key: cord-0985668-wnkyr22j authors: Gastañaduy, Arturo S.; Bégué, Rodolfo E. title: 162 Acute Gastroenteritis Viruses date: 2017-12-31 journal: Infectious Diseases DOI: 10.1016/b978-0-7020-6285-8.00162-3 sha: 29e8c886510037166c31f0e2f6a4cf81c64c43c9 doc_id: 985668 cord_uid: wnkyr22j nan Acute diarrhea is the leading cause of morbidity and second commonest cause of mortality in children aged 0-5 years old. Worldwide estimates for this age group in 2010 were: 1.731 billion cases, with 36 million severe episodes, and 700 000 deaths. 1 For older children, adolescents and adults, the estimate is 2.8 billion cases of diarrhea per year. 2 Viruses account for most of acute diarrhea illness, 3 Described in 1973 by Bishop et al. 4 human rotaviruses (RVs) represent the main agent of acute gastroenteritis in infants and young children worldwide. Rotaviruses (RVs) belong to the family Reoviridae. 5 Intact 75 nm particles have a triple-layered structure with a core, and the inner and outer capsid layers. The core encloses the viral genome, consisting of 11 segments of double-stranded RNA. Each segment encodes for one protein, except segment 11 that encodes for two ( Figure 162 -1, Table 162 -4). Six proteins (VP1-VP4, VP6-VP7) form the virion structure. The core is made of VP1, VP2 (its major constituent) and VP3; VP6 is the sole component of the inner capsid; and the outer capsid is composed of VP7 (90%) and VP4. VP4 forms the capsomers, spikelike structures that radiate from the inner to the outer capsid giving the virus its characteristic wheel-like appearance (rota = wheel). In addition, six nonstructural proteins (NSP1-NSP6) are expressed in the infected cell and participate in the replicative cycle. 6, 7 KEY CONCEPTS • Acute diarrhea is the leading cause of morbidity and second commonest cause of mortality in children <5 years old worldwide. • Most acute diarrheal illnesses are caused by viruses. • Noroviruses are the commonest cause of diarrhea in all age groups combined, and rotaviruses are still the leading cause of diarrhea for children <5 years old. • Transmission is mainly by the fecal-oral route through personto-person contact, contaminated food and water. • Most cases of viral diarrhea are mild and self-limiting, but severe cases occur, leading to dehydration and death. Repeated episodes lead to malnutrition. • Most cases can be managed at home with oral rehydration solutions and feeding a regular diet. • Vaccines will be the best preventive measure. Only rotavirus vaccines are available. • Breast-feeding, vitamin A supplementation and zinc significantly reduce the frequency and/or severity of diarrhea. Usual Clinical Characteristics of Gastroenteritis Virus Infections mature particles. NSP4 plays a key role in the assembly process of these particles, which is Ca 2+ dependent. Lastly, mature viruses are released by cell lysis or by vesicular transport. 7 Infected intestinal cells change from columnar to cuboidal, with fewer and shorter microvilli; the cells are sloughed off resulting in shorter villi. Changes occur within 24 hours of infection, start proximally and progress caudally. 4, 29 Diarrhea results from a mixture of causes: decreased absorption of salt and water secondary to enterocyte damage and replacement of absorptive intestinal cells by secreting cells from the crypts; loss of disaccharides at the damaged brush border (Table 162- 5) . 5, 56 Both NoV and SaV produce diarrheal illness in humans and NoV is the leading cause of acute gastroenteritis worldwide. The CV genomes are about 7.3-8.5 kilobases in length and organized in two or three open reading frames (ORFs). In the genera with three ORFs (NoV and Vesivirus) the first ORF (ORF1) encodes for a large protein that by proteolytic cleavage produces the NSPs. The ORF2 encodes for the single major structural protein (VP1), and the ORF3 encodes for a minor structural protein (VP2). The Nebovirus and Lagovirus have only 2 ORFs. In these viruses, VP1 and VP2 are encoded in ORF1 and ORF2, respectively. 56 A typical CV (Norwalk virus) capsid is formed by 90 VP1 dimers with 90 arch-like protruding capsomers arranged in such a way as to leave 32 calices on the viral surface. The VP1 has two major domains: the shell (S) domain and the protruding (P) domain. The S domain forms the inner part of the capsid. It has 225 amino acids (aa), including aa 10-49 corresponding to the N terminal region of the protein (N subdomain), which faces the interior of the capsid. The P domain includes amino acids 226-520 and is subdivided into subdomains P1 and P2. The P1 subdomain (aa 226-278 and 406-520) form the sides of the capsomers whereas the P2 subdomain (aa 279-405) form the most protruding part of the capsomers' arch ( Figure 162 -2). Each virion has only one or two copies of the VP2 (~22-29 kDa). The VP2 resulting in carbohydrate malabsorption and osmotic diarrhea; and the effect of NSP4, a viral enterotoxin that increases plasma membrane chloride permeability leading to secretory diarrhea. 