean survival time. Reviews on the subject include those by Piazza (1969) , Mcintosh (1977) , Kapikian (1975) , Andrewes et aL (1978) , Holmes (1979) , Garwes (1979) , and Robb and Bond (1980) . Based on their own electron microscopic studies and on those of David-Ferreira and Manaker (1965) , Becker et aL (1967) considered that MHV might be an 'TBV-like" (infecti ous bronchitis viruslike) agent. Virions of similar moφhology seen in electron micrographs and also ether sensitive, as is IBV, were being isolated at that time from human cases of colds (Almeida and Tyrell, 1967) . The following year, the term Coronavirus was proposed for the group (Tyrell et aL, 1968) , and in 1975 the Coronaviridae became an official fam ily with a single genus, Coronavirus (Tyrell etaL, 1975 Additional agents may be added to this group, e.g., ''runde" virus (Traavik et aL, 1977) , a Coronavirus causing car diomyopathy in rabbits (Small et aL, 1979) . As noted, many strains of MHV have been recovered from mice under various circumstances. In addition to JHM, these include: MHVl, from "white mice" (P or Parkes strain), dur ing attempts to adapt human hepatitis virus to animals (the strain was originally isolated as a dual agent consisting of the virus and a protozoon parasite, Eperythrozoon coccoides (Gledhill and Andrewes, 1951) ; MHV2, from mice used to propagate murine leukemia virus (Nelson, 1952a,b) ; MHV3, also found during studies on adaptation of human hepatitis virus to mice (Dick et aL, 1956) ; MHV-B (EHF-120), from mice used for human epidemic hemorrhagic fever (HEHF) adaptation attempts (Buescher, 1952) ; an unnamed strain from mice undergoing murine leukemia chemotherapy trials (Braunsteiner and Friend, 1954) ; H747, following intracere bral inoculation of suckling mice with HEHF materials (Morris, 1959) ; MHV-A59, during transfer of Moloney leukemia virus in mice (Manaker et aL, 1961) ; MHV-S, from cesareanderived mice that had been barrier-maintained before exposure to conventional mice ; MHV-C (MHV-BALB/c), isolated during passage of spleens from leukemic mice (Nelson, 1955) ; four addiiional strains from spleens of leukemic mice or from natural outbreaks (MHV-SRl, -SR2, -SR3, -SR4) (Nelson, 1963 (Nelson, , 1965 ; lethal intestinal virus of infant mice (LIVIM), from infant mice dying of a spontaneous infection (Kraft, 1962a) , identified as an MHV strain by Broderson et aL (1976) and Hierholzer et aL (1979) ; and NuU, NuA, Nu66, from nude mice with hepatitis and wasting syndrome . Other isolates have also been derived from nude mice (Sebesteny and Hill, 1974; Ward et aL, 1977) , and Fox et aL (1977) have described a strain that appeared during passage of an ascites myeloma cell line in BALB/c mice. *HEV may also denote the hepatoencephalomyelitis virus of Stanley et al. (1954) , which is identical to reovirus 3. A s reviewed by Mcintosh (1974) , coronaviruses are p l e o m o φ h i c , enveloped, and variable in size, measuring about 8 0 -1 5 0 n m in diameter. Peplomers are 1 2 -2 4 n m in length (Fig. 4 ) . Using various techniques, a n u m b e r of workers have con firmed the diameter of M H V virions to fall within the range of the coronaviruses (Gledhill et al., 1955; Miyazaki et al., 1957; Kraft, 1962a; Starr etal., 1960) . Svoboda etal. (1962) further described the virion as consisting of a nucleoid sepa rated from an outer m e m b r a n e by an electron-lucent space. David-Ferreira and Manaker (1965) , working with M H V -A 5 9 in tissue culture, found that the virions had a m e a n diameter of 75 nm with an electron-dense inner shell, 55 nm in diameter, separated from the outer double m e m b r a n e by an electronlucent space 8 nm wide. Peplomers were 1 6 . 6 -2 3 . 4 n m long. Not only was the virion significantly smaller than that of I B V , but the peplomers dif fered from those of both I B V and H C V 2 2 9 E , being conerather than club-shaped. Mallucci (1965) In general, coronaviruses are inacti vated at 56°C in 10-15 min, at 37°C in several days, and at 4°C in several months (Tyrell etal., 1968; Kapikian, 1975) . Wildtype MHV isolates also fall into this range of sensitivity Gledhill and Andrewes, 1951; Gledhill et al., 1955; Kraft, 1962a) . Hirano et al. (1978) , however, indicated that MHV2 is not completely destroyed at 56°C for 30 min and is stable at 50T for 15 min in 1 Μ MgClg or MgS04 but not in water. Freezing and thawing or sonication at 20 kc for 3 min does not affect the virus titer. c. Effect of Chemicals. All coronaviruses are sensitive to ether when exposed overnight at 2°-4°C. Chloroform also de stroys or reduces infectivity (Mcintosh, 1974) . Fifty percent glycerol inactivates MHVl after 6 weeks at 2°C (Gledhill and Andrewes (1951) . Sodium deoxycholate reduces the titer of LIVIM significantly (Kraft, 1962a) , but Calisher and Rowe (1966) regard MHV virus as moderately resistant. According to Hirano et al. (1978) , MHV2 is completely inactivated by ether, chloroform, sodium deoxycholate, and /3-propiolactone, but it is completely resistant to trypsin. Mutagenesis has been reported by means of Nmethyl-/V'-nitroguanidine or 5-fluorouridine and by 5-azacytidine or 5-fluorouracil (Haspel et al., 1978) . The pH stability of all known murine hepatitis viruses has not been reported. For coronaviruses in general, acid sensitivity is regarded as variable (Mcintosh, 1974) . Hirano et al. (1978) found that MHV2 is stable be tween pH 3 and 9 at 37°C for 30 min. Calisher and Rowe (1966) Although they have been sought, hemagglutinins have not been demonstrated for MHV strains (see, e.g., Hirano et al., 1978; Kraft, 1962a; Bradbume, 1970; Miyazaki etal., 1957) , but two human Coronavirus strains do agglutinate human 0 erythrocytes (Kaye and Dowdle, 1969 Cheever et al. (1949) found JHM virus to be unrelated to other neurotropic viruses, including GD VII, Pseudorabies, Lansing poliomyelitis, and Mengo virus. Kraft (1962b) found no relationship between LIVIM, EDIM, and reovirus 3. With regard to other coronaviruses, the picture is somewhat different, for as a group, coronaviruses display complex serologic variability (Bradburne, 1970; Mcintosh et al., 1969) . MHV is serologically closely related to RCV and SDAV in complement fixation tests and distantly related to RCV in