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

Profiling of humoral immune responses to norovirus in children across Europe

Norovirus is a leading cause of epidemic acute gastroenteritis. More than 30 genotypes circulate in humans, some are common, and others are only sporadically detected. Here, we investigated whether serology can be used to determine which genotypes infect children. We established a multiplex protein microarray with structural and non-structural norovirus antigens that allowed simultaneous antibody testing against 30 human GI and GII genotypes. Antibody responses of sera obtained from 287 children aged < 1 month to 5.5 years were profiled. Most specific IgG and IgA responses were directed against the GII.2, GII.3, GII.4, and GII.6 capsid genotypes. While we detected antibody responses against rare genotypes, we found no evidence for wide circulation. We also detected genotype-specific antibodies against the non-structural proteins p48 and p22 in sera of older children. In this study, we show the age-dependent antibody responses to a broad range of norovirus capsid and polymerase genotypes, which will aid in the development of vaccines.

Potential zoonotic swine enteric viruses: The risk ignored for public health

Swine could serve as a natural reservoir for a large variety of viruses, including potential zoonotic enteric viruses. The presence of viruses with high genetic similarity between porcine and human strains may result in the emergence of zoonotic or xenozoonotic infections. Furthermore, the globalization and intensification of swine industries exacerbate the transmission and evolution of zoonotic viruses among swine herds and individuals working in swine-related occupations. To effectively prevent the public health risks posed by zoonotic swine enteric viruses, designing, and implementing a comprehensive measure for early diagnosis, prevention, and mitigation, requires interdisciplinary a collaborative ''One Health" approach from veterinarians, environmental and public health professionals, and the swine industry. In this paper, we reviewed the current knowledge of selected potential zoonotic swine enteric viruses and explored swine intensive production and its associated public health risks.

Age-seroprevalence curves for the multi-strain structure of influenza A virus

The relationship between age and seroprevalence can be used to estimate the annual attack rate of an infectious disease. For pathogens with multiple serologically distinct strains, there is a need to describe composite exposure to an antigenically variable group of pathogens. In this study, we assay 24,402 general-population serum samples, collected in Vietnam between 2009 to 2015, for antibodies to eleven human influenza A strains. We report that a principal components decomposition of antibody titer data gives the first principal component as an appropriate surrogate for seroprevalence; this results in annual attack rate estimates of 25.6% (95% CI: 24.1% - 27.1%) for subtype H3 and 16.0% (95% CI: 14.7% - 17.3%) for subtype H1. The remaining principal components separate the strains by serological similarity and associate birth cohorts with their particular influenza histories. Our work shows that dimensionality reduction can be used on human antibody profiles to construct an age-seroprevalence relationship for antigenically variable pathogens.

Persistence of Antibodies to 2 Virus-Like Particle Norovirus Vaccine Candidate Formulations in Healthy Adults: 1-Year Follow-up With Memory Probe Vaccination

BACKGROUND

We previously reported the tolerability and immunogenicity 1 month after intramuscular administration of 2 bivalent virus-like particle (VLP)-based candidate norovirus vaccine formulations in adults. We now describe the persistence of immunity and responses to a memory probe vaccination 1 year later.

METHODS

A total of 454 healthy men and women aged 18-49 years in 3 equal groups received placebo (saline) or 15/50 or 50/50 vaccine formulations (ie, 15 or 50 µg of GI.1 genotype VLPs, respectively, and 50 µg of GII.4c VLPs) with MPL and Al(OH)3. Immunogenicity and safety were assessed up to day 365, when 351 participants received a memory probe vaccination of 15 µg each of GI.1 and GII.4c VLPs with Al(OH)3.

RESULTS

No safety signals were detected up to 1 year after the first vaccination. Pan-immunoglobulin, immunoglobulin A, and histo-blood group antigen-blocking (HBGA) antibody levels among vaccinees waned but remained higher than levels before vaccination and levels in placebo recipients on days 180 and 365. Memory probe vaccination increased all antibody titers. Levels of HBGA antibodies to GI.1 but not GII.4c were higher after the first vaccination in candidate vaccine groups, compared with those in the placebo group.

CONCLUSION

Levels of antibodies to both candidate norovirus VLP formulations persisted above baseline levels for at least 1 year after primary vaccination. HBGA-blocking responses to the memory probe for GI.1 but not GII.4c displayed characteristics of immune memory.

CLINICAL TRIALS REGISTRATION

NCT02142504.

Norovirus Seroprevalence among Adults in the United States: Analysis of NHANES Serum Specimens from 1999-2000 and 2003-2004

Norovirus is the most common cause of epidemic and endemic acute gastroenteritis. However, national estimates of the infection burden are challenging. This study used a nationally representative serum bank to estimate the seroprevalence to five norovirus genotypes including three GII variants: GI.1 Norwalk, GI.4, GII.3, GII.4 US95/96, GII.4 Farmington Hills, GII.4 New Orleans, and GIV.1 in the USA population (aged 16 to 49 years). Changes in seroprevalence to the three norovirus GII.4 variants between 1999 and 2000, as well as 2003 and 2004, were measured to examine the role of population immunity in the emergence of pandemic GII.4 noroviruses. The overall population-adjusted seroprevalence to any norovirus was 90.0% (1999 to 2000) and 95.9% (2003 to 2004). Seroprevalence was highest to GI.1 Norwalk, GII.3, and the three GII.4 noroviruses. Seroprevalence to GII.4 Farmington Hills increased significantly between the 1999 and 2000, as well as the 2003 and 2004, study cycles, consistent with the emergence of this pandemic strain. Seroprevalence to GII.4 New Orleans also increased over time, but to a lesser degree. Antibodies against the GIV.1 norovirus were consistently detected (population-adjusted seroprevalence 19.1% to 25.9%), with rates increasing with age. This study confirms the high burden of norovirus infection in US adults, with most adults having multiple norovirus infections over their lifetime.

