key: cord-0040206-gj0b6d2x authors: Cunliffe, Nigel A.; Glass, Roger I.; Nakagomi, Osamu title: Rotavirus and Other Viral Diarrhoea date: 2013-10-21 journal: Manson's Tropical Infectious Diseases DOI: 10.1016/b978-0-7020-5101-2.00019-4 sha: 90cbea7f58609fe0371754c8ded54d174bfcf222 doc_id: 40206 cord_uid: gj0b6d2x nan The gastrointestinal tract is the commonest portal of entry for a variety of pathogens, including viruses, but not all of these viruses are causally associated with diarrhoeal disease. Among the viruses that infect enterocytes, or at least use them as a portal of entry, there are two major groups. The first group comprises those viruses that cause systemic infections after entering into the body through the gastrointestinal tract, and diarrhoea, if ever present, is not a major feature of infection. This group includes many enteroviruses, including poliovirus and coxsackieviruses, hepatitis A and E viruses and some adenoviruses. The second group comprises viruses that infect the upper small intestine and cause non-inflammatory diarrhoea. There are currently five established gastroenteritis viruses affecting humans, i.e. Rotavirus, Norovirus, Sapovirus, Human Astrovirus, and Human Adenovirus F (formerly called group F adenovirus). Human rotavirus was discovered in 1973 on thin-section electron microscopy of duodenal biopsies from a child with acute gastroenteritis. 1 Virus particles were subsequently identified in large numbers in faeces by direct negative-stain electron microscopy 2 and significant antibody titre rises were demonstrated between acute and convalescent sera from diarrhoeal children by using immune electron microscopy. 3 The virus was named rotavirus because of its characteristic wheel-shaped (rota = Latin for wheel) morphology on electron microscopy ( Figure 18 .1). Virtually all children are infected with rotavirus at least once by the age of 3-5 years, whether they live in developing or developed countries. However, the consequences of infection are markedly different according to geographic location, with over 95% of deaths due to rotavirus diarrhoea occurring in the developing countries of the Indian subcontinent, sub-Saharan Africa and Latin America (Figure 18 .2). [4] [5] [6] Rotavirus diarrhoea occurs at an earlier age in children in developing countries than in children in developed countries (Figure 18 .3). The median age of children hospitalized with rotavirus diarrhoea in many African and Asian counties is 6-9 months, and up to 80% are less than 1 year old. In contrast, the median age in developed countries is 13-16 months and the highest proportion of cases occurs in the 2nd year of life. 7, 8 In temperate countries, rotavirus infections peak in the winter and early spring, with fewer cases detected at other times. In tropical countries, rotavirus infections characteristically occur throughout the year, although more cases are typically observed in the cooler and drier months. Although the mode(s) of transmission of rotavirus are not completely understood, person-to-person spread of rotavirus by the faecal-oral route is likely to play a central role. In both developing and developed countries, rotavirus is the major cause of severe gastroenteritis requiring hospitalization. It was estimated that, from 1986 to 1999, a median of 22% (range 17-28%) of acute diarrhoea cases in children less than 5 years of age were due to rotavirus 4 but this proportion nearly doubled from 2000 to 2004 to 39% (range 29-45%), 5 related in part to the widespread application of more sensitive detection methods, and to a decrease in the proportion of gastroenteritis caused by bacterial pathogens. The annual global mortality due to rotavirus diarrhoea among children less than 5 years of age has been estimated as 453 000 in the pre-rotavirus vaccine era, with rotavirus accounting for 37% of all diarrhoea deaths and 5% of all-cause deaths in children under 5 years of age. 9 The Democratic Republic of Congo, Ethiopia, India, Nigeria, and • Rotavirus, norovirus, sapovirus, enteric adenovirus and astrovirus are established aetiological agents of acute gastroenteritis across all age groups in all settings. • Rotavirus is the single most important pathogen associated with severe dehydrating gastroenteritis in infants and young children worldwide. • Norovirus causes sporadic and epidemic disease in adults and children. • All gastroenteritis viruses infect the epithelial cells of the intestinal mucosa, causing acute, non-inflammatory watery diarrhoea mostly of less than 1 week duration. • Aetiological diagnosis requires the detection of either specific antigens of each virus with immunologic assays, or the presence of the viral genome with molecular assays or visualization of virus by electron microscopy. • Treatment is primarily supportive and consists of rehydration and restoration of electrolyte balance. • Two live, oral, attenuated vaccines, Rotarix and RotaTeq, have been developed to prevent global morbidity and mortality due to rotavirus infection. • Both rotavirus vaccines are entering childhood immunization schedules following successful clinical trials in representative populations worldwide, with early evidence of substantial impact. By conventional negative-stain electron microscopy, rotavirus has a characteristic double capsid appearance measuring approximately 75 nm in diameter ( Figure 18 .1), but cryoelectron microscopic studies demonstrated that the rotavirus virion comprises a triple-layered capsid with 60 spikes protruding from its surface, making its overall diameter nearly 100 nm. The outermost layer (outer capsid) consists of