cross-neutralization tests (Parker et al., 1970; Bhatt et al., 1972) . Several strains of MHV are closely related to human coronaviruses OC 38 and OC 43 , and MHV3 is related to HCV-229E (Bradbume, 1970) . Antibody to MHV strains commonly found in human sera is probably present because of endemic human infection with related coronavimses (Hartley et al., 1964) . Electron micrographs and studies using fluorochrome stains indicate that coronaviruses develop exclusively in the cyto plasm of infected cells, that the virions collect in cytoplasmic vesicles of diverse size, that particles may also be seen in the matrix outside of the endoplasmic reticulum as well as in the Golgi apparatus, and that they are not observed in the nucleus. In the main, replication involves budding into cytoplasmic cis temae, but tubular structures have also been seen within the cytoplasm during virus formation (Ruebner et al., 1967; Stan di α/., 1960; Watanabe, 1969a,b) . Wilsnack (1971) , confirming the work of Boss and Jones (1963) , elicited immunofluorescent antigen staining in sinusoidal lining cells in necrotic liver foci of weanling mice within 24 hr after intraperitoneal inoculation of the A59 strain. Stainable antigen in intestinal impression smears of mice in fected by cage contact was also demonstrated. Piazza et al. (1967) examined the fate of MHV3 after in travenous inoculation. The agent was not demonstrable be tween 40 min and 3.5 hr, when it appeared first in the spleen, then in the liver (4 hr) and blood (4.5 hr). At 5 hr it was recoverable from brain and kidney. High titers were then reached in all organs. Barinsky and Dementiev (1968) Thereafter, the cells of the olfactory bulb and other brain re gions are affected. A number of cell systems have been successfully employed for in vitro growth of mouse hepatitis viruses: MHV-C in mouse embryo explants (Mosley, 1961) ; MHVl in newborn mouse kidney explants (Starr and Pollard, 1959) ; MHV-S in mouse embryo explants (Compels, 1953) and in liver (Gallily et aL, 1964) ; MHV-B in liver cell monolayers (Paradisi and Piccinino, 1968) ; MHV3 in liver explants (Vainio, 1961) ; MHV-B in liver cells (Miyazaki et aL, 1957) ; MHV2 and MHV3 in DBT cells (Hirano et aL, 1978; Takayama and Kim, 1978) ; and various strains in NCTC 1469 cells (David-Ferreira and Manaker, 1965; Wilsnack etaL, 1971; Hartley and Rowe, 1963) . Mallucci (1965) , Seamer (1965) , and Lewis and Starr (1972) described syncytium formation by MHV in mouse macrophage cultures, and a plaque assay for MHV2 in primary peritoneal macrophage cultures was described by Shif and Bang (1966) . Laufs (1967) also described multinucleated giant cells with as many as 200 nuclei per cell in macrophage cultures infected with MHV3. Using autoradiography, he ascertained that there was no DNA synthesis in them and that they originated from cell fusion. Macrophages derived from either liver or peritoneal wash ings are of enormous interest for the question of host cell-vims interactions. Bang and Warwick (1959, 1960) Macrophages from the mice mirror these changes in resistance as the animals age. Kantoch et al. (1963) determined that temporary susceptibility could be induced in resistant cells in culture if they were exposed to homogenates of susceptible cells, and Gallily et al. (1964) showed that macrophages from genetically resistant mice treated with cortisone to enhance susceptibility behave in culture as if they were from susceptible animals. Macrophages from mice susceptible to MHV2 virus can be converted to resistance by the intraperitoneal inoculation of concanavalin A in the donor mice. This enhanced resistance is also expressed in vivo (Weiser and Bang, 1977) . Cheever etal. (1949) , Nelson (1952b) , and Kraft (1962a) In suckling mice, rapid wasting with or without neurologic signs may take place, accompanied in some cases by diarrhea, inanition, and dehydration (Fig. 2) . Mortality and morbidity are variable, ranging between al most 0 and 100% depending on factors like those affecting clinical signs. Of importance to users and breeders of mice alike is the fact that a number of agents and procedures are known to modify the reactivity (and therefore the clinical signs) of mice to both spontaneous and experimental infection. Examples of these, together with pertinent references, are presented in Table I . LePrévost et al. (1975a,b) have taken the view that there are three types of sensitivity to MHV3 infection in mice: resis tance, full susceptibility, and semisusceptibility. These are re flected in the susceptibility of their macrophages Response of nuInu mice to sheep erythrocytes DBA/2 mice, on the other hand, are regarded as fully suscep tible since deaths begin 4-6 days after infection, even when the mice are 90 days old, whereas the A/J strain is resistant, being susceptible to the acute disease only up to 3-4 weeks of age. Although C3H mice are partially susceptible to the acute phase of the disease, they are fully susceptible to the chronic stage. In nude (nu/nu) mice, MHV takes on special significance. Indeed, perhaps the best description of the clinical signs may be found in the original report describing this mutant mouse (Flanagan, 1966) , published before runt disease, as the wast ing syndrome was called, came to be recognized as something other than a genetic effect. MHV-infected nude mice lose weight slowly or rapidly. They move stiffly with a stilted gait, and their faces assume a pointed, anxious appearance. Partial paralysis may develop first in the hindlimbs and then in the forelimbs, resulting in almost total immobility. Nu/+ heterozygotes are not affected in this way. Flanagan (1966) found that at weaning, the nude animals were much smaller than controls (heterozygotes), that 55% died within 2 weeks of birth, and that 100% were dead by 25 weeks of age, whereas only 6% of controls died in the same period. It was not until Sebesteny and Hill (1974) UV-inactivated virus did not elicit the effect. The authors be lieve that fixed macrophages in athymic mice may be acti-vated, as was indicated by Nickol and Bonventre (1977) and by Cheers and Waller (1975) in certain bacterial infections in nude mice. T a m u r a et aL (1979) (see, e . g . , R u e b n e r and Bramhall, 1960; Gledhill etal., 1952; Nelson, 