30 RV RNA and replicating viruses are frequently detected in blood and cerebrospinal fluid, 31 showing that RV represents a systemic infection with increase of pro-inflammatory cytokines. 32 Immunity against RVs is likely multifactorial; involving local (mucosal) and systemic (serum) antibodies as well as innate and cellular immunity. 33, 34 VP7 and VP4 induce serum-neutralizing antibodies against the infecting serotype (homotypic) that appear within 2 weeks of infection and correlate with protection. 21 Heterotypic antibodies (those against different serotypes) also occur, but mainly among adults and are dependent on the infecting strain. Homotypic protection lasts longer than heterotypic protection but is incomplete and short lived. 21 Anti-RV antibody levels are high at birth (transplacentally acquired), decline by 3-6 months, rise to a peak at 2-3 years and remain elevated throughout life (probably because of repeated, mostly asymptomatic infections). 35 Serum antibodies do not always prevent infection, pointing to the potential role of mucosal immunity. For example, IgA deficient mice shed RV for a prolonged time and are not protected against reinfection. 31 Furthermore, mucosal immunity, passively acquired by breast-feeding 36 or by orally administered immune globulins 37 ameliorates RV symptoms. Mucosal immunity develops 4 weeks after infection and persists for several months, eventually decreasing with advancing age. 38 Experimental and clinical data suggest a role for non-neutralizing anti-VP6 39-41 and other antibodies 42 in protection against RV disease. Cell-mediated immunity also seems important. In mice, RV-specific cytotoxic T cells appear in the intestinal mucosa soon after infection, and mice with severe combined immunodeficiency are able to clear RV infection when reconstituted with CD8 T cells, despite their lack of antibodies against the virus. 43 Lastly, the role of innate immunity is being explored. 44 The clinical spectrum of RV infections ranges from asymptomatic to severe disease with dehydration and death; severity may be associated with antigenemia. 45 The usual clinical picture is presented in Table 162 -3; in addition, transaminase elevation occurs in about 15% of cases 46 and neurological manifestations are increasingly recognized. 47 The disease is self-limiting and chronic infection has not been described in the normal host. 35 Neonatal RV infections are symptomatic in only 10-20% of cases and usually mild, 48 but severe infections may occur among premature infants and those in special care units. 49 Immunodeficient individuals can present a chronic or serious course with associated mortality. 50 Children with human immunodeficiency virus (HIV) infection, and not receiving antiretroviral therapy, may have a twofold risk of RV symptomatic infection and more prolonged virus shedding, but the severity of the illness itself may be similar to that seen in HIV-uninfected children. 51, 52 Diagnostic Microbiology Antigen detection kits based on enzyme immunoassays (EIAs) and latex agglutination are the tests of choice for most clinical circumstances with high sensitivity and specificity (70-100%). Samples should be obtained during the symptomatic period. If samples are not to be processed immediately, they can be stored at 39.2°F (4°C) or frozen. A semi-nested reverse transcription polymerase chain reaction (RT-PCR) test allows for G and P genotyping. 53 In special situations, other tests can be considered: electron microscopy (EM), gel electrophoresis of viral RNA, hybridization of radiolabeled nucleic acid probes and viral culture. Serologic tests are rarely used. Neutralizing antibodies can be detected by plaque reduction or cytopathic effect inhibition. In 1972, Kapikian et al., investigating a gastroenteritis outbreak in Norwalk, Ohio, visualized 27 nm particles in a stool filtrate and noted Norwalk virus-like particle months and 91% after 5 years of age. 68 A birth cohort study in Peru followed 220 and 189 children for 1 and 2 years, respectively. By 1 year 80% of the children had at least one norovirus infection and by 2 years 71% had one or more episodes of norovirus-associated diarrhea. 