Contrasting Results from Two Commercial Kits Testing for the Presence of Clostridium perfringens Enterotoxin in Feces from Norovirus-Infected Human Patients

BACKGROUND

Detection of Clostridium perfringens enterotoxin (CPE) is critical for disease surveillance; however, commercial testing kits produce contrasting results.

METHODS

We examined the cause of the differing results from a reversed passive latex agglutination (RPLA) assay (PET-RPLA Toxin Detection Kit) and an enzyme-linked immunosorbent assay (C. perfringens Enterotoxin ELISA Kit) using 73 human norovirus-positive fecal samples from gastroenteritis patients across 22 episodes in Japan.

RESULTS

CPE was detected in 39/73 samples using the RPLA method; however, ELISA-based examination of 10 RPLA-positive samples produced negative results. Moreover, cpe was not detected in any of the RPLA-positive (n = 32) or -negative (n = 5) samples, and C. perfringens was only isolated from one RPLA-positive sample.

CONCLUSIONS

An ELISA-based testing approach may be more reliable than RPLA assays for CPE detection from human fecal samples. These findings may also be applicable to the detection of other foodborne diseases.

Feline calicivirus infection in cats with virulent systemic disease, Italy

Feline calicivirus (FCV) is a contagious viral pathogen that usually causes a mild, self-limiting respiratory disease. More recently, highly virulent FCV strains have emerged and have been associated with severe systemic infection, referred to as virulent systemic disease (VSD). The objective of this study is to report VSD cases in Italian cats along with the molecular characterization of two detected FCV strains. Three client-owned cats showed clinical signs resembling to those described for VSD cases. The cats were subjected to molecular investigations for detection of FCV and other feline pathogens. Histopathology and immunohistochemistry were performed on internal organs of one cat; molecular characterization of two detected FCV strains was obtained through sequence and phylogenetic analyses. Putative VS-FCV strains were detected in all three cats, which were co-infected with feline panleukopenia virus. The cat submitted to histopathology and immunohistochemistry displayed severe histological changes and FCV antigens in internal organs. Two Italian FCV strains, for which amplification of ORF2 was successful, were strictly related and formed a unique phylogenetic cluster. These viruses did not show consistent changes in the amino acid sequences with respect to reference VS-FCVs. The results of our study confirm that VS-FCV strains are circulating in Italy and that VSD diagnosis is complicated since both genetic and clinical markers have not been identified so far.

Melatonin modulates the autophagic response in acute liver failure induced by the rabbit hemorrhagic disease virus

Autophagy is an important survival pathway and participates in the host response to infection. Beneficial effects of melatonin have been previously reported in an animal model of acute liver failure (ALF) induced by the rabbit hemorrhagic disease virus (RHDV). This study was aimed to investigate whether melatonin protection against liver injury induced by the RHDV associates to modulation of autophagy. Rabbits were infected with 2 × 10(4) hemagglutination units of a RHDV isolate and received 20 mg/kg melatonin at 0, 12, and 24 hr postinfection. RHDV induced autophagy, with increased expression of beclin-1, ubiquitin-like autophagy-related (Atg)5, Atg12, Atg16L1 and sequestrosome 1 (p62/SQSTM1), protein 1 light chain 3 (LC3) staining, and conversion of LC3-I to autophagosome-associated LC3-II. These effects reached a maximum at 24 hr postinfection, in parallel to extensive colocalization of LC3 and lysosome-associated membrane protein (LAMP)-1. The autophagic response induced by RHDV infection was significantly inhibited by melatonin administration. Melatonin treatment also resulted in decreased immunoreactivity for RHDV viral VP60 antigen and a significantly reduction in RHDV VP60 mRNA levels, oxidized to reduced glutathione ratio (GSSG/GSH), caspase-3 activity, and immunoglobulin-heavy-chain-binding protein (BiP) and CCAAT/enhancer-binding protein homologous protein (CHOP) expression. Results indicate that, in addition to its antioxidant and antiapoptotic effects, and the suppression of ER stress, melatonin induces a decrease in autophagy associated with RHDV infection and inhibits RHDV RNA replication. Results obtained reveal novel molecular pathways accounting for the protective effect of melatonin in this animal model of ALF.

Norwalk virus does not replicate in human macrophages or dendritic cells derived from the peripheral blood of susceptible humans

Human noroviruses are difficult to study due to the lack of an efficient in vitro cell culture system or small animal model. Murine norovirus replicates in murine macrophages (MPhi) and dendritic cells (DCs), raising the possibility that human NoVs might replicate in such human cell types. To test this hypothesis, we evaluated DCs and MPhi derived from monocyte subsets and CD11c(+) DCs isolated from peripheral blood mononuclear cells of individuals susceptible to Norwalk virus (NV) infection. These cells were exposed to NV and replication was evaluated by immunofluorescence and by quantitative RT-PCR. A few PBMC-derived DCs expressed NV proteins. However, NV RNA did not increase in any of the cells tested. These results demonstrate that NV does not replicate in human CD11c(+) DCs, monocyte-derived DCs and MPhi, but abortive infection may occur in a few DCs. These results suggest that NV tropism is distinct from that of murine noroviruses.