1953) . In Liver regeneration m a y take place as early as 1 0 -1 4 days after infection (Ruebner and Bramhall, 1960) , ranging from complete healing to chronic scarring with intermediate gradations. Kupffer cells were examined by R u e b n e r and Miyai (1962) and R u e b n e r et al. (1967) . T h e y m a y undergo nuclear pyknosis and karyorrhexis 24 hr after intravenous inoculation of M H V 3 . In infection with neurotropic variants, such as J H M , the principal lesions appear in the central nervous system . Meningitis is present but varies in degree and loca tion. In the brain, lesions m a y be found in all regions, but the hippocampus and its connections, the olfactory lobes, the periependymal tissues, and the brain stem seem to b e affected most often. Necrotizing lesions predominate in the olfactory lobes and hippocampal regions, whereas demyelination is the major change in the brain stem. S o m e exudate m a y be found around blood vessels associated with lesions, and at about 5 days after infection, proliferating pericytes and scant lym phocytic cuffing can be seen. Peripheral nerves show n o change. In sucklings, J H M virus produces extensive lesions in the brain and cord at 6 -8 days. Meningitis is present, and large regions of necrosis with m a n y giant cells occur throughout the brain. In the cord, the lesions consist of spongy necrosis of the central gray matter. Ganglion cells appear unaffected. Powell and Lampert (1975) resolved into small foci of fibrillary gliosis with an increased size and n u m b e r of astrocytic processes. T h e importance of this finding for investigations into the cause of multiple sclerosis and other demyelinating diseases in m a n is obvious and has been addressed b y , a m o n g others, Lucas et al. (1977) and Lampert (1978) . In sucklings infected with enterotropic strains (Kraft, 1962a; Broderson et al., 1976; Ishida et al., 1978; Ishida and Fuji wara, 1979; R o w e et al., 1963; Hierholzer et al., 1979) Strains (Dick et al., 1956; R u e b n e r and Bramhall, 1960; Hirano and Ruebner, 1966) , and Biggart and Ruebner (1970) attribute the change to virus replication in lymphocytes. In other organs, minute superficial necrotic foci m a y be found in the stomach. N o changes are seen in the heart, lungs, pancreas, kidney, adrenals, voluntary m u s c l e , femoral o r ver tebral bone m a r r o w , or pituitary gland, although virus m a y be isolated from some of those organs. Occasional giant cells are found in peripancreatic lymph nodes and in P e y e r ' s patches. Flanagan (1966) islands of hepatocytes, markedly hypertrophied, remained. Changes in other organs were not described. The liver lesions observed in other nude mice infected with MHV were similar. Sebesteny and Hill (1974) noted central nervous system lesions in their nude mice. Ward et al. (1977) also encountered central nervous system lesions in addition to vascular changes, giant cell peritonitis, ascites, and giant cells in the villous epithelium of the intestines. Since virus can be transmitted perorally and intranasally, it may be assumed that these are the principal routes of natural infection. Transmission may be mediated by both the airborne and contact modes. Feces, nasopharyngeal exudates, and perhaps urine would be sources of infection. Evidence of vertical transmission is at hand, but reports are conflicting. Piccinino et al. (1966) with or without booster, showed no antibody in the same colony. In a conventional colony of DDD mice, furthermore, seropositivity increased from 0 to 12% and in ddY mice from 6.3 to 45% as a result of the booster technique. In barrier-maintained animals, the booster did not elicit antibodies where there had been none before. Presumably, these animals were free from MHV infection. From the foregoing, it is evident that the classic humoral immune response to MHV seems to be weak, and that a colony In contrast to the findings of Bang and Warwick (1960) , who concluded that one gene (or factor) was responsible for host susceptibility in MHV2 infection, Stohlmann and Freiinger (1978) showed that two genes are required for resistance of the central nervous system in SJL mice to fatal disease due to MHV-JHM. Further, Stohlmann et al. (1980) reported that there is an age-related change in resistant mice that protects them from acute central nervous system disease. They iden tified this change as due to a maturing adherent spleen or peritoneal exudate cell population. In extensive genetic studies, Levy-LeBlond et al. (1979) found no correlation between the H-2 locus and either the acute or chronic disease in C57BL (susceptible) or A/J (resistant) animals. Using congenie C3H lines, however, they were able to show that the H-2^ allele enables both heterozygous and homozygous animals to resist the development of the chronic disease. They believe, therefore, that MHV sensitivity appears to be influenced by at least two major genes: one for the acute disease, and the other, linked to the H-2 gene complex, for the chronic disease. Mice also produce interferon as a result of MHV infection Virelizier and Gresser, 1978) , and Taguchi et aL (1979a) ascribe the greater susceptibility of suckling C3H/HeJms mice to serum levels of interferon that are considerably lower than in weanling and aduh mice, as well as to greater macrophage sensitivity in the neonates. MHV-induced interferon may be regarded as the principal mechanism by which the virus modifies the immune respon siveness of mice to sheep red blood cells, for example. (See also (1949) infected cotton rats, rats, and hamsters intracerebrally, but rabbits and guinea pigs failed to respond. Sebesteny and Hill (1974) at tempted to infect infant Wistar rats and hamsters using virus recovered from nude mice. All survived at least 21 days with out signs of illness. Of considerable importance is a report by Taguchi et aL (1979c) concerning asymptomatic MHV-S infection in suckl ing rats following intranasal inoculation. The agent multiplied mainly in the nasal epithelium without any clinical signs. Neu tralizing antibodies were produced, however, and could also be demonstrated in adult rats following infection. Necrotic changes took place in the nasal mucosa, and cytoplasmic im munofluorescence was demonstrated