69 Genogroups I and II strains produce the majority of infections. At a given time, most infections are caused by a major circulating strain. For example, after 2000, GII genogroup caused 96% of sporadic infections in children worldwide 70 and genogroup II.4 strains has caused more than 80% of US outbreaks since the 1990s. 71 Coinfections with different strains occur, giving the opportunity for the exchange of genetic material between strains and the generation of new virus variants. 72 Pandemic variants emerge every 2-4 years. Outbreaks occur mainly in daycare centers, schools, colleges, hospitals, nursing homes, military barracks, restaurants, vacation facilities and cruise ships. NoV also causes travelers' diarrhea. NoV can spread internationally through contaminated food or beverages. 73 A study of 8271 food-borne outbreaks of gastroenteritis showed a median of affected persons of 25 versus 10 for the bacterial outbreaks. Ten percent of the individuals required medical care and 1% were hospitalized. 74 Sapovirus epidemiology is summarized in Table 162 -2. Detection rates vary for different countries, and are much lower than those of NoV and illness is milder. Environment, eating habits and hygiene practices likely play a role in the different attack rates. 75 Caliciviruses are ubiquitous and stable in the environment, providing a persistent source of infection. Noroviruses survive freezing, heating to 60°C (140°F) for 30 minutes and are stable in water chlorinated to 6.25 mg/L; most municipal water systems contain <5 mg/L of chlorine. The virus is also acid-resistant and ether-stable. 76, 77 Caliciviruses are transmitted by the fecal-oral and vomit-oral routes. Sporadic and outbreak cases are spread mainly by person-to-person contact; the patients are more contagious during the first few days of illness. Contaminated food or water are important causes of outbreaks. Transmission through contaminated objects or surfaces in the environment is likely important and may last 2 weeks or longer. 78 Inhalation and swallowing of aerosols produced by vomiting or toilet flushing may also play a role in norovirus spread. 79 Genogroups Taxonomy of the Caliciviridae Family function is not completely understood; it appears to interact with the genome RNA during virus replication. 57 VP1 and VP2 self assemble into virus-like particles (VLPs) without RNA participation. VP2 is not needed for VLPs assembly but is essential for infections in feline calicivirus. The VLPs are morphologically and antigenically similar to natural virions. 58 The NoV has six nonstructural proteins with different functions: NSP 1/2 (p48), replication complex formation; NSP3 (NTPase), nucleoside triphosphatase/RNA helicase; NSP4 (p22), replication complex formation; NSP5 (VPg), genome linked protein involved in translation and replication; NSP6 (3CL, Pro), protease; and NSP7 (Pol, RdRp), RNA-dependent RNA polymerase. They play a role in the replication process of the genome RNA. 57, 59 Epidemiology Human caliciviruses (HuCV) have worldwide distribution, and NoV infects persons of all ages, both in high-income and low-and middleincome countries (LMIC). 60 They are the most common cause of gastroenteritis outbreaks, and they are also recognized as the most common cause of endemic gastroenteritis. 61 In the USA, NoV produces 400 000 emergency department visits and 1.7 million office visits per year; 62 it also accounts for 19-21 million illnesses, 56 000-71 000 hospitalizations and 570-800 deaths. 63 Norovirus is the most commonly detected pathogen (26%) in adults with gastroenteritis. 64, 65 In a 2009-2010 study of children under 5 years of age with acute gastroenteritis, RV and NoV were detected in 12 and 21 of the cases, respectively. The study conclusion is that 'norovirus has become the leading cause of medically attended gastroenteritis in US children' being responsible for approximately 1 million healthcare visits yearly. 66 Norovirus infections occur mainly during the cold seasons. Almost 80% of cases and 71% of outbreaks occur from October to March in the northern hemisphere and from April to September in the southern hemisphere. The reasons for seasonality are not well understood but rainfall may play a role. Breaks in seasonality pattern have been observed with the emergence of new variant strains. 67 Norovirus infections start early in life; a Finnish study found that the prevalence of GII-4 IgG antibodies was 47% in children aged 7-23 production protects against infection. 94 Earlier studies suggested that immunity is mostly short-term (6 months-2 years) and type-specific; however, several clinical and epidemiological observations were inconsistent with this notion. Mathematical models of community transmission of norovirus estimated immunity duration for gastroenteritis at 4.1-8.7 years. 