Relationship between genotypes and serotypes of genogroup 1 recoviruses: a model for human norovirus antigenic diversity

Human norovirus (NoV) research greatly relies on cell culture-propagable surrogate caliciviruses, including murine NoVs and the prototype 'recovirus' (ReCV), Tulane virus. However, the extreme biological diversity of human NoVs cannot be modelled by a uniform group of viruses or single isolate. Based on a diverse group of recently described ReCVs, a more advanced model reflecting human NoV biological diversity is currently under development. Here, we have reported the genotypic and serotypic relationships among 10 G1 ReCV isolates, including Tulane virus and nine other recent cell culture-adapted strains. Based on the amino acid sequences of virus capsid protein, VP1, and classification constraints established for NoVs, G1 ReCVs were separated into three genotypes, with variable organization of the three open reading frames. Interestingly, cross-neutralization plaque assays revealed the existence of four distinct serotypes, two of which were detected among the G1.2 strains. The amino acid (aa) difference between the two G1.2 ReCV serotypes (12%) was less than the minimum 13% difference established between NoV genotypes. Interestingly, one of the G1.3 ReCVs was equally neutralized by antisera raised against the G1.3 (6% aa difference) and G1.1 (25% aa difference) representative strains. These results imply the existence of a large number of human NoV serotypes, but also shared cross-neutralization epitopes between some strains of different genotypes. In conclusion, the newly developed ReCV surrogate model can be applied to address biologically relevant questions pertaining to enteric CV diversity.

Experimental inoculation of juvenile rhesus macaques with primate enteric caliciviruses

BACKGROUND

Tissue culture-adapted Tulane virus (TV), a GI.1 rhesus enteric calicivirus (ReCV), and a mixture of GII.2 and GII.4 human norovirus (NoV)-containing stool sample were used to intrastomacheally inoculate juvenile rhesus macaques (Macaca mulatta) in order to evaluate infection caused by these viruses. METHODOLOGY & FINDINGS: Two of the three TV-inoculated macaques developed diarrhea, fever, virus-shedding in stools, inflammation of duodenum and 16-fold increase of TV-neutralizing (VN) serum antibodies but no vomiting or viremia. No VN-antibody responses could be detected against a GI.2 ReCV strain FT285, suggesting that TV and FT285 represent different ReCV serotypes. Both NoV-inoculated macaques remained asymptomatic but with demonstrable virus shedding in one animal. Examination of duodenum biopsies of the TV-inoculated macaques showed lymphocytic infiltration of the lamina propria and villous blunting. TV antigen-positive (TV+) cells were detected in the lamina propria. In most of the TV+ cells TV co-localized perinuclearly with calnexin--an endoplasmic reticulum protein. A few CD20+TV+ double-positive B cells were also identified in duodenum. To corroborate the authenticity of CD20+TV+ B cells, in vitro cultures of peripheral blood mononuclear cells (PBMCs) from healthy macaques were inoculated with TV. Multicolor flow cytometry confirmed the presence of TV antigen-containing B cells of predominantly CD20+HLA-DR+ phenotype. A 2-log increase of viral RNA by 6 days post inoculation (p<0.05) suggested active TV replication in cultured lymphocytes.

CONCLUSIONS/SIGNIFICANCE

Taken together, our results show that ReCVs represent an alternative cell culture and animal model to study enteric calicivirus replication, pathogenesis and immunity.

Detection of norovirus-, sapovirus- and rhesus enteric calicivirus-specific antibodies in captive juvenile macaques

The objective of this study was to determine the prevalence of anti-norovirus (NoV), -sapovirus (SaV) and -Tulane virus (TV) antibodies in rhesus macaques of the Tulane National Primate Research Center and to evaluate the antigenic relationship between these viruses. A high prevalence of NoV-binding (51-61 %) and SaV-binding (50-56 %) antibodies and TV-neutralizing (69 %) antibodies were detected. Serum samples obtained during a human NoV outbreak and a multivalent anti-NoV hyperimmune serum were not able to neutralize TV infectivity. Conversely, low levels of cross-reactivity between the prototype TV and NoVs, but not between the TV and SaVs were detected by ELISA. These data indicate the preservation of some cross-reactive B-cell epitopes between the rhesus and human caliciviruses (CVs). The high prevalence of human and rhesus CV-specific serum antibodies suggests the frequent exposure of colony macaques to enteric CVs including the possibility of CV transmission between human and non-human primate hosts.

[Human caliciviruses and an immune response]

The review deals with calicivirus infection that has long been known in animals, but also just recently disclosed in humans. Human caliciviruses induce outbreaks of acute gastroenteritis in all countries of the world, which makes this immunobiological research very actual. The history of this discovery, evolution of caliciviruses, the host resistance and immune response mechanisms are described in this review.

Immunobiology of Norwalk virus

Clinical immunity to Norwalk virus in inoculated human volunteers appears to be unusual for gastroenteritis viruses, as certain individuals are repeatedly ill on long-term virus rechallenge and others remain persistently well. In these volunteers there is a paradoxical inverse correlation between the prechallenge serum (and jejunal fluid) Norwalk antibody level (measured by radioimmunoassay) and resistance to illness, suggesting that non-immunological factors, perhaps genetic, may be important in determining resistance. Most reported naturally occurring Norwalk disease outbreaks in developed nations also show that humoral antibody fails to correlate with immunity to infection. The unusual pattern of clinical immunity to Norwalk virus indicates a need for caution in the development of vaccines against this agent as well as a need for additional information on its immunobiological characteristics. The virus is known to contain a single protein, like the caliciviruses. Recently we have found evidence for at least a one-way serological cross-relatedness between Norwalk virus and human calicivirus. Twelve of 20 paired sera from ill patients in outbreaks due to calicivirus strain UK4 seroconverted to Norwalk virus by radioimmunoassay and two of eight paired sera from UK2 outbreaks showed seroconversion. Future studies of outbreaks caused by various calicivirus strains should be designed to correlate acute-phase serum antibody titres to Norwalk virus with clinical susceptibility and immunity to infection.