Family income and exposure to norovirus in childhood: Findings from the UK Millennium Cohort Study

Children from low income families are at greater risk of poorer health outcomes than their wealthier peers. Hospital admissions for children with gastroenteritis increase as deprivation increases. Noroviruses are responsible for 47-96% of outbreaks of acute paediatric gastroenteritis, and 5-36% of sporadic cases worldwide. However, evidence on the relationship between family income and childhood exposure to norovirus is still limited, with published studies pointing to conflicting results. This study explored the relationship between family income and early childhood exposure to norovirus in the United Kingdom using data from the Millennium Cohort Study linked to serological data. Exposure to norovirus was measured by the level of human norovirus-specific antibodies (titres) obtained from oral fluid samples collected from 5962 pre-school age UK children and tested for Norovirus-specific Immunoglobulin G (IgG). Multivariable linear and quantile regression analyses were conducted to investigate the extent to which family income was associated with child norovirus exposure, and to explore the potential mechanisms through which income might translate into norovirus exposure. Higher norovirus-specific IgG titres were associated with higher family income, but the relationship weakened after controlling for potential mediating factors, mainly increased opportunities for person-to-person contacts, such as formal childcare arrangements. This study provides novel evidence that can help inform and prioritise policy interventions (e.g. vaccination) and health promotion programmes to reduce child health inequalities in the area of gastrointestinal infections.

A Bacterial Surface Display System Expressing Cleavable Capsid Proteins of Human Norovirus: A Novel System to Discover Candidate Receptors

Human noroviruses (HuNoVs) are the dominant cause of food-borne outbreaks of acute gastroenteritis. However, fundamental researches on HuNoVs, such as identification of viral receptors have been limited by the currently immature system to culture HuNoVs and the lack of efficient small animal models. Previously, we demonstrated that the recombinant protruding domain (P domain) of HuNoVs capsid proteins were successfully anchored on the surface of Escherichia coli BL21 cells after the bacteria were transformed with a plasmid expressing HuNoVs P protein fused with bacterial transmembrane anchor protein. The cell-surface-displayed P proteins could specifically recognize and bind to histo-blood group antigens (HBGAs, receptors of HuNoVs). In this study, an upgraded bacterial surface displayed system was developed as a new platform to discover candidate receptors of HuNoVs. A thrombin-susceptible “linker” sequence was added between the sequences of bacterial transmembrane anchor protein and P domain of HuNoV (GII.4) capsid protein in a plasmid that displays the functional P proteins on the surface of bacteria. In this new system, the surface-displayed HuNoV P proteins could be released by thrombin treatment. The released P proteins self-assembled into small particles, which were visualized by electron microscopy. The bacteria with the surface-displayed P proteins were incubated with pig stomach mucin which contained HBGAs. The bacteria-HuNoV P proteins-HBGAs complex could be collected by low speed centrifugation. The HuNoV P proteins-HBGAs complex was then separated from the recombinant bacterial surface by thrombin treatment. The released viral receptor was confirmed by using the monoclonal antibody against type A HBGA. It demonstrated that the new system was able to capture and easily isolate receptors of HuNoVs. This new strategy provides an alternative, easier approach for isolating unknown receptors/ligands of HuNoVs from different samples including mammalian cell lines, oysters, and fresh produce.

Targeting pediatric versus elderly populations for norovirus vaccines: a model-based analysis of mass vaccination options

BACKGROUND

Noroviruses are the leading cause of acute gastroenteritis and foodborne diarrheal disease in the United States. Norovirus vaccine development has progressed in recent years, but critical questions remain regarding which age groups should be vaccinated to maximize population impact.

METHODS

We developed a deterministic, age-structured compartmental model of norovirus transmission and immunity in the U.S.

POPULATION

The model was fit to age-specific monthly U.S. hospitalizations between 1996 and 2007. We simulated mass immunization of both pediatric and elderly populations assuming realistic coverages of 90% and 65%, respectively. We considered two mechanism of vaccine action, resulting in lower vaccine efficacy (lVE) between 22% and 43% and higher VE (hVE) of 50%.

RESULTS

Pediatric vaccination was predicted to avert 33% (95% CI: 27%, 40%) and 60% (95% CI: 49%, 71%) of norovirus episodes among children under five years for lVE and hVE, respectively. Vaccinating the elderly averted 17% (95% CI: 12%, 20%) and 38% (95% CI: 34%, 42%) of cases in 65+ year olds for lVE and hVE, respectively. At a population level, pediatric vaccination was predicted to avert 18-21 times more cases and twice as many deaths per vaccinee compared to elderly vaccination.

CONCLUSIONS

The potential benefits are likely greater for a pediatric program, both via direct protection of vaccinated children and indirect protection of unvaccinated individuals, including adults and the elderly. These findings argue for a clinical development plan that will deliver a vaccine with a safety and efficacy profile suitable for use in children.

Prevalence and molecular characterization of human noroviruses and sapoviruses in Ethiopia

Viral gastroenteritis is a major public health problem worldwide. In Ethiopia, very limited studies have been done on the epidemiology of enteropathogenic viruses. The aim of this study was to detect and characterize noroviruses (NoVs) and sapoviruses (SaVs) from acute gastroenteritis patients of all ages. Fecal samples were collected from diarrheic patients (n = 213) in five different health centers in Addis Ababa during June-September 2013. The samples were screened for caliciviruses by reverse transcription polymerase chain reaction (RT-PCR) using universal and genogroup-specific primer pairs. Phylogenetic analyses were conducted using the sequences of the PCR products. Of the clinical samples, 25.3 % and 4.2 % were positive for NoV and SaV RNA, respectively. Among the norovirus positives, 22 were sequenced further, and diverse norovirus strains were identified: GI (n = 4), GII (n = 17) and GIV (n = 1). Most strains were GII (n = 17/22: 77.2 %), which were further divided into three different genotypes (GII.4, GII.12/GII.g recombinant-like and GII.17), with GII.17 being the dominant (7/17) strain detected. GI noroviruses, in particular GI.4 (n = 1), GI.5 (n = 2) and GI.8 (n = 1), were also detected and characterized. The GIV strain detected is the first from East Africa. The sapoviruses sequenced were also the first reported from Ethiopia. Collectively, this study showed the high burden and diversity of noroviruses and circulation of sapoviruses in diarrheic patients in Ethiopia. Continued surveillance to assess their association with diarrhea is needed to define their epidemiology, disease burden, and impact on public health.