in the nasal epithelium 2 days after intranasal inoculation of 10-day-old rats. Age susceptibility has been amply addressed above in the consideration of virus growth in mice and tissue culture and in the discussion of the clinical picture. There appears to be no difference in susceptibility between the sexes (Taguchi et al., 1976) . Parker et al. (1966) found that the incidence of complement-fixing antibodies was greater in females than in males under colony conditions, as cribing this difference to continual exposure to virus-infected litters. There appears to be no evidence that first litters are significantly more susceptible than later ones. As noted above (Section IV,Β, 2 and C,l), the susceptibility of various mouse strains depends on the age of the host at the time of infection, the virus strain, and the host genotype. A completely resistant mouse strain has not been reported. Prevalence of MHV infection in an animal colony is often difficult to ascertain. In addition to examples given earlier, Descoteaux et al. (1977) found a low prevalence of hepatitis antibodies in three of five colonies studied in Canada. Complement-fixing antibodies ranged in titer from 8 to 32, 8 being considered positive. Fewer than 20% of the animals, which were 6-9 months old at the time of testing, were posi tive. In distribution, MHV is regarded as occurring worldwide. These have been defined as occurring more than 2 months after intracerebral, intraperitoneal, intranasal, or intravenous inoculation (as reviewed in Robb and Bond, 1980) . The chronic clinical manifestations range from none to porenceph aly, paralysis, hepatitis, immunodeficiency manifestations, encephalitis, lymph node adenopathy, and vasculitis. Virus may or may not be isolated. Cells stainable by immunofluores cence may be found. Demyelination with or without remyelination may occur. Occasional scattered mononuclear cell infil trates may be evident. There is no evidence that seasonal changes influence the oc currence of epizootics of MHV infection. As indicated above, serologic testing is routinely carried out by means of the complement fixation test. Cross-reactions with other coronaviruses must be taken into account when inteφreting the results, however. Neutralization tests performed in tis sue culture systems are also possible. Employing virus strain A59 as antigen in the ELISA, Peters et al. (1979) found a high prevalence of MHV antibodies in colonies with a low incidence of both complement-fixing and neutralizing antibodies. Hierholzer and Tannock (1977) have used the single radial hemolysis test for human Coronavirus serodiagnosis. They then applied it to some MHV strains (Hierholzer et aL, 1979) . These techniques are helpful under certain circumstances, e.g., experimental investigations, but they are inefficient for field conditions. Necropsy of dead or sick animals is always useful, although a definitive diagnosis in the absence of serologic evidence cannot be made. Nevertheless, wherever possible, gross and microscopic pathologic examination should be undertaken. Sentinel animals, especially gnotobiotes, could be Ιηοοφοrated into a program of colony health surveillance. These ani mals can then be checked at predetermined intervals for clini cal, serologic, and histopathologic evidence of endemic dis ease in the colony. Control of MHV is difficult in mouse colonies unless caesa rian derivation coupled with barrier maintenance is under taken. With the finding that vertical transmission is possible, however, barrier maintenance alone may not be adequate if, for example, such transmission is frequent. Using small number of animals for experimental puφoses, Kraft (1962a) Tamura et aL (1976) found that nu/nu mice could resist MHV infection when they previously received thymocytes from weanling nu/+ littermates. They were then not only able to produce antibody but survived a challenge infection as well. Studies on rotaviral antibody in bovine serum and lacteal secretions, using radioimmunoassay Epidemic diarrhea of infant mice. Identification of the etiologic agent Electron microscopic study of the intestinal epithelium of mice infected with the agent of epizootic diarrhea of infant mice (EDIM virus) The morphology of three pre viously uncharacterized human respiratory viruses that grow in organ culture The effect of trypsin on the growth of rotavirus Viruses of Verte brates Panel Report of the Colloquium on Selected Diarrheal Diseases of the Young Rotavirus isolation and cultivation in the presence of trypsin A murine virus (JHM) causing disseminated encephalomyelitis with extensive destruction of myelin. II In vitro detection of human rotaviruses Further observa tions on the virus of epizootic diarrhea of infant mice. An electron microscopic study Genetics of resistance of animals to viruses: I. Introduc tion and studies in mice Macrophages and mouse hepatitis Mouse macrophages as host cells for the mouse hepatitis virus and the genetic basis of their susceptibility Virological and cytogenetic studies on the involvement of bone marrow of mice in some hepatoencephalotropic viral infections Rotavirus serotypes by serum neutralisation Moφhogenesis of avian infectious bronchitis virus and a related human virus (Strain 229E) Preparation of type-specific antisera to reoviruses Isolation of a reovirus from a case of Burkitt's lymphoma Isolation of a non-pathogenic tumour-destroying virus from mouse ascites Characteristics of a newborn runt disease induced by neonatal infection with an oncolytic strain of reovirus type 3 (reo3MH). II. Immunological aspects of the disease in mice Characteristics of a newborn runt disease induced by neonatal infection with an oncolytic strain of reovirus type 3 (reo3MH). I. Pathological investigations in rats and mice Characterization of the virus of sialodacryoadenitis of rats: A member of the Coronavirus group Lymphoid necrosis in the mouse spleen produced by mouse hepatitis virus (MHV3): An electronmicroscopic study Lethal intestinal virus infection of mice (LIVIM). An important new model for study of the response of the intestinal mucosa to injury Virus particles in epithelial cells of duodenal mucosa from children with acute non-bacterial gastroenteritis Serological studies with an agent of epizootic