two proteins, VP4 and VP7, each of which independently serves as a neutralization antigen (Figure 18 .4). The serotype defined by the VP4 protein is called the P type, for protease-sensitive protein (because VP4 is proteolytically cleaved into VP8* and VP5*), and the serotype defined by the VP7 protein is called the G type, for glycoprotein. The middle capsid consists of the most abundant viral protein, VP6, which is the major protein against which non-neutralizing antibodies are raised during infection. The core or the innermost layer consists of VP2, a scaffolding protein, and inside this layer are VP1 (viral RNA-dependent RNA polymerase) and VP3 (guanyltransferase), which is present in association with the 11 segments of double-stranded genomic RNA. In addition to these five structural proteins, there are six non-structural proteins (NSPs), each of which is encoded by a single genome segment, except for NSP5 and NSP6 (encoded by RNA segment 11), which carry out various functions during replication and morphogenesis. NSP4 is a chaperone protein enabling the subviral particle to acquire the outer capsid proteins VP4 and VP7 during the later phases of viral morphogenesis. NSP4 also acts as a viral enterotoxin, causing diarrhoea in newborn mice. [15] [16] [17] Rotavirus genomic RNA can be extracted directly from clinical specimens and separated by polyacrylamide gel electrophoresis (PAGE). With this, two major RNA migration patterns are recognized in which genome segments 10 and 11 of long RNA pattern viruses migrate faster than do those of short RNA pattern viruses (Figure 18 .5). 18 The precise migration pattern is Pakistan accounted for more than half of all rotavirus deaths, with India alone accounting for 22% of deaths. 9 Rotavirus is a genus within the family Reoviridae, and within the genus there are seven groups (A-G), each of which represents a separate species, e.g. Rotavirus A, Rotavirus B, etc. 10 Only group A, B and C rotaviruses are established human pathogens. Group A rotavirus has the greatest medical importance and, unless mentioned otherwise, the word rotavirus usually infers Group A rotavirus. Group B rotavirus infection is rare and affects both adults and children, causing both outbreaks and sporadic infections, primarily in China, India and Bangladesh. 11, 12 Group C rotaviruses tend to affect older children than do group A rotaviruses, and up to one-third of adult humans have serological evidence of infection with Group C rotavirus. 13,14 Rotavirus exclusively infects the mature differentiated villous enterocytes of the small intestine. Rotavirus attaches to its cellular receptors (sialoglycoprotein and integrins) via the VP4 protein. The minimum infective dose is as low as 10 2 -10 3 virus particles in adult volunteers. 29 Progeny virus is produced after 10-12 h, and released in large numbers into the intestinal lumen ready to infect other cells. The pathogenesis of rotavirus diarrhoea includes both malabsorptive and secretory components. 30 Malabsorption may be consequent upon damage to mature absorptive enterocytes resulting in malabsorption of nutrients, electrolytes and water; virus-induced downregulation of the expression of absorptive enzymes; and functional changes in tight junctions between enterocytes leading to paracellular leakage. Biopsies show atrophy of the villi and mononuclear cell infiltrates in the lamina propria. Secretory mechanisms include those mediated by activation of the enteric nervous system and the effect of NSP4, the latter being via activation of cellular Cl − channels, leading to increased Cl − and consequently water secretion. Rotavirus infection was previously thought to be limited to the intestine, but rotavirus causes viraemia for at least a short period in the acute phase of infection in immunocompetent infants as well as in experimentally infected animals. 31 The clinical significance of this systemic spread of rotavirus remains unclear. In general, one or more episodes of rotavirus infection confer protection against subsequent moderate or severe rotavirus diarrhoea but not against asymptomatic reinfection or mild diarrhoea. Furthermore, infection with one serotype generally provides serotype-specific (homotypic) protection, and repeated infections lead to partial cross-serotype (heterotypic) protection. These beliefs are supported by the findings of a cohort study in Mexico, where children who had experienced one, two or three episodes of rotavirus diarrhoea had adjusted relative risks of experiencing a further attack of rotavirus diarrhoea of 0.23, 0.17 and 0.08, respectively, and of asymptomatic rotavirus infection of 0.62, 0.40 and 0.34, respectively. 32 However in a cohort study in Vellore, India, while protection against moderate or severe disease increased with successive infections it was only 79% after three infections and no evidence of homotypic protection was demonstrated, indicating that immune protection following natural infection may vary by location. 33 In the Indian study, multiple infections were common, with only 30% of all identified infections being primary. Immunity following natural rotavirus infection is believed to be mediated by both humoral and cell-mediated immune responses. 34 Rotavirus-specific immunoglobulin (Ig) A antibodies on the enteric mucosal surface are thought to be the primary mediator of protective immunity. Cellular immunity is considered to be important in the resolution of rotavirus infection and appears to be cross-protective between the different G serotypes. 