95 The 50% human infectious dose is 1320 genome equivalents. 80 The median incubation period is 1.2 days, 5% of patients develop symptoms in 0.5 days and 95% of them will be symptomatic in 2.6 days. 81 Studies of NoV infections in volunteers described pathological changes in the proximal portions of the small intestine with broadening and blunting of the villi, crypt cell hyperplasia, cytoplasm vacuolization and mononuclear cell infiltration in the lamina propria. Brush border enzymes are decreased, producing malabsorption of carbohydrates and fat. The changes are transient and resolve within 2 weeks. 82, 83 No histological lesions are seen in the gastric or rectal mucosa, and the secretion of hydrochloric acid, pepsin and intrinsic factor remain normal. 84 Gastric emptying is markedly delayed, which could explain the frequency of nausea and vomiting; however, the degree of delay does not correlate with the severity of vomiting. 85 Reduction of villous surface area, and sealing junctional proteins as well as increased active anion secretion, cytotoxic intraepithelial lymphocytes and apoptosis, have been observed suggesting that norovirus diarrhea is caused by a leak flux and secretory component. 86 Virus shedding in the stools begins during the prodrome stage, lasts 13-56 days (median 28 days) 87 and it can persist for several weeks after resolution of symptoms, especially in infants and for months to years in immunocompromised patients. 88, 89 Norovirus infection starts when the protruding domain (P) of the VP1 binds specific carbohydrate receptors on the cell membrane; thereafter NoV enters the cell by a process that requires a protein receptor. This is followed by virus uncoating and release of VPglinked RNA genome to the cytoplasm. Genome replication starts with a negative-sense RNA intermediate. This process is performed by NSP7 (RdRp). The genome functions as an mRNA for the first viral RNA translation, and becomes a template for a double-stranded replication form (RF). Thereafter positive-sense RNA synthesis begins. During the replication process, full genome and subgenomic RNA are formed. Subgenomic RNA consists of the last 2.4 kb of the genome (ORF2+ORF3), and it is also attached to VPg. The ORF1 generates the polyprotein that after cleavage produces the NSPs. NS1/2 and NS4 recruit cellular membranes to form a replication complex. Both VP1 and VP2 capsid proteins are translated mainly by subgenomic RNA. VP1 self-assembles to form the capsid or VLP. Nevertheless VP2 is required for infectivity. The mechanisms of viral assembly and release of the virions are poorly understood; apoptosis has been proposed as an exit strategy. It is assumed that HuNoV replication occurs in the epithelial cells of the upper gastrointestinal tract; however, no viral particles have been observed by EM of the jejunum mucosa 59,90 (Figure 162-3) . Susceptibility to NV is peculiar. Some individuals have natural resistance to the infection. They lack virus receptors; repeated challenges with the virus fail to produce illness or antibody response. Norovirus receptors are the histo-blood group antigens (HBGAs). HBGAs are complex carbohydrates present on the surface of erythrocytes, enterocytes and other mucosal cells. HBGAs include the ABO, Lewis and secretor families. HBGAs production is genetically controlled. The FUT2 gene controls the expression of fucosyltransferase 2 in saliva and mucosal secretions. Individuals who do not have the FUT2 gene are called non-secretors. Twenty percent of Europeans are non-secretors and resistant to infection with the NV. Recognition of carbohydrate receptors is a common characteristic of calicivirus. Different CV have different carbohydrates receptors which determine host and tissue tropism. 91, 92 Norovirus immunity studies are difficult because there is no cell culture system or small animal model. Human volunteer and natural infections studies demonstrate virus-specific antibody response. Serum IgG, IgM and IgA as well as mucosal IgA antibodies are produced. Cell-mediated immunity has been induced by VLP. Serum IgG antibodies persist for months, IgM and IgA are short lived, mucosal IgA persistence is not known. 90, 93 Antibody presence does not always correlate with protection; however, early (<5 days) mucosal IgA 104 PCR amplification can be used for serotype determination. Serological tests are rarely used but specific antibodies can be detected by neutralization or hemagglutination inhibition assays. Enteric adenoviruses are difficult to grow in routine cell lines (e.g. Intestine 407, HEK293 and others), but isolation methods are improving. 