High efficiency cross-reactive monoclonal antibody production by oral immunization with recombinant norwalk virus-like particles

Monoclonal antibodies (MAbs) are important for in-depth antigenic characterization and diagnosis of infections with human caliciviruses that cause almost all outbreaks of nonbacterial gastroenteritis. We compared different routes of immunization with nonreplicating virus-like particles (VLPs) from recombinant Norwalk virus (rNV) and recombinant Mexico virus (rMX) administered to BALB/c mice to determine the efficiency of hybridoma production. Oral immunization with VLPs without adjuvant resulted in high yields of MAb-secreting hybridomas (90%) to these VLPs of IgG (61%), IgM (29%) and IgA (10%) isotypes. Fusions with mesenteric lymph node lymphocytes yielded MAbs of various subclasses including IgG2a, IgG3, IgM and IgA. These results suggest that an immunization route that mimics the natural route of viral infection pathway may facilitate MAb technology by increasing the yields of antibody secreting hybridoma cells.

NEW VARIANTS OF EUROPEAN BROWN HARE SYNDROME VIRUS STRAINS IN FREE-RANGING EUROPEAN BROWN HARES (LEPUS EUROPAEUS) FROM SLOVAKIA

Investigations regarding European brown hare syndrome virus (EBHSV) in European brown hares (Lepus europaeus) in Slovakia were undertaken in order to detect the possible presence of EBHSV and to evaluate its phylogenetic position. Liver and/or serum samples were obtained from 135 European brown hares shot by hunters in eight regional hunting areas. From 36 animals corresponding liver and serum samples were available; from the remaining 49 and 50 animals only liver or serum samples were examined, respectively. Samples were tested for antibodies against EBHSV and for viral RNA by reverse transcriptase-polymerase chain reaction (RT-PCR) and RT-PCR products were subsequently sequenced. Additionally, matrilinear hare haplotypes were analyzed in order to detect potential familial susceptibility to EBHSV. Sixty-three of 86 sera contained antibodies against EBHSV, whereas 15 of 85 liver samples were PCR positive. Of the latter, 14 were sequenced, revealing three new strains of EBHSV. Fifteen different matrilinear haplotypes were identified, but no correlation was found between haplotype and susceptibility to EBHSV infection. Our findings confirmed the existence of EBHSV in Slovakia and reinforce the need for determining EBHSV status when importing hares for restocking.

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

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

Comparison of two polymer-based immunohistochemical detection systems: ENVISION+? and ImmPRESS?

The non-specific background reaction produced in avidin-biotin-based immunohistochemistry, particularly after harsh antigen retrieval procedures, has promoted the use of non-avidin-biotin systems, yet there are few reports comparing the performance of non-avidin-biotin, polymer-based methods. In this study we compare two of these methods, ENVISION+trade mark and ImmPRESS, in animal tissues. We examined the immunoreactivity of 18 antigens in formalin-fixed, paraffin-embedded tissues. Antigens were located in the cytoplasmic membrane (CD11d, CD18 and CD79a), cytoplasm (calretinin, COX-1, COX-2, Glut-1, HepPar 1, KIT, Melan A, tryptase and uroplakin III) or nucleus (MUM-1, PGP 9.5 and thyroid transcription factor 1). We also evaluated three infectious agents (Aspergillus, calicivirus and West Nile virus). The staining with ENVISION+ or ImmPRESS was performed simultaneously for each antigen. The intensity of the reaction and background staining were scored. ImmPRESS yielded similar or higher reaction intensity than ENVISION+trade mark in 16/18 antigens. ImmPRESS produced abundant background with the other two antigens (calretinin and COX-2), which hindered interpretation of the specific reaction. The cost of ImmPRESS was 25% lower than for ENVISION+trade mark. Based on these results, ImmPRESS is a good polymer-based detection system for routine immunohistochemistry.

SEROLOGIC SURVEY FOR SELECTED VIRUS INFECTIONS IN POLAR BEARS AT SVALBARD

Polar bears (Ursus maritimus) were chemically immobilized and sampled at Svalbard, Norway, and on the pack ice in the Barents Sea from late March to mid-May between 1990 and 1998. Plasma samples were tested for the presence of antibodies to canine distemper virus (CDV), calicivirus, phocid herpesvirus type 1 (PhHV-1), and rabies virus. A seroprevalence of 8% to CDV and 2% to calicivirus were found, whereas no antibodies were detected against PhHV-1 or rabies virus. This serologic survey indicates that polar bears in this region are exposed to morbillivirus and calicivirus, although the nature of these viruses and infections are unknown. Morbillivirus and calicivirus are potential pathogens in seals, but it is unknown whether they may cause health problems in polar bears.

Leukocyte-hepatocyte interaction in calicivirus infection: differences between rabbits that are resistant or susceptible to rabbit haemorrhagic disease (RHD)

Calicivirus infection is lethal for adult rabbits, whereas young rabbits (less than 8-weeks-old) are resistant to the same infectious agent. The virus replicates in the liver and causes a fulminant hepatitis in adult rabbits leading to rabbit haemorrhagic disease (RHD); this is in contrast with the mild and transient hepatitis observed in infected young rabbits. We have used electron microscopy to compare liver leukocyte infiltrates between young (resistant) and adult (susceptible) rabbits, 36-48 h after inoculation of the animals with caliciviruses. In adult rabbits, liver infiltrates were made up mostly of heterophils, and they were located near hepatocytes showing severe cellular damage. In contrast, liver leukocyte infiltrates of RHD-resistant young rabbits were dominated by lymphocytes that depicted membrane contacts with the cell surface of undamaged hepatocytes. We conclude that: (i) the cellular inflammatory response of the liver to calicivirus infection is different in rabbits that are susceptible (adult) or resistant (young) to RHD; (ii) leukocyte infiltration of the adult liver by heterophils is probably directed at the removal of dead hepatocytes, whereas the liver lymphocytic infiltration of young rabbits suggests the expression of viral antigens on the surface of liver cells of the RHD-resistant animals.