35 Protection of neonates against rotavirus infection appears to be mediated by transplacentally acquired maternal antibody 36, 37 and by antibodies and other factors in breast milk. 38 However, a study in Bangladesh showed that hospitalized children with rotavirus diarrhoea were more likely to be breast-fed than were children with diarrhoea due to other infectious agents. 39 Rotavirus infection in neonates often results in asymptomatic infection and Malawi Japan characteristic for each rotavirus strain and is called an 'electropherotype' , which was extensively applied in molecular epidemiological studies, until the use of genotyping and sequencing methods became more widespread. 19 The serotype is the most important antigenic determinant of rotavirus and is defined by serological assays. However, serological typing methods have been largely replaced by molecular typing (genotyping). In addition to VP7 (G) and VP4 (P) genotyping, a nucleotide sequence-based, complete genome classification system has recently been introduced for rotavirus classification; 20 the genome of individual rotavirus strains is given the complete descriptor of Gx-P[x]-Ix-Rx-Cx-Mx-Ax-Nx-Tx-Ex-Hx. Of these 11 genotypes, the G and P genotypes have been extensively investigated because of their importance in protective immunity. There are thus far 26 G genotypes and 35 P genotypes reported among human and animal rotaviruses, but the G and P type combinations (Figure 18 .6) detected in human rotaviruses are mostly limited to G1P [8] , G2P [4] , G3P [8] , G4P [8] and G9P [8] . 21, 22 However, G12 strains have now emerged across the world, 23 and G8 strains with either P [6] or P [4] account for a significant proportion of human rotavirus strains in Africa. 24, 25 Such genetic diversity is generated by frequent reassortment of the genome segments and interspecies transmission of rotaviruses between humans and animals. [26] [27] [28] rotavirus can therefore circulate silently in neonatal units. Neonatal strains are often unusual and can infect even in the presence of high titres of transplacental antibody from the mother. Asymptomatic neonatal infections may induce protection against subsequent severe rotavirus gastroenteritis. 40 Finally, it is increasingly recognized that otherwise healthy adults can experience rotavirus diarrhoea and elderly people can develop severe rotavirus gastroenteritis as their immunity wanes. 41, 42 The outcome of rotavirus infection varies from asymptomatic, through mild short-lived watery diarrhoea, to an overwhelming gastroenteritis with dehydration leading to death. The onset of symptoms is abrupt after a short incubation period of 1-2 days. Fever, vomiting and watery diarrhoea are seen in the majority of infected children and last for 2-6 days. Rotavirus diarrhoea tends to be more severe than that due to other common enteropathogens. 43 Extraintestinal manifestations during rotavirus gastroenteritis, including encephalopathy, have captured attention since rotavirus viraemia was reported. 44 It is not possible to distinguish rotavirus gastroenteritis from other viral causes of diarrhoea solely on clinical grounds. 45 The stools are usually watery or loose, and are seldom blood-stained. In severe cases, the cause of death is dehydration, which can be hypo-or hypernatraemic and is often associated with metabolic acidosis. Underlying conditions such as malnutrition may be a risk factor for a more severe disease outcome. Rotavirus does not appear to produce more severe disease in HIV-infected infants. 46 Large numbers of rotavirus particles (up to 10 11 /g of faeces) are excreted during the acute phase of infection. Children with severe diarrhoea excrete more virus than do children with less severe diarrhoea. 48 Rotavirus can be detected in stool specimens by a number of techniques, including electron microscopy, PAGE, antigen detection assays, RT-PCR and virus isolation. Electron microscopy remains a valuable diagnostic tool since it is a catch-all technique that will also detect other potential viral enteropathogens. PAGE is a convenient diagnostic tool for the detection of rotavirus RNA extracted directly from stool specimens ( Figure 18 .5). The assay also allows detection of nongroup A rotaviruses, which fail to react in most antigen detection assays. PAGE is a relatively simple technique with high specificity for rotavirus (100%) and reasonable sensitivity (80-90%), and can be performed in tropical countries relatively cheaply. 49 It has the added advantage of providing epidemiological information because the electrophoretic migration pattern of the 11 segments of the double-stranded RNA genome is specific to each rotavirus strain. 18, 50 Antigen detection tests are currently the most widely used assays for rotavirus infection in diagnostic laboratories and include enzyme-linked immunosorbent assays (ELISAs), and immunochromatographic assays. 51 The sensitivity and specificity of the majority of these tests are generally high (90-95%) but they are designed to detect only group A rotaviruses. Detection of viral genome by RT-PCR is predominantly a research tool which provides information on the genotypes of the circulating strains 52-54 and the duration of viral shedding in stool Since virtually all children will have experienced rotavirus infection by the age of 3-5 years in both developing and developed countries, it is clear that hygiene and sanitation practices are not sufficient to prevent the spread of rotavirus infection within the community. Thus, prevention of severe rotavirus gastroenteritis by vaccines remains the only practical preven tive measure. 