Engineering Bacterial Surface Displayed Human Norovirus Capsid Proteins: A Novel System to Explore Interaction Between Norovirus and Ligands

Human noroviruses (HuNoVs) are major contributors to acute nonbacterial gastroenteritis outbreaks. Many aspects of HuNoVs are poorly understood due to both the current inability to culture HuNoVs, and the lack of efficient small animal models. Surrogates for HuNoVs, such as recombinant viral like particles (VLPs) expressed in eukaryotic system or P particles expressed in prokaryotic system, have been used for studies in immunology and interaction between the virus and its receptors. However, it is difficult to use VLPs or P particles to collect or isolate potential ligands binding to these recombinant capsid proteins. In this study, a new strategy was used to collect HuNoVs binding ligands through the use of ice nucleation protein (INP) to display recombinant capsid proteins of HuNoVs on bacterial surfaces. The viral protein-ligand complex could be easily separated by a low speed centrifugation step. This system was also used to explore interaction between recombinant capsid proteins of HuNoVs and their receptors. In this system, the VP1 capsid encoding gene (ORF2) and the protruding domain (P domain) encoding gene (3′ terminal fragment of ORF2) of HuNoVs GI.1 and GII.4 were fused with 5′ terminal fragment of INP encoding gene (inaQn). The results demonstrated that the recombinant VP1 and P domains of HuNoVs were expressed and anchored on the surface of Escherichia coli BL21 cells after the bacteria were transformed with the corresponding plasmids. Both cell surface displayed VP1 and P domains could be recognized by HuNoVs specific antibodies and interact with the viral histo-blood group antigens receptors. In both cases, displayed P domains had better binding abilities than VP1. This new strategy of using displayed HuNoVs capsid proteins on the bacterial surface could be utilized to separate HuNoVs binding components from complex samples, to investigate interaction between the virus and its receptors, as well as to develop an oral vaccine for HuNoVs.

Norovirus infections and seroprevalence of genotype GII.4-specific antibodies in a Spanish population

Genotype II.4 noroviruses (NoVs) are a leading cause of epidemic acute gastroenteritis in children and adults worldwide. The prevalence of different NoV genotypes causing outbreaks and sporadic cases of acute gastroenteritis in the region of Valencia, Spain, during a 4-year period (2008-11) was investigated. NoVs were detected in 42 out of 55 (76.3%) outbreaks and in 26 out of 332 (7.8%) sporadic cases of acute gastroenteritis. Genogroup GII strains were predominant in outbreaks and sporadic cases. Different genotype GII.4 variants were found (Yerseke_2006a, Den Haag_2006b, Apeldoorn_2007, and New Orleans_2009), with the latter variant detected most frequently (35.3%). A recombinant P domain of the NoV GII.4 Apeldoorn_2007 variant was produced in Escherichia coli and used as the coating antigen in an enzyme immunoassay to survey the IgG antibody seroprevalence against NoV GII.4 in a Spanish population. Baculovirus-expressed virus-like particles (VLPs) of NoV GII.4 Den Haag_2006b variant were also produced and used as antigen to compare seroreactivity. Of the 434 serum specimens analyzed, 429 (98.6%) had antibodies against the P domain. The comparison of reactivities of 30 serum samples to the NoV GII.4 P polypeptide and VLP showed reproducible results with a correlation coefficient of r = 0.794. Titers of antibodies to the P domain increased gradually and significantly with age, reaching the highest levels at the age group of 41-50 years. These results confirm the high prevalence of NoV GII.4 infections in Valencia from early childhood.

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.

Seroprevalence of norovirus genogroup IV antibodies among humans, Italy, 2010-2011

Antibodies specific to genogroup IV identified in human specimens suggest zoonotic exposure.

Noroviruses (NoVs) of genogroup IV (GIV) (Alphatron-like) cause infections in humans and in carnivorous animals such as dogs and cats. We screened an age-stratified collection of serum samples from 535 humans in Italy, using virus-like particles of genotypes GIV.1, circulating in humans, and GIV.2, identified in animals, in ELISA, in order to investigate the prevalence of GIV NoV-specific IgG antibodies. Antibodies specific for both genotypes were detected, ranging from a prevalence of 6.6% to 44.8% for GIV.1 and from 6.8% to 15.1% for GIV.2 among different age groups. These data are consistent with a higher prevalence of GIV.1 strains in the human population. Analysis of antibodies against GIV.2 suggests zoonotic transmission of animal NoVs, likely attributable to interaction between humans and domestic pets. This finding, and recent documentation of human transmission of NoVs to dogs, indicate the possibility of an evolutionary relationship between human and animal NoVs.

Detection of Hepatitis E Virus Antibodies in Dogs in the United Kingdom

Hepatitis E virus (HEV) genotypes 3 and 4 are zoonotic pathogens, with pigs predominantly implicated in disease transmission. The rapid rise in human cases in developed countries over the past decade indicates a change in epidemiology of HEV, and it has been suggested that additional animal species may be involved in transmission of infection. Multiple studies have identified contact with dogs as a risk factor for HEV infection in industrialised nations, and a low seroprevalence to HEV has previously been reported in dogs in low-income countries. In this study we aimed to evaluate the possibility that dogs are susceptible to HEV, and determine the frequency with which this occurs. Serum samples from UK dogs with and without hepatitis were screened for HEV-specific antibodies, and canine liver and stool samples were analysed by qPCR for the presence of HEV RNA. We describe evidence to show HEV infection occurs at low levels in dogs in the UK, but the strain of origin is undetermined. The low seroprevalence level of HEV in dogs implies the risk of zoonotic disease transmission is likely to be limited, but further investigations will be required to determine if HEV-infected dogs can transmit HEV to man.

Role of noroviruses as aetiological agents of diarrhoea in developing countries

Diarrhoea is considered to be the second leading cause of death due to infections among children  < 5 years of age worldwide that may be caused by bacteria, parasites, viruses and non-infectious agents. The major causative agents of diarrhoea in developing countries may vary from those in developed countries. Noroviruses are considered to be the most common cause of acute diarrhoea in both children and adults in industrialized countries. On the other hand, there is a lack of comprehensive epidemiological evidence from developing countries that norovirus is a major cause of diarrhoea. In these regions, asymptomatic norovirus infections are very common, and similar detection rates have been observed in patients with diarrhoea and asymptomatic persons. This review summarizes the current knowledge of norovirus infection in developing countries and seeks to position infections with noroviruses among those of other enteropathogens in terms of disease burden in these regions.

