Prevalence of antibody to the Norwalk virus in various countries

Vaccines for viral and bacterial pathogens causing acute gastroenteritis: Part I: Overview, vaccines for enteric viruses and Vibrio cholerae

Efforts to develop vaccines for prevention of acute diarrhea have been going on for more than 40 y with partial success. The myriad of pathogens, more than 20, that have been identified as a cause of acute diarrhea throughout the years pose a significant challenge for selecting and further developing the most relevant vaccine candidates. Based on pathogen distribution as identified in epidemiological studies performed mostly in low-resource countries, rotavirus, Cryptosporidium, Shigella, diarrheogenic E. coli and V. cholerae are predominant, and thus the main targets for vaccine development and implementation. Vaccination against norovirus is most relevant in middle/high-income countries and possibly in resource-deprived countries, pending a more precise characterization of disease impact. Only a few licensed vaccines are currently available, of which rotavirus vaccines have been the most outstanding in demonstrating a significant impact in a short time period. This is a comprehensive review, divided into 2 articles, of nearly 50 vaccine candidates against the most relevant viral and bacterial pathogens that cause acute gastroenteritis. In order to facilitate reading, sections for each pathogen are organized as follows: i) a discussion of the main epidemiological and pathogenic features; and ii) a discussion of vaccines based on their stage of development, moving from current licensed vaccines to vaccines in advanced stage of development (in phase IIb or III trials) to vaccines in early stages of clinical development (in phase I/II) or preclinical development in animal models. In this first article we discuss rotavirus, norovirus and Vibrio cholerae. In the following article we will discuss Shigella, Salmonella (non-typhoidal), diarrheogenic E. coli (enterotoxigenic and enterohemorragic), and Campylobacter jejuni.

Noroviruses: epidemiology, immunity and prospects for prevention

In recent years, noroviruses have become recognized as an important cause of both sporadic and epidemic acute gastroenteritis (AGE), largely due to the improved availability of broadly reactive real-time RT-PCR (TaqMan-based RT-PCR) assays. While there is substantial diversity among noroviruses, one specific genotype, GII.4, is the most common etiology in sporadic and epidemic AGE. Outbreaks of norovirus AGE most commonly occur in healthcare facilities and restaurants and result in significant morbidity and mortality and substantial healthcare costs. Norovirus vaccine development is progressing, and Phase I and II human trials have shown proof-of-principle that norovirus vaccines can reduce illness and infection.

Exposure to human and bovine noroviruses in a birth cohort in southern India from 2002 to 2006

Human and bovine norovirus virus-like particles were used to evaluate antibodies in Indian children at ages 6 and 36 months and their mothers. Antibodies to genogroup II viruses were acquired early and were more prevalent than antibodies to genogroup I. Low levels of IgG antibodies against bovine noroviruses indicate possible zoonotic transmission.

High level of gastrointestinal nosocomial infections in the german surveillance system, 2002-2008

OBJECTIVE

Surveillance of nosocomial infections (NIs) is well established in many countries but often does not include gastrointestinal infections. We sought to determine the proportion of NIs among all hospitalized cases for the 4 most prevalent types of gastrointestinal infections in Germany.

METHODS

We analyzed all notifications of laboratory-confirmed or epidemiologically linked gastrointestinal infections due to norovirus, rotavirus, Salmonella species, and Campylobacter species reported to the Robert Koch Institute in Berlin, Germany, from 2002 through 2008. Infections were considered nosocomial if disease onset was more than 2 days after hospitalization for norovirus, rotavirus, and Salmonella infection and more than 5 days after hospitalization for Campylobacter infection.

RESULTS

  During the study period, 710,725 norovirus, 394,500 rotavirus, 395,736 Salmonella, and 405,234 Campylobacter gastrointestinal infections were reported. Excluding cases for which nosocomial status could not be determined, we identified 39,424 (49%) of 80,650 norovirus, 11,592 (14%) of 83,451 rotavirus, 3,432 (8%) of 43,348 Salmonella, and 645 (2%) of 33,503 Campylobacter gastrointestinal infections as definite nosocomial cases. Multivariate analysis confirmed higher risk of gastrointestinal NIs for patients aged more than 70 years (relative risk [RR], 7.0 [95% confidence interval {CI}, 6.7-7.2]; [Formula: see text]) and residents of western states (RR, 1.3 [95% CI, 1.2-1.3]; [Formula: see text]) and lower risk for female patients (RR, 0.9 [95% CI, 0.9-0.9; [Formula: see text]). Yearly NI proportions remained stable except for norovirus.