Norwalk virus does not replicate in human macrophages or dendritic cells derived from the peripheral blood of susceptible humans

Human noroviruses are difficult to study due to the lack of an efficient in vitro cell culture system or small animal model. Murine norovirus replicates in murine macrophages (MPhi) and dendritic cells (DCs), raising the possibility that human NoVs might replicate in such human cell types. To test this hypothesis, we evaluated DCs and MPhi derived from monocyte subsets and CD11c(+) DCs isolated from peripheral blood mononuclear cells of individuals susceptible to Norwalk virus (NV) infection. These cells were exposed to NV and replication was evaluated by immunofluorescence and by quantitative RT-PCR. A few PBMC-derived DCs expressed NV proteins. However, NV RNA did not increase in any of the cells tested. These results demonstrate that NV does not replicate in human CD11c(+) DCs, monocyte-derived DCs and MPhi, but abortive infection may occur in a few DCs. These results suggest that NV tropism is distinct from that of murine noroviruses.

Effects of murine norovirus infection on a mouse model of diet-induced obesity and insulin resistance

Murine norovirus (MNV) is prevalent in SPF mouse facilities in the United States, and we currently lack sufficient data to determine whether it should be eliminated. It is generally accepted that the virus does not cause clinical symptoms in immuno-competent mice. However, we previously reported that MNV infection alters the phenotype of a mouse model of bacteria-induced inflammatory bowel disease in part through its effects on dendritic cells. The tropism of MNV toward macrophages and dendritic cells makes MNV a potential intercurrent variable in murine models of macrophage-driven inflammatory diseases, such as obesity, insulin resistance, and atherosclerosis. Therefore, we determined whether MNV infection altered obesity and insulin resistance phenotypes in C57BL/6 mice, a widely used model of diet-induced obesity. We found that MNV did not alter weight gain, food intake, and glucose metabolism in this model, but it did induce subtle changes in lymphoid tissue. Further studies using other models of metabolic diseases are needed to provide additional information on the potential role this 'subclinical' virus might have on disease progression in mouse models of inflammatory diseases.

[Studies on the apoptosis of RK13 cells induced by rabbit hemorrhagic disease virus]

The apoptosis of RK13 cells induced by RHDV was investigated with DAPI staining, DNA ladder, Caspase 3 activity and flow cytometry, etc. The results showed that nuclear staining of infected cells with DAPI showed gradually morphological changes of the nuclei. As shown in the paper, a canonic oligonucleosome-sized DNA ladder was observed in cells harvested at 24h, 48h and 72h post-infection, confirming that DNA fragmentation was induced by RHDV infection. The results of flow cytometry showed that about 63% of cells were in apoptosis at 48h post-infection. Besides, we also demonstrated that the activation of Caspase 3 occurred during the infection process. In conclusion, our results showed that apoptosis in RHD might be determinant in the development of the pathogenesis of RHD.

Genetic susceptibility to symptomatic norovirus infection in Nicaragua

Host genetic resistance to Norovirus (NoV) has been observed in challenge and outbreak studies in populations from Europe, Asia, and USA. In this study, we have investigated if histo-blood group antigens can predict susceptibility to diarrhea caused by NoV in Nicaragua, Central America, and if this can be reflected in antibody-prevalence and titer to NoV among individuals with different histo-blood group antigen phenotypes. Investigation of 28 individuals infected with NoV and 131 population controls revealed 6% of non-secretors in the population and nil non-secretors among patients infected with NoV, suggesting that non-secretors may be protected against NoV disease in Nicaragua. Surprisingly, 25% of the population was Lewis negative (Le(a-b-)). NoV infections with genogroup I (GI) and GII occurred irrespective of Lewis genotype, but none of the Lewis a positive (Le(a + b-)) were infected. The globally dominating GII.4 virus infected individuals of all blood groups except AB (n = 5), while the GI viruses (n = 4) infected only blood type O individuals. Furthermore, O blood types were susceptible to infections with GI.4, GII.4, GII.7, GII.17, and GII.18-Nica viruses, suggesting that secretors with blood type O are susceptible (OR = 1.52) and non-secretors resistant. The overall antibody-prevalence to NoV GII.3 VLP was 62% with the highest prevalence among blood type B carriers (70%) followed by A (68%) and O (62%). All four investigated individuals carrying blood type AB were antibody-negative. Among secretors, 63% were antibody-positive compared to 33% among non-secretors (P = 0.151). This study extends previous knowledge about the histo-blood group antigens role in NoV disease in a population with different genetic background than North American and European.