Seroepidemiology of Norovirus GII.3 and GII.4 Infections in Children with Diarrhea in Xi'an, China

OBJECTIVE

The objective of this study was to investigate the seroepidemiology of immunoglobulin G (IgG) antibodies against Norovirus (NoV) GII.3 and GII.4 genotypes among children younger than 5 years with acute diarrhea in Xi'an, China.

MATERIALS AND METHODS

A total of 362 serum samples were collected from diarrheal children in the Department of Digestive Diseases of Xi'an Children's Hospital between March 2009 and October 2012. Recombinant capsid proteins of NoV genotypes GII.3 and GII.4 were expressed using the baculovirus expression system. The viruslike particles (VLPs) were examined by electron microscopy and Western blot, and VLPs were used as antigens for serological IgG tests using enzyme-linked immunosorbent assays.

RESULTS

The overall seroprevalence for GII.4 (86.2%) was significantly higher (p<0.01) than for GII.3 (67.9%). The seroprevalence remained in a high and stable level (70.9% for GII.3 and 88.7% for GII.4) in children under 1 year of age, then dropped in the age group 12-17 months (49.3% for GII.3 and 68.1% for GII.4), and finally increased to 77.8% for GII.3 and 96.8% for GII.4 in the group >18 months. The seroprevalence in the age group 12-17 months showed more statistically significant differences than the other age groups for both GII.3 and GII.4 (p<0.05).

CONCLUSIONS

In conclusion, seroprevalence of NoV GII.3 and GII.4 was high in young children in Xi'an, China, and the anti-GII.4-positive rates were statistically higher than GII.3 across all the age groups.

Norovirus GII.4 antibodies in breast milk and serum samples: their role preventing virus-like particles binding to their receptors

BACKGROUND

Norovirus GII.4 genotype is a leading cause of nonbacterial gastroenteritis in infants. Effective vaccines against noroviruses are not yet available, enhancing the interest of the protection mechanisms elicited by breast milk that may contain norovirus-specific antibodies and histo-blood group antigens. The aims of our study were to analyze norovirus GII.4-specific antibodies in breast milk and serum and to assess their blocking activity on recombinant norovirus virus-like particles (VLPs) binding to saliva.

METHODS

Mature milk and serum from 108 mothers were analyzed for specific IgA to norovirus GII.4-2006b and for their blocking activity on the binding of norovirus GII.4-2006b VLPs to fucosyltransferase FUT2-positive and negative saliva. Norovirus GII.4-2006b-specific IgG antibodies were also analyzed in serum samples.

RESULTS

Higher specific IgA titers were detected in mature milk (75%) than in serum samples (62%), showing a correlation between both results (ρ = 0.427, P = 0.000). However, only 56.3% of the serum samples contained norovirus-specific IgG. Almost all mature milk samples (99.1%) inhibited the binding of norovirus VLPs to FUT2-negative saliva; however, only 25% did so to FUT2-positive saliva (P = 0.000). Ninety percent of serum samples inhibited the binding of norovirus VLPs to FUT2-negative saliva.

CONCLUSIONS

Breast milk inhibits norovirus GII.4-2006b VLPs binding to receptors in saliva, and anti-norovirus IgA antibodies are only partly responsible for this activity. The FUT2 status of the receptor seems to be a strong predictor of this effect, but more studies to ascertain the participation of histo-blood group antigens in the protection against norovirus infections elicited by breast milk are required.

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.

Comparison of age-stratified seroprevalence of antibodies against norovirus GII in India and the United Kingdom

Noroviruses are a common cause of gastroenteritis worldwide, but outbreaks appear to be more common in industrialized countries than in developing countries, possibly reflecting differences in exposure and immunity. In this study, age-stratified sera from India and UK populations were analysed for the presence of norovirus-genogroup II specific IgG by a time resolved immunofluorescence assay and relative levels of antibodies in the two populations were compared. Antibody levels were higher among all age groups in India than in UK and increased with age in India, whereas in the UK, levels of antibody decreased in adulthood. These results indicate different patterns of exposure to noroviruses in the two countries.

Prevalence of norovirus GII-4 antibodies in Finnish children

Noroviruses (NoVs) are the second most common cause of viral gastroenteritis after rotavirus in children. NoV genotype GII-4 has emerged as the major type not only in outbreaks of NoV gastroenteritis but also endemic gastroenteritis among infants and young children worldwide. Using baculovirus-insect cell system virus-like particles (VLPs) of NoV genotype GII-4 and an uncommon genotype GII-12 were produced. These VLPs were used in enzyme-linked immunosorbent assays (ELISA) for detection of NoV-specific immunoglobulin G (IgG) and IgA antibodies in 492 serum specimens from Finnish children 0-14 years of age collected between 2006 and 2008. NoV IgG antibody prevalence was 47.3% in the age group 7-23 months and increased up to 91.2% after the age of 5 years. Avidity of NoV IgG antibodies was low in the primary infections while high avidity antibodies were detected in the recurrent infections of the older children. In GII-4 infections, the homologous antibody response to GII-4 VLPs was stronger than to GII-12 VLPs but cross-reactivity between GII-4 and GII-12 was observed. Binding of GII-4 VLPs to a putative carbohydrate antigen receptor H-type 3 could be blocked by sera from children not infected with NoV during a waterborne outbreak of acute gastroenteritis. Therefore, protection against NoV infection correlated with strong blocking activity.

Seroprevalence of St-Valerien-like caliciviruses in Italian swine

St-Valérien-like viruses are newly recognized porcine caliciviruses recently detected in North America and Europe. In this study, baculovirus-expressed virus-like particles of the St-Valérien strain 25A/ITA were generated and used for the development of an antibody-detection ELISA kit to assess the seroprevalence of these novel caliciviruses in swine. Antibodies specific for St-Valérien-like virus were detected in 63 (10.3 %) of 614 serum samples tested with titres ranging from 1 : 50 (28.6 %) to 1 : 800 (40.7 %). These results indicate that St-Valérien-like infections are common among domestic pigs, italy.