105 The clinical manifestations of enteric adenoviruses are presented in Table 162 -3. In general, the disease is milder but more prolonged than that with RV. Treatment is supportive. Cidofovir (or its oral lipid conjugate brincidofovir) alone or with ribavirin have been used for immunocompromised patients. Astroviruses belong to the family Astroviridae. They were first described in 1975 as small (28 nm) particles with a five-or sixpointed star appearance on EM. 106 Later studies showed an icosahedral, 41 nm morphology with well-defined spikes (Figure 162-4) . Subjected to high pH, they transform to the previously described star. 106 The virus is non-enveloped, with a single-stranded, positivesense RNA genome that contains three ORFs. ORF1a and ORF1b encode the viral protease and polymerase, respectively. ORF2 encodes a protein capsid precursor, which gives rise to VP32, VP29 and VP26 (structural capsid proteins). VP26 and VP29 appear to be responsible for antigenic variation. 107 Eight serotypes have been described (HAstV-1 to HAstV-8). Astroviruses infect mammals and birds and some transmission may be zoonotic. 108 Human astroviruses are responsible for 2-4% of endemic diarrhea in children worldwide; HAstV-1 is the most prevalent. 109, 110 They have been associated with outbreaks in daycare centers, schools and pediatric wards. Infection confers protective antibodies, which increase with age (>80% of adults have antibodies). Immunocompromised subjects and the elderly may also be affected. 111 Histopathologic studies show infection of mature epithelial cells of the small intestine, 112 without inflammatory response. The virus is inactivated by methanol 70-90% and heating at 140°F (60°C) for 10 minutes; however, it is resistant to chloroform and ethanol. Diagnosis can be made by commercial immunoassays with good sensitivity and specificity when compared with EM and RT-PCR. 110 Astroviruses can be grown in Caco-2 cells. The clinical characteristics of astrovirus infection are presented in Table 162 -3. Symptoms are similar to those of RV infection but less severe. Management is supportive. The usual clinical characteristics of norovirus and sapovirus infections are presented in Table 162 -3. Most of the time, infections are acute, short-lived or asymptomatic. Nevertheless, severe or prolonged illness and death may occur. Severe outcomes have been associated with the GII.4 NoV strains. Populations at risk include the elderly in healthcare facilities, young infants, and immunosuppressed individuals. Chronic debilitating conditions are usually present. Immediate causes of death include: aspiration pneumonia, sepsis, gastrointestinal bleeding, perforation or necrotizing enterocolitis. 96 The preferred method for NoV and SaV detection is real-time reverse transcription-PCR (RT-PCR). It is very sensitive (10-100 virions) and can be used for clinical and environmental specimens. It is also used to quantify viral load (RT-qPCR). RT-PCR is used for genotyping by Centers of Disease Control and Prevention (CDC) surveillance of NoV outbreaks. Enzyme immunoassays (EIAs) are rapid and useful for testing multiple specimens during outbreaks; however, their sensitivity is about 50% and negative samples should be retested by RT-PCR. EIAs should not replace RT-PCR during outbreak investigations. EIAs have been very useful for the detection of antibodies to the viruses in sero-epidemiological studies. 97 Whole diarrhea stools should be collected within 48-72 hours of illness. If testing is done within 3 weeks, the sample should be kept refrigerated at 39°F (4°C); for longer times, samples should be frozen at −4°F (−20°C). For shipping, each sample should be sealed in a separate plastic bag and kept on frozen refrigerant packs in an insulated, waterproof, polystyrene container. Vomitus samples should be processed in the same way as stools. Water and environmental samples, and food and shellfish samples, should be processed under CDC and FDA guidance respectively. 98 Enteric adenoviruses were first described in 1975. 99 The family Adenoviridae includes 57 human adenoviruses classified into seven groups (A-G). Most are respiratory adenoviruses but two, serotypes 40 and 41 that belong to group F, are enteric pathogens. Group D adenoviruses may also be enteropathogenic in some populations. 