An outbreak of food-borne gastroenteritis due to sapovirus among junior high school students

The human sapovirus (SaV) causes acute gastroenteritis mainly in infants and young children. A food-borne outbreak of gastroenteritis associated with SaV occurred among junior high school students in Yokohama, Japan, during and after a study trip. The nucleotide sequences of the partial capsid gene derived from the students exhibited 98% homology to a SaV genogroup IV strain, Hu/Angelholm/SW278/2004/SE, which was isolated from an adult with gastroenteritis in Solna, Sweden. An identical nucleotide sequence was detected from a food handler at the hotel restaurant, suggesting that the causative agent of the outbreak was transmitted from the food handler. This is the first description of a food-borne outbreak associated with the SaV genogroup IV strain in Japan.

Comparison of clinical features of childhood norovirus and rotavirus gastroenteritis in Taiwan

BACKGROUND

Viral gastroenteritis is a common acute infectious disease in infants and young children. This study compared the incidence and clinical features of childhood norovirus (NV) and rotavirus (RV) gastroenteritis in Taiwan.

METHODS

Stool specimens were collected from children with acute gastroenteritis aged 6 months to 14 years who were treated at the Children's Medical Center of Taipei Veterans General Hospital between January 2004 and March 2005. The incidence, clinical manifestations, and laboratory findings of childhood NV gastroenteritis were analyzed and compared with those of patients with RV gastroenteritis. Patients with underlying diseases associated with diarrhea or those diagnosed with bacterial gastroenteritis were excluded. Stool specimens were tested for NV and RV using enzyme immunoassay (EIA). NV genogroups were determined by reverse-transcriptase polymerase chain reaction.

RESULTS

Among the 201 patients included in this study, NV was detected in 44 (21.9%) by 1 or more tests (22 by EIA). Five of these isolates were genogroup I (11.3%), and 39 were genogroup II (88.7%). Fifty-two (25.9%) specimens had a positive EIA result for RV. Compared with NV, patients with RV gastroenteritis had a significantly higher percentage of diarrhea (94 vs. 69%, p < 0.001), fever (82 vs. 26.2%, p < 0.001), and longer hospital stay (3.81 vs. 2.93 days, p = 0.048). Laboratory studies showed significantly higher liver enzymes and C-reactive protein levels in patients with RV infection. In contrast, white blood cell counts were significantly higher in patients with NV infection.

CONCLUSION

Norovirus is one of the leading agents of acute gastroenteritis in children in Taiwan, and genogroup II is the predominant type.

Vitamin A supplementation has divergent effects on norovirus infections and clinical symptoms among Mexican children

BACKGROUND

The effect of vitamin A supplementation on viral gastrointestinal infections among young children living in developing countries remains unclear.

METHODS

The effect of vitamin A supplementation on norovirus (NoV) infection among 127 Mexican children 5-15 months of age was studied in a randomized, placebo-controlled trial during June-August 1998. Stool samples collected every 2 weeks and after diarrheal episodes were screened for NoV and characterized at the genogroup level (GI and GII).

RESULTS

Of the stool samples collected, 29.9% were positive for NoV, and NoV GI and NoV GII were found in 55.4% and 46.4% of the positive samples, respectively. Vitamin A supplementation reduced the prevalence of NoV GII infections (rate ratio [RR], 0.60 [95% confidence interval {CI}, 0.20-0.82]), increased the length of both NoV GI and GII shedding, and decreased the prevalence of NoV-associated diarrhea (RR, 0.51 [95% CI, 0.26-0.97]).

CONCLUSIONS

These findings suggest that NoV is an important cause of pediatric diarrhea in this study population and that vitamin A supplementation has divergent effects on specific outcomes of NoV infection.

Feline caliciviruses (FCVs) isolated from cats with virulent systemic disease possess in vitro phenotypes distinct from those of other FCV isolates

During the past decade, several outbreaks of severe systemic disease associated with Feline calicivirus (FCV) have occurred in the USA and the UK. This new disease has caused high mortality in the affected animals and has been termed virulent systemic (VS)-FCV disease. Currently, there are no genetic or in vitro diagnostic methods to distinguish viruses isolated from cases of VS-FCV disease from other isolates. Here, five in vitro properties, as well as the capsid and proteinase-polymerase (pro-pol) sequences, of a set of FCV isolates that included seven isolates from five distinct VS-FCV outbreaks ('VS isolates') were investigated. Although all of the FCV isolates investigated had similar kinetics of growth under single-cycle conditions, VS isolates infected tissue-culture cells more efficiently under multiple-cycle growth conditions. Moreover, it was found that cells infected with VS isolates showed cytopathic effects earlier than cells infected with non-VS isolates, although no difference in relative ATP levels were noted at times when morphological changes were first seen. Both VS- and other (non-VS) isolates of FCV demonstrated similar temperature stabilities. Phylogenetic analyses and alignments of the capsid and pro-pol regions of the genome did not reveal any conserved changes that correlated with virulence, and the VS isolates did not segregate into a unique clade. These results suggest that VS isolates have arisen independently several times since first being described and can spread more efficiently in tissue culture than other isolates when infected at low multiplicity.