CONCLUSIONS

The investigated gastrointestinal NIs in Germany do not show a clear trend, but they are at high level, revealing potential for public health action and improvement of hospital infection control mainly among older patients. National prevalence studies on gastrointestinal NIs would be of additional value to give more insight on how and where to improve hospital infection control.

Norovirus highly prevalent cause of endemic acute diarrhea in children in the peruvian Amazon

To determine the burden of norovirus infections in children stools from a longitudinal community cohort were evaluated using reverse transcription polymerase chain reaction. Norovirus was detected in 21.3% of diarrheal and 8.0% of nondiarrheal stools (P < 0.01). Norovirus diarrhea was highly associated with age and the odds ratio for norovirus diarrhea fell by 2.8% per month (OR = 0.97, 95% CI: 0.95-0.99). Norovirus seems to be an important etiology of community acquired diarrhea in this study population.

Chapter 9 Infections caused by rubella, reoviridae, retro, Norwalk and ronaviruses

This chapter focuses on infections caused by rubella, reoviridae, retro, Norwalk and coronaviruses. High incidence of acute gastroenteritis caused by rotaviruses calls for prophylactic and therapeutic measures. Although no vaccine is presently available, it seems likely that vaccines will be developed in the next few years. There are also several rotavirus enzymes useful as targets for antiviral drugs. However, no antiviral drugs have shown therapeutic effects against rotavirus infections. The newly discovered human retrovirus (HTLV) has not yet been investigated in such detail as to predict the usefulness of vaccine or antiviral drugs. Several compounds are known to inhibit other retrovirus enzymes but the implication of this for chemotherapy of HTLV infection is unknown at present. The possibility and need for vaccination or chemotherapy against Norwalk virus and related agents is unclear. Very little work has been carried out to date with human coronaviruses, either from the point of view of vaccine development or specific antivirals. Both approaches may be usefully investigated in the future. Genetic cloning may be particularly useful for development of inactivated vaccines because the virus itself would be difficult to replicate and purify in large quantities for conventional vaccines.

Immunology of Norovirus Infection

Noroviruses are the leading cause of epidemic non-bacterial gastroenteritis worldwide. Despite their discovery over three decades ago, little is known about the host immune response to norovirus infection. The purpose of this chapter is to review the field of norovirus immunology and discuss the contributions of outbreak investigations, human and animal challenge studies and population-based studies. This chapter will survey both humoral and cellular immunity as well as recent advances in norovirus vaccine development.

The diagnostic gap in diarrhoeal aetiology

It is well established that rotaviruses of group A are the most important cause of severe diarrhoea in children. The causes of most cases of infectious diarrhoea still remain unidentified, however, and there must be other viruses to be found. 'Novel' rotaviruses have recently been discovered, mainly in animals (serogroups B and C in pigs and humans, D in birds, and one or more further groups in sheep and other mammals). Except for the group B virus which has caused widespread outbreaks of quite severe diarrhoea in adults in China (still not reported from outside China) these novel rotaviruses are rarities in the human and probably represent uncommon zoonotic infections. We speculate that the Chinese virus might have arisen by reassortment of genetic segments of animal group B viruses or perhaps by mutation, and so became infectious for man. The problem of identifying and determining the importance of small round viruses is reviewed. It seems likely that the group of small, round structured viruses, including Norwalk and the viruses of plainly calicivirus morphology, are all representatives of a whole group of enteric caliciviruses. Until they can be more easily cultivated it will be difficult to make diagnostic reagents available to all. Astroviruses and genuine parvoviruses have been found by many people in many countries. Astroviruses are probably more important as pathogens in lambs than in children or calves; parvoviruses can only be established as significant in epidemics. The coronavirus-like particles, first found in Vellore and Bristol, are still enigmatic and their role in diarrhoea is uncertain. Toroviridae, recently discovered as causes of diarrhoea in ungulates, do not seem to be at all important as causes of diarrhoea in humans. Possibly fruitful approaches to future searches are outlined: firstly to make more extensive use of immuno-electron microscopy; and secondly to try to improve existing tissue culture systems to make them more sensitive to enteric viruses.

