Microtiter solid-phase radioimmunoassay for detection of human calicivirus in stools

Epidemiology of Acute Gastroenteritis Outbreaks Caused by Human Calicivirus (Norovirus and Sapovirus) in Catalonia: A Two Year Prospective Study, 2010-2011

Background

The epidemiology of cases of acute gastroenteritis (AGE) of viral etiology is a relevant public health issue. Due to underreporting, the study of outbreaks is an accepted approach to investigate their epidemiology. The objective of this study was to investigate the epidemiological characteristics of AGE outbreaks due to norovirus (NoV) and sapovirus (SV) in Catalonia.

Material and Methods

Prospective study of AGE outbreaks of possible viral etiology notified during two years in Catalonia. NoV and SV were detected by real time reverse transcription polymerase (RT-PCR).

Results

A total of 101 outbreaks were registered affecting a total of 2756 persons and 12 hospitalizations (hospitalization rate: 0.8x1,000,000 persons-year); 49.5% of outbreaks were foodborne, 45.5% person to person and 5% waterborne. The distribution of outbreaks according to the setting showed a predominance of catering services (39.6%), nursing homes and long term care facilities (26.8%) and schools (11.9%). The median number of cases per outbreak was 17 (range 2–191). The total Incidence rate (IR) was 18.3 per 100,000 persons-years (95%CI: 17.6–19.0). The highest IR was in persons aged ≥65 years (43.6x100,000 (95% CI: 41.0–46.2)) (p<0.001). A total of 1065 samples were analyzed with a positivity rate of 60.8%. 98% of positive samples were NoV (GII 56.3%; GI 4.2%; GII+GI 4.2%; non- typable 33.0%). SV was identified in two person-to-person transmission outbreaks in children.

Conclusions

These results confirm the relevance of viral AGE outbreaks, both foodborne and person-to-person, especially in institutionalized persons. SV should be taken into account when investigating viral AGE outbreaks.

Quantification and genotyping of human sapoviruses in the Llobregat river catchment, Spain

Human sapoviruses (SaVs) were quantified and characterized in an 18-month survey conducted along the Llobregat river catchment area in Spain. Sample types included freshwater, untreated and treated wastewater, and drinking water. All genogroups were recovered, and a seasonal distribution was observed. This is the first report of SaV quantification and genotyping in the environment outside Japan.

Molecular characterization and phylogenetic analysis of the complete genome of a porcine sapovirus from Chinese swine

Background

Porcine sapovirus was first identified in the United States in 1980, hitherto, several Asian countries have detected this virus. In 2008, the first outbreak of gastroenteritis in piglets caused by porcine sapovirus in China was reported. The complete genome of the identified SaV strain Ch-sw-sav1 was sequenced and analyzed to provide gene profile for this outbreak.

Methods

The whole genome of Ch-sw-sav1 was amplified by RT-PCR and was sequenced. Sequence alignment of the complete genome or RNA dependent RNA polymerase (RdRp) gene was done. 3' end of ORF2 with 21-nt nucleotide insertion was further analyzed using software.

Results

Sequence analysis indicated that the genome of Ch-sw-sav1 was 7541 nucleotide long with two ORFs, excluding the 17 nucleotides ploy (A) at the 3' end. Phylogenetic analysis based on part of RdRp gene of this strain showed that it was classified into subgroup GIII. Sequence alignment indicated that there was an inserted 21-nt long nucleotide sequence at the 3' end of ORF2. The insertion showed high antigenicity index comparing to other regions in ORF2.

Conclusion

Ch-sw-sav1 shared similar genetic profile with an American PEC strain except the 21-nt nucleotide at the 3' end of ORF2. The insert sequence shared high identity with part gene of Sus scrofa clone RP44-484M10.