Feline calicivirus

Feline calicivirus (FCV) is an important and highly prevalent pathogen of cats. It belongs to the family Caliciviridae which includes other significant pathogens of man and animals. As an RNA virus, high polymerase error rates convey upon FCV a high genome plasticity, and allow the virus to respond rapidly to environmental selection pressures. This makes the virus very adaptable and has important implications for clinical disease and its control. Being genetically diverse, FCV is associated with a range of clinical syndromes from inapparent infections to relatively mild oral and upper respiratory tract disease with or without acute lameness. More recently, highly virulent forms of the virus have emerged associated with a systemic infection that is frequently fatal. A proportion of FCV infected cats that recover from acute disease, remain persistently infected. In such cats, virus evolution is believed to help the virus to evade the host immune response. Such long-term carriers may only represent a minority of the feline population but are likely to be crucial to the epidemiology of the virus. Vaccination against FCV has been available for many years and has effectively reduced the incidence of clinical disease. However, the vaccines do not prevent infection and vaccinated cats can still become persistently infected. In addition, FCV strain variability means that not all strains are protected against equally. Much progress has been made in understanding the biology and pathogenesis of this important feline virus. Challenges for the future will necessarily focus on how to control the variability of this virus particularly in relation to emerging virulent strains and vaccination.

Asymptomatic norovirus infection in Mexican children

Sixty-three children in periurban Mexico City were examined for the occurrence of asymptomatic norovirus (NoV) infection from June to August 1998. NoV was detected in 48 of 161 stool specimens (29.8%), with 31 children (49.2%) having at least one positive stool. Asymptomatic NoV infection occurred commonly during summertime in a Mexican pediatric population.

Severe leukopenia and liver biochemistry changes in adult rabbits after calicivirus infection

Calicivirus infection is the major cause of the severe decrease in the stocks of wild and farm rabbits that has occurred worldwide during the last two decades. Adult rabbits (10-weeks-old) were experimentally infected with a calicivirus inoculum that killed all animals by causing rabbit haemorrhagic disease (RHD) within 24-62 h of infection. The rabbits were used to evaluate blood cell numbers and serum biochemistry every 6h, starting 12h after the inoculation of the caliciviruses. No significant changes in blood parameters were observed in most of the rabbits up to 18 h of infection. Severe leukopenia was seen 6h before death of the infected rabbits; both heterophils and lymphocytes contributed to the decrease in circulating white blood cells. Platelets were also severely decreased in number. Marked enhancement in liver enzymes was seen 6-12 h before death of the infected rabbits. There was also evidence both for cholestasis, as expressed by the elevated levels of direct (conjugated) bilirubin, and for hypoglycemia, an alteration that it is likely to contribute for the seizures that rabbits show during the late stages of RHD. Liver ultrastructure of rabbits that died from RHD revealed extensive hepatocyte vacuolization, severe changes in mitochondrial structure, and depletion of glycogen granules. We conclude that: (i) severe leukopenia characterizes the final hours of calicivirus-induced RHD; (ii) hypoglycemia and cholestasis precede death of rabbits from RHD; (iii) the kinetics of liver enzymes allows an accurate prediction of the time of death of rabbits from calicivirus-induced RHD.

Virological, serological, and clinical features of an outbreak of acute gastroenteritis due to recombinant genogroup II norovirus in an infant home

Norovirus (NV) is an important cause of acute nonbacterial gastroenteritis worldwide. Recently, several sporadic cases due to naturally occurring recombinant NVs have been reported. In January 2000, there was an outbreak of gastroenteritis in an infant home in Sapporo, Japan. Of 34 residents of the home that were less than 2 years old, 23 developed gastrointestinal symptoms and NV infection was confirmed by conventional reverse transcription-PCR to detect the RNA polymerase region of genogroup II NV. In this virus, the RNA polymerase region shared 86% nucleotide identity with Hawaii virus but only 77% with Mexico virus; however, its capsid region shared only 70% identity with Hawaii virus but 90% with Mexico virus. On the other hand, both regions shared a higher 96% nucleotide identity with Arg320 virus, which was found in Mendoza, Argentina, in 1995 and considered to be a recombinant of Hawaii and Mexico viruses. The findings indicate that the virus involved in the outbreak was similar and may have evolved from the Arg320 virus. Clinically the cases were more severe than those of previously reported sporadic or outbreak cases of NV infection.