Comparative evolution of GII.3 and GII.4 norovirus over a 31-year period

Noroviruses are the most common cause of epidemic gastroenteritis. Genotype II.3 is one of the most frequently detected noroviruses associated with sporadic infections. We studied the evolution of the major capsid gene from seven archival GII.3 noroviruses collected during a cross-sectional study at the Children's Hospital in Washington, DC, from 1975 through 1991, together with capsid sequence from 56 strains available in GenBank. Evolutionary analysis concluded that GII.3 viruses evolved at a rate of 4.16 × 10(-3) nucleotide substitutions/site/year (strict clock), which is similar to that described for the more prevalent GII.4 noroviruses. The analysis of the amino acid changes over the 31-year period found that GII.3 viruses evolve at a relatively steady state, maintaining 4% distance, and have a tendency to revert back to previously used residues while preserving the same carbohydrate binding profile. In contrast, GII.4 viruses demonstrate increasing rates of distance over time because of the continued integration of new amino acids and changing HBGA binding patterns. In GII.3 strains, seven sites acting under positive selection were predicted to be surface-exposed residues in the P2 domain, in contrast to GII.4 positively selected sites located primarily in the shell domain. Our study suggests that GII.3 noroviruses caused disease as early as 1975 and that they evolve via a specific pattern, responding to selective pressures induced by the host rather than presenting a nucleotide evolution rate lower than that of GII.4 noroviruses, as previously proposed. Understanding the evolutionary dynamics of prevalent noroviruses is relevant to the development of effective prevention and control strategies.

Noroviruses: The leading cause of gastroenteritis worldwide

Noroviruses are the leading cause of foodborne disease outbreaks worldwide, and may soon eclipse rotaviruses as the most common cause of severe pediatric gastroenteritis, as the use of rotavirus vaccines becomes more widespread. Genetic mutations and recombinations contribute to the broad heterogeneity of noroviruses and the emergence of new epidemic strains. Although typically a self-limited disease, norovirus gastroenteritis can cause significant morbidity and mortality among children, the elderly, and the immunocompromised. The lack of a cell culture or small animal model has hindered norovirus research and the development of novel therapeutic and preventative interventions. However, vaccines based on norovirus capsid protein virus-like particles are promising and may one day become widely available through transgenic expression in plants.

Viral gastroenteritis

The virology, immunology, diagnosis, clinical symptoms, treatment, epidemiology and prevention measures relating to the most common viral causes of acute gastroenteritis (rotaviruses, human caliciviruses, astroviruses and enteric adenoviruses) are briefly reviewed. Uncommon viral causes of acute gastroenteritis and viruses causing gastroenteritis in immunodeficient patients are mentioned. The main change over the past three years has been the development, licensing and wide application of new live attenuated rotavirus vaccines.

Prolonged norovirus shedding in infants <or=6 months of age with gastroenteritis

BACKGROUND

Noroviruses (NV) are one of the leading causes of gastroenteritis in young children; however, the duration of NV shedding in young children is not well known.

METHODS

Fecal specimens were collected from children with acute gastroenteritis at a pediatric clinic during the period from November to December 2002 and tested for NV by reverse transcription-polymerase chain reaction.

RESULTS

Of 71 children infected with NV, 60 (84.5%) were less than 3 years old. Among children aged <2 years and those aged 2 to 5 years, the duration of illness was longer (7 days versus 3.5 days, P = 0.0069), the maximum number of stools in a 24-hour period was greater (7 versus 3, P = 0.0078) and a 20-point severity score was higher (11 versus 8, P = 0.0031) in patients aged <2 years than in patients aged 2 to 5 years. Among the 23 children whose follow-up specimens were obtained, the median duration of NV shedding was 16 days (range, 5-47 days). Virus shedding for more than 2 weeks after onset was observed in 75% (6 of 8), 71.4% (5 of 7) and 25% (2 of 8) of children aged <1 year, 1 year and 2 to 3 years, respectively. Three infants aged <or=6 months continued to excrete NV for an extremely long period (more than 42, 44 and 47 days from onset) after recovery.

CONCLUSION

Long-term virus shedding after the disappearance of clinical symptoms was observed. Caution should be exercised when handling the excrement of infants and young children infected with NV.

Porcine enteric caliciviruses: genetic and antigenic relatedness to human caliciviruses, diagnosis and epidemiology

Porcine enteric caliciviruses include sapoviruses and noroviruses. Porcine sapoviruses infect pigs of all ages and cause diarrhea in young pigs, whereas porcine noroviruses were detected exclusively from adult pigs without clinical signs. Importantly, certain porcine norovirus strains were genetically and antigenically related to human noroviruses. This raises public health concerns that pigs may be reservoirs for emergence of epidemic human norovirus strains. This article reviews the discovery of porcine noroviruses and sapoviruses, their classification, diagnosis, epidemiology and genetic and antigenic relatedness to human caliciviruses.

Viral gastroenteritis

Rotaviruses, caliciviruses, enteric adenoviruses and astroviruses are common causes of acute gastroenteritis in humans. Their particle and genome structure, classification, replication and pathogenesis, diagnosis, clinical features, epidemiology, disease and outbreak management, and vaccine development are discussed. In the immunocompromized (often infected with HIV), cytomegalovirus, herpes simplex virus, picobirnaviruses and atypical adenoviruses have also been found to be associated with diarrhoea, often chronic. Uncommon causes of diarrhoea are infections with enteroviruses, orthoreoviruses, toroviruses, coronaviruses and parvoviruses.

[Norovirus infections in Germany]

Noroviruses are responsible for the majority of acute viral gastroenteritis infections worldwide. Transmission may be faecal-oral or through contaminated food and water or airborne by virus-containing aerosols. Characteristics of noroviruses that facilitate their spread are their high concentration in stool and vomitus, their extreme environmental stability, their low infectious dose as well as the lack of long-lasting immunity. The majority of norovirus infections occur in large outbreaks among persons living in institutional settings, such as hospitals and nursing homes, although sporadic cases also occur. Children and elderly persons are most often affected. Illness is characterized by acute onset of projectile vomiting. For prevention and control of norovirus outbreaks strict control management is necessary. Based on the high genomic variability new variant noroviruses with different pathogenic factors can arise. Depending on the circulating variant the extent of the usual winter peak can vary enormously. Available diagnostic methods include RT-PCR assays for detection of viral RNA, electron microscopy and enzyme immunoassays (EIA) for detection of viral antigens. The implicated virus can be subtyped through nucleotide sequencing and linked to a specific outbreak. With the enactment of the Protection against Infection Act in January 2001 a mandatory reporting system of norovirus infections was established. Analysis of surveillance data from this system permits a detailed overview of the nationwide epidemiology of this disease in Germany.