Antigenic diversity of human sapoviruses

Sapovirus (SaV) is a causative agent of gastroenteritis. On the basis of capsid protein (VP1) nucleotide sequences, SaV can be divided into 5 genogroups (GI-GV), of which the GI, GII, GIV, and GV strains infect humans. SaV is uncultivable, but expression of recombinant VP1 in insect cells results in formation of viruslike particles (VLPs) that are antigenically similar to native SaV. In this study, we newly expressed SaV GII and GIV VLPs to compare genetic and antigenic relationships among all human SaV genogroups. Hyperimmune antiserum samples against VLPs reacted strongly with homologous VLPs. However, several antiserum samples weakly cross-reacted against heterologous VLPs in an antibody ELISA. Conversely, an antigen ELISA showed that VLPs of SaV in all human genogroups were antigenically distinct. These findings indicate a likely correspondence between SaV antigenicity and VP1 genogrouping and genotyping.

Human sapoviruses: genetic diversity, recombination, and classification

The family Caliciviridae contains four genera Sapovirus, Norovirus, Lagovirus and Vesivirus, which include Sapporo virus (SaV), Norwalk virus (NoV), Rabbit hemorrhagic disease virus (RHDV) and Feline calicivirus (FCV), respectively. SaV is a causative agent of gastroenteritis in children and adults. SaV can be divided into five genogroups (GI-GV), among which GI, GII, GIV and GV are known to infect humans, whereas SaV GIII infects porcine species. Detection methods include ELISA, RT-PCR and real-time RT-PCR. Since few SaV studies have been conducted, it is difficult to draw correlations between or conclusions about rates of incidence, detection and overall prevalence. Nevertheless, most studies agree that SaV infection is more frequent in young children than adults and that infection in children almost always occurs by 5 years of age. In addition, children at day-care centres and institutions are at greatest risk of SaV-associated infection and transmission. Recently, a number of important findings concerning human SaV were discovered. SaV strains were detected in water samples, which included untreated wastewater specimens, treated wastewater samples and river samples. SaV strains were also detected in shellfish samples destined for human consumption, and recombinant SaV strains were identified in a number of different countries. The purpose of this review was to highlight the current knowledge of human SaV, which appears to be an increasingly important virus causing gastroenteritis in humans.

Genetic analysis of calicivirus genomes detected in intestinal contents of piglets in Japan

Enteric caliciviruses, noroviruses, and sapoviruses are emerging pathogens responsible for diarrhea or gastroenteritis in their respective hosts. In this study, swine enteric caliciviruses were detected in ten samples of intestinal contents from 24 piglets in Japan by reverse transcription-polymerase chain reaction using a broadly reactive primer pair (P290/289) that targeted the highly conserved RNA polymerase regions of the enteric caliciviruses. From the positive samples, the entire viral genome of strain K7/JP and 3'-end parts of the genomes of strains K5/JP and K10/JP were cloned and sequenced. K7/JP had an RNA genome of 7144 bases, excluding its 3' poly (A) tail. The K7/JP genome possessed two open reading frames and characteristics common to sapoviruses. In phylogenetic analysis using amino acid sequences of VP1, K5/JP was demonstrated to be close to the noroviruses previously detected in pigs, and K7/JP and K10/JP were considered to be classified as a new genogroup of sapoviruses.

Development of an antigen ELISA to detect sapovirus in clinical stool specimens

Human sapovirus (SaV) strains are etiological agents of mild and/or acute gastroenteritis in children and adults. In this study, we describe the development of a novel antigen enzyme-linked immunosorbent assay (ELISA) detection system that was based on hyperimmune rabbit and guinea pig antisera raised against SaV genogroup I (GI) virus-like particles. The ELISA had 100% specificity, and sensitivities of 60% and 25% when compared to single-round PCR and nested PCR, respectively. Our results have shown the ELISA was useful in detecting SaV GI antigens in clinical stool specimens collected two days after the onset of illness.