Risk groups for clinical complications of norovirus infections: an outbreak investigation

Norovirus infections have been described as self-limiting diseases of short duration. An investigation of a norovirus outbreak in a university hospital provided evidence for severe clinical features in patients with several underlying diseases. Clinical outcomes of norovirus infection were defined. Risk-factor analysis targeting underlying diseases and medication was performed using multivariate analyses. In five outbreak wards, 84 patients and 60 nurses were infected (an overall attack rate of 32% in patients, and 76% in nurses). The causative agent was the new variant Grimsby virus. Severe clinical features, including acute renal failure, arrhythmia and signs of acute graft organ rejection in renal transplant patients, were observed in seven (8.3%) patients. In multivariate analyses, cardiovascular disease (OR 17.1, 95% CI 2.17-403) and renal transplant (OR 13.0, 95% CI 1.63-281) were risk-factors for a potassium decrease of >20%. Age >65 years (OR 11.6, 95% CI 1.89-224) was a risk-factor for diarrhoea lasting >2 days. Immunosuppression (OR 5.7, 95% CI 1.78-20.1) was a risk-factor for a creatinine increase of >10%. Norovirus infections in patients with underlying conditions such as cardiovascular disease, renal transplant and immunosuppressive therapy may lead to severe consequences typified by decreased potassium levels, increased levels of C-reactive protein and creatine phosphokinase. In the elderly, norovirus infection may lead to an increased duration of diarrhoea. Therefore patients at risk should be hospitalised early and monitored frequently. Strict preventional measures should be implemented as early as possible to minimise the risk of nosocomial outbreaks.

A homozygous nonsense mutation (428G-->A) in the human secretor (FUT2) gene provides resistance to symptomatic norovirus (GGII) infections

Noroviruses (formerly Norwalk-like viruses) are a major cause of acute gastroenteritis worldwide and are associated with a significant number of nosocomial and food-borne outbreaks. In this study we show that the human secretor FUT2 gene, which codes for an alpha(1,2)-fucosyltransferase synthesizing the H-type 1 antigen in saliva and mucosa, is associated with susceptibility to norovirus infections. Allelic polymorphism characterization at nucleotide 428 for symptomatic (n = 53) and asymptomatic (n = 62) individuals associated with nosocomial and sporadic norovirus outbreaks revealed that homozygous nonsense mutation (428G-->A) in FUT2 segregated with complete resistance for the disease. Of all symptomatic individuals, 49% were homozygous (SeSe) and 51% heterozygous (Sese428) secretors, and none were secretor negative (se428se428), in contrast to 20% nonsecretors (se428se428) among Swedish blood donors (n = 104) (P < 0.0002) and 29% for asymptomatic individuals associated with nosocomial outbreaks (P < 0.00001). Furthermore, saliva from secretor-positive and symptomatic patients but not from secretor-negative and asymptomatic individuals bound the norovirus strain responsible for that particular outbreak. This is the first report showing that the FUT2 nonsecretor (se428se428) genotype is associated with resistance to nosocomial and sporadic outbreaks with norovirus.

Reverse genetics system for porcine enteric calicivirus, a prototype sapovirus in the Caliciviridae

A porcine enteric calicivirus (PEC), strain Cowden in the genus Sapovirus of the Caliciviridae family, can be propagated in a porcine kidney continuous cell line (LLC-PK) in the presence of bile acids in the cell culture medium. A full-length cDNA copy of the Cowden PEC genome was cloned into a plasmid vector directly downstream from the T7 RNA polymerase promoter, and capped RNA transcripts derived from this clone were infectious when transfected into LLC-PK cells. The recovery of PEC after transfection of RNA transcripts was dependent on the presence of bile acids, consistent with our recent identification of a bile acid-mediated signaling pathway required for PEC replication (Chang et al., Proc. Natl. Acad. Sci. USA 101:8733-8788, 2004). Recovery of virus was verified by detection of PEC antigen in transfected cells by immunofluorescence and enzyme-linked immunosorbent assays, direct observation of recovered viral particles by electron microscopy, and partial sequence analysis of their genomes (first 1,070 nucleotides) to differentiate them from tissue culture-adapted parental virus. The recovered virus retained its ability to infect piglets when administered by the oral route and showed an attenuated phenotype similar to that of the tissue culture-adapted parental virus. This reverse genetics system for PEC provides a new tool to study the molecular basis of replication and pathogenesis for caliciviruses associated with diarrheal disease.

Long-term features of norovirus gastroenteritis in the elderly

Noroviruses are important pathogens in both sporadic cases and outbreaks of gastroenteritis in humans. Noroviruses can affect individuals of all ages in a variety of settings, but are a particularly important cause of gastroenteritis in aged-care facilities. The relationship between clinical symptoms and norovirus excretion and the possible role of asymptomatic carriage of norovirus in the elderly are poorly understood. This study examined symptoms and norovirus excretion in elderly individuals associated with a norovirus outbreak in an aged-care facility. Ten individuals aged 79-94 years were recruited for the study. Nine were symptomatic and one was an asymptomatic contact who subsequently developed gastroenteritis. The 10 participants were interviewed regarding their clinical symptoms between two and six times over a three-week study period. One or more sequential faecal samples were collected from all participants over the same period and tested by reverse transcription-polymerase chain reaction for the presence of norovirus. Norovirus was detected in faecal samples from all 10 study participants and was commonly detected in formed stools. In the nine symptomatic participants, acute symptoms such as diarrhoea and vomiting had largely resolved by the third or fourth day of illness, but non-specific symptoms such as headache, thirst and vertigo could persist for as long as 19 days. Both acute and non-specific symptoms appeared to resolve and recur in some participants. The median excretion time for norovirus was 8.6 days (range 2-15 days) in symptomatic participants (N=5). There was no general relationship between the duration of norovirus excretion and the duration of either acute or non-specific symptoms. A faecal sample collected from the asymptomatic contact the day before gastroenteritis symptoms began was positive for norovirus, demonstrating prodromal excretion of norovirus. The results of this study indicate that infection control guidelines should consider both long-term excretion and prodromal excretion of norovirus, and the possibility that formed stools can contain norovirus. Furthermore, the care of elderly individuals recovering from a norovirus infection should take long-term non-specific clinical symptoms into account.