Norovirus–host interaction: implications for disease control and prevention

Noroviruses (NVs) are a major cause of acute gastroenteritis epidemics in both developing and developed countries and affect people of all ages. Three main human histo-blood group antigens (HBGAs) – the ABO, Lewis and secretor families – are involved in NV recognition and eight strain-specific receptor-binding patterns in two major binding groups have been described. The receptor-binding interface is located at the outermost surface of the P domain of the viral capsid. Each interface contains two major binding sites and each site interacts with a carbohydrate side-chain of the HBGAs via multiple hydrogen bonds. Soluble HBGAs in human milk are able to block binding of NV to HBGA receptors, suggesting a potential decoy receptor for the protection of infants from NV infection. Phylogenetic analysis has revealed limited genetic relatedness among NVs with similar receptor-binding patterns. This review summarises and discusses recent advances and highlights implications for future studies in the control and prevention of NV gastroenteritis.

Defining susceptibility for microbial risk assessment: results of a workshop

An interdisciplinary workshop was convened by the George Washington University in June 2001 to discuss how to incorporate new knowledge about susceptibility to microbial pathogens into risk assessment and management strategies. Experts from government, academic, and private sector organizations discussed definitions, methods, data needs, and issues related to susceptibility in microbial risk assessment. The participants agreed that modeling approaches need to account for the highly specific nature of host-pathogen relationships, and the wide variability of infectivity, immunity, disease transmission, and outcome rates within microbial species and strains. Concerns were raised about distinguishing between exposure and dose more clearly, interpreting experimental and outbreak data correctly, and using thresholds and possibly linearity at low doses. Recommendations were made to advance microbial risk assessment by defining specific terms and concepts more precisely, designing explicit conceptual frameworks to guide development of more complex models and data collection, addressing susceptibility in all steps of the model, measuring components of immunity to characterize susceptibility, reexamining underlying assumptions, applying default methods appropriately, obtaining more mechanistic data to improve default methods, and developing more biologically relevant and continuous risk estimators. The interrelated impacts of selecting specific subpopulations and health outcomes, and of increasing model complexity and data demands, were considered in the contexts of public policy goals and resources required. The participants stated that zero risk is unattainable, so targeted and effective risk reduction and communication strategies are essential not only to raise pubic awareness about water quality but also to protect the most susceptible members of the population.

Human caliciviruses in Europe

Caliciviruses are single-stranded RNA viruses, which are divided into four genera based on their morphology and genomic structure. Viruses from two genera, the Norwalk like viruses and Sapporo like viruses, are a common cause of acute, nonbacterial gastroenteritis in humans. Although the first human calicivirus discovered nearly 30 years ago, much of the epidemiological and biological character of these viruses is only now beginning to unfold. Investigation has been difficult due to a number of factors, the viruses cannot be amplified by in vitro cell culture or animal models and electron microscopy (EM) is often not sensitive enough to detect the viruses in stool samples. Recent advances in molecular diagnostic techniques and the advent of a baculovirus expression system have highlighted the clinical and public health importance of calicivirus in all age groups, their ability to cause infection via a number of transmission routes as well as their considerable genetic diversity. These characteristics, in conjunction with the inability of humans to develop long-term immunity make HuCV an important public health issue in Europe and worldwide.

Interaction of cellular proteins with the 5' end of Norwalk virus genomic RNA

The lack of a susceptible cell line and an animal model for Norwalk virus (NV) infection has prompted the development of alternative strategies to generate in vitro RNAs that approximate the authentic viral genome. This approach has allowed the study of viral RNA replication and gene expression. In this study, using mobility shift and cross-linking assays, we detected several cellular proteins from HeLa and CaCo-2 cell extracts that bind to, and form stable complexes with, the first 110 nucleotides of the 5' end of NV genomic RNA, a region previously predicted to form a double stem-loop structure. These proteins had molecular weights similar to those of the HeLa cellular proteins that bind to the internal ribosomal entry site of poliovirus RNA. HeLa proteins La, PCBP-2, and PTB, which are important for poliovirus translation, and hnRNP L, which is possibly implicated in hepatitis C virus translation, interact with NV RNA. These protein-RNA interactions are likely to play a role in NV translation and/or replication.