60 The first licensed rotavirus vaccine, a rhesus monkey rotavirus-based tetravalent human reassortant vaccine (RotaShield®), was withdrawn after this live, oral vaccine was associated with the development of intestinal intussusception in approximately 1 : 10 000 vaccine recipients in the USA, with intussusception cases occurring disproportionately in those infants who received their first dose of vaccine at over three months of age. 61, 62 These unfortunate events stimulated the further development and testing of two additional live, oral rotavirus vaccines, Rotarix® (GlaxoSmithKline Biologicals) and RotaTeq® (Merck & Co.). Rotarix® is a monovalent, human rotavirus vaccine of serotype G1P1A [8] administered as a twodose schedule, whereas RotaTeq® is a pentavalent, bovinehuman reassortant vaccine comprising types G1, G2, G3, G4 and P [8] and is given in a 3-dose schedule. 63 Both vaccines were found to be safe in large, phase III clinical trials, each involving more than 60 000 infants and were 85-95% efficacious in preventing severe gastroenteritis due to rotavirus. 64, 65 In countries that have introduced rotavirus vaccine into their childhood immunization programmes, hospitalizations due to rotavirus gastroenteritis have dramatically fallen. 66, 67 Evidence of an indirect effect of rotavirus vaccines has been presented from the USA and other settings, with reduced incidence of disease in children too old to have been vaccinated and in adults. 66, 67 Both vaccines have recently been evaluated in clinical trials in Africa and Asia, where efficacy against severe rotavirus gastroenteritis was lower than previously experienced in other settings (50-75%), with poorer countries generally having lower efficacy (e.g. 50% in Malawi). [68] [69] [70] The reason for reduced efficacy in low-income countries is not yet known, but other live, oral vaccines against polio and cholera are known to be less efficacious in developing countries. 71, 72 Despite more modest efficacy in low-income countries, the high burden of rotavirus disease led the WHO to issue a recommendation that rotavirus which can be prolonged. 55, 56 Group A and group C rotaviruses can be isolated in cell culture but viral culture is limited to research purposes. The mainstay of management consists of assessment of dehydration and replacement of lost fluid by oral rehydration with fluids of specified electrolyte and glucose composition, together with administration of zinc in children over age 6 months and where the prevalence of malnutrition is high. 57 Intravenous rehydration therapy is indicated for patients with severe dehydration, shock or reduced levels of consciousness. Human or bovine colostrum and hyperimmune human serum immunoglobulin have been used to manage chronic rotavirus infection in immunocompromised children. Administration of probiotics such as Lactobacillus casei GG also appears beneficial. The antiprotozoal drug nitazoxanide was shown to decrease the median duration of rotavirus gastroenteritis by 44 hours in a randomized double-blind placebo-controlled trial in Egyptian children. 58 As an adjunct to oral rehydration, the antisecretory agent racecadotril reduces diarrhoea duration and stool volume in children with acute gastroenteritis. 59 adenoviruses account for approximately 5% of cases of infantile diarrhoea, occurring most often in children under 2 years of age without a clear seasonality. 79 However, it was reported that enteric adenoviruses were detected in as many as 20% of hospitalized children in northern Taiwan. 80 Enteric adenoviruses are spread from person-to-person by the faecal-oral route. Adenoviruses were found contaminating water in poor sanitary settings, 81 but these adenoviruses are unlikely to be enteric adenoviruses. No food-borne nor water-borne spread of enteric adenoviruses has been documented. The clinical features of enteric adenovirus gastroenteritis do not differ from those of rotavirus but the duration of diarrhoea tends to be longer in adenovirus infection than in rotavirus infection. 82, 83 Other than gastroenteritis, adenovirus is implicated as a cause of idiopathic intussusception in infants. 84, 85 These adenoviruses are of serotypes 1, 2, 3 and 5, and rarely of 40 or 41 (enteric adenoviruses). The diagnosis of adenovirus infection is by visualization of characteristic virions in stool specimens under the electron microscope; demonstration of adenovirus antigens in stool by ELISA or immunochromatography or by detection of the genome by PCR which has much higher sensitivity. 80 Treatment of adenovirus diarrhoea is by managing dehydration. There is neither a specific therapeutic intervention nor an available vaccine. Human astrovirus, a species in genus Mamastrovirus, family Astroviridae, has an unenveloped virion measuring 28-30 nm in diameter with a characteristic star shape 'stamped' on its surface, a five-or six-pointed star with an electron-dense centre (astron = Greek for a 'star') ( Figure 18.8) . Its genome is positivesense single-stranded RNA approximately 7 kb in length, which encodes an RNA polymerase (ORF1a), a serine protease (ORF1b) and three capsid proteins (ORF2). While astrovirus was first described in humans in 1975, astrovirus can infect a variety of animal species. There are eight serotypes of Human astrovirus with serotype 1 the most frequently detected. 86 Other serotypes can cause outbreaks of food-borne infections and there appears to be more diversity in developing countries. 87 More recently, however, a greater number of astroviruses in human stool have been found far beyond the eight serotypes of Human astrovirus; vaccines should be incorporated in all childhood immunization programmes worldwide, with a strong recommendation for countries where diarrhoeal disease accounts for more than 10% of childhood mortality. 