Association of histo-blood group antigens and susceptibility to norovirus infections

BACKGROUND

Noroviruses (NoVs) are the leading cause of viral gastroenteritis in humans of all ages. Challenge studies that used the NoV prototype strain Norwalk virus (NV) have shown that some individuals are not susceptible to infection, suggesting the absence of a receptor. Recent studies have identified histo-blood group antigens (HBGAs) as possible receptors. Being a nonsecretor and presence of HBGA type B were associated with protection against infection with NV, a genogroup (GG) I NoV.

METHODS

In the present retrospective study, we investigated the association between presence of HBGAs and the risk of infection with another NoV belonging to GGI (Hu/NV/I/Birmingham/93/UK). The study was done as part of an investigation of a waterborne outbreak in a group of schoolchildren and of a cohort of healthy adults. The ABH histo-blood group phenotype was determined by use of saliva or serum samples from these individuals.

RESULTS

Presence of HBGA type B was significantly correlated with a lack of susceptibility to infection with GGI NoV and with an absence of antibodies. No correlation was found with GGII NoV. Although the infection rate in nonsecretors was lower, this difference was not statistically significant, and several children lacking HBGAs in saliva were found to be infected.

CONCLUSIONS

Individuals with the HBGA type B may be protected against infection with GGI (but not GGII) NoVs. The association between susceptibility to NoV infection and being a secretor may be restricted to GGI NoV.

Bayesian model choice and infection route modelling in an outbreak of Norovirus

A data set from an outbreak of gastroenteritis in a school is analysed using a stochastic transmission model. The causative agent of the outbreak is believed to be a Norovirus, spread through person-to-person contact. Particular attention is given to the question of whether or not vomiting episodes enhance the spread of the virus via aerosol transmission. The methodology developed uses Bayesian model choice, implemented with reversible-jump Markov chain Monte Carlo methods. The methodology appears to be highly sensitive to assumptions made concerning the data, which provides some assurance that the conclusions are driven by observations rather than the underlying model and methodology.

Internet use and epidemiologic investigation of gastroenteritis outbreak

In March 2000, a large outbreak of gastroenteritis occurred in a community where a regional computer network provides free Internet access for 42% of the households. We conducted an epidemiologic investigation using the Internet for data collection. Norovirus was identified in stool samples of nine patients but not in the municipal water supply. Of households with access to the network, 19% participated in the survey. The overall attack rate by household was 63%. Drinking water from the nonchlorinated community water system was associated with illness (relative risk [RR] 1.6; 95% confidence interval [CI] 1.1 to 2.2); drinking water only from a private well was associated with decreased likelihood of illness (RR 0.3; 95% CI 0.1 to 0.8). Data collection through the Internet was efficient. Internet surveys may become more common in epidemiologic investigations and have the potential to provide data rapidly, enabling appropriate public health action. However, methods should be developed to increase response rates and minimize bias.

Nosocomial outbreak of norovirus gastroenteritis and investigation of ABO histo-blood group type in infected staff and patients

The blood groups were analysed of staff and patients (N=45) infected during two nosocomial outbreaks of norovirus gastroenteritis at a German University hospital. Persons with O phenotype were significantly less affected than was expected from the normal distribution of blood group types in Southwest Germany (OR 2.45; 95% CI 1.22-4.95; P=0.01).

Incidence and characteristics of endemic Norwalk-like virus-associated gastroenteritis

Endemic gastroenteritis associated with the Norwalk-like viruses (NLVs) is little understood. This study tested for NLV in gastroenteritis cases in 257 households in Melbourne, Australia, for the period September 1997 to February 1999 by a reverse transcription hemi-nested polymerase chain reaction. Positive samples were studied by nucleotide sequencing and phylogenetic analysis. NLV was detected in 73 (11.4%) of 638 faecal specimens tested. Twelve (1.9%) were NLV genogroup 1 (G1) and 61 (9.6%) NLV genogroup 2 (G2). Gastroenteritis symptoms associated with NLV G2/no other pathogens were significantly more severe than where no NLV was detected. NLV G1 and NLV G2 were detected in adults and children, males and females. NLV G2 incidence showed a marked seasonal periodicity with significant peaks in the Australian late spring/early summer periods. NLV G1 seasonality was significantly different from that of NLV G2. Seven major NLV clusters were identified by phylogenetic analysis.