Detection and characterization of human caliciviruses in hospitalized children with acute gastroenteritis in Blantyre, Malawi

The human caliciviruses (HuCVs), including Norovirus and Sapovirus, are recognized causes of acute gastroenteritis in children and adults. A 1-year study was undertaken in Blantyre, Malawi, to examine the prevalence, and genetic diversity, of human caliciviruses (HuCVs) amongst children under 5 years of age hospitalized with acute gastroenteritis. Using the reverse transcription-polymerase chain reaction (RT-PCR), combined with nucleotide sequencing of the RT-PCR products, HuCVs were detected in 34/398 (8.5%) of children. Twelve (35.3%) of the children were co-infected with additional enteric viruses (predominantly rotavirus). The HuCVs comprised 26 Noroviruses (6.5%) and 8 Sapoviruses (2.0%). Each of the Noroviruses belonged to genogroup II, and could be further classified into six genotypes, including GII/3 (18 strains), GII/4 (2 strains), GII/11 (1 strain), GII/13 (1 strain), GII/16 (2 strains), and a putative new genotype GII/20 (2 strains). Each of the Sapoviruses belonged to genogroup GIII. HuCVs are the second most commonly identified viral enteropathogens (after rotavirus) among hospitalized children with gastroenteritis in Malawi.

Cross-reactivity among sapovirus recombinant capsid proteins

Sapovirus (SaV), a member of the genus Sapovirus in the family Caliciviridae, is an agent of human and porcine gastroenteritis. SaV strains are divided into five genogroups (GI-GV) based on their capsid (VP1) sequences. Human SaV strains are noncultivable, but expression of the recombinant capsid protein (rVP1) in a baculovirus expression system results in the self-assembly of virus-like particles (VLPs) that are morphologically similar to native SaV. In this study, rVP1 constructs of SaV GI, GII, and GV strains were expressed in a baculovirus expression system. The structures of the GI, GII, and GV VLPs, with diameters of 41-48 nm, were morphologically similar to those of native SaV. However a fraction of GV VLPs were smaller, with diameters of 26-31 nm and spikes on the outline. This is the first report of GII and GV VLP formation and the first identification of small VLPs. To examine the cross-reactivities among GI, GII, and GV rVP1, hyperimmune rabbit antisera were raised against Escherichia coli-expressed GI, GII, and GV N- and C-terminal VP1. Western blotting showed the GI antisera cross-reacted with GV rVP1 but not GII rVP1; GII antisera cross-reacted weakly with GI rVP1 but did not cross-react with GV rVP1; and GV antisera reacted only with GV rVP1. Also, hyperimmune rabbit and guinea pig antisera raised against purified GI VLPs were used to examine the cross-reactivities among GI, GII, and GV VLPs by an antigen enzyme-linked immunosorbent assay (ELISA). The ELISA showed that the GI VLPs were antigenically distinct from GII and GV VLPs.

Human Caliciviruses as a Cause of Severe Gastroenteritis in Peruvian Children

To define the role of human caliciviruses (HuCVs) in severe childhood gastroenteritis, fecal and paired serum samples from 233 Peruvian children hospitalized with gastroenteritis (case patients) and fecal samples from 248 control subjects were evaluated. Overall, 128 case patients (55%) demonstrated HuCV infection by either fecal (n=81 [35%]) or serological (n=96 [41%]) testing. HuCVs were more prevalent in fecal samples from case patients than those from control subjects (35% vs. 13%; P<.001). HuCV infection was more prevalent among case patients without another pathogen than in those who had a coinfecting pathogen (77% [40/52] vs. 49% [88/181]; P<.001). HuCVs appear to be an important cause of gastroenteritis in Peruvian children.

Laboratory diagnosis of norovirus: which method is the best?

Noroviruses (NV) are transmitted by fecally contaminated food, vomit, and person-to-person contact. They are one of the main causes of non-bacterial acute gastroenteritis in nursing, old people and children's homes. NV outbreaks are characterized by a short incubation period (12-48 h), nausea, vomiting and diarrhea, and high secondary attack rates. The illness is generally mild and self-limiting. The aim of diagnostic procedures in viral gastroenteritis is to avoid nosocomial infections on the one hand and unnecessary antibiotic treatment on the other. Diagnostic procedures for NV are based on the detection of virus in stool samples by (immune) transmission electron microscopy (TEM), antigen ELISA, or polymerase chain reaction (PCR). In our study, a total of 244 stool samples obtained from 227 patients between March and May 2002 were tested by TEM, antigen ELISA and in-house PCR. Our data showed that PCR has the highest sensitivity (94.1%), followed by TEM (58.3%), and ELISA (31.3%), while specificity was highest for TEM (98.0%), followed by ELISA (94.9%), and PCR (92.4%). All three methods tested (TEM, ELISA and PCR) are useful for epidemiological investigations in gastroenteritis outbreaks; however, to maximize diagnostic validity for individual cases, at least two of the methods should be combined.

[Epidemiological study of human caliciviruses among children with acute diarrhea in Lulong county, 1999 - 2001]

OBJECTIVE

To investigate the epidemiological characteristus of human caliciviruses (HuCVs) among children under 5 years of age with acute diarrhea and to estimate the disease burden in Lulong county.