Seroprevalence and seroincidence of Norwalk-like virus infection among Brazilian infants and children

To determine the importance of Norwalk-like viruses (NLVs) as pediatric pathogens in a developing country, the seroprevalence and seroincidence of this group of viruses in a cohort of children less than 4 years of age in an urban shantytown in northeastern Brazil was examined. Serum samples were collected approximately every 6 months from 135 children who were surveyed three times each week for diarrhea and vomiting. NLV IgG was measured by an enzyme immunosorbent assay (EIA) with recombinant Norwalk virus capsid protein. Overall NLV seroprevalence was 71%, and the overall NLV seroconversion rate was 0.7 seroconversions per child-year. The highest age-specific NLV seroconversion rate (0.8 seroconversions per child-year) was observed in the 13-24-month age group. For all study children, the incidence of diarrhea and vomiting was significantly greater (P < 0.01) during time periods spanned by serum pairs that indicated NLV seroconversion compared with time periods without NLV seroconversion. However, NLV seroconversion was not associated with gastrointestinal symptoms during the first year of life.

Immunity to calicivirus infection

The evolution of our understanding of immunity to calicivirus infection, using Norwalk virus as the prototype, is discussed in three stages: (1) "ancient times (1972-1978), when human volunteer studies prevailed, (2) the "middle ages (1978-1990), which were characterized by the development and implementation of solid-phase immunoassays based on native viral antigens, and (3) "modern times (1990 to present), which began with the cloning of the genome of the noncultivatable 8FIIa strain of Norwalk virus and resulted in a readily available source of recombinant virus-like particles that have revolutionized the study of caliciviruses. Throughout these stages, it has been shown repeatedly that short-term immunity develops to homologous virus. However, the search for determinants of long-term immunity continues. These studies will likely be facilitated by the newest reagents-the noninfectious recombinant virus-like particles-used in the setting of human volunteer studies and large epidemiologic studies.

Norwalk-like virus infection in military forces: epidemic potential, sporadic disease, and the future direction of prevention and control efforts

The impact of Norwalk-like virus (NLV) infection on military forces is evaluated in this report. NLVs were a major cause of both outbreaks and sporadic disease among crowded US ground troops in the 1991 war with Iraq. NLVs also have been found to be a cause of acute gastroenteritis in other ground and shipboard deployments. Four large outbreaks of acute gastroenteritis were investigated aboard US Navy aircraft carriers between 1992 and 1997. In these outbreaks, NLVs were identified as the probable cause, and crowding was a major risk factor for transmission. An evaluation of a routine shipboard deployment also suggests that NLVs cause sporadic gastroenteritis. These data indicate that NLV infection is a major cause of acute morbidity in military forces. Because of the limitations of available prevention and control methods, development of a vaccine against these viruses may be the best solution in the military environment.

Study of Norwalk virus and Mexico virus infections at Ga-Rankuwa Hospital, Ga-Rankuwa, South Africa

Small round-structured viruses (SRSVs) or Norwalk-like viruses have been implicated as an important causative agent of gastroenteritis outbreaks. We used the relatively newly developed recombinant enzyme immunoassays (EIAs) to determine the seroprevalence of Norwalk virus (NV) and Mexico virus (MxV) in a family-based cohort and an antenatal clinic cohort at Ga-Rankuwa Hospital, Ga-Rankuwa, South Africa. High prevalences (96 to 99%) of anti-NV and anti-MxV antibodies were detected in both cohorts. We also investigated the pattern of antibody acquisition in a cohort of infants and young children without gastroenteritis and found that by 48 months of age all children had acquired adult antibody levels to both these viruses. Lastly, we tested 276 stool specimens collected from infants and young children with gastroenteritis for the presence of NV or MxV antigen by recombinant EIAs to each virus, by electron microscopy (EM), and by reverse transcription (RT)-PCR. NV and MxV antigens were present in 1.8 and 4.3% of the stool specimens, respectively, by the recombinant EIAs; 9.2% were positive for SRSVs by EM, and 25% of these SRSVs gave a positive result by RT-PCR for primer pair 35-36 directed to a region of the RNA-dependent RNA polymerase gene. The seroprevalence studies indicate a high level of exposure to these viruses in both children and adults. Although the viral antigens are not highly prevalent in diarrheal stools, it was determined by the two assays for NV and MxV that children are, nevertheless, infected early in life.