Genetic and antigenic diversity among noroviruses

Human norovirus (NoV) strains cause a considerable number of outbreaks of gastroenteritis worldwide. Based on their capsid gene (VP1) sequence, human NoV strains can be grouped into two genogroups (GI and GII) and at least 14 GI and 17 GII genotypes (GI/1–14 and GII/1–17). Human NoV strains cannot be propagated in cell-culture systems, but expression of recombinant VP1 in insect cells results in the formation of virus-like particles (VLPs). In order to understand NoV antigenic relationships better, cross-reactivity among 26 different NoV VLPs was analysed. Phylogenetic analyses grouped these NoV strains into six GI and 12 GII genotypes. An antibody ELISA using polyclonal antisera raised against these VLPs was used to determine cross-reactivity. Antisera reacted strongly with homologous VLPs; however, a number of novel cross-reactivities among different genotypes was observed. For example, GI/11 antiserum showed a broad-range cross-reactivity, detecting two GI and 10 GII genotypes. Likewise, GII/1, GII/10 and GII/12 antisera showed a broad-range cross-reactivity, detecting several other distinct GII genotypes. Alignment of VP1 amino acid sequences suggested that these broad-range cross-reactivities were due to conserved amino acid residues located within the shell and/or P1-1 domains. However, unusual cross-reactivities among different GII/3 antisera were found, with the results indicating that both conserved amino acid residues and VP1 secondary structures influence antigenicity.

Self-assembly of the recombinant capsid protein of a bovine norovirus (BoNV) into virus-like particles and evaluation of cross-reactivity of BoNV with human noroviruses

None of the enteric caliciviruses except Po/Sapo/GIII/Cowden/80/US replicates in cell culture, which complicates efforts to develop control strategies or to study viral replication. To develop serological assays for bovine noroviruses (BoNVs) and to determine the cross-reactivity of BoNV with human noroviruses, we generated two recombinant baculoviruses, rCV186-OH and rJNCV, to express the capsid genes of Bo/CV186-OH/00/US (Norovirus genogroup III [GIII], genotype 2 [GIII/2]). rCV186-OH expressed the expected 57-kDa capsid protein, but rJNCV expressed a truncated capsid protein of 35 kDa. Sequence analysis of rJNCV identified a single nucleotide deletion in the P domain of the capsid gene, which introduced a stop codon at amino acid 323. The recombinant capsid protein produced by rCV186-OH but not that produced by rJNCV self-assembled into virus-like particles (VLPs) similar to native BoNV. An antibody-capture enzyme-linked immunosorbent assay (ELISA) and antigen-capture ELISA (Ag-ELISA) detected serum antibody and antigen, respectively, from calves infected with Bo/CV186-OH/00/US but not antibodies or antigens to other enteric viruses. In other tests of the GIII/2 BoNV Ag-ELISA, no cross-reactivity was observed with VLPs from one GI and four GII human noroviruses and porcine sapovirus Cowden strain. Because, like human noroviruses, BoNVs do not grow in cell culture, the BoNV VLPs will be useful in the serological assays described for the detection of BoNV antibody and antigen. Consistent with the phylogenetic analysis of the capsid genes of bovine and human noroviruses (M. G. Han, J. R. Smiley, C. Thomas, and L. J. Saif, J. Clin. Microbiol. 42:5214-5224, 2004), the results suggest that GIII/2 BoNV does not share significant antigenic relationships with the five characterized human noroviruses tested.

Diagnosis of norwalk virus infection by indirect enzyme immunoassay detection of salivary antibodies to recombinant norwalk virus antigen

Simple diagnostic tests are needed for the detection of norovirus (NoV) outbreaks. Salivary antibody assays provide an attractive alternative to collecting and testing serum or stool samples. Antibodies to Norwalk virus (NV) in oral fluid samples were compared with NV antibodies in serum collected from 38 volunteers challenged with NV inoculum. Pre- and postchallenge (day 4, 8, 14, and 21) saliva and serum samples were examined by enzyme immunoassay (EIA) using recombinant NV antigen. Of 18 infected subjects (those who shed NV in stool or who demonstrated immunoglobulin G [IgG] seroconversion), 15 (83%) had > or =4-fold increases in NV-specific salivary IgA and 15 (83%) had > or =4-fold increases in NV-specific salivary IgG when prechallenge and postchallenge saliva samples were compared. When the results of the IgA and IgG assays were combined, all 18 infected subjects showed > or =4-fold increases in NV-specific salivary IgG or IgA postchallenge titers compared to their prechallenge titers. One of 19 uninfected subjects had a > or =4-fold increase in NV-specific salivary IgG. The sensitivity of the combined assay results was 100%, and the specificity was 95%. NV-specific salivary IgA titers peaked around 14 days postchallenge. NV-specific salivary IgG and serum IgG titers continued to rise through 21 days postchallenge. The application of this EIA to an elementary school outbreak indicated that 67% of the subjects with confirmed infections had >4-fold rises in anti-NoV IgA when an antigen in the same genetic cluster as the outbreak virus was used. This is the first documented mucosal antibody response to NoV in children. This EIA provides a useful approach for diagnosing NoV outbreaks.

Expression and antigenicity of virus-like particles of norovirus and their application for detection of noroviruses in stool samples

Human noroviruses (NoVs), members of the genus Norovirus in the family Caliciviridae, are the leading agents of nonbacterial acute gastroenteritis worldwide. Human NoVs are currently divided into at least two genogroups, genogroup I (GI) and genogroup II (GII), each of which contains at least 14 and 17 genotypes. To explore the genetic and antigenic relationship among NoVs, we expressed the capsid protein of four genetically distinct NoVs, the GI/3 Kashiwa645 virus, the GII/3 Sanbu809 virus, the GII/5 Ichikawa754 virus, and the GII/7 Osaka10-25 virus in baculovirus expression system. An antigen enzyme-linked immunosorbent assay (ELISA) with hyperimmune serum against the four recombinant capsid proteins and characterized previously three capsid proteins derived from GI/1, GI/4, and GII/12 was developed to detect the NoVs antigen in stools. The antigen ELISA was highly specific to the homotypic strains, allowing assignment of a strain to a Norovirus genetic cluster within a genogroup.