73 Because of the age-related occurrence of intussusception, the WHO recommended that the first dose of vaccine should be administered by 15 weeks of age and that the full course should be completed by 32 weeks of age. 73 An early indication of the major public health benefit that rotavirus vaccination can bring has been demonstrated in Mexico, where diarrhoea mortality has fallen since the introduction of Rotarix into its childhood immunization programme. 74 A small increase in the risk of intussusception noted following the first vaccine dose in Mexico and after the second vaccine dose in Brazil has been noted, but the risk is outweighed by the number of diarrhoea deaths that will be prevented. 75 A re-evaluation of the risk/benefit ratio of rotavirus vaccination, in particular the impact of vaccination on severe disease in high mortality settings, has led to a WHO recommendation that the age restrictions on immunization be removed but that surveillance for intussusception should be implemented to monitor vaccine safety. 76 Additional assessments should include examination of the impact of rotavirus vaccination on rotavirus epidemiology including the distribution of rotavirus strains. Early studies suggested an increase in prevalence of G2P [4] strains following Rotarix introduction in Brazil, but it remains unclear whether this results from immune pressure secondary to vaccine use or natural fluctuation in strain types. 77 Continuous global strain surveillance is required to address this question. 78 Adenovirus is an unenveloped DNA virus with an icosahedral capsid measuring 70-75 nm in diameter (Figure 18.7) . Its genome comprises double-stranded linear DNA of 33-45 kbp. Taxonomically, human adenoviruses that primarily cause diarrhoea are classified as species Human adenovirus F (formerly called group F) within the genus Mastadenovirus, family Adenoviridae. Within Human adenovirus F, more often referred to as 'enteric adenovirus' , two serotypes 40 and 41 are distinguished based upon virus neutralization assays. These enteric than human volunteers, serotypes of Norovirus have not been established. The genome of norovirus exhibits a great diversity and there are more than 30 genotypes that are distributed into five genogroups (GI-GV) 95 of which human noroviruses cluster into GI, GII and GIV. 96 Norovirus spreads faeco-orally from person to person and from contaminated food and water; the respiratory route has also been suggested from epidemiological observations that aerosolized saliva or vomitus can be the source of infection. 97 In temperate countries, norovirus gastroenteritis tends to show winter seasonality. Norovirus was initially thought solely to cause epidemic gastroenteritis limited to older children and adults, but it is the cause of gastroenteritis in four epidemiological settings. These include: (1) Epidemic food-borne gastroenteritis that affects a large number of otherwise healthy adults over a short period of time; the illness usually resolves spontaneously without sequelae. (2) Sporadic gastroenteritis in the community. 98 (3) Healthcare-associated infections occurring in semiclosed settings such as hospital wards and residential homes resulting in often prolonged illness with increased severity. (4) Infantile diarrhoea in both developing and developed countries. 99 In a study in Finnish children, norovirus was responsible for 20% of gastroenteritis cases. 100 Similarly, in Iraq, 101 Libya, 102 and Brazil, 103 norovirus was detected in 30%, 18%, 15%, of diarrhoeal children less than 5 years of age, respectively. Norovirus is now the most common virus detected in children with acute gastroenteritis seeking medical attention in the US, where rotavirus vaccine has been part of the childhood immunization programme since 2006. 104 Norovirus causes an illness with an abrupt onset of vomiting, diarrhoea and abdominal pain following an incubation period of 1-2 days. The illness is generally mild and fever rarely exceeds 38°C. Recovery follows within 1-3 days, but excretion of norovirus into stool lasts longer, sometimes up to 4 weeks. Approximately half of those infected with norovirus remain asymptomatic. Similar to other viral gastroenteritis cases, diagnosis is based on the detection of virus in stool specimens. Historically, immuneelectron microscopy was used to detect norovirus particles in stool specimens obtained in the acute phase of the illness. However, the diagnosis of norovirus gastroenteritis is now most commonly undertaken by sensitive, real-time PCR assays with genogroup-specific Taqman probes that provide both virus detection and quantification. 105 When the amount of virus is abundant, this will be followed by qualitative RT-PCR to amplify the end of ORF1 and the first part of ORF2 and subsequent sequencing to determine the genotype of a strain. In practice, a web-based genotyping tool is conveniently used (see: http:// www.rivm.nl/mpf/norovirus/typingtool). Although much less sensitive than these molecular-based assays, commercial antigen detection kits have been developed; immune-chromatography, in particular, allows diagnosis at the point of care. While the while their association with disease has yet to be established, there are five additional novel astroviruses, MLB1, MLB2, VA1, VA2 and VA3, described on the basis of phylogenetic analysis. 88 Astrovirus infections predominate in young children aged between 4 months and 4 years, and account for between 2% and 10% of cases of diarrhoea in children. The disease tends to be milder and more frequently encountered in community-based studies. 