100 Adenoviruses are non-enveloped viruses with a dsDNA genome surrounded by an icosahedral capsid with fiber-like projections from each of the 12 vertices (Table 162-1) . Each virion contains 240 hexons (the major surface protein) and 12 pentons. Each penton consists of a base and a fiber. Genus-specific antigens are located in the hexon. Type-specific antigens are located in the hexon and the fiber and elicit serum-neutralizing antibodies. The fiber protein of most adenoviruses binds to the coxsackie-adenovirus receptor (CAR) of epithelial cells. The penton base mediates internalization of the virus. Infected cells degenerate in a process dependent on the E3 virus protein. 101 The mechanism(s) by which serotypes 40 and 41 induce gastroenteritis remains unclear. Enteric adenoviruses have worldwide distribution, mainly affecting young children, and are responsible for 4% of acute gastroenteritis episodes seen in outpatient clinics and 2-22% seen in hospitalized children. 102 Outbreaks lasting 7-44 days have occurred in hospitals and daycare centers with approximately 40% of children infected, half of them asymptomatically. 103 Transmission is person-to-person by the fecal-oral route. Infected persons develop group-and type-specific antibodies that confer long-term immunity. Stool excretion of adenoviruses lasts 10-14 days, from 2 days before to 5 days after end of diarrhea. Asymptomatic excretion may last months to years; thus, their isolation in diarrheic stools does not necessarily mean acute infection. Adenoviruses are less resistant than RVs and are rapidly inactivated at 133°F (56°C) and by exposure to ultraviolet light or formalin. Viral antigen detection in stool by immunoassay is the studied, 125, 126 artificial formulas supplemented with probiotics may reduce the incidence of diarrhea and shorten RV shedding. 127 The most practical and effective intervention to prevent gastroenteritis is vaccination. However, such vaccines are available only for rotavirus. The first commercial RV vaccine, RotaShield® (Wyeth-Ayerst Laboratories), was licensed in the USA in 1998. The vaccine was 49% effective in preventing all RV diarrheas and 80% effective in preventing severe RV diarrhea, 128 but it was suspended due to an association with intussusception, estimated as one additional case/10 000 vaccinated infants. 129 A decade later, two new RV vaccines were licensed. RotaTeq® (or RV5), a live vaccine (Table 162-6) containing five bovine-human reassortant strains, four expressing human G1-G4 with bovine P7 5 specificity, and one expressing bovine G6 with human P1 [8] . Three doses administered at 2, 4 and 6 months of age demonstrated 74% efficacy to prevent any RV disease and 98% of severe disease. 130 A second RV vaccine, Rotarix® (or RV1) is a live monovalent vaccine (Table 162-6) derived of a human attenuated strain 89-12 of G1P [8] specificity. Two doses at 2 and 4 months proved effective in preventing any (73%) or severe (85%) RV disease. 131 The World Health Organization recommended inclusion of RV vaccines into national immunization programs in the Americas and Europe in 2007 and worldwide in 2009. 132 In the USA, RV5 was introduced in 2006 and RV1 in 2008, resulting in >80% reduction in RV-related hospitalization, emergency department (ED) visits and outpatient visits. Concomitantly, there was ~50% decrease in all-cause gastroenteritis visits and hospitalizations. The benefit has been noted even with single dose of either vaccine and has included heterotypic protection. 133 Herd immunity is also present with either vaccine. 134 Countries that introduced RV vaccines have seen a virtual disappearance of the previously predominant G1P [8] strains and a proportional increase of other genotypes, especially G3P [8] (mainly seen in those using RV5) and G2P [4] (mainly in those using RV1). [135] [136] [137] Whether the change represents an effect of vaccine pressure or rather secular changes in circulating RV strains is unclear. Studies in LMIC in Africa 138 and Asia 139 showed lower efficacy of RV5 and RV1 with prevention of severe disease varying between 39% and 77%. 140 Cases of human gastroenteritis have been associated with parechoviruses, enteroviruses, cardioviruses, kuboviruses, coronaviruses, toroviruses, pestiviruses; parvoviruses, picobirnaviruses; and others, but their role as agents of gastroenteritis is under study. Most viral gastroenteritis cases are of mild to moderate severity and self-limited. Severe illness occurs mainly in young children, the elderly and immunocompromised patients. No specific antivirals exist for any of the gastroenteritis viruses. Primary objectives of management are prevention and treatment of dehydration and malnutrition. Most patients can be treated at home with oral rehydration solutions (ORS) and feeding with their regular diet. 113 ORS may prevent 93% of diarrheal deaths. 