Seroprevalence of antibodies against noroviruses among students in a Chinese military medical university

Noroviruses (NVs) are important causes of nonbacterial gastroenteritis in humans, but the role of NVs as a cause of diseases in the Chinese people, particularly in Chinese military personnel, remains unclear. This study investigated antibody prevalence and factors that associate with the prevalence of antibody to NVs among students attending a military medical university. Serum specimens were tested by an enzyme-linked immunosorbent assay for immunoglobulin G antibody to recombinant capsid antigens of three NVs (rNorwalk, rMxV, and rVA387). Of 588 serum samples tested, the antibody prevalence was 88.9, 54.1, or 90.0% for the three antigens, respectively. There were significant differences in the prevalence of antibody to rMxV between blood types (P < 0.05); the prevalence for type O was the highest (62.5%), and the prevalence for type B was the lowest (49.1%). The average optical density values for antibody to rNorwalk and rMxV were lowest among students with type B. The number of students who did not have antibody to any of the three antigens was the highest for blood type B (6.9%) compared to other blood types (0.8 to 3.4% [P < 0.006]). The antibody prevalence also varied with the hometown residencies of the students before joining the military, with the highest rates for students from rural areas, lower rates for students from small towns or villages, and the lowest rates for students from large cities. The numbers of students who did not have antibody to any of the three antigens were highest for students from the large cities, lower for students from small towns or villages, and lowest for students from rural areas. The distribution of ABO blood types did not differ among the three groups. These data suggest that NVs are prevalent in China and that both genetic and environmental factors play a role in NV infection.

Seroepidemiology of group C rotavirus infection in England and Wales

A total of 3199 serum samples collected in 1993--1994 from two population cohorts from England and Wales were tested for the prevalence of IgG antibodies specifically directed against group C rotavirus VP6. Seroprevalence was 39% (95% confidence intervals: 37.0-40.4%). Seroprevalence was highest (46.0%) in the oldest age group (61-70 years of age). Infection with group C rotaviruses occurred at an earlier age and with higher incidence in rural than in urban populations. These results may suggest transmission from animals to humans, however further work is required to identify the reservoir of group C rotavirus for human infection.

Human caliciviruses and pediatric gastroenteritis

Surveillance using molecular diagnostic methods developed in the past decade shows that human caliciviruses, particularly the Noroviruses, are the most important cause of pediatric acute gastroenteritis, next to rotavirus. Noroviruses also cause severe gastroenteritis in children, requiring hospitalization. The Sapovirus, a morphologically and genetically distinct genus of calicivirus, cause mainly milder endemic pediatric gastroenteritis. Noroviruses and Sapoviruses are genetically and antigenetically diverse, and multiple genetic types cocirculate in the same community. Human caliciviruses still cannot be cultivated in cell culture or in an animal model. Significant progress has been made in the past decade in the classification, diagnosis, and vaccine development, as well as in the recent discovery of Norovirus recognizing human histoblood group antigens as receptors. Major developments in this field are expected to occur in the near future.

Genogroup II noroviruses efficiently bind to heparan sulfate proteoglycan associated with the cellular membrane

Norovirus (NV), a member of the family Caliciviridae, is one of the important causative agents of acute gastroenteritis. In the present study, we found that virus-like particles (VLPs) derived from genogroup II (GII) NV were bound to cell surface heparan sulfate proteoglycan. Interestingly, the VLPs derived from GII were more than ten times likelier to bind to cells than were those derived from genogroup I (GI). Heparin, a sulfated glycosaminoglycan, and suramin, a highly sulfated derivative of urea, efficiently blocked VLP binding to mammalian cell surfaces. The reagents known to bind to cell surface heparan sulfate, as well as the enzymes that specifically digest heparan sulfate, markedly reduced VLP binding to the cells. Treatment of the cells with chlorate revealed that sulfation of heparan sulfate plays an important role in the NV-heparan sulfate interaction. The binding efficiency of NV to undifferentiated Caco-2 (U-Caco-2) cells differed largely between GI NV and GII NV, whereas the efficiency of binding to differentiated Caco-2 (D-Caco-2) cells did not differ significantly between the two genogroups, although slight differences between strains were observed. Digestion with heparinase I resulted in a reduction of up to 90% in U-Caco-2 cells and a reduction of up to only 50% in D-Caco-2 cells, indicating that heparan sulfate is the major binding molecule for U-Caco-2 cells, while it contributed to only half of the binding in the case of D-Caco-2 cells. The other half of those VLPs was likely to be associated with H-type blood antigen, suggesting that GII NV has two separate binding sites. The present study is the first to address the possible role of cell surface glycosaminoglycans in the binding of recombinant VLPs of NV.

Precise characterization of norovirus (Norwalk-like virus)-specific monoclonal antibodies with broad reactivity

We have been characterizing monoclonal antibodies against Norovirus (Norwalk-like virus). In the course of our study, two monoclonal antibodies generated against Norovirus genogroup II capsid protein were found to react not only to genogroup II but also to genogroup I recombinant capsid proteins. In addition, we showed that these two monoclonal antibodies reacted to a 40-amino-acid-fragment located close to the N-terminal region of genogroup II Norovirus. Similar reactivity was observed with the equivalent region of genogroup I Norovirus. In this study, we confirmed that the epitopes of the two monoclonal antibodies existed within an 11-amino-acid peptide. To obtain an idea of the reactive ranges of the two monoclonal antibodies toward different strains of Norovirus, their reactivities were investigated using 16 types of peptide constructed according to the data in GenBank and 8 recombinant capsid proteins (7 whole capsid proteins and 1 short [80-amino-acid] protein fragment). A characteristic broad reactivity of the two monoclonal antibodies is clearly shown by the results of this study. Thus, these monoclonal antibodies could be useful tools for detecting a broad range of Norovirus strains.