89 One such study in Mexico estimated the incidence of astrovirus gastroenteritis to be 0.1 episodes/child per year. 90 Seroepidemiological studies have demonstrated that more than 90% of children in the USA will have experienced astrovirus infections by the age of 6-9 years. 91 Astrovirus has been detected in all countries where sufficiently sensitive detection methods have been used. In temperate countries it shows a similar seasonal distribution to rotavirus but peaks earlier. Astrovirus is transmitted faeco-orally either directly or by ingestion of food. It infects the upper small intestine but the mechanism of diarrhoea is not known. The features of the illness are similar to those of rotavirus but may be milder and its duration is 4-5 days on average. However, in Bangladesh, astrovirus was found to be associated with prolonged diarrhoea. 87 Diagnosis used to be solely by electron microscopy, but this is now being replaced by more sensitive and easy-to-perform ELISA or by detection of the genome by RT-PCR. Treatment is by managing dehydration. There is no vaccine available and little is known of immunity to infection, other than that children with immunodeficiency syndromes excrete the virus for long periods. 92 Norovirus VIROLOGY Genus Norovirus, of which Norwalk virus 93 is the type species, belongs to the family Caliciviridae. Norovirus has an unenveloped virion with icosahedral symmetry, measuring 27-35 nm in diameter with a feathery-ragged outline (Figure 18 .9). Its genome is positive-sense, single-stranded RNA, approximately 7 kb in length, with a stretch of poly A sequence at its 3′ terminus. 94 The genome contains three ORFs, of which ORF2 encodes VP1, a 59 kDa protein, on which the antigenicity of a virus strain is expressed. Since neither animal model nor cell culture systems are available to test the infectivity of norovirus other Figure 18 .9 Negative-stain electron micrograph of norovirus with a feathery-ragged outline (×200 000). Illness due to sapovirus tends to predominantly occur in young children, and virtually all children appear to have experienced infection by sapovirus by the age of 5 years. Sapovirus gastroenteritis may occur year-round, although it seems to occur more frequently in winter. Sapovirus accounts for approximately 5% of cases of infantile diarrhoea 111, 112 and is distributed globally. Sapovirus rarely causes outbreaks of foodborne gastroenteritis. Sapovirus spreads faeco-orally and infects, and causes predominantly diarrhoea in infants and young children. Protective immunity appears to follow infection, since adults rarely get sapovirus gastroenteritis. While a typical calicivirus-like morphology under the electron microscope strongly suggests the presence of sapovirus, the definitive diagnosis needs to be made based on either antigen detection or identification of the sapovirus genome by RT-PCR. 106 Treatment is by management of dehydration. There is neither specific antiviral chemotherapy nor a vaccine available. A number of other viruses, including coronavirus 113 torovirus, 114 picobirnavirus 115,116 pestivirus, 117 Aichi virus 118 and bocavirus 119 have been detected in stool specimens of patients with acute gastroenteritis. Their clinical and epidemiologic significance as aetiological agents of diarrhoea is being investigated. specificity of such immunoassays is close to 100% for those norovirus genotypes to which antibodies used in the kit are raised, diagnostic accuracy in practice may be lower because of the antigenic diversity likely to be encountered. Short-term homologous immunity (against the infecting strain) appears to follow an episode of norovirus gastroenteritis. However, great antigenic diversity permits repeated illness with different norovirus strains. It was noticed in early challenge studies with volunteers that there are individuals with natural resistance against some strains of norovirus. Recent progress in understanding the relationships between norovirus and histoblood group antigens has partly solved this mystery. 106 Norovirus appears to use ABO and Lewis blood group antigens expressed on the mucosal surface of the enterocytes as viral receptors; thus, non-secretors, in whom such antigens are not expressed on the intestinal mucosa, are resistant to norovirus infection. 107 Recent studies propose an evolutionary model in which the most prevalent GII.4 noroviruses persist by altering histo-blood group antigen binding targets as well as changing epitopes surrounding the binding pocket over time. 108 There is no specific therapy. Vaccines using virus-like particles are under clinical development. Genus Sapovirus (the type species Sapporovirus was found in Sapporo, Japan 109 ), within the family Caliciviridae, has an unenveloped virion with icosahedral symmetry, measuring 30-35 nm in diameter, with characteristic cup-like depressions (calyx = Greek for a 'cup' , hence, calici 110 ), on its surface (Figure 18 .10). Negative-stain electron microscopy reveals characteristic particle morphology with cup-like depressions, often described as the 'Star of David' (Figure 18 .10). Its genome is positive-sense, single-stranded RNA of approximately 7 kb in length with a stretch of poly A sequence at its 3′ terminus. Unlike norovirus, sapovirus encodes the capsid protein contiguous with the large non-structural polyprotein (ORF1). The junction that corresponds to ORF1 and ORF2 of norovirus consists of a one-or four-nucleotide overlap between the stop codon of ORF1 and the first AUG codon of ORF2. This creates a −1 frameshift. The 3′ end of ORF1 encodes a single polypeptide of 62 kDa. WHO-coordinated Global Rotavirus Surveillance Network. 