diarrhea of infant mice Pathogenic murine coronaviruses. II. Characterization of virus-specific proteins of murine coronaviruses JHMV and A59V Specific monovalent cation effects on modification of reovirus infectivity by chymotrypsin digestion in vitro Ex traordinary effects of specific monovalent cations on activation of reovirus transcriptase by chymotrypsin in vitro New intermediate subviral particles in the in vitro uncoating of reovirus virions by chymotrypsin Reovirus transcriptase activation in vitro: involvement of an endogenous uncoating activity in the second stage of the process Two modes of entry of reovirus particles into L cells Hepatic localization of infectious agent in murine viral hepatitis Antigenic relationships amongst coronaviruses A solid-phase system (SPACE) for the detection and quantification of rotavirus in faeces Small intestinal epithelial brush border enzymatic changes in suckling mice infected with reovirus type 3 Reovirus type 3 infection in a suckling mouse: the effects on pancreatic structure and enzyme content Viral hepatitis associated with trans plantable mouse leukemia. I. Acute hepatic manifestations following treatment with urethane or methylformamide Neonatal calf diarrhoea: identifica tion of reovirus-like (rotavirus) agent in faeces by immunofluorescence and immune electron microscopy Lethal en teritis in infant mice caused by mouse hepatitis virus The laboratory diagnosis of epizoo tic diarrhoea of infant mice A rabbit rotavirus. Vet. Ree. 99 Diagnosis of rotavirus infection by cell culture A Hepatitis Virus of Mice Two coronaviruses isolated from central nervous system tissue of two multi ple sclerosis patients Mouse hepatitis, reo-3, and the Theiler viruses Activated macrophages in congenitally athymic "nude" mice and in lethally irradiated mice Epidemic diarrheal disease of suckling mice Epidemic diarrheal disease of suckling mice. I. Manifestations, epidemiology, and attempts to trans mit the disease Epidemic diarrheal disease of suckling mice. III. The effect of strain, litter, and season upon the incidence of the disease A murine virus (JHM) causing disseminated encephalomyelitis with extensive destruction of myelin. I. Isolation and biological prop erties of the virus Serological inter relationships of murine hepatitis viruses Production of high-titer bovine rotavirus with trypsin Murine virus contaminants of leukemia viruses and transplantable tumors Reovirus type 3 infection in laboratory mice Temperature-sensitive mutants of reovirus type 3: Studies on the synthesis of viral RNA Effect of corticosteroids on mouse hepatitis virus infection An electron microscope study of the development of a mouse hepatitis virus in tissue culture cells Importance of a new virus in acute sporadic enteritis in children Comparison of the morphology of three coronaviruses Classification of rotaviruses: Report from the Worid Health Organization/Food and Agriculture Or ganization Comparative Virology Program Serologic study on the prevalence of murine viruses in five Canadian mouse colonies A virus related to that causing hepatitis in mice (MHV) Immunopathology of mouse hepatitis virus type 3. II. Effect of im munosuppression in resistant mice The appearance of a hepatotrophic virus in mice thymectomized at birth Comparison of five diagnostic methods for the detection of rotavirus antigens in calf faeces Morphological studies on simian virus SA 11 and the "related" 0 agent Electron microscopic identification and subsequent isolation of a rotavirus from a dog with fatal neonatal diarrhea Enhancement of rotavirus infectivity by trypsin and elastase Identification of rotaviruses of different origins by the plaque-reduction test Hemagglutination and hemagglutination-inhibition studies with a strain of Nebraska calf diarrhea virus (bovine rotavirus) Isolation and preliminary genetic and biochemical characterization of temperature-sensitive mutants of reovirus Altered disease in rats due to mutants of reovirus type 3 Temperature-sensitive mutants of reovirus type 3: Studies on the synthesis of viral peptides Generation of cytolytic Τ lymphocytes after reovirus infection: role of the SI gene Nude", a new hairless gene with pleiotropic effects in the mouse Electron microscopy in the diagnosis of infectious diarrhea The rotaviruses Relation between viruses from acute gastroen teritis of children and newborn calves Virus diarrhoea in foals and other animals. Vet. Ree. 96 Fluorescent virus precipitin test Adverse effects of mouse hepatitis virus on ascites myeloma passage in the Balb/cJ mouse Problems in checking inapparent infections in laboratory mouse colonies: An attempt at serological checking by anamnestic re sponse Implication pancréatique chez la souris infectée avec le virus de l'hépatite murine Immunisation de la souris "nude" contre le virus de l'hépatite murine par transfert de lymphocytes sensibilisés Carrier state of anti body and viruses in a mouse breeding colony persistently infected with Sendai and mouse hepatitis viruses Effect of cortisone on genetic resistance to mouse hepatitis virus in vivo and in vitro Ontogeny of macrophage resistance to mouse hepatitis in vivo and in vitro Structure and physicochemical properties of coronaviruses Comparison of an enzyme-linked immunosorbent assay for quantitation of rotavirus an tibodies with complement fixation in an epidemiological survey Enhancement of the pathogenicity of mouse hepatitis virus (MHVl) by prior infection of mice with certain leukaemia agents A hepatitis virus of mice Production of hepatitis in mice by the combined action of two filterable agents Mouse hepatitis virus and its pathogenic action Reactive sites of reovirus type 3 and their interaction with receptor substances Reovirus type 3: Physical characteristics and interaction with L cells The propagation of S virus of mouse hepatitis in tissue culture Comparison of methods for immunocytochemical detection of rotavirus infections Delayed hypersensitivity in mice infected with reovirus. II. Induction of tolerance and suppressor Τ cells to viral specific gene products Spontaneous diseases and their control in laboratory animals Electron microscopic examination of cells infected with reovirus Tissue culture cytopathic and plaque assays for mouse