Cross-reactivity among several recombinant calicivirus virus-like particles (VLPs) with monoclonal antibodies obtained from mice immunized orally with one type of VLP

Human caliciviruses (HuCVs) are classified into the Norwalk-like viruses (NLV) and Sapporo-like viruses (SLV) as genera within the family CALICIVIRIDAE: The NLV genus is further classified into genogroups I and II, based on sequence similarities. To study the antigenic determinants on the HuCV capsid protein and develop new diagnostic tools for field samples, we established and characterized monoclonal antibodies (MAbs) against baculovirus-expressed recombinant HuCV virus-like particles (VLPs). Hybrid clones producing MAbs were obtained from cultures of PAI myeloma cells fused with spleen or mesenteric lymph node cells from mice immunized orally with either a single type of recombinant Norwalk virus (rNV), Kashiwa 47 virus (rKAV), Snow Mountain agent (rSMA), or Sapporo virus (rSV) VLP or with mixtures of two types of VLPs from different genogroups. Twenty MAbs, obtained as mouse ascites, were characterized and classified into six groups according to their enzyme-linked immunosorbent assay (ELISA) and Western blotting (WB) cross-reactivity patterns to VLPs. Five groups of MAbs reacted by both WB and ELISA and were classified as follows: common cross-reactive MAbs for four genogroup I and six genogroup II VLPs (group A), genogroup I-specific MAbs (group B), genogroup II-specific MAbs (group C), and strain-specific MAbs (groups D and E). One MAb group (group F) reacted only by ELISA. The group A MAbs, which showed broad cross-reactivity with VLPs of both NLV genogroups, were obtained from mice immunized orally with a single type of VLP (either rNV or rKAV). Two MAbs, which were obtained from mice immunized with rSV, reacted with rSV but not with any NLV VLP. These are the first MAbs to be reported for any SLV. These strain-, genogroup-, and genus-reactive MAbs will be useful tools for further study of the antigenic and structural topography of the HuCV virion and for diagnostic assays for HuCVs.

Characterization of Norwalk-like virus associated with gastroenteritis in Indonesia

Norwalk Virus and Norwalk-like viruses (NLVs) are reportedly responsible for 2.5-4.0% of nonbacterial acute gastroenteritis (NBAG) worldwide. To help clarify the impact of NLVs on NBAG in Indonesia, stool specimens from 102 patients, 74 with NBAG and 28 with BAG, were screened for the presence of NLVs, using a reverse transcription-polymerase chain reaction (RT-PCR) assay. The specimens were subtyped using prototype-specific oligonucleotide probes and were sequenced and compared with published NLV sequences. Of the 102 specimens examined, 31 (30%) were found to be positive for NLVs. Type-specific probe analysis of the RT-PCR products indicated that 31 isolates hybridized to UK1 (Taunton agent) and UK3/4 (Hawaii agent/Snow Mountain agent) prototype strains. The results of this study indicate that prototype strains of NV or NLVs co-circulate in Indonesia and contribute to the overall level of acute gastroenteritis throughout the region.

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.

Outbreaks of acute gastroenteritis associated with Norwalk-like viruses in campus settings

Norwalk-like viruses (NLVs) are transmitted by fecally contaminated food, water, fomites, and person-to-person contact. They are a leading cause of acute gastroenteritis epidemics in industrialized countries. NLV outbreaks are characterized by a 12- to 48-hour incubation period; nausea, vomiting, and diarrhea for 24 to 72 hours; and high secondary attack rates. NLV infections spread rapidly on college and university campuses because of close living quarters, shared bathrooms and common rooms, many food handlers, popular self-service salad bars in dining halls, and person-to-person contact through sports and recreational activities. The illness is generally mild and self-limited but an outbreak can strain the resources of campus health services and cause high absenteeism among both students and staff. Treatment is primarily through antiemetic medication and oral rehydration. Prevention and control of NLV outbreaks rests on promoting hand washing; enforcement of strict hygiene in all food preparation areas; and prompt, rigorous cleaning of potentially contaminated areas where someone has been ill.

"Norwalk-like viruses" as a cause of foodborne disease outbreaks

While outbreaks of foodborne disease remain an important public health concern, their aetiology is not identified in a majority of instances. In targeted studies, the application of newly developed molecular assays has demonstrated that a large proportion of these outbreaks may be caused by the "Norwalk-like viruses" (NLV), a genus of genetically related viruses belonging to the family Caliciviridae. NLV outbreaks associated with consumption of faecally contaminated oysters are frequently reported and can best be controlled by preventing contamination of oyster-harvesting waters. Infectious foodhandlers are another frequent source of contamination, and such transmission can be minimised by exclusion of ill foodhandlers and the maintenance of strict personal hygiene. Molecular assays have greatly refined the epidemiological investigation of foodborne NLV outbreaks, allowing the linking of outbreaks in different locations and permitting the identification of the virus in the implicated vehicle. The development of simpler and more sensitive assays and their use on a broader scale will assist in defining the true burden of foodborne NLV outbreaks and improve strategies for their prevention and control.

Expression of recombinant capsid proteins of chitta virus, a genogroup II Norwalk virus, and development of an ELISA to detect the viral antigen

The second open reading frame (ORF2) gene of the Chitta virus (CHV) was cloned to construct a recombinant baculovirus. The CHV ORF2 is predicted to encode a capsid protein of 535 amino acids (aa). CHV showed a high aa identity in the capsid region with genogroup II Norwalk virus (NV) (65-85%), but a low aa identity with genogroup I NV (44-46%). Phylogenetic analysis of the ORF2 gene demonstrated that CHV is genetically closely related to the Hawaii virus included in genogroup II NV. The recombinant capsid protein of CHV (rCHV) self-assembled to form empty virus-like particles (VLPs) when expressed in insect cells with the recombinant baculovirus. An enzyme-linked immunosorbent assay (ELISA) based on antisera to rCHV was developed to detect CHV antigen in stools. The antigen ELISA appeared to be highly specific to both rCHV and CHV-like strains. In addition, combined use of antigen ELISAs using antibodies against two antigenically distinct recombinant VLPs, the recombinant Chiba virus (rCV) and recombinant Seto virus (rSEV), enabled us to determine the genetic as well as antigenic relationship among these three viruses.