2008 estimate of worldwide rotavirus-associated mortality in children younger than 5 years before the introduction of universal rotavirus vaccination programmes: a systematic review and meta-analysis Protective effect of natural rotavirus infection in an Indian birth cohort Effect of human rotavirus vaccine on severe gastroenteritis in African infants Effect of rotavirus vaccination on death from childhood diarrhea in Mexico Norovirus gastroenteritis Virus particles in epithelial cells of duodenal mucosa from children with acute non-bacterial gastroenteritis Detection of a new virus by electron microscopy of faecal extracts from children with acute gastroenteritis Reovirus like agent in stools: association with infantile diarrhea and development of serologic tests Global illness and deaths caused by rotavirus disease in children Rotavirus and severe childhood diarrhea Burden of disease and circulating serotypes of rotavirus infection in sub-Saharan Africa: systematic review and meta-analysis Incidence and burden of rotavirus gastroenteritis in Japan as estimated from a prospective sentinel hospital study Epidemiology of rotavirus infections in children in WHO-coordinated Global Rotavirus Surveillance Network. 2008 estimate of worldwide rotavirus-associated mortality in children younger than 5 years before the introduction of universal rotavirus vaccination programmes: a systematic review and meta-analysis Philadelphia: Kluwer Health/Lippincott, Williams and Wilkins Rotaviruslike agent in adult non-bacterial diarrhoea in China The evolution of human group B rotaviruses Seroepidemiology of human group C rotavirus in Japan based on a blocking enzyme-linked immunosorbent assay Epidemiology of group C rotavirus infection in Western New York women of childbearing age Age-dependent diarrhea induced by a rotaviral nonstructural glycoprotein Diarrhea induction by rotavirus NSP4 in the homologous mouse model system Group C rotavirus NSP4 induces diarrhea in neonatal mice Molecular characterization of serotype G2 and G3 human rotavirus strains that have an apparently identical electropherotype of the short RNA pattern Development of rotavirus molecular epidemiology: electropherotyping Recommendations for the classification of group A rotaviruses using all 11 genomic RNA segments Serotype diversity and reassortment between human and animal rotavirus strains: implications for rotavirus vaccine programs Global distribution of rotavirus serotypes/genotypes and its implication for the development and implementation of an effective rotavirus vaccine Evolutionary history and global spread of the emerging G12 human rotaviruses Molecular and serologic characterization of novel serotype G8 human rotavirus strains detected in Rotavirus strain types circulating in Africa: review of studies published from 1997 to The expanding diversity of rotaviruses Genomic relationships among rotaviruses recovered from various animal species as revealed by RNA-RNA hybridization assays Full genome-based classification of rotaviruses reveals common origin between human Wa-like and porcine rotavirus strains and human DS-1-like and bovine rotavirus strains Human rotavirus studies in volunteers: determination of infectious dose and serological response to infection Rotaviruses: from pathogenesis to vaccination Rotavirus antigenaemia and viraemia: a common event Rotavirus infections in infants as protection against subsequent infections Protective effect of natural rotavirus infection in an Indian birth cohort Mechanisms of protection against rotavirus infection and disease Mapping of the target antigens of the rotavirus-specific cytotoxic T cell response Lack of maternal antibodies to P serotypes may predispose neonates to infections with unusual rotavirus strains Emerging group A rotavirus and a nosocomial outbreak of diarrhoea Protection against neonatal rotavirus infection by breast milk antibodies and trypsin inhibitors Observations questioning a protective role for breast-feeding in severe rotavirus diarrhea Clinical immunity after neonatal rotavirus infection. A prospective longitudinal study in young children Winter seasonality and rotavirus diarrhoea in adults Rotavirus infection in adults Prospective study of diarrheal diseases in Venezuelan children to evaluate the efficacy of rhesus rotavirus vaccine Rotavirus antigenemia in children with encephalopathy accompanied by rotavirus gastroenteritis Viral gastroenteritis Effect of concomitant HIV on presentation and outcome of rotavirus gastroenteritis in Malawian children A review of rotavirus infection in and vaccination of human immunodeficiency virus-infected children Quantitation of group A rotavirus by real-time reverse-transcription-polymerase chain reaction: correlation with clinical severity in children in South India Rapid diagnosis of rotavirus infection by direct detection of viral nucleic acid in silver-stained polyacrylamide gels Direct evidence for genome segment reassortment between concurrently-circulating human rotavirus strains Evaluation of seven immunoassays for detection of rotavirus in pediatric stool samples Polymerase chain reaction amplification and typing of rotavirus nucleic acid from stool specimens Identification of group A rotavirus gene 4 types by polymerase chain reaction Relative frequency of VP4 gene alleles among human rotaviruses recovered over a 10-year 214.e2 SECTION 5 Viral Infections period (1982-91) from Japanese children with diarrhea Improved detection of rotavirus shedding