METHODS

HuCVs were detected by enzyme linked immunosorbent assay (ELISA) and reverse transcription-polymerase chain reaction (RT-PCR). Some PCR amplicons were cloned and sequenced. Phylogenetic tree was constructed for strain characterization. The rate of HuCVs-attributed hospitalization was estimated according to the positive rate of HuCVs detection in fecal specimens collected from hospitalized diarrhea patients.

RESULTS

Between July 1999 and June 2001, 708 fecal specimens were collected, of which 393 rotavirus-negative and 5 rotavirus-positive specimens were detected for HuCVs. Thirty-one point six percentage of fecal specimens from patients with diarrhea was HuCVs positive. Among inpatients, HuCVs positive rate was 17.5%. HuCVs detection was mainly distributed in 3 - 17 mouth-old children, in winter. All 11 strains belonged to NLV GII in which 6 strains GII-3, 2 strains GII-4 and 3 strains GII-7, and they shared 55.1% - 100% nucleotide identity. NLV GII-4 and GII-7 were identified in 2000, while NLV GII-3 and GII-7 in 2001. The preliminary estimate of HuCVs-attributed hospitalization rate was 3.6 per thousand.

CONCLUSION

Human caliciviruses with different genotypes circulated among children in Lulong county with GII NLVs were the prevalent strains. The disease burden of HuCVs was second to rotavirus.

EPIZOOTIOLOGIC AND ECOLOGIC INVESTIGATIONS OF EUROPEAN BROWN HARES (LEPUS EUROPAEUS) IN SELECTED POPULATIONS FROM SCHLESWIG-HOLSTEIN, GERMANY

From 1997-99 European brown hare (Lepus europaeus) population densities were estimated by spotlight surveys within different areas in Schleswig-Holstein, Germany. These areas showed a wide variation in local hare population densities. In addition, red fox (Vulpes vulpes) densities were estimated in 1997 by surveys of fox dens and litters. Sera of 321 hares (shot between 1998-2000) from four study areas were examined for antibodies against European brown hare syndrome virus (EBHSV) by enzyme linked immunosorbent assay (ELISA), Yersinia spp. (n = 299) and Francisella tularensis (n = 299) by western blotting, Brucella spp. by Rose Bengal test, and Toxoplasma gondii by Sabin-Feldman test (n = 318). Tissue samples comprising lung, liver, spleen, kidney, heart, and adrenal glands were collected for histopathology. Liver (n = 201) and spleen (n = 201) samples were processed for the detection of T. gondii-antigen in tissue sections and 321 liver and spleen samples were investigated for EBHSV-antigen by ELISA. Furthermore, 116 hares were examined macro- and microscopically for lungworms. Significant negative correlations between hare and fox densities were found in spring and autumn 1997. Antibodies against EBHSV were detected in 92 of 321 (29%), against Yersinia spp. in 163 of 299 (55%), and against T. gondii in 147 of 318 (46%) hares. We evaluated the potential influence of origin and hunting season on exposure rates of hares using logistic regression analysis. A strong association between hare densities and exposure rates was observed for various agents. One hundred and eight of 201 (57%) hares were positive for T. gondii-antigen. All sera were negative for antibodies against Brucella spp. and F. tularensis and all lung samples were negative for lungworms. In conclusion, variation in red fox densities may have an impact on the hare populations examined and the infectious diseases we studied seem to play a subordinate role in the dynamics of European brown hare populations from Schleswig-Holstein.

An epizootic of highly virulent feline calicivirus disease in a hospital setting in New England

This article reports an outbreak of 24 cases of an unusually virulent feline calicivirus (FCV) infection in a small animal hospital. The circumstances and disease signs were very similar to those recently described in an outbreak of FCV hemorrhagic disease in Northern California (Vet. Microbiol. 73 (2000) 281). The virus entered the facility through shelter cats showing upper respiratory signs. Affected cats manifested high fever, anorexia, labored respirations, oral ulceration, facial and limb edema, icterus, and pancreatitis. The infection spread rapidly among the patients by contaminated animal caretakers and hospital equipment. One case of fomite transmission from an employee to a housecat was documented. Prior vaccination, even with multiple doses of FCV-F9-based live calicivirus vaccine, was not protective. Affected cats often required extensive supportive care for 7-10 days, and the overall mortality from death and euthanasia was 32%. The strain of FCV responsible for this outbreak was genetically and serologically distinct from the FCV strain responsible for a similar epizootic and the FCV-F9 strain contained in most vaccines. Outbreaks of this type are being reported with increasing frequency, and are often associated with the practice of treating sick shelter cats in private practices. Similar to the present epizootic, outbreaks of FCV hemorrhagic disease have been self-limiting, but require prompt application of strict quarantine, isolation, personnel sanitation, and disinfection procedures.

Molecular cloning, expression, self-assembly, antigenicity, and seroepidemiology of a genogroup II norovirus isolated in France

Virus-like particles of Dijon171/96 virus, a genogroup II norovirus, were expressed in a baculovirus system and were used for a seroepidemiological study of 1078 age-stratified human sera collected in Dijon, France. The results showed a seroprevalence of 74.1%. Furthermore, we showed that murine antibodies generated against recombinant Dijon171/96 virus, and human antibodies recognized discontinuous epitopes on the particles.