114 Occasionally, hospitalization and intravenous fluids may be needed for severe illness. Although lactose malabsorption develops frequently during acute gastroenteritis, most children can be fed lactose-containing formulas in small frequent feeds. Human milk, despite its high lactose content, reduces stool output and provides excellent nutrients and antiinfectious factors; therefore, breast-feeding should be continued. The protective effects of breast-feeding on diarrhea morbidity and mortality have been confirmed. 115 A specially formulated ORS (ReSoMal) with less sodium, more potassium and glucose and the addition of magnesium, copper and zinc, as well as continuous feeding with calorie-dense foods, are recommended for malnourished patients. 116 The Ready-to-Use Therapeutic Foods have been proven successful. 117 In LMIC, vitamin A supplementation reduces all-cause diarrhea mortality by 30% in children aged 6-59 months; and zinc, given for 10-14 days during and after a diarrheal episode, decreases diarrhea mortality by 23%. 118, 119 Antiemetics are usually unnecessary; single dose ondansetron can reduce vomiting, use of intravenous fluids and length of stay 120 but its routine use is not supported by the CDC. 121 Adsorbents (kaolin, pectin) and antimotility agents (opiates, loperamide) do not affect the diarrhea mechanisms and may have serious side effects such as paralytic ileus. Nitazoxanide, bismuth subsalicylate, probiotics, bovine colostrum and human serum immunoglobulin have been tried in patients with severe illness with modest effect. Development of specific antivirals is still in a very early stage. 122 Prevention Hygienic measures decrease person-to-person spread; however, these measures are difficult to enforce in situations involving crowding, young children, nursing homes, etc. Some viruses may survive in the environment for weeks and are resistant to commonly used disinfectants, so transmission of the disease continues even in places with good sanitation. Outbreaks require furloughing ill personnel, thoroughly cooking food, disinfecting the environment and properly handling food, water and sanitation. Careful hand washing cannot be overemphasized, especially among food handlers and personnel from hospitals, schools and daycare centers. Hospitalized or other institutionalized patients should be placed under universal precautions with added contact isolation until 48-72 hours after symptoms resolution. 123 Chemical disinfectants can interrupt virus spread from the environment. Special attention should be given to bathrooms, door knobs, hand rails and food preparation surfaces. Commonly used disinfectants are 70% ethanol, 6% hydrogen peroxide, 2500 ppm chlorine, povidone-iodine, ultraviolet radiation and heat. Since fecal matter inactivates the hypochlorites, it should be removed before application. Household laundry can be washed with detergent and bleach, followed by a drying cycle. Heat (176°F (80°C)) for at least 1 minute or high pressure processing have also been used. 124 Breast-feeding may reduce the severity and duration of RV illness, but not the incidence, 36 No licensed vaccine exists against norovirus. Vaccine development has been complicated by several factors including: multiple virus types; antigenic variation; inability to culture the virus; no small animal model; partial understanding of immunity; and effect of previous infections. NoV VLPs given orally to mice and human volunteers are safe and induce IgG1 and IgA antibody responses 147 and a NoV VLP vaccine given intranasally to volunteers reduced the frequency of gastroenteritis and subclinical infections when the participants were given the Norwalk virus. 148 References available online at expertconsult.com. Post-licensure surveillance has detected risk of intussusception for RV5 and RV1, mainly after the first dose and estimated at 1-5 additional cases/100 000 infants vaccinated. 141, 142 This risk is considered small and is outweighed by the benefits of vaccination. 143 Some countries are pursuing their own RV vaccines but few have advanced through clinical testing. The Lanzhou Lamb RV (LLR) vaccine has been licensed in China since 2000 with reported effectiveness of 73% and 44% for RV-hospitalizations and all RV diarrhea respectively. 144, 145 In India, a vaccine is being developed based on a natural human-bovine RV reassortant (116E) with 54% efficacy to prevent severe RV disease. 146 Few other candidate vaccines have entered early phase clinical trials. 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