by polymerase chain reaction Extended excretion of rotavirus after severe diarrhoea in young children Oral zinc for treating diarrhoea in children Effect of nitazoxanide for treatment of severe rotavirus diarrhoea: randomised double-blind placebo-controlled trial Racecadotril for childhood gastroenteritis: an individual patient data meta-analysis Rotavirus vaccines: current prospects and future challenges Intussusception among infants given an oral rotavirus vaccine History of rotavirus vaccines. Part I: RotaShield A critical time for rotavirus vaccines: a review Safety and efficacy of an attenuated vaccine against severe rotavirus gastroenteritis Safety and efficacy of a pentavalent human-bovine (WC3) reassortant rotavirus vaccine Uptake, impact, and effectiveness of rotavirus vaccination in the United States: review of the first 3 years of postlicensure data Fulfilling the promise of rotavirus vaccines: how far have we come since licensure? Effect of human rotavirus vaccine on severe gastroenteritis in African infants Efficacy of pentavalent rotavirus vaccine against severe rotavirus gastroenteritis in infants in developing countries in sub-Saharan Africa: a randomised, double-blind, placebo-controlled trial Efficacy of pentavalent rotavirus vaccine against severe rotavirus gastroenteritis in infants in developing countries in Asia: a randomised, doubleblind, placebo-controlled trial Oral rotavirus vaccines: how well will they work where they are needed most? Performance of rotavirus vaccines in developed and developing countries World Health Organization. Meeting of the immunization Strategic Advisory Group of Experts Effect of rotavirus vaccination on death from childhood diarrhea in Mexico Intussusception risk and health benefits of rotavirus vaccination in Mexico and Brazil -conclusions and recommendations Human rotavirus vaccines: too early for the strain to tell Rotavirus disease and vaccination: impact on genotype diversity Etiology of acute gastroenteritis in hospitalized children in Molecular epidemiology and clinical manifestations of viral gastroenteritis in hospitalized pediatric patients in Northern Taiwan Occurrence of water-borne enteric viruses in two settlements based in Eastern Chad: analysis of hepatitis E virus, hepatitis A virus and human adenovirus in water sources Gastroenteritis associated with enteric type adenovirus in hospitalized infants Enteric adenovirus infection and childhood diarrhea: an epidemiologic study in three clinical settings Intussusception, adenovirus and children: a brief reaffirmation Risk factors for intussusception in infants in Vietnam and Australia: adenovirus implicated, but not rotavirus Molecular epidemiology of astroviruses in Japan from 1995 to 1998 by reverse transcription-polymerase chain reaction with serotype-specific primers (1 to 8) Astrovirus infection in association with acute, persistent and nosocomial diarrhea in Bangladesh Human stool contains a previously unrecognized diversity of novel astroviruses Population-based prevalence of symptomatic and asymptomatic astrovirus infection in rural Mayan infants A prospective study of astrovirus diarrhea of infancy in Mexico City Molecular epidemiology of childhood astrovirus infection in child care centers Etiology and outcome of diarrhea after marrow transplantation: a prospective study Visualization by immune electron microscopy of a 27-nm particle associated with acute infectious nonbacterial gastroenteritis Norwalk virus genome cloning and characterization Human norovirus infection and the lessons from animal caliciviruses Noroviruses: a comprehensive review Transmission of Norwalk virus during football game IID2 Study Executive Committee. Longitudinal study of infectious intestinal disease in the UK (IID2 study): incidence in the community and presenting to general practice Norovirus gastroenteritis Human caliciviruses in acute gastroenteritis of young children in the community Norovirus gastroenteritis among children in Iraqi Kurdistan Clinical features and molecular epidemiology of rotavirus and norovirus infections in Libyan children Norovirus infection among children with acute gastroenteritis in Recife, Brazil: disease severity is comparable to rotavirus gastroenteritis Norovirus and medically attended gastroenteritis in U.S. children Broadly reactive and highly sensitive assay for Norwalk-like viruses based on real-time quantitative reverse transcription-PCR Human caliciviruses and pediatric gastroenteritis Human susceptibility and resistance to Norwalk virus infection Mechanisms of GII.4 norovirus persistence in human populations An outbreak of gastroenteritis associated with calicivirus in an infant home Caliciviruses in man Prevalence of human calicivirus infections in Kenya as determined by enzyme immunoassays for three genogroups of the virus Human calicivirus in symptomatic and asymptomatic infections in children in Vellore, South India Biological and genetic characterization of a hemagglutinating coronavirus isolated from a diarrhoeic child Human torovirus: a new nosocomial gastrointestinal pathogen Identification of viruses with bi-and tri-segmented double-stranded RNA genome in faeces of children with gastroenteritis Complete nucleotide sequences of two RNA segments of human picobirnavirus Infantile gastroenteritis associated with excretion of pestivirus antigens Complete nucleotide sequence and genetic organization of Aichi virus, a distinct member of the Picornaviridae associated with acute gastroenteritis in humans Human bocaviruses are highly diverse, dispersed, recombination prone, and prevalent in enteric infections