hepatitis viruses Recovery of reoviruses from wild and laboratory mice Antibodies to mouse hepatitis viruses in human sera Temperature-sensitive mutants of mouse hepatitis virus produce a high incidence of demyelination Mouse hepatitis virus-induced recurrent demyelination Quantitation of antibody to non-hemagglutinating viruses by single radial hemolysis: Serological test for human coronaviruses New strain of mouse hepatitis virus as the cause of lethal enteritis in infant mice Isolation of low-virulent mouse hepatitis virus from nude mice with wasting syndrome and hepatitis Studies on the mechanism of destruc tion of lymphoid tissue in murine hepatitis virus (MHV3) infection. I. Selective prevention of lymphoid necrosis by cortisone and puromycin Physico-chemical properties of mouse hepatitis virus (MHV-2) grown on DBT cell culture Viral gastroenteritis Infantile enteritis viruses: morphogenesis and morphology Is lactase the receptor and uncoating enzyme for infantile enteritis (rota) viruses? Some distinctive biological characteristics of ECHO-10 virus New viral agents recovered from tissue cultures of monkey kidney cells. I. Origin and properties of cytopathogenic agents SVj, SV2, SV4, SV5, SVg, SVn, SV12, and SV15 Pathology of diarrhea due to mouse hepatitis virus in the infant mouse Isolation of mouse hepatitis virus from infant mice with fatal diarrhea Some aspects on the transmission of hepatitis Β antigen; model experiments by mosquitoes with murine hepatitis virus The molecular biology of reovirus Studies on the effect of chymotrypsin on reovirions Reproduction of reoviridae The effect of a murine hepatitis virus on the liver The fine structure of reovirus, a new member of the icosahedral series A microtiter solid phase radioimmunoassay for detection of the human reovirus-like agent in stools Detection of differences among human and animal rotaviruses using analysis of viral RNA The cellular nature of genetic susceptibility to a virus The coronaviruses Reoviruslike agent in stools: Association with infantile diarrhea and development of serologic tests Antigentic relationships among five reovirus-like agents by complement fixation Vertical transmission of mouse hepatitis virus infection in mice Some characteristics of hemaggluti nation of certain strains of "IBV-like" virus Studies on the etiology and transmission of epidemic diarrhea of infant mice Observations on the control and natural history of epidemic diarrhea of infant mice (EDIM) Responses of the mouse to the virus of epidemic diarrhea of infant mice. Neutralizing antibodies and carrier state Two viruses causing diarrhea in infant mice An apparently new lethal virus disease of infant mice Epizootic diarrhea of infant mice and lethal intestinal virus infection of infant mice Practical control of diarrheal disease in a commercial mouse colony Reovirus infection in suckl ing mice: Immunofluorescent and infectivity studies Discussion of Kraft, L. M. Two viruses causing diarrhea in infant mice In vivo interference between heterologous rotaviruses The induction of interferon by temperature-sensitive mutants of reovirus, UV-irradiated reovirus, and subviral reovirus particles Diagnosis of rotavirus, adenovirus, and heφes virus infections by immune electron microscopy using a serum-in-agar diffusion method Autoimmune and virus-induced demyelinating dis eases Mechanism of demyelination of JHM virus encephalomyelitis Untersuchungen über die Entstehung von Riesenzellen in Mäusemakrophagenkulturen nach Infektion mit dem Mäusehepatitisvirus (MHV-3) Differential growth of MHV(PRI) and MHV(C3H) in genetically resistant C3H rendered susceptible by Eperythrozoon coccoides Relationship of phagocytic activity to pathogenicitiy of mouse hepatitis virus as affected by triolein and cor tisone Immunodiffusion and immunoelectrophoretic studies of reovirus antigens Immunopathology of mouse hepatitis virus type 3 infection. III. Clinical and virologic observation of a persistent viral infection Immunopathology of mouse hepatitis virus type 3 infection. I. Role of humoral and cell-mediated immunity in resistance mechanisms Neonatal susceptibility to MHV3 infection in mice. I. Transfer of resistance Genetic study of mouse sensitivity to MHV3 infection: Influence of the H-2 complex Polykaryocytosis and replication of mouse hepatitis virus in peritoneal macrophages In vivo and in vitro models of demyelinating diseases: tropism of the JHM strain of murine hepatitis virus for cells of glial origin An ultrastructural study of virions and cores of reovirus type 3 Infectivity assay of reoviruses: Comparison of immunofluorescent cell count and plaque methods The digestive system The nature of the polypeptide encoded by each of the 10 double-stranded segments of reovirus type 3 Trans-stadial maintenance of reovirus type 3 in the mosquito Culex pipiens fatigans Weidmann and its implications Coronaviruses: A comparative review Coronaviruses as causes of diseases: Clinical observa tions and diagnosis Growth in suckling-mouse brain of "IBV-like" viruses from patients with upper respiratory tract disease Antigenic relationships among the coronaviruses of man and between human and animal coronaviruses The polypeptides of human and mouse coronaviruses Rotaviruses-a review Moφhology and chemical composition of rotaviruses Observations on the growth of mouse hepatitis virus (MHV-3) in mouse macrophages A. hepatitis virus complicating studies with mouse leukemia Identity of Cowdry type Β inclusions and nuclear bodies: observations in reovirus encephalitis An antigenic subunit pre sent in rotavirus infected faeces Plaque assay of neonatal calf diarrhoea and the neutralising antibody in human sera The classification and nomenclature of viruses Calf diarrhea (scours) reproduced with a virus from a field outbreak Taxonomy of viruses A reo-like virus isolated from juvenile American oys ters (Crassostrea virginica) Moφhology of a reo-like virus isolated from juvenile American oysters (Crassostrea virginica) Pathogenesis of rotaviral infection Counter-immunoelectro-osmophoresis for the detection of infantile gastroenteritis virus (orbi-group) antigen and antibody Solid phase radioimmunoassay for the detection of rotavirus Experimental studies on hepatitis virus of mice