Studies of epidemiology and seroprevalence of bovine noroviruses in Germany

Jena virus (JV) is a bovine enteric calicivirus that causes diarrhea in calves. The virus is approximately 30 nm in diameter and has a surface morphology similar to the human Norwalk virus. The genome sequence of JV was recently described, and the virus has been assigned to the genus Norovirus of the family CALICIVIRIDAE: In the present study, the JV capsid gene encoded by open reading frame 2 was cloned into the baculovirus transfer vector pFastBac 1, and this was used to transform Escherichia coli to generate a recombinant bacmid. Transfection of insect cells with the recombinant baculovirus DNA resulted in expression of the JV capsid protein. The recombinant JV capsid protein undergoes self-assembly into virus-like particles (VLPs) similar to JV virions in size and appearance. JV VLPs were released into the cell culture supernatant, concentrated, and then purified by CsCl equilibrium gradient centrifugation. Purified JV VLPs were used to hyperimmunize laboratory animals. An antigen capture enzyme-linked immunosorbent assay (ELISA) was developed and characterized initially with clinical specimens containing defined human noroviruses and bovine diarrheal samples from calves experimentally infected with JV; the ELISA was specific only for JV. The ELISA was used to screen 381 diarrheal samples collected from dairy herds in Thuringia, Hesse, and Bavaria, Germany, from 1999 to 2002; 34 of these samples (8.9%) were positive for JV infection. The unexpectedly high prevalence of JV was confirmed in a seroepidemiological study using 824 serum or plasma samples screened using an anti-JV ELISA, which showed that 99.1% of cattle from Thuringia have antibodies to JV.

Molecular detection and sequence analysis of human caliciviruses from acute gastroenteritis outbreaks in Hungary

Three viral gastroenteritis (VGE) outbreaks that occurred in 1998-1999, in Hungary were investigated for the presence of human caliciviruses (HuCVs). HuCVs in stool specimens were detected by reverse transcription-polymerase chain reaction (RT-PCR) using primer pair 289/290, which was designed based on the RNA-dependent RNA polymerase (RdRp) sequence. RT-PCR results were confirmed by sequencing showing that all three outbreak strains belonged to genogroup II of "Norwalk-like viruses" (NLVs). Two strains had high sequence identity with strains in known genetic clusters (Hawaii and Lordsdale clusters). The third strain (MOH) had distinct RdRp sequence, sharing 77/86% (nt/aa) identity with Snow Mountain virus (SMV), the closest genogroup II virus. To characterize MOH further, we cloned, sequenced, and expressed in baculovirus its capsid gene. It had 75/79% (nt/aa) identity with SMV, but 97/98% (nt/aa) identity with NLV/Hillingdon/90/UK, a recently identified genetic cluster of HuCVs. The recombinant MOH (rMOH) capsid protein self-assembled into virus-like particles (VLPs), which is antigenically distinct from other recombinant HuCV capsid antigens available in our laboratory. Further study of this VLP will have important applications in antigenic characterization and diagnosis of HuCVs.

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

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

Molecular and seroepidemiological evidence of canine calicivirus infections in Japan

Calicivirus infection of dogs was epidemiologically investigated by using canine calicivirus (CaCV) strain 48 as a reference. Similar RNA polymerase gene sequences and neutralizing antibodies against CaCV were detected in 1.7% of clinical specimens and 57% of serum samples, respectively, suggesting a high prevalence of CaCV in dog populations.

European brown hare syndrome in free-ranging European brown and mountain hares from Switzerland

From 1997 to 2000, complete necropsy and histopathologic investigations were performed on 157 free-ranging European brown hares (Lepus europaeus) found dead throughout Switzerland. Organ samples of all these individuals (157 livers and 107 spleens available) were tested for European brown hare syndrome virus (EBHSV)-antigen by enzyme-linked immunosorbent assay (ELISA) test kit. Furthermore, 60 additional blood samples were tested for antibodies against EBHSV by ELISA. In addition, liver samples of 87 free-ranging mountain hares (Lepus timidus) hunted in 1996 were tested for EBHSV-antigen. In two European brown hares from southern Switzerland lesions suggestive of changes induced by EBHSV were present, and high titers of EBHSV-antigen were detected in both liver and spleen samples of these animals. Based on negative staining electron microscopy investigations of liver and spleen homogenates, we observed calicivirus in one antigen-positive hare. Low EBHSV-antigen titers were found in three additional European brown hares from central and western Switzerland, but EBHS-lesions were absent. Antibodies against EBHSV were not detected in any of the sera of European brown hares, and EBHSV-antigen was not found in the samples of mountain hares. This is the first report of EBHS in European brown hares from Switzerland.

Identification of conformational neutralizing epitopes on the capsid protein of canine calicivirus

Two neutralizing monoclonal antibodies (MAbs) against canine calicivirus (CaCV), which has a distinct antigenicity from feline calicivirus (FCV), were obtained. Both MAbs recognized conformational epitopes on the capsid protein of CaCV and were used to identify these epitopes. Neutralization-resistant variants of CaCV were selected in the presence of individual MAbs in a cell culture. Cross-neutralization tests using the variants indicated that the MAbs recognized functionally independent epitopes on the capsid protein. Recombinantly expressed ORF2 products (capsid precursors) of the variants showed no reactivity to the MAbs used for the selection, suggesting that the resistance was induced by a failing in binding of the MAbs to the variant capsid proteins. Several nucleotide changes resulting in amino acid substitutions in the capsid protein were found by sequence analysis. Reactivities of the MAbs to the revertant ORF2 products produced from each variant ORF2 by site-directed mutagenesis identified a single amino acid substitution in each variant capsid protein responsible for the failure of MAb binding. The amino acid residues related to forming the conformational neutralizing epitopes were located in regions equivalent to the 5' and 3' hypervariable regions of the FCV capsid protein, where antigenic sites were demonstrated in previous studies. The recombinant ORF2 products expressed in bacteria failed to induce neutralizing antibody, suggesting that neutralizing antibodies were only generated when properly folded capsid protein was used as an antigen. In CaCV, the conformational epitopes may play a more important role in neutralization than do linear epitopes.