Sequence diversity of human caliciviruses recovered from children with diarrhea in Mendoza, Argentina, 1995-1998

Human caliciviruses were detected by EIA and/or RT-PCR in stool specimens from children with diarrhea treated at out- or in-patient facilities between 1995 and 1998 in Mendoza, Argentina. Mexico virus-like strains detected by primers NV36/51 were transiently prevalent in 1995/1996. Significantly more human caliciviruses were detected when primers were designed from contemporaneously circulating strains. Nucleotide sequences of a highly conserved region in the RNA polymerase gene of 10 selected human caliciviruses were determined. Eight strains were Norwalk-like viruses and two strains were Sapporo-like viruses. Seven of the eight Norwalk-like viruses also were positive by the recombinant Mexico virus antigen EIA. The seven Mexico virus EIA-positive strains revealed two patterns in the RNA polymerase sequences: two strains were closest to Mexico virus and the other five strains were closest to Lordsdale virus. One of the five "Lordsdale" viruses was found to be a naturally occurring recombinant between the Mexico virus and Lordsdale human calicivirus genetic clusters [Jiang et al., (1999b) Archives of Virology 144:2377-2387]. The Mexico virus EIA-negative strain had 73-77% nucleotide identity with the closest related Norwalk-like viruses, indicating it might belong to a new genetic cluster of the Norwalk-like virus genus. The two Sapporo-like viruses were distinct genetically; one belonged to the Houston/90 or Parkville cluster and the other to a new cluster. Some strains appeared to have short periods of prevalence and locally adapted primer pairs significantly increased detection rates. The finding of high diversity of circulating strains, including recombinant strains and strains with previously unrecognized genetic identities, highlights a need for studies of human caliciviruses in these children and other populations.

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.

Diagnosis of noncultivatable gastroenteritis viruses, the human caliciviruses

Gastroenteritis is one of the most common illnesses of humans, and many different viruses have been causally associated with this disease. Of those enteric viruses that have been established as etiologic agents of gastroenteritis, only the human caliciviruses cannot be cultivated in vitro. The cloning of Norwalk virus and subsequently of other human caliciviruses has led to the development of several new diagnostic assays. Antigen detection enzyme immunoassays (EIAs) using polyclonal hyperimmune animal sera and antibody detection EIAs using recombinant virus-like particles have supplanted the use of human-derived reagents, but the use of these assays has been restricted to research laboratories. Reverse transcription-PCR assays for the detection of human caliciviruses are more widely available, and these assays have been used to identify virus in clinical specimens as well as in food, water, and other environmental samples. The application of these newer assays has significantly increased the recognition of the importance of human caliciviruses as causes of sporadic and outbreak-associated gastroenteritis.

Expression and characterization of Sapporo-like human calicivirus capsid proteins in baculovirus

Sapporo-like caliciviruses reveal typical calicivirus morphology and cause acute gastroenteritis. This study describes the expression in baculovirus of capsid proteins of two Sapporo-like calicivirus strains (Hou/86 and Hou/90). Eight different constructs of the capsid genes were compared for production of the proteins. Constructs containing short (9 or 19 nt) upstream sequences failed to produce capsid proteins but extension of the upstream sequence to 73 nt resulted in production of capsid proteins. Expressed capsid protein with the MEG tri-peptide as the N-terminus self-formed virus-like particles (VLPs). Expressed protein with an upstream AUG failed to form VLPs. Addition of His-tag to the N-terminus of capsid protein also blocked VLP formation. Of three Norwalk-Hou/90 chimeric capsid gene constructs, one resulted in production of chimeric capsid and the protein did not form VLPs. Recombinant capsid proteins for each of Hou/86 and Hou/90 were further characterized. The expressed capsid antigens of the two strains were antigenically distinct but shared a common epitope(s). Further study of these proteins should allow development of immunologic assays for diagnosis and should help to clarify the epidemiology of Sapporo-like caliciviruses in humans.