Foodborne viral gastroenteritis: challenges and opportunities

Norwalk-like viruses (NLVs) are estimated to be the most common causes of foodborne disease in the United States, accounting for two-thirds of all food-related illnesses. The epidemiologic features and disease burden associated with NLVs have, until recently, been poorly understood because of the lack of sensitive detection assays and the underuse of available diagnostic tools. However, the application of molecular techniques to diagnose and investigate outbreaks of infection during recent years has led to a growing appreciation of the importance of these agents. NLVs are a principal cause of outbreaks of acute-onset vomiting and diarrhea in all age groups-most commonly, via contamination of uncooked foods by infected foodhandlers, but also via foods contaminated at their sources, such as oysters and raspberries. NLVs may also account for >10% of sporadic cases of gastroenteritis in children and adults. Future research will focus on the development of easy-to-use diagnostic assays based on antigen and antibody detection as well as vaccine development. Implementation of simple prevention measures, including correct food-handling practices, will continue to be a priority.

Natural history of human calicivirus infection: a prospective cohort study

We investigated the natural history of human Calicivirus infection in the community. Clinical information was obtained from 99 subjects infected with Norwalk-like viruses (NLV) and 40 subjects infected with Sapporo-like viruses (SLV) in a prospective, community-based cohort study. NLV infection was common in all age groups, whereas SLV infection was mainly restricted to children aged <5 years. Symptoms lasted for a median of 5 and 6 days for NLV and SLV infections, respectively. Disease was characterized by diarrhea during the first 5 days (87% of patients with NLV infection and 95% of patients with SLV infection) and vomiting on the first day (74% for NLV and 60% for SLV). Vomiting was less common in children aged <1 year (59% for NLV and 44% for SLV) than it was among children aged >/=1 year (>75% for NLV and >67% for SLV). Overall, NLV was detected in 26% of patients up to 3 weeks after the onset of illness. This proportion was highest (38%) for children aged <1 year. SLV shedding subsided after 14 days. These data show that the durations of disease and viral shedding of caliciviruses are longer than has been described elsewhere. Therefore, the impact of these infections may have been underestimated.

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.

Comparative pathogenesis of tissue culture-adapted and wild-type Cowden porcine enteric calicivirus (PEC) in gnotobiotic pigs and induction of diarrhea by intravenous inoculation of wild-type PEC

Porcine enteric calicivirus (PEC/Cowden) causes diarrhea in pigs, grows in cell culture, and is morphologically and genetically similar to the Sapporo-like human caliciviruses. Genetic analysis revealed that the tissue culture-adapted (TC) Cowden PEC has one distant and three clustered amino acid substitutions in the capsid region and 2 amino acid changes in the RNA polymerase region compared to wild-type (WT) PEC (M. Guo, K.-O. Chang, M. E. Hardy, Q. Zhang, A. V. Parwani, and L. J. Saif, J. Virol. 73:9625-9631, 1999). In this study, the TC PEC, passaged in a porcine kidney cell line, and the WT PEC, passaged in gnotobiotic (Gn) pigs, were used to orally inoculate 13 4- to 6-day-old Gn pigs. No diarrhea developed in the TC-PEC-exposed pigs, whereas moderate diarrhea developed in the WT-PEC orally inoculated pigs, persisting for 2 to 5 days. Fecal virus shedding persisting for at least 7 days was detected by both reverse transcription (RT)-PCR and antigen-enzyme-linked immunosorbent assay (antigen-ELISA) in both TC-PEC and WT-PEC orally inoculated pigs but not in mock-inoculated pigs. The PEC particles were detected by immunoelectron microscopy (IEM) in intestinal contents from all the WT-PEC-inoculated pigs, but not from the TC-PEC-inoculated pigs. Mild (duodenum and jejunum) or no (ileum) villous atrophy was observed in histologic sections of the small intestines of TC-PEC-inoculated pigs, whereas WT PEC caused mild to severe (duodenum and jejunum) villous atrophy and fusion. Scanning electron microscopy confirmed mild shortening and blunting of villi in the duodenum and jejunum of the TC-PEC-inoculated pigs, in contrast to moderate to severe villous shortening and blunting in the duodenum and jejunum of WT-PEC-inoculated pigs. Higher numbers of PEC antigen-positive villous enterocytes were detected by immunofluorescent (IF) staining in the proximal small intestine of the WT-PEC-inoculated pigs, in contrast to low numbers of PEC antigen-positive enterocytes in only one of four TC-PEC-inoculated pigs. No PEC antigen-positive cells were observed in the colon or extraintestinal tissues of all inoculated pigs or in the small intestine of one mock-inoculated pig. Thus, the TC PEC was at least partially attenuated (no diarrhea, mild lesions) after serial passage in cell culture. In further experiments, three 4- to 6-day-old Gn pigs were intravenously (i.v.) inoculated with WT PEC, and all pigs developed diarrhea and villous atrophy in the small intestines resembling that observed in the orally inoculated pigs. Fecal viral shedding persisting for 8 days was detected by both RT-PCR and antigen-ELISA, and PEC was detected by IEM in feces or intestinal contents. The PEC RNA and antigens (at low titers) were detected in acute-phase sera from all the WT-PEC i.v.-inoculated pigs and also from seven of nine of the WT-PEC orally inoculated pigs. Oral or i.v. inoculation of four additional pigs with the PEC-positive acute-phase sera induced diarrhea, small intestinal lesions, PEC shedding in feces, and seroconversion to PEC, confirming the occurrence of viremia during PEC infection, with infectious PEC present in acute-phase sera. No diarrhea, histopathologic changes, or IF staining in the small intestine or fecal or serum detection of PEC was evident in two pigs i.v. mock-inoculated or a pig inoculated i.v. with inactivated WT PEC. To our knowledge, this is the first report of an attenuated enteric calicivirus, the induction of diarrhea, and intestinal lesions in Gn pigs caused by i.v. inoculation of WT PEC and the presence of viremia following PEC infection.