Antibody response of dogs inoculated with a large number of cultured canine monocytes adsorbed with a calicivirus in advance

Five conventional Beagle dogs were intravenously injected with ten million canine monocyte cells (Cn/K99) cultured in vitro (Kadoi, 2000) adsorbed with a strain of calicivirus originally isolated from lions (Kadoi et al., 1997). Another two Beagle dogs were injected similarly with the virus suspension solely as control. Serum samples were collected from these dogs at intervals and specific seroneutralizing antibody production against the virus was measured in vitro. A significantly higher antibody production was demonstrated in the five dogs group. A clear booster effect was also proved in the sera of the dogs after the second virus inoculation made on day 100. A possibility of antigen presentation function of non-self monocytes is suggested.

Expression and self-assembly in baculovirus of porcine enteric calicivirus capsids into virus-like particles and their use in an enzyme-linked immunosorbent assay for antibody detection in swine

Porcine enteric calicivirus (PEC) causes diarrhea and intestinal lesions in pigs. PEC strain Cowden grows to low to moderate titers in cell culture but only with the addition of intestinal contents from uninfected gnotobiotic pigs (W. T. Flynn and L. J. Saif, J. Clin. Microbiol. 26:206--212, 1988; A. V. Parwani, W. T. Flynn, K. L. Gadfield, and L. J. Saif, Arch. Virol. 120:115--122, 1991). Cloning and sequence analysis of the PEC Cowden full-length genome revealed that it is most closely related genetically to the human Sapporo-like viruses. In this study, the complete PEC capsid gene was subcloned into the plasmid pBlueBac4.5 and the recombinant baculoviruses were identified by plaque assay and PCR. The PEC capsid protein was expressed in insect (Sf9) cells inoculated with the recombinant baculoviruses, and the recombinant capsid proteins self- assembled into virus-like particles (VLPs) that were released into the cell supernatant and purified by CsCl gradient centrifugation. The PEC VLPs had the same molecular mass (58 kDa) as the native virus capsid and reacted with pig hyperimmune and convalescent-phase sera to PEC Cowden in enzyme-linked immunosorbent assay (ELISA) and Western blotting. The PEC capsid VLPs were morphologically and antigenically similar to the native virus by immune electron microscopy. High titers (1:102,400 to 204,800) of PEC-specific antibodies were induced in guinea pigs inoculated with PEC VLPs, suggesting that the VLPs could be useful for future candidate PEC vaccines. A fixed-cell ELISA and VLP ELISA were developed to detect PEC serum antibodies in pigs. For the fixed-cell ELISA, Sf9 cells were infected with recombinant baculoviruses expressing PEC capsids, followed by cell fixation with formalin. For the VLP ELISA, the VLPs were used for the coating antigen. Our data indicate that both tests were rapid, specific, and reproducible and might be used for large-scale serological investigations of PEC antibodies in swine.

Serotype-specific antigen ELISA for detection of Chiba virus in stools

Chiba virus (CV), a Norwalk-like virus (NLV), was first identified as a cause of oyster-associated outbreak of gastroenteritis that occurred in Chiba prefecture, Japan, in 1987. An enzyme-linked immunosorbent assay (ELISA), based on hyperimmune antisera to recombinant baculovirus-expressed capsid proteins of CV (rCV), was developed to detect CV antigen in stools. No cross-reactions were observed with other enteric viruses including enteroviruses, rotaviruses, astroviruses, or enteric adenoviruses. The ELISA was used to screen 101 stools collected from 16 oyster-associated outbreaks of acute gastroenteritis. Twelve stools (11.9%) from seven outbreaks were positive for CV antigen. Ten rCV ELISA-positive strains were confirmed by RT-PCR and nucleotide sequencing. ELISA-positive strains showed 96-100% nucleotide sequence identity to each other, though they were obtained nine years apart. Phylogenetic analysis demonstrated that all ten strains clustered with the prototype CV in genogroup I viruses. We concluded that the antigen ELISA described in this study is highly type-specific, and that this method should be useful for epidemiological surveys of Chiba virus infections.

Molecular cloning, expression, and antigenicity of Seto virus belonging to genogroup I Norwalk-like viruses

The viral capsid protein of the Seto virus (SeV), a Japanese strain of genogroup I Norwalk-like viruses (NLVs), was expressed as virus-like particles using a baculovirus expression system. An antigen detection enzyme-linked immunosorbent assay based on hyperimmune antisera to recombinant SeV was highly specific to homologous SeV-like strains but not heterologous strains in stools, allowing us type-specific detection of NLVs.

Epizootic vesicular disease in captive California sea lions

An epizootic of vesicular disease occurred in a group of semi-domesticated California sea lions (Zalophus californianus) during the months of April and May 1997. Ten castrated mature male sea lions, ages 12 to 19 yr, were housed in three adjacent open-ocean net enclosures in San Diego Bay (California, USA). Four animals (40%) developed oral and extremity vesicles, anorexia, and were reluctant to perform learned behaviors. One animal developed vesicles but maintained a normal appetite and behavior. The remaining animals showed no clinical signs of infection. Virus (designated FADDL 7005) was isolated from four of the five animals that developed vesicles. Serum antibody titers to FADDL 7005, a previously untyped calicivirus, were demonstrated in animals that showed any combination of clinical signs and in two animals that did not show any clinical signs. No virus was isolated from five fecal samples collected from four of the group animals. Clinical signs lasted 4 to 20 days in affected animals. All affected animals recovered from infection. An experimental swine was inoculated with FADDL 7005 and developed vesicular disease, which was transmitted to another experimental swine upon contact. It is proposed that FADDL 7005 is a new San Miguel sea lion virus.

Sapporo virus: history and recent findings

Morphologically distinct caliciviruses of human origin were first found in stools of children with gastroenteritis in 1976. Sapporo virus, or human calicivirus Sapporo, with typical surface morphology was first detected during a gastroenteritis outbreak in a home for infants in Sapporo, Japan, in 1977. Since then, morphologically and antigenically identical virus has been detected frequently in the same institution in association with outbreaks of gastroenteritis. Sapporo virus is widely distributed worldwide, as evidenced by the appearance of antigenically or genetically similar viruses and seroepidemiologic findings. Sapporo virus plays an important role in outbreaks of infantile gastroenteritis and is less important in foodborne outbreaks. Sapporo virus has been approved as the type species of the genus "Sapporo-like viruses in the family Caliciviridae. The history of and recent findings, as obtained by newly developed techniques, about Sapporo viruses are presented.