Characterization of Toronto virus capsid protein expressed in baculovirus

Toronto virus (TV), previously called "minireovirus", a human calicivirus classified as genogroup 2 and phylogenetic type P2-A, was originally described in association with diarrhea in children. The second open reading frame, encoding the capsid protein of TV24, was expressed in a baculovirus recombinant. The recombinant baculovirus produced a protein (rTV) with an apparent molecular mass of 58 kDa that self-assembled into virus-like particles approximately 30 nm in diameter with a density of 1.29 g/ml. Antigenic and immunogenic characteristics of these particles were determined by protein immunoblot, immunoprecipitation, and enzyme immunoassay. Seroconversion to the rTV protein was detected in 6 of 8 (75%) patients from a recent outbreak of gastroenteritis associated with a virus of similar phylogenetic type. These results confirm and extend the previous reports of the expression of the Norwalk and Mexico virus capsid proteins.

An epidemiological investigation of Norwalk virus infection in South Africa

A study was carried out to determine the incidence and seroprevalence of Norwalk virus (NV) in the Pretoria area, South Africa, using a recombinant NV (rNV) immunoassay for the detection of serum IgG antibodies. Maternal antibody was detectable in infants' sera up to approximately 6 months of age. Infection with NV was detected serologically in the second year of life and the seroprevalence of NV IgG rose from 37.1% at 7-11 months of age to 62.1% by the age of 40 years. No significant differences in seroprevalence of NV IgG antibody was evident between subjects of European or African ethnic origin, where overall seroprevalence rates were 56.4% and 53.9% respectively.

Antibody prevalence and immunoglobulin IgG subclass pattern to Norwalk virus in Sweden

The antibody prevalence in Sweden to Norwalk virus (NV) was investigated using a baculovirus expressed capsid antigen. One hundred thirty-two serum samples were examined for IgA, total IgG and IgG subclass antibodies to Norwalk virus. In young children, NV IgG antibody prevalence was higher than the IgA prevalence, whereas no difference was found in individuals older than 21 years. The IgG antibody prevalence was 50% in children below 5 years of age and increased to > 80% in individuals older than 10 years of age. To examine the IgG antibody response in more detail, IgG subclass patterns were characterized. IgG 1 predominated in all age groups. IgG 4, usually detected after repeated exposure to antigen, was the second most prevalent subclass, but was only found in individuals older than 21 years of age. IgG 3 subclass antibodies were found in 13% and IgG 2 in 3% of the sera examined. IgG 3 subclass antibodies have been recognized as a marker for recent or ongoing viral infections.

Seroprevalence studies using a recombinant Norwalk virus protein enzyme immunoassay

A recombinant Norwalk virus (NV) protein enzyme immunoassay was used to study the age of acquisition of NV IgG in various populations. In London, England, there was little evidence of infection during the first 2 years of life. However, the prevalence of NV IgG rose steadily throughout the period that children attend school, reaching a peak of 70% in the group aged 11-16 years. High levels of maternal antibody were detected in infants aged < 3 months. Comparison of the acquisition of antibodies to three strains of human calicivirus in Japanese children in northern Japan indicated that although the majority had experienced infection with strains Japan and UK1 by the age of 12 years, only 22% possessed antibodies to NV. In Australian aborigines NV infection occurs early in life; by the age of 6 years over 90% of children were seropositive.

Epidemiological study of Norwalk virus infections in Japan and Southeast Asia by enzyme-linked immunosorbent assays with Norwalk virus capsid protein produced by the baculovirus expression system

In this study, we investigated Norwalk virus (NV) antigen and antibody to recombinant NV (rNV) in human populations in Japan and Southeast Asia by enzyme-linked immunosorbent assays (ELISAs). Baculovirus-expressed recombinant NV (rNV) capsid protein was used for preparing antisera to rNV or used as an antigen for detecting antibody to rNV. The ELISAs were specific for NV and had sensitivities equivalent to or higher than those of the previously developed radioimmunoassays. In 159 stool samples obtained from children, mainly younger than 10 years old, with acute gastroenteritis due to small round structured viruses in Japan, only 1 was positive for NV antigen. The pattern of acquisition of antibody to rNV was quite different from those of antibodies to group A rotavirus and human calicivirus Sapporo (HuCV-Sa) strain. The prevalence of antibody to rNV remained at a low level throughout childhood and then showed a steep rise during school age and early adulthood in Japan. A high prevalence of antibody was observed in samples collected from healthy adults in Japan and Southeast Asia. These results suggested that NV infection is common in adults in Japan and Southeast Asia but may be rare in infants in Japan. The HuCV-Sa strain was negative by the ELISA, and no serological relationship between NV and the HuCV-Sa strain was found. NV may be quite different from the HuCV-Sa strain, although both viruses are classified in the family Caliciviridae.

Outbreaks of food-borne and waterborne viral gastroenteritis

Norwalk virus infection is the epidemiologic prototype for outbreaks of food-borne and waterborne gastroenteritis. Around the world, Norwalk virus and Norwalk-like viruses appear to be major causes of food-borne and waterborne illness. Assessment of the overall significance of viral agents to the epidemiology of food-borne and waterborne illness is hampered by the lack of surveillance throughout much of the world. In areas where food-borne and waterborne illness surveillance is conducted, outbreaks of viral gastroenteritis are underreported because of the lack of availability of routine laboratory services to confirm the viral etiology. Routine use of epidemiologic criteria as an alternative to laboratory confirmation will allow better assessments of the importance of viral gastroenteritis until effective laboratory methods can be widely implemented. Outbreaks of viral gastroenteritis have been propagated by contamination of water supplies, raw foods, and ill food handlers. Controlling an outbreak depends on identifying and removing the source of contamination. The demonstrated occurrence of person-to-person transmission and the likely occurrence of transmission of Norwalk-like viruses by aerosol make it necessary to evaluate the potential for transmission by food handlers and servers in every outbreak, regardless of primary source.

Infectious diarrhoea. Viruses

Increased knowledge has been gained into the aetiology and pathogenesis of viral gastroenteritis during the past two decades. There are now thought to be four major subclassifications of gastroenteritis-causing viruses; these include rotavirus, enteric adenovirus, calicivirus, including Norwalk and Norwalk-like viruses, and astrovirus. The association of these agents with gastroenteritis has been made by their electron microscopic detection in stool and intestinal biopsy specimens from affected patients, the inability to detect the viruses after recovery from disease, and the subsequent development of immunoglobulin responses after infection; in some instances disease transmission was achieved in human volunteers. The association of these viral agents with gastroenteritis has facilitated the study of classification, epidemiology, immunity, diagnostic tests, methods of treatment and, most importantly, disease prevention strategies such as vaccine development for rotavirus. This chapter highlights the major features of these agents, with special attention being given to the pertinent molecular biology as well as current and future prospects for vaccination. Enteric viral infections of the gastrointestinal tract in patients with AIDS are also discussed.

Prevalence of antibodies to Norwalk virus in England: detection by enzyme-linked immunosorbent assay using baculovirus-expressed Norwalk virus capsid antigen

A total of 3,250 serum specimens collected in England in 1991 and 1992 were tested by an indirect enzyme-linked immunosorbent assay for antibody to Norwalk virus using baculovirus-expressed capsid antigen, and 2,382 (73.3%) were positive. The prevalence of Norwalk virus antibody differed regionally. It was lowest (24.6%) in 6- to 11-month-old infants and increased to 89.7% in persons over 60 years old.

Prevalence of enteric viruses among hospital patients with AIDS in Kinshasa, Zaire

Diarrhoea is the most common manifestation of acquired immunodeficiency syndrome (AIDS) in Africa. Numerous parasitic or bacterial agents have been implicated, but a pathogen-specific aetiology has not been found. Enteric viruses (i.e., rotavirus, small round structured viruses, coronavirus, and adenovirus) were detected by enzyme-linked immunosorbent assay or electron microscopy in faecal specimens of 17% of 198 consecutive adult admissions to a general medical ward of an urban hospital in Kinshasa, Zaire. Overall, 57% of patients were seropositive for infection with human immunodeficiency virus (HIV) 1; of these, 50% were classified as World Health Organization AIDS stage IV. The prevalence of enteric viruses in stool specimens did not differ significantly between patients with and without HIV infection, and was not associated with acute or chronic diarrhoea, or constitutional symptoms. However, a trend (P = 0.14) towards greater frequency of virus in stools from patients in the lower 3 quintiles of the CD4/CD8 T cell ratio was seen. This trend approached statistical significance (P = 0.07) with stratification by HIV infection. Although we found no evidence in this population to support a major pathogenic role for these viruses alone in the enteropathy of AIDS, increased viral shedding was weakly associated with immunodeficiency.