in tissue culture Mechanisms in the pathogenesis of diarrhea: a review A new member of hepatoencephalitis group of murine viruses Multiplication and cytopathogenicity of mouse hepatitis virus in mouse cell cultures Purification and characterization of epi zootic diarrhea of infant mice virus Acute hepatitis associated with mouse leukemia. I. Etiology and host range of the causal agent in mice Acute hepatitis associated with mouse leukemia. I. Pathological features and transmission of the disease Acute hepatitis associated with mouse leukemia. IV. The relationship of Eperythrozoon coccoides to the hepatitis virus of Prince ton mice Acute hepatitis associated with mouse leukemia. V. The neurotropic properties of the causal virus Recovery and behavior of hepatitis virus from Swiss mice injected with ascites tumor Pathogenicity of murine hepatitis virus recovered from infant Swiss mice An oncolytic virus recovered from Swiss mice during passage of an ascites tumour Anomalous high native resistance of athymic mice to bacterial pathogens Detection of rotavirus by serological trapping on antibody-coated electron micro scope grids Further light on mouse hepatitis Defective virions of reovirus Virusinduced diabetes mellitus: reovirus infection of pancreatic /3-cells in mice Electron micrographic features of acute murine reovirus hepatitis Ultrastructural features of chronic murine hepatitis after reovirus type 3 infection An electron microscopic study of murine reovirus-3 encephalitis The biliary tract in acute murine reovirus 3 infection Studies on the exocrine pancreas. Π. ultrastructural investigation of reovirus pancreatitis Epidemic diarrheal disease of suckling mice. IV. Cytoplasmic inclusion bodies in intestinal epithelium in relation to the disease An epidemic diarrheal dis ease of suckling mice. II. Inclusions in the intestinal epithelial cells Propagation of mouse hepatitis virus (MHV-3) in monolayer cell cultures from liver of newborn mice Virus studies with germfree mice. I. Preparation of serologic diagnostic rea gents and survey of germfree and monocontaminated mice for indige nous murine viruses Prevalence of viruses in mouse colonies Rat Coronavirus (RCV): A prevalent, naturally occurring pneumotropic virus of rats The isolation of reovirus type 3 from mosquitoes and a sentinel infant mouse Enzyme-linked immunosorbent assay for detection of antibodies to murine hepatitis virus Detection of neonatal calf diarrhea virus, infant reovirus-like diarrhea virus, and a Coronavirus using the fluorescent virus precipitin test Chronic obstructive jaundice induced by reovirus type 3 in weanling mice Experimental Viral Hepatitis The fate of murine hepatitis virus (MHV-3) after intravenous injection into susceptible mice Lack of transplacental transmissibility of MHV-3 virus Oligodendrocytes and their myelin-plasma membrane connections in JHM mouse hepatitis virus encephalomyelitis Proteolytic enzymes and rotavirus SA-11 plaque formation A genetic map of reovirus. II. Assignment of the double-stranded RNAnegative mutant groups C, D, and Ε to genome segments Plaque formation by reoviruses Cytochemical, fluorescent-antibody and electron microscopic studies on the growth of reovirus (ECHO 10) in tissue culture Pathogenic murine coronaviruses. I. Characterization of biological behavior in vitro and virus-specific in tracellular RNA of strongly neurotropic JHMV and weakly neurotropic A59V viruses Pathogenic murine coronaviruses. III. Biological and biochemical characterization of temperature-sensitive mutants of JHMV Demonstration of reovirus-like particles in intestinal contents of piglets with diarrhoea Comparison of the genomes of simian, bovine, and human rotaviruses by gel electrophoresis and detec tion of genomic variation among bovine isolates Serologic grouping of reoviruses by hemagglutinationinhibition Mouse hepatitis virus infection as a highly contagious, prevalent, enteric infection of mice Chloroform inactivation of reovirus hemagglutinins The growth of the virus of epidemic diarrhea of infant mice (EDIM) in organ cultures of intestinal epithelium Pathology of experimental hepatitis in mice The Kupffer cell reaction in murine and human viral hepatitis with particular reference to the origin of acidophilic bodies Electron microscopy of the hepatocellular and Kupffer-cell lesions of mouse hepatitis, with par ticular reference to the effect of cortisone Factors associated with the incidence of infantile diarrhea in mice Reoviruses. A new group of respiratory and enteric viruses formerly classified as ECHO type 10 is described Application d'une technique immunoenzymologique (ELISA) á la detection du rotavirus bovin et des anticorps diriges contre lui Enhancement of antigen incorporation and infectivity of cell cultures by human rotavirus Rotavirus in goats. Vet. Ree. 103 Mouse macrophages as host cells for murine viruses Some virus infections of mice Hepatitis and brain lesions due to mouse hepatitis virus accompanied by wasting in nude mice A genetic map of reovirus. I. Correlation of genome RNAs between serotypes 1, 2, and 3 Replication of reovirus Mouse hepatitis virus (MHV) infection in thymectomized C3H mice Rotavirus infection of neonatal mice: characterization of the humoral immune response Plaque assay for mouse hepatitis virus (MHV-2) on primary macrophage cell cultures In vitro interaction of mouse hepatitis virus and macrophages from genetically resistant mice. I. Adsorption of virus and growth curves Arboviruses The mechanisms of reoviris uncoating and gene activation in vivo Anti-rotavirus antibody in human colos trum The Laboratory Mouse. Selection and Management Rabbit cardiomyopathy, associated with a virus antigenically related to human Coronavirus strain 229E Gel electrophoresis of rotavirus RNA derived from six different animal species Rotavirus infection in lambs: Studies on passive protection A rotavirus in lambs with diarrhoea Test for reovirus-like agent Enhancement of reovirus infectivity by extracellular removal or alteration of the virus capsid by proteolyitic enzymes Relationship of hepatoencephalomyelitis virus and reoviruses The reovirus murine models Diagnosis of reovirus infection: Comparative aspects Murine infection with reovirus type 3 and the runting syndrome