Tissue distribution of virus replication in cats experimentally infected with distinct feline calicivirus isolates

Four specific pathogen-free (SPF) cats were each inoculated with one of two genetically and antigenically well characterized feline caliciviruses originally isolated from cats with acute respiratory disease (FCV-KS100/2), or with chronic stomatitis (FCV-KS20). Two cats of each group were euthanized at day 10 post infection and two cats at day 28. No clear differences between the clinical disease induced by the two isolates could be observed, and no apparent differences in the tissue spectrum were seen between day 10 and 28. No persistent virus shedding was observed over the 4-week period of this experiment.

Comparison of the primary signs induced by experimental exposure to either a pneumotrophic or a 'limping' strain of feline calicivirus

Two strains of feline calicivirus, one reportedly pneumotrophic (FPV 255) and the other associated with a limping syndrome (2280) were compared with respect to the signs induced in kittens after oronasal exposure. Neither strain induced severe upper respiratory symptoms, and both caused oral ulcers and lameness. However oral ulcers were more prevalent, and lameness and depression were more pronounced in the kittens which received strain 2280. Kittens which exhibited lameness also had elevated blood levels of alpha 1-acid glycoprotein. A decline in lymphocyte count was noted only in kittens which received strain 2280. These data demonstrate that despite reported antigenic and genetic differences between these strains, no distinct differences in pathogenicity could be determined.

Susceptibility of wild rabbits (Oryctolagus cuniculus) in the United Kingdom to rabbit haemorrhagic disease (RHD)

Adult wild rabbits from the southern UK, previously unexposed to rabbit haemorrhagic disease (RHD), were experimentally challenged with a UK strain of the virus in laboratory conditions. Initial serum antibodies were measured by an haemagglutination inhibition test and all seropositive rabbits, with reciprocal titres > 10, were protected against fatal infection. These results are consistent with the behaviour of laboratory and commercially bred rabbits in similar circumstances, and are relevant to consideration of the overall impact of RHD in wild populations.

Viral gastroenteritis: small round structured viruses, caliciviruses and astroviruses. Part I. The clinical and diagnostic perspective

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Historical background and classification of caliciviruses and astroviruses

Infections caused by caliciviruses, i.e., vesicular exanthema virus of swine were recognised as a major cause of economic loss in the 1930s. However, it was not until the application of electronmicroscopy in the 1970s that caliciviruses and astroviruses were recognised and proven to be a cause of diarrhoea and vomiting. The following review briefly describes the steps which have led to the development of diagnostic tests and enabled the characterization of several members of the Caliciviridae and Astroviridae. In the past five years this has culminated in the sequencing of their genomes and the expression of viral proteins. This in turn has led to the development of improved diagnostic tests e.g., RT-PCR and enzyme immunoassays, and may pave the way towards producing effective vaccines in the future.

[Feline calicivirus: a review]

The contagious coryza is an acute disease in cats, which is caused by feline calicivirus (FCV) and feline herpesvirus type-1 (FHV-1). FCV appears to be isolated more frequently from cats than FHV-1. This review summarizes the current knowledge about FCV and about the clinic, epidemiology, and pathogenesis of the disease induced. Particular problems of immunoprophylaxis of infection with FCV are also discussed.

Norwalk virus infection of volunteers: new insights based on improved assays

Norwalk virus infection is a common cause of gastroenteritis in humans. The clinical features and virologic and immunologic responses following oral administration of Norwalk virus to 50 volunteers were monitored. New ELISAs using recombinant virus particles as the antigen source were used to assess the pattern of virus shedding and the specific immune responses. Forty-one subjects (82%) became infected; 68% were symptomatic and 32% were asymptomatic. The proportion of subjects infected was similar for those with and without preexisting antibody (82% vs. 60%; P > .2). The magnitude of seroconversion was highest in subjects who had vomiting. The peak of viral shedding was between 25 and 72 h, and virus first appeared in stool at 15 h. Specimens collected 7 days after inoculation remained positive. These results show a higher infection rate, more subclinical infections, and longer virus excretion following Norwalk virus inoculation than previously recognized.