Human, small round structured viruses, caliciviruses and astroviruses

Epidemiological studies on SRSVs, human calicivirus and astroviruses have been limited by the problems of establishing them in cell culture and the inability to transmit them to animals or to use strains from animals as a source of antigen for diagnostic tests. The use of EM and the subsequent development of RIAs and EIAs in a few research centres has shown that they are a cause of outbreaks and sporadic cases of diarrhoea and vomiting. SRSVs have increasingly been recognized as a major cause of outbreaks of gastroenteritis in the community and in hospital wards. The symptoms of illness are generally mild and of short duration and patients seldom require medical attention. However, because of the high attack rates and large numbers of persons of all age groups involved, there is often considerable economic loss and disruption of services. Evidence is accumulating that polluted water, molluscan shellfish, and contaminated cold foods are major sources of infection. Recently a SRSV has been shown to be the cause of epidemics and sporadic cases of waterborne enterically transmitted non-A, non-B hepatitis (hepatitis E virus) which have occurred in the USSR, India, Mexico and Africa. Astroviruses and human caliciviruses are occasional causes of outbreaks of vomiting and diarrhoea in infants and the elderly which can necessitate the closure of hospital wards and cause considerable disruption. Symptoms are generally mild and of short duration and therefore the majority of cases are unlikely to be investigated by laboratories. Diagnosis of infections is at present limited to the few laboratories that have developed their own assays or have access to electronmicroscopy facilities.

Human viral gastroenteritis

During the last 15 years, several different groups of fastidious viruses that are responsible for a large proportion of acute viral gastroenteritis cases have been discovered by the electron microscopic examination of stool specimens. This disease is one of the most prevalent and serious clinical syndromes seen around the world, especially in children. Rotaviruses, in the family Reoviridae, and fastidious fecal adenoviruses account for much of the viral gastroenteritis in infants and young children, whereas the small caliciviruses and unclassified astroviruses, and possibly enteric coronaviruses, are responsible for significantly fewer cases overall. In addition to electron microscopy, enzyme immunoassays and other rapid antigen detection systems have been developed to detect rotaviruses and fastidious fecal adenoviruses in the stool specimens of both nonhospitalized patients and those hospitalized for dehydration and electrolyte imbalance. Experimental rotavirus vaccines have also been developed, due to the prevalence and seriousness of rotavirus infection. The small, unclassified Norwalk virus and morphologically similar viruses are responsible for large and small outbreaks of acute gastroenteritis in older children, adolescents, and adults. Hospitalization of older patients infected with these viruses is usually not required, and their laboratory diagnoses have been limited primarily to research laboratories.

Production of a monoclonal antibody against the Snow Mountain agent of gastroenteritis by in vitro immunization of murine spleen cells

The Snow Mountain agent (SMA) is a 27- to 32-nm noncultivatable virus that causes acute gastroenteritis in humans. SMA is morphologically similar to but immunologically distinct from the Norwalk agent. SMA has been partially purified from the stool of experimentally infected volunteers and contains a single structural protein of Mr 62,000 as well as one or more non-virion-associated soluble proteins. Further characterization of this important human pathogen and other Norwalk-like viruses has been hindered by the lack of reagents with which to study them. To further characterize SMA, we developed a monoclonal antibody to SMA using in vitro immunization--a technique that permitted use of small quantities of antigen for immunization. The monoclonal antibody, SM-4, was specific for SMA and did not react with the Norwalk or Hawaii agents. In addition, SM-4 reacted with purified virion but not with the soluble protein. SM-4 also blocked the ability of labeled postinfection human IgG to bind to purified virion. Finally, both SM-4 and human postinfection sera specifically recognized the Mr 62,000 virion-associated protein. Thus, SM-4 is directed against an epitope present on the SMA structural protein that is not shared by the Norwalk or Hawaii agents and that is not present on the soluble protein. The availability of a monoclonal antibody against SMA should facilitate further purification and characterization of this agent. The techniques utilized in these studies provide a method for the production of additional monoclonal antibodies to this group of viruses and also should be useful for the study of other occult viral agents.