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

Images

Dot blot hybridization with a cDNA probe derived from the human calicivirus Sapporo 1982 strain

A dot blot hybridization assay was developed for detection of human calicivirus/Sapporo/82/J (HuCV/Sa/82) or strains closely related to HuCV/Sa/82 in stool specimens. The cDNA derived from the RNA-dependent RNA polymerase (RDRP) region of HuCV/Sa/82 was used as a positive probe and the pBR322 DNA as a negative control probe. Both probes were labeled with digoxigenin and the products of hybridization reaction were detected with an anti-digoxigenin antibody-alkaline phosphatase conjugate. This assay was specific for HuCV/Sa/82 and for HuCV antigenically related to HuCV/Sa/82. The lower limit of sensitivity of this assay was estimated to be about 10(5) physical particles or 10 pg of cDNA, similar to that of the previously developed ELISA for HuCV. In 1273 stool specimens obtained from children with acute gastroenteritis in Sapporo, Japan, 110 (8.6%) contained small round structured viruses by EM and 23 (1.8%) were positive for HuCV antigenically related to HuCV/Sa/82 by either the hybridization assay or ELISA. A higher positive rate was obtained with the dot blot assay (21%) than by ELISA (10%), suggesting that the dot blot assay either detects HuCV more broadly than the ELISA or detects HuCV covered with fecal antibodies which interrupt antigen-antibody reactions in the ELISA. Negative results for detection of Norwalk virus (NV) cDNA and feline calicivirus (FCV) RNA by both this assay and the ELISA indicated that the HuCV/Sa/82 strain is distinct antigenically and genetically from NV and FCV.

Genetic and antigenic diversity of human caliciviruses (HuCVs) using RT-PCR and new EIAs

RT-PCR using primers from conserved regions of calicivirus genomes, followed by sequencing, permits characterization of genetic variation within the family. EIAs based on baculovirus-expressed viral capsid proteins and hyperimmune antisera against the capsid proteins were developed to detect HuCV antigens and antibodies. Serologic surveys using recombinant Norwalk virus (rNV) and recombinant Mexico virus (rMX, a SMA-like virus) EIAs showed that infections by HuCVs are common and that children acquire antibodies to HuCVs at an early age in both developed and developing countries. Three HuCV genogroups have been described that are represented by Norwalk virus (NV), Snow Mountain agent (SMA), and Sapporo virus, although recently accumulated sequences of HuCV strains indicate these genogroups can be further divided. These genogroups also correspond to distinct antigenic groups based on the results of the recombinant EIAs. The three genogroups co-circulate and have a worldwide distribution, although the SMA genogroup seems to be predominant currently. Application of these new assays for further characterization of the genetic and antigenic properties of HuCVs remains an important task for HuCV research.

The epidemiology of human calicivirus/Sapporo/82/Japan

Based on genome analysis of the RNA-dependent RNA polymerase region, it has been proposed that human caliciviruses (HuCV) can be classified into at least three genogroups: genogroup I is represented by Norwalk virus (NV), genogroup II by Snow Mountain agent (SMA) and genogroup III by HuCV/Sapporo/82/Japan (HuCV/Sa/82/J) virus. HuCV/Sa/82/J strain is genetically unique and more closely related to animal caliciviruses than are other known HuCVs, such as NV and SMA. HuCV/Sa/82/J strain was detected in four outbreaks of HuCV gastroenteritis occurring between 1977 and 1982 in an infant home in Sapporo. The HuCVs detected from these four outbreaks all showed a typical "Star of David" configuration by electron microscopy (EM), and they were identical antigenically and genetically. This strain has also been detected in other prefectures in Japan, as well as in the USA, UK, Saudi Arabia and Kenya. Seroepidemiological studies have shown a worldwide distribution of this virus, including Japan, USA, UK, Southeast Asia, Canada, China and Kenya. This virus has been circulating in Sapporo for at least 19 years (1977-1995). HuCV/Sa/82/J strain is thought to be one of the common causes of viral gastroenteritis worldwide. The HuCV/Sa/82/J strain has been detected mainly in infants. Age-related prevalence of antibody to this strain also shows that infections commonly occur in children less than 5 years old, although viruses in the NV and SMA genogroups commonly infect adults. The pattern of acquisition of antibodies to strain HuCV/Sa/82/J is similar to that of other common viral infections. HuCV/Sa/82/J strain is unique virologically and clinically among caliciviruses.

Molecular characterization of a human calicivirus with sequence relationships closer to animal caliciviruses than other known human caliciviruses

cDNA clones were produced from a morphologically typical human calicivirus (HuCV) in stool specimens collected in 1982 during an outbreak of gastroenteritis in Sapporo, Japan. The cDNA clones were generated separately in two laboratories by reverse transcriptase-polymerase chain reaction (RT-PCR) using primers 35 and 36 derived from Norwalk virus. The RT-PCR product from six specimens was of the predicted size, had a continuous protein encoding frame on the positive strand, and contained GLPS and YGDD amino acid motifs at the predicted distance from the primers. RT-PCR amplification with primer 35 and a HuCV/Sapporo-specific primer 36 of four HuCV/Sapporo-positive stool specimens from a 1986 Houston day care center outbreak yielded products with 93% nucleotide and 99% predicted amino acid sequence identity with the HuCV/Sapporo strain from the 1982 outbreak. The HuCV/Sapporo strains are genetically distinct from previously characterized HuCVs and more closely related to known animal CVs than other known HuCVs.

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

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

Human viral gastroenteritis

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

Detection of human calicivirus antigen and antibody by enzyme-linked immunosorbent assays

Enzyme-linked immunosorbent assays (ELISAs) were developed to detect human calicivirus (HCV) antigen and antibody to HCV. The ELISAs were specific for HCV and as sensitive as a previously developed radioimmunoassay. These ELISAs were used to search for evidence of HCV infection in the United States, where HCV gastroenteritis has rarely been reported. One hundred sixty-three stool samples collected from children hospitalized with diarrhea were examined; one sample was positive in the ELISA. Typical calicivirus particles were found in this stool sample, and these particles reacted with a hyperimmune guinea pig anti-HCV serum by immune electron microscopy. The age-related acquisition of antibody to HCV in hospitalized infants and children (from birth to 19 years old) without gastroenteritis and in healthy adults was also evaluated. The pattern of acquisition of antibody to HCV was similar to that for group A rotaviruses, namely, beginning in infancy and becoming 100% by the age of 4 years. These data suggest that HCV is associated with infantile gastroenteritis in the United States, that infections with HCV are common, and that many infections with HCV (Sapporo strain) may not require hospitalization.

Detection of antibody to group B adult diarrhea rotaviruses in humans

Group B rotaviruses have been responsible for annual epidemics of severe diarrhea affecting both adults and children in China. We developed a specific and sensitive enzyme-linked immunosorbent blocking assay to detect antibody to group B rotaviruses that will be useful to assess the role of group B rotavirus infections as a cause of human gastroenteritis. We tested 219 human sera and 18 immunoglobulin pools collected from eight countries for antibodies to both group A and group B rotaviruses. Overall, a low proportion (10 of 237 or 4.2%) of sera contained antibody to group B rotaviruses. Antibody to group B rotavirus was detected in only 1 of 155 serum samples from healthy or hospitalized individuals in the United States, including patients with the chronic inflammatory bowel diseases Crohn's disease and ulcerative colitis. No antibody was detected in 15 serum samples from Australia and from an outbreak of gastroenteritis on a cruise ship or in nine immunoglobulin pools from Japan and the United Kingdom. Antibody to group B rotaviruses was detected in 8 convalescent-(but not acute-)phase serum samples from Chinese patients with group B gastroenteritis, in five immunoglobulin pools from China, in 1 of 6 serum samples from Chinese students in the United States, and in 1 each of 10 serum samples from Kenya, 20 from Thailand, and 15 from Canada. In contrast, most of these samples (226 of 237 or 95.4%) had antibody to group A rotaviruses. These results indicate that human infection with group B rotavirus has not been widespread in areas outside China. Seroconversion observed between the acute-and convalescent-phase serum samples from China also suggests that infections with this virus are primary infections. Continued surveillance for this new group of rotaviruses should determine whether the many susceptible people become infected of whether other factors influence the severe pathogenicity of human infections with these viruses in China.

Seroepidemiological survey of the prevalence of antibodies to a strain of human calicivirus

Batches of pooled immune globulins and sera were tested by immune electron microscopy (IEM) for the presence of antibodies to a strain of human calicivirus (HCV, UK1). The results show that this strain of HCV is prevalent throughout many parts of the world and that the majority of the population experience infection by the age of 12 years. The survey carried out in the United Kingdom indicates that the presence of maternal antibody correlates with some degree of protection during the first few weeks of life; the peak incidence of cases and acquisition of antibody occur between 3 months and 6 years. Tests on sera from Japan show a similar pattern of acquisition of antibodies and demonstrate that infection with more than one strain of HCV commonly occurs during childhood.

Demonstration of calicivirus in human faeces by immunosorbent and immunogold-labelling electron microscopy methods

Immunosorbent electron microscopy (ISEM) and immuno-gold staining (IGS) electron microscopy methods have been applied to human faeces, shown by direct electron microscopy (EM) to contain calicivirus. Caliciviruses were successfully trapped on grids coated with positive rabbit or human antisera against calicivirus, but not with negative sera. Caliciviruses were specifically labelled with gold particles, when treated with positive rabbit or human antisera against calicivirus followed by protein A-gold and goat anti-rabbit or anti-human IgG gold conjugates in an indirect method in suspension. Goat anti-human IgM gold complexes did not react with the available antisera. Attempts to label caliciviruses trapped on the grids were unsuccessful. No cross-reactions were observed with Norwalk agent-like particles, hepatitis A virus or poliovirus type 3 by any of the methods. The results indicate that ISEM and IGS may be useful techniques for detection and identification of small viruses present in low concentrations in faeces.

Prevalence of antibody to human calicivirus in Japan and Southeast Asia determined by radioimmunoassay

Three hundred ninety single sera from adults in Japan, Indonesia, Singapore, and Papua New Guinea were tested for antibodies to human calicivirus (HCV) by a radioimmunoassay blocking test. A high prevalence of antibodies was observed in samples collected in Japan and Southeast Asia. Of 240 serum specimens collected from five districts in Japan, 209 (87.1%) were positive for HCV antibodies. No striking difference in the prevalence of the antibody was seen among those districts. In sera collected in Southeast Asia, 84.0% (126 of 150) had antibodies to HCV (70% [35 of 50] in Singapore, 88% [44 of 50] in Indonesia, and 94% [47 of 50] in Papua New Guinea). These results indicate that HCV is a common infectious agent in Japan and Southeast Asia.

Virus-like particles with T = 19 icosahedral symmetry in a human gastroenteritis stool

Virus-like particles not previously described were observed in a human gastroenteritis stool using negative-stain TEM. The stool was among a number of acute-phase illness stools which had been collected in Egypt during 1980. The particles measured 65–70 nm in diameter, and it was possible to detect individual capsomeres on many of these particles. The capsomeric pattern identified on the particles corresponded to an icosahedrally symmetric T = 19 capsid. Distinctive five-fold vertices, usually appearing as darker spots on the capsid, were an additional feature of these particles. The capsid structure, which is skew, could readily be distinguished from the T = 25 capsid of adenovirus and the holey capsids of rotavirus and reovirus. Antibody to the particles was detected in both the shedding individual's acute- and convalescent-phase serum specimens using IEM, although an antibody increase was not demonstrated.