Studies on the pathogenesis of a hitherto undescribed virus (Hepatoencephalomyelitis) producing unusual symptoms in suckling mice Studies on the hepato-encephalomyelitis virus (HEV) Murine infection with reovirus. II. The chronic disease following reovirus type 3 infection Propagation of mouse hepatitis virus (Gledhill) in tissue culture Electron and fluorescence microscopy of mouse hepatitis virus Resistance to fatal central nervous system disease by mouse hepatitis virus, strain JHM. I. Genetic analysis Resistance to fatal central nervous system disease by mouse hepatitis virus, strain JHM. II. Adherent cell-mediated protection Postsplenectomy viral hepatitis Characterization of a Coronavirus. I. Structural pro teins: Effects of preparative conditions on the migration of protein in Polyacrylamide gels An electron microscopic study of viral hepatitis in mice Difference in response to mouse hepatitis virus among susceptible mouse strains Factors involved in the age-dependent resistance of mice infected with low virulence mouse hepatitis virus Pathogenesis of mouse hepatitis infection. The role of nasal epithelial cells as a primary target of low virulence virus Asymptomatic infection of mouse hepatitis virus in the rat In vitro growth characteristics and heterogeneity of mouse hepatitis virus type 3 IgM and IgG response to sheep red blood cells in mouse hepatitis virus-infected nude mice Response of nude mice to a mouse hepatitis virus isolated from a wasting nude mouse Persistent infection with mouse hepatitis virus of low virulence in nude mice The role of macrophages in the early resistance to mouse hepatitis virus infection in nude mice Enhanced phagocytic activity of macrophages in mouse hepatitis virus-infected nude mice Neonatal susceptibility to MHV3 infection in mice. II. Role of natural effector marrow cells in transfer of resistance Techniques for rotaviral propagation Rotavirus neutralization by human milk Serological relation ships between rotaviruses from different species as studied by comple ment fixation and neutralization Potentiating effect of K-virus on mouse hepatitis virus (MHV-S) in weanling mice Runde" virus, a coronavirus-like agent associated with seabirds and ticks Immunoelectroosmophoresis for de tection of reo-like virus: Methodology and comparision with electron microscopy Inducers of interferon and host resistance. III. Double-stranded RNA from reovirus type 3 virions (Reo 3-RNA) Isolation of rotavirus from deer Use of horseradish peroxidase labelled antibody for light and electron microscopic localiza tion of reovirus antigen Studies on murine hepatitis virus (MHV3) in vitro The moφhology of reovirus New inteφretation of reovirus struc ture Effect of X radiation and cortisone on mouse hepatitis virus infection in germfree mice Correlation of persistent mouse hepatitis virus (MHV-3) infection with its effect on mouse macrophage cultures Role of interferon in the pathogenesis of viral diseases of mice as demonstrated by the use of anti-interferon serum. V. Protective role in mouse hepatitis virus type 3 infection of susceptible and resistant strains of mice Neuropathological effects of persistent infection of mice by mouse hepatitis virus The role of circulating interferon in the modifications of immune responsiveness by mouse hepatitis virus (MHV-3) Reovirus activation by heating and inactivation by cooling in MgCl2 solutions Effects of pancreatin on the growth of reovirus Murine infection with reovirus: I. Pathology of the acute phase Naturally occurring mouse hepatitis virus infection in the nude mouse Identification of detergents as compo nents of wastewater sludge that modify the thermal stability of reovirus and enteroviruses Effects of wastewater sludge and its detergents on the stability of rotavirus Comparative study on the mechanisms of rotavirus inactivation by sodium dodecyl sulfate and ethylenediaminetetracetate Electron microscopic studies of experimental viral hepatitis in mice. II. Ultrastructural changes of hepatocytes associated with virus multiplication Electron microscopic studies of experimental viral hepatitis in mice. I. Virus particles and their relationship to hepatocytes and Kupffer cells Structural polypeptidesofthe murinecoronavims Neutralization of reovirus: the gene responsible for the neutralization antigen Molecular basis of reovirus virulence: role of the SI gene Identification of the gene coding for the hemagglutinin of reovirus Absolute linkage of virulence and central nervous system cell tropism of reoviruses to viral hemagglutinin Delayed hypersen sitivity in mice infected with reovirus. I. Identification of host and viral gene products responsible for the immune response Interaction of reovirus with cell surface receptors. I. Murine and human lymphocytes have a receptor for the hemagglutinin of reovirus type 3 Pathogenesis of demyelination induced by a mouse hepatitis vims (JHM virus) Blocking of in vitro and in vivo susceptibility to mouse hepatitis vims Importance of local immunity in enteric infection Effect of cy clophosphamide on the genetic resistance of C3H mice to mouse hepatitis vims The circadian rhythm of thymosin therapy during acute reovirus type 3 infection of neonatal mice Immunofluorescent detection of murine virus anti gens Identification of an agent of epizootic diarrhea of infant mice by immunofluorescent and complement-fixation tests Intestinal Μ cells: a pathway for entry of reovirus into the host Moφhological and an tigenic relationships between viruses (rotaviruses) from acute gastroen teritis of children, calves, piglets, mice, and foals Intestinal damage in rotavirus infected calves assessed by D-xylose malabsoφtion Heat and moisture transfer in fllter-top rodent cages Reovirus-like agents (Rotavimses) associated with diarrheal illness in animals and man Human rotavirus type 2: cultivation in vitro Enzyme-linked fluorescence assay: ultrasensitive solid-phase assay for detection of human rotavirus Enzyme-linked immunosorbent assay for identification of rotaviruses from different animal species Measurement of rotavirus antibody by an enzyme-linked immunosorbent assay blocking assay Secretory antibody directed against rotavirus in human milk-measurement by means of enzyme-linked immunosorbent assay