Norwalk-like gastroenteritis epidemic in a Toronto hospital

An epidemic of gastroenteritis in a teaching hospital affected 57 patients and 69 staff over a 26-day period. The index case was a patient admitted with acute abdominal pain and diarrhea two days prior to the outbreak. The epidemic curve indicated person-to-person transmission. The incubation period, duration and types of symptoms were typical of Norwalk gastroenteritis, and Norwalk-like virus particles, serologically different from the prototype Norwalk virus strain, were observed in 17 of 20 fecal specimens examined by immune-electron microscopy.

Enzyme-linked immunosorbent assays for Snow Mountain and Norwalk agents of viral gastroenteritis

Enzyme-linked immunosorbent assays (ELISAs) for antigen detection and blocking ELISAs for serum antibody rises were developed for the Snow Mountain and Norwalk agents of viral gastroenteritis. The ELISAs were as sensitive as the existing radioimmunoassays and were specific for the Snow Mountain or Norwalk agent. The blocking ELISAs detected the same number of significant rises in antibodies to these agents as did the existing blocking radioimmunoassays.

Radioimmunoassay for detection of the Snow Mountain Agent of viral gastroenteritis

The Snow Mountain Agent (SMA) is a Norwalk-like viral agent of acute gastroenteritis that has been detected only by immune electron microscopy (IEM). We established a solid phase microtiter radioimmunoassay (RIA) for SMA antigen employing pre-and post-challenge sera from volunteer studies as capture antibodies. SMA was detected in 12 of 67 stool samples from volunteers who were ill after oral challenge with SMA. All samples in which virus particles were detected by IEM were positive by RIA, but the RIA was 10-80 times more sensitive than IEM. To detect serum antibody to SMA, a blocking test was developed, employing diarrheal stool containing SMA as a standard source of antigen. Serum antibody rises were detected in eight out of nine volunteers with experimentally induced illness following challenge with SMA, as well as in three out of three naturally occurring cases. A preliminary sero-epidemiologic survey suggested that infection with SMA was common in the population surveyed. This RIA should permit large scale seroepidemiologic studies of SMA to be carried out, and should also facilitate characterization of this agent.

Detection of Norwalk virus antibodies and antigen with a biotin-avidin immunoassay

Biotin-avidin immunoassays (BAIs) were developed to detect Norwalk virus antigen and to measure Norwalk virus antibody. The BAI detected Norwalk virus infections by a fourfold titer rise in antibody in sera or by antigen in stool, with a sensitivity similar to or greater than that of the radioimmunoassay (RIA), and the BAI appeared to be more sensitive than the RIA for detecting antibody in single serum specimens. The BAI antigen test detected Norwalk antigen in all stools that were positive by the RIA, and in two stools negative by the RIA. Of 106 serum pairs tested by both the RIA and BAI, 94 demonstrated seroconversion, or lack of seroconversion, in both assays; 12 gave discordant results. Titers by the BAI generally exceeded those by the RIA by two- or fourfold. The BAI had advantages over the RIA in that it had added sensitivity in the detection of Norwalk antibody, was less time consuming, did not require frequent labeling of antibody, and did not have the problems associated with the use of isotopes.

Protective effect of anticholinergic drugs and psyllium in a nosocomial outbreak of Norwalk gastroenteritis

An outbreak of Norwalk agent gastroenteritis occurred in a chronic-care hospital in Tennessee in April 1981. Fifty-five per cent of the elderly psychiatric patients and 61 per cent of the nursing employees on one floor became ill. Infection was most likely to have spread from patient-to-patient by nursing employees. Certain chronic medications seemed to protect patients from symptomatic infection. Anticholinergic drugs appeared to mask the symptoms of this disease; psyllium ('Metamucil') may have prevented infection in some patients. We suggest that prospective studies be undertaken to confirm the possible value of psyllium in averting infection with Norwalk agent.

Age-specific prevalence of antibody to rotavirus, Escherichia coli heat-labile enterotoxin, Norwalk virus, and hepatitis A virus in a rural community in Thailand

A serological survey in rural Thailand demonstrated that inhabitants acquired antibody to rotavirus between the ages of 6 months and 6 years, to Norwalk virus between the ages of 4 and 5 years, and to hepatitis A between the ages of 6 and 35 years. Antibody of Escherichia coli heat-labile toxin was most prevalent between 1 and 4 years and 18 and 25 years of age.