Seroprevalence against Norwalk-like human caliciviruses in beijing, China

Serum specimens from 1,109 individuals at different ages in Beijing, China, were collected between April 1996 and March 1997 and tested for IgG antibodies against human caliciviruses using enzyme immune assays (EIAs). Baculovirus-expressed recombinant Norwalk virus (rNV) and Mexican virus (rMxV) capsid proteins were used as antigens. The seroprevalence was 89% for rNV and 91% for rMxV. Similar seroprevalence between the two antigens was observed in individual age groups and both genders. Infants had a high seroprevalence (99% for NV and 94% for MxV) at birth. The lowest seroprevalence (41% for rNV and 36% for rMxV) was at 7-11 months of age. A sharp increase in seroprevalence occurred in early childhood, with 65% and 70% at one, 85% and 90% at three, and 100% and 98% at 8-9 years of age for rNV and rMxV, respectively. Forty-three individuals had antibody against rNV but not rMxV and 63 individuals had antibody against rMxV but not rNV, indicating different levels of exposure to the two strains in these individuals. This is the first report of surveillance of antibodies against NV-like viruses in China. The observed high prevalence and early age antibody acquisition suggest that infection by these two human calicivirus strains is common in this population.

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.

Expression and self-assembly of Grimsby virus: antigenic distinction from Norwalk and Mexico viruses

A cDNA obtained from Grimsby virus (GRV), a Norwalk-like virus, purified from a stool sample of a symptomatic adult associated with a gastroenteritis outbreak in the United Kingdom, was used to obtain the complete nucleotide sequence of the second open reading frame (ORF2). The ORF2 sequence of GRV predicts a capsid of 539 amino acids (aa) which exhibits aa identities of 96% to Lordsdale virus, 67% to Mexico virus (MXV), and 43% to Norwalk virus (NV). The GRV capsid protein was expressed in insects cells by using a recombinant baculovirus, and the resulting virus-like particles (VLPs) possessed a protein with an apparent molecular weight of 58,000. Hyperimmune antisera raised against purified GRV, MXV, and NV VLPs were tested in an indirect enzyme-linked immunosorbent assay (ELISA) against GRV, NV, and MXV VLPs, revealing that GRV is antigenically distinct from both NV and MXV. The antigenic specificity of the GRV-hyperimmune antiserum was confirmed in an antigen capture ELISA using GRV-, NV-, or MXV-containing fecal specimens. The expression of the GRV capsid protein has, for the first time, allowed the antigenic comparison of three distinct recombinant Norwalk-like viruses.

Prevalence of human calicivirus infections in Kenya as determined by enzyme immunoassays for three genogroups of the virus

An epidemiological survey on human calicivirus (HuCV) infections and associated gastroenteritis in infants was conducted to clarify the prevalence of HuCV infections in infants and adults in Kenya. Enzyme immunoassays (EIAs) for three genogroups of HuCVs, Norwalk virus (NV), Mexico virus (MXV), and Sapporo virus (SV), were used to detect antigen or antibody. We tested 1,431 stool samples obtained from children younger than 6 years old with acute gastroenteritis who visited outpatient clinics in three districts in Kenya from August 1991 to July 1994. Thirty-two (2.2%) of these stool samples were positive for SV antigen. Only one (0.1%) of 1,186 samples was positive for NV antigen and none of 246 samples was positive for MXV antigen. One hundred ninety-three serum samples were tested for antibodies to NV and MXV, and 64 of them were examined for antibody to SV. The pattern of the age-related prevalence of serum antibody to NV was different from that of antibodies to MXV and SV. The acquisition of serum antibodies to HuCVs in the three genogroups appeared in early childhood, at about 1 to 2 years of age. The prevalence of serum antibody to NV was low (about 60%) throughout adulthood compared with a high prevalence of antibody (approximately 80 to 90%) to MXV and SV. These data indicate that infections with viruses in the three genogroups of HuCVs are common in Kenya, and immunological responses to NV may be different from those to MXV and SV. The EIAs for the detection of NV and MXV antigens appear to be quite specific for prototype NV and MXV strains, respectively, so that they can detect only a few strains of HuCVs related to them. Alternatively, NV and MXV caused less severe infections that did not bring children to the outpatient clinics for gastroenteritis in Kenya.

Sapporo-like human caliciviruses are genetically and antigenically diverse

The Sapporo-like human caliciviruses (HuCVs) comprise one of three genogroups of HuCVs associated with acute gastroenteritis. Phylogenetic analysis has shown that Sapporo-like HuCVs are related more closely to animal caliciviruses than to other known HuCVs. We produced 3.2 kb cDNA fragments from the 3' end to three Sapporo-like HuCVs that were associated with acute gastroenteritis in children (Houston/86, Houston/90, and London/92). Sequence analysis of the 3.2 kb cDNAs showed that two of the three viruses had a genomic organization similar to that of other Sapporo-like strains and the third strain (London/92) lacked an open reading frame overlapping the 5' end of the capsid gene. Alignment of the capsid sequences of these three strains showed 44-78% amino acid identity among the three strains. Phylogenetic analysis of the aligned sequences indicated the three strains are related but each belongs to a distinct genetic cluster. The genetic differences are associated with antigenic differences in that an enzyme immune assay (EIA) specific for the prototype Sapporo/82 strain detected the Houston/86 strain, but not the Houston/90 and London/92 strains. In vitro transcription and translation of viral cDNA containing the predicted capsid gene of Houston/90 resulted in a protein of 63 K, which is immunoprecipitated by sera from children infected with the strain. Genetically and antigenically distinct strains in the Sapporo-like HuCVs have not been described previously and the occurrence of such diverse strains in the same community likely increases the importance of these strains as a cause of illness in children.

Isolation of reptilian calicivirus Crotalus type 1 from feral pinnipeds

Ten virus isolates were obtained from three species of marine mammals sampled on San Miguel Island (California, USA) and 1,200 km north on Rogue Reef (Oregon, USA) during tagging operations in 1986-87. Seven of these 10 were derived from 30 sampled Steller sea lion (Eumetopias jubatus pups, while two of 10 were isolated from one of 19 sampled California sea lion (Zalophus californianus californianus pups, and the remaining isolate was derived from 30 sampled northern fur seal (Callorhinus ursinus) pups. All 10 isolates were identified as belonging to a single serotype, reptilian calicivirus Crotalus type 1 (RCV Cro-1), previously isolated from both healthy and diseased snakes and frogs in a California zoologic collection. The marine samples also showed that nine of 30 Steller sea lion pups, one of 19 California sea lion pups and zero of 30 fur seal pups were producing type specific neutralizing antibodies to RCV Cro-1. This represents the first reported instance of the isolation from marine sources of calicivirus originally isolated from a terrestrial species.

Antibody response of lions inoculated with inactivated calicivirus vaccine experimentally prepared

The majority of lions and tigers in a Safari park in Japan were suffering from acute vesicular disease caused by a calicivirus infection. All of these animals were injected subcutaneously with an inactivated calicivirus vaccine experimentally prepared with one of the seed viruses originally isolated from sick lions. Seroneutralizing antibody of paired sera collected from ten female lions at two week intervals was measured. A significant elevation of specific antibody was detected in the serum samples and no local or systemic reactions associated with vaccination were observed.

Prevalence of antibodies to the Hawaii strain of human calicivirus as measured by a recombinant protein based immunoassay

The evaluation of an enzyme immunoassay using recombinant Hawaii virus-like particles (rHV-LPs) with a panel of sera which had been screened previously for antibodies to Norwalk virus (NV) and Mexico virus (MxV) is described. The assay was also applied to study the epidemiology of Hawaii virus. Adult volunteers challenged with the prototype (genogroup II, human calicivirus) HV developed significant IgG responses (16-32 fold rises) following challenge whereas adults challenged or naturally infected with NV (genogroup I) did not. Lesser antibody responses (4-8 fold rises) were demonstrated in volunteers challenged with Snow Mountain agent (SMA) and patients infected by SRSV 'UK3' and 'UK4' strains, indicating a degree of antigenic relatedness among viruses within genogroup II. Comparison of the seroprevalence of IgG antibodies to rHV, rMxV and rNV in 338 children in London showed that infections with genogroup II viruses are prevalent and occur earlier in life than NV. Many young children had antibodies to MxV but not HV indicating that genogroup II viruses have both conserved and antigenically distinct epitopes. A serological study on 566 Canadians aged between 9 and 79 years showed that the prevalence of antibodies to rHV rose with age from 65-100% and from 53-100% for NV. Measurement of antibody response in a heart transplant patient infected with an MxV-like virus showed significant responses to both rMxV and rHV. Continuous monitoring of the patient over two years showed that antibody levels declined rapidly to prechallenge levels after a year.

Viral serologic survey of bowhead whales in Alaska

Serum samples from 21 of 36 Eskimo harvested bowhead whales (Balaena mysticetus) were positive by virus neutralization (50% endpoint titer > or = 1:28 and/or 100% endpoint titer > or = 1:20) for antibodies to at least one virus serotype from the calicivirus family, vesicular exanthema of swine virus (VESV) and San Miguel sea lion virus (SMSV). Many animals were positive to more than one serotype when using the Spearman-Karber (S-K) method for calculating antibody titers. The most common serotype detected was VESV F55 with 6 of 36 (17%) by the Monto and Bryan (MB) titer calculation method, and 17 of 36 (47%) by the S-K titer calculation method. Vesicular exanthema of swine virus 1934B antibody was detected in 3 of 36 (8%) and 5 of 36 (14%) whales using the MB and S-K methods, respectively. Vesicular exanthema of swine virus J56 antibody was detected in 3 of 36 (8%) by the S-K method only. All whales < 8.5 m (estimated yearlings, n = 6) were seronegative for VESV J56 and 1934B while 10% and 17% of the whales > 8.5 m were positive, respectively. Whales assumed to be sexually mature (> 13 m) had a higher prevalence of antibody to VESV 1934B and SMSV 8 than those < 13 m. Gender had an effect on seroprevalence of antibody to VESV 1934B as titers > or = 1:28 (S-K method) occurred in 18% of the females and 7% of the males. Antibody to other serotypes (SMSV 8 and 12) occurred less frequently (< 6%) at an antibody titer > or = 1:28 by the S-K method. All 36 whale sera were negative for antibody to VESV-A48, B51, C52, D53, E54, G55, H54, I55, and K54; Tillamook calicivirus, and dolphin morbillivirus; and SMSV-1, 2, 4, 5, 6, 7, 9, 10, 11, and 13 by the S-K method.

The role of human caliciviruses in epidemic gastroenteritis

Members of the Caliciviridae family of small, positive-sense RNA viruses exhibit a broad host range. The Norwalk and Norwalk-like caliciviruses in this family are major etiologic agents of epidemic gastroenteritis in humans. This illness characteristically lasts 24-48 h and often occurs in group settings such as families, schools, institutions, or communities. The spread of the human caliciviruses is considered to be predominantly by person-to-person contact via the fecal-oral-route. However, the ingestion of calicivirus-contