The 33- to 39-nm virus-like particles, tentatively designed as Sapporo agent, associated with an outbreak of acute gastroenteritis

Sapovirus: an emerging cause of childhood diarrhea

PURPOSE OF REVIEW

Sapovirus, a genus in the Caliciviridae family alongside norovirus, is increasingly recognized as an important cause of childhood diarrhea. Some challenges exist in our ability to better understand sapovirus infections, including the inability to grow sapovirus in cell culture, which has hindered diagnosis and studies of immunity. Another challenge is that individuals with sapovirus infection are commonly coinfected with other enteric pathogens, complicating our ability to attribute the diarrhea episode to a single pathogen.

RECENT FINDINGS

Development of molecular methods for sapovirus detection has increased our ability to measure disease prevalence. The prevalence of sapovirus varies between 1 and 17% of diarrhea episodes worldwide, with the highest burden in young children and older adults. Further, epidemiological studies have used novel approaches to account for the presence of coinfections with other enteric pathogens; one multisite cohort study of children under two years of age found that sapovirus had the second-highest attributable incidence among all diarrheal pathogens studied.

SUMMARY

Especially in settings where rotavirus vaccines have been introduced, efforts to reduce the overall burden of childhood diarrhea should focus on the reduction of sapovirus transmission and disease burden.

The role of electron microscopy in the rapid diagnosis of viral infections--review

Electron microscopy (EM) allows fast visualization of viruses in a wide range of clinical specimens. Viruses are grouped into families based on their morphology. Viruses from various families look distinctly and these morphological variances are the basis for identification of viruses by EM. The identification to the family level is often sufficient for the clinician or recognition of an unknown infectious agent. Diagnostic EM has two advantages over enzyme-linked immunosorbent assay and nucleic acid amplification tests. After a simple and fast negative staining, EM allows fast morphological identification and differential diagnosis of infectious agents contained in the specimen without the need for special considerations and/or reagents. Nevertheless, EM has the disadvantage of being unsuitable as a screening method.

Identification of a porcine calicivirus related genetically to human sapoviruses

Whether animals may act as reservoirs for human caliciviruses is unclear. By sequence analysis of a short fragment of the RNA-dependent RNA polymerase (RdRp) region, porcine sapovirus (SaV) strains that genetically resemble human SaVs have been detected in piglets, but more-informative sequences (capsid gene) were not available for a precise characterization. In this study, the 3' terminus (the 3' end of open reading frame 1 [ORF1], including the polymerase complex and the complete capsid; ORF2; and the 3' untranslated region) of one such human SaV-like strain, 43/06-18p3/2006/It, was determined, revealing that these viruses are more related genetically to human (47.4 to 54.9% amino acid identity) than to animal (35.2 to 44.7% amino acid identity) SaVs in the capsid gene. In addition, the recombination-prone RdRp-capsid junction region was highly conserved with those of human SaVs of genogroup GI. The presence of porcine viruses similar to human SaVs is a significant finding because of the potential for zoonotic infections or generation of porcine/human recombinants.

Small round viruses: classification and role in food-borne infections

Since the first observation of Norwalk virus in the electron microscope in 1972, many different small virus particles in the size range 20-40 nm have been described world-wide in association with outbreaks of gastroenteritis. Progress characterizing these agents has been hampered by the relatively small numbers of particles present in clinical material and the lack of success in culturing them. Although the relationship between some of these viruses remains confusing, a number of distinct groups has emerged, based on morphological features and limited physical data. Immuno-electron microscopy has proved valuable in detecting viruses but the addition of antibody can mask surface morphological features. Examination of viruses in negatively stained preparations without added antibody has revealed distinct morphological differences and viruses previously thought to be simply antigenic variants within the Norwalk group of viruses clearly belong to other groups. Preliminary evidence suggests that one human virus unrelated to Norwalk has a single-stranded DNA genome and is a parvovirus. Some groups have been implicated in outbreaks of food-borne gastroenteritis, particularly after the consumption of shellfish, and their role in other food-borne and water-borne outbreaks is being increasingly recognized.

Characterization of sapoviruses collected in the United Kingdom from 1989 to 2004

A fecal archive containing 115 sapovirus (SaV) strains detected in samples collected from 15 outbreaks and 98 sporadic cases of gastroenteritis between 1989 and 2004 in the UK were characterized in order to determine the genomic diversity within SaV co-circulating in the human population. Strains were characterized by partial sequencing of the genes encoding the RNA-dependent RNA polymerase (RdRp) region and/or the polymerase/capsid (Pol/Cap) junction of the open reading frame (Orf) 1. Overall, SaV of genogroup I genotype 1 (GI 1) were the predominant strains circulating in the UK in each year between 1989 and 2004. During 2004, GII 1 was the predominant strain. These two SaV types accounted for 89.5% of the sporadic cases and outbreaks in the UK. The remaining cases were caused by six other SaV genotypes. On the basis of partial sequencing of the RdRp and capsid encoding genes of strains, which did not show sufficient homology to any of the currently recognized genotypes, we propose the inclusion of a presumptive fourth genotype within genogroup I (GI 4).

Application of transmission electron microscopy to the clinical study of viral and bacterial infections: present and future

Transmission electron microscopy has had a profound impact on our knowledge and understanding of viruses and bacteria. The 1000-fold improvement in resolution provided by electron microscopy (EM) has allowed visualization of viruses, the existence of which had previously only been suspected as the causative agents of transmissible infectious disease. Viruses are grouped into families based on their morphology. Viruses from different families look different and these morphological variances are the basis for identification of viruses by EM.

Electron microscopy initially came to prominence in diagnostic microbiology in the late 1960s when it was used in the rapid diagnosis of smallpox, by differentiating, on a morphological basis, poxviruses from the less problematic herpesviruses in skin lesions. Subsequently, the technique was employed in the diagnosis of other viral infections, such as hepatitis B and parvovirus B19. Electron microscopy has led to the discovery of many new viruses, most notably the various viruses associated with gastroenteritis, for which it remained the principal diagnostic method until fairly recent times. Development of molecular techniques, which offer greater sensitivity and often the capacity to easily process large numbers of samples, has replaced EM in many areas of diagnostic virology. Hence the role of EM in clinical virology is evolving with less emphasis on diagnosis and more on research, although this is likely only to be undertaken in specialist centres. However, EM still offers tremendous advantages to the microbiologist, both in the speed of diagnosis and the potential for detecting, by a single test, any viral pathogen or even multiple pathogens present within a sample.

There is continuing use of EM for the investigation of new and emerging agents, such as SARS and human monkeypox virus. Furthermore, EM forms a vital part of the national emergency response programme of many countries and will provide a frontline diagnostic service in the event of a bioterrorism incident, particularly in the scenario of a deliberate release of smallpox virus.

In the field of bacteriology, EM is of little use diagnostically, although some bacterial pathogens can be identified in biopsy material processed for EM examination. Electron microscopy has been used, however, to elucidate the structure and function of many bacterial features, such as flagellae, fimbriae and spores and in the study of bacteriophages. The combined use of EM and gold-labelled antibodies provides a powerful tool for the ultrastructural localisation of bacterial and viral antigens.

Selection of more appropriate PCR primer pairs for improved efficiency in detecting Norwalk-like virus (NLV) RNA

A pair of primers, NV35 and NV36, and another pair of primers, NV81 and NV82/SM82, are commonly used for polymerase chain reaction (PCR) detection of Norwalk-like virus (NLV) genome RNA sequences in authorized test laboratories in Japan. However, the efficiency of NLV genome RNA detection with these primer pairs has been less than satisfactory. In the present study, we attempted to establish more appropriately matched primer pairs for improved detection of NLV genome RNA sequences using a combination of primers including NV35, NV36, NV81, NV82/SM82, SR33, and SRs (a mixture of 4 primers SR46, SR48, SR50, and SR52). We also evaluated appropriate primers for improved reverse transcription of NLV genome RNA. Stool samples used for detection of NLV included 18 samples collected from NLV-infected patients who ingested oysters (group 1) and 13 samples collected from those who did not ingest oysters (group 2). Reverse transcription of RNA genome with primer NV35 was less efficient compared with that with primer SR33 or NV81. When PCR products obtained with NV35 and NV36 as a pair of primers were subjected to gel electrophoresis, a strong extra band was detected compared with those obtained with other primer pairs. Since this extra band may represent heterodimeric or homodimeric hybrids, or intramolecular hybrids derived from these primers, this template-independent hybridization could lower the efficiency of primer-dependent polymerase reaction. Of 18 primer pairs, a pair of NV81 and SRs provided the best detection of PCR products following reverse transcription of NLV RNA with SR33 or NV81. The detection rate was 61% for both reverse transcription with SR33 and that with NV81. After reverse transcription using SR33 as a primer, nested PCR using a pair of NV81 and SRs following primary PCR using a pair of NV81 and NV82/SM82 increased the detection rate to 89% in group 1 and 100% in group 2.

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.

Small, round-structured viruses (SRSVs) associated with acute gastroenteritis outbreaks in Gifu, Japan

Two outbreaks of non-bacterial gastroenteritis occurred in Gifu prefecture in January 1989 and in January 1991. Both outbreaks were closely related to the consumption of raw oysters, and showed similar clinical features. Small, round-structured virus particles were found in patient stools in both outbreaks by electron microscopy. The role of these particles as the causative agents of the outbreaks were strongly suggested by immune electron microscopy and/or western-blotting immunoassay. When compared with SRSV-9 (Tokyo/SRSV/86-510) reported previously (Hayashi et al, J. Clin. Microbiol., 27: 1728-1733, 1989), it was found that these viral particles were antigenically similar to SRSV-9, and had a major structural protein of 63 kilodaltons (kDa). Further, the prevalence of this agent in Gifu area was examined by western blot antibody assay using 67 serum samples collected from the inhabitants in 1991. The results indicated the circulation of the same or antigenically similar agent in this area.

Demonstration of low molecular weight polypeptides associated with small, round-structured viruses by western immunoblot analysis

Small, round-structured viruses (SRSV) were detected in 14 of 300 fecal specimens obtained from patients with acute gastroenteritis by electron microscopy. These SRSV strains were morphologically indistinguishable from one another. While 11 of these strains had a single usual major structural protein with molecular weight of 63,000 (63K) daltons (p63), interestingly, three strains possessed a single major structural protein with molecular weight of 33K daltons (p33). Treatments of p63-SRSV with proteolytic enzymes or denaturating reagents did not affect the molecular weight of p63, and the p33 was not detectable by Western immunoblot in the ultracentrifugal supernatant of the p63-SRSV suspension. These results suggest that the p33 is neither a definitive subunit of p63 nor disintegrated component derived from the p63-SRSV but a novel polypeptide of SRSV. Immune electron microscopy and Western immunoblot analyses indicated that p63- and p33-SRSVs may share an antigenic determinant(s).

Western blot (immunoblot) assay of small, round-structured virus associated with an acute gastroenteritis outbreak in Tokyo

Small, round-structured virus (SRSV) was detected in a stool specimen of a patient during an acute gastroenteritis outbreak in Tokyo and was tentatively named SRSV-9. SRSV-9 was purified by sucrose velocity gradient centrifugation after CsCl density gradient centrifugation. The buoyant density of SRSV-9 appeared to be 1.36 g/ml in CsCl. A Western blot (immunoblot) assay using the biotin-avidin system revealed that SRSV-9 was antigenically related to the Hawaii agent but distinct from the Norwalk agent and contained a single major structural protein with a molecular size of 63.0 +/- 0.6 kilodaltons. The prevalence of SRSV-9 infection in Tokyo was surveyed by the Western blot antibody assay by using a crude virus preparation as the antigen. Seroconversion was observed in 56.5% of the patients involved in the outbreaks from which SRSV was detected by electron microscopy.

Prevalence of small round structured virus infections in acute gastroenteritis outbreaks in Tokyo

During the three-year period from 1984 to 1987, 506 acute gastroenteritis outbreaks involving 14,383 patients were reported to the Bureau of Public Health, Tokyo Metropolitan Government. Eighty (4,324 patients) of 150 outbreaks (4,860 patients) from which etiologic agents were not identified were subjected to virological investigation. Spherical particles of 28-32 nm in diameter with capsomere-like structures on the surface were detected in patients' stool specimens. Buoyant density of the particles appeared to be 1.36 to 1.40 g/ml in CsCl. Seroconversion to the particles was observed in patients by immune electron microscopy. From these observations, we concluded that the detected particles were members of small round structured virus (SRSV), and that they were implicated in the etiologically ill-defined outbreaks encountered. Prevalence of SRSV infections in these outbreaks was examined by electron microscopy. SRSV was positive in 83.8% of the outbreaks, and 96.4% of the cases. SRSV-positive outbreaks usually occurred during winter in contrast to bacterial outbreaks which often occurred in the summer season. Of 80 outbreaks examined, 53 were associated with the ingestion of oysters, and the remaining 27 mostly with food other than oysters. Oyster-associated outbreaks usually occurred on a small scale, while unassociated ones on diverse scales ranged from family clusters to large outbreaks.

Viruses and virus-like particles in the faeces of dogs with and without diarrhoea

Negative staining electron microscopy was used to identify viruses in 157 normal and 29 diarrhoeal faecal samples collected from 156 dogs admitted to an animal shelter during an 8 month period (March to October) in 1982. Seven distinct viral types were detected: 21-26 nm parvovirus-like particles, 28-31 nm astrovirus-like particles, a previously undescribed 34-35 nm "round" virus particle, coronavirus, coronavirus-like particles ( CVLP ), rotavirus and papova-like virus. Parvovirus-like particles alone were detected in 14 diarrhoeal and 50 normal faeces, astrovirus-like particles in 3 normal faeces, "round" viruses in 4 normal faeces, coronavirus in 2 diarrhoeal and 5 normal faeces, CVLP in one diarrhoeal and one normal faeces, rotavirus in 2 normal faeces, papova-like virus in one normal faeces, both parvovirus-like particles and coronavirus in 2 diarrhoeal and 2 normal faeces, parvovirus-like particles and rotavirus in one normal faeces and parvovirus-like and papova-like virus in one normal faeces. The significance of these findings in canine and human disease is discussed.

Characterization of a calici-like virus (Newbury agent) found in association with astrovirus in bovine diarrhea

A bovine calici-like virus and astrovirus, present in the same fecal sample from an outbreak of diarrhea, were separated from each other by calf passage. The calici-like virus (Newbury agent SRV-1) caused anorexia, diarrhea, and xylose malabsorption in gnotobiotic calves aged 17 to 60 days, whereas the bovine astrovirus was nonpathogenic in similar calves. The calici-like virus was shown to be antigenically distinct from a previously described isolate (Newbury agent SRV-2) by two-way cross-protection experiments in calves; calves immune to homologous challenge became clinically ill and excreted virus when challenged with the heterologous virus.

Outbreak of infantile gastroenteritis due to type 40 adenovirus

Genetic and antigenic characterisation was performed on a strain of adenovirus (EAd) isolated from an outbreak of gastroenteritis which occurred in an orphanage in the City of Sapporo, in the room housing the eldest children, who ranged in age from 14 to 22 months. 7 of the 11 children housed in that room had diarrhoea between July 11 and July 22, 1982. All 7 shed adenoviruses detectable by electron microscopy in their stools. Immune electron microscopy showed that all patients as well as the healthy contacts sharing the room underwent seroconversion to EAd. There was no homology, or very slight homology, between DNA of EAd and those of adenoviruses belonging to subgroups A to E. Antigenically EAd was closely related to type 40 adenovirus, so far the sole member of the newly identified subgroup F. This outbreak of gastroenteritis is the first in which the causative agent has been identified as being a member of subgroup F adenoviruses.

Potential spectrum of etiological agents of viral enteritis in hospitalized infants

Fecal specimens were obtained from 1,160 infants and young children with acute nonbacterial gastroenteritis over a period of 2 years. A total of 100 specimens were obtained from age-matched asymptomatic controls. The specimens were examined for the presence of viruses by electron microscopy. Viruses or virus-like particles frequently associated with enteritis were detected in 27% (314 of 1,160) of the symptomatic patients. No viruses or virus-like particles were detected in the 100 control subjects. Rotavirus was detected in 73% (230 of 314) of the virus-positive samples. The mean age of rotavirus-positive patients was 11.5 months, although the patients ranged in age from 2 weeks to 5 years. Of the symptomatic patients, 45 (14%) exhibited small virus-like particles (15 to 40 nm) in the feces in the absence of any other detectable pathogen. Some of the virus-like particles observed in these patients appeared to be similar to astrovirus, and some appeared to be similar to the Otofuke agent or possibly minireovirus. Significantly, however, the mean age of infants with enteritis from whom these small virus-like particles were recovered was 4.5 months (range, 10 days to 19 months). Our findings confirmed the already-known fact that rotaviruses constitute the most important cause of viral enteritis in young children. In addition, small viruses may be an important cause of gastroenteritis in infants under 5 months of age.

The electron microscopical and physical characteristics of small round human fecal viruses: an interim scheme for classification

Many of the small round human fecal viruses implicated in outbreaks of nonbacterial gastroenteritis have been collected together and examined under the electron microscope. Negatively stained preparations without the addition of antibody were used so that the surface morphology of the virus particles remained clearly visible. It was apparent that several viruses, previously thought to be simply antigenic variants within the Norwalk group of viruses, show distinct morphological differences and quite clearly belong to other virus groups. By comparing the features of all the viruses examined in this study, both with each other and with standard cell culture strains of enterovirus, parvovirus, and calicivirus, it has been possible to propose an interim classification scheme, based primarily on the morphological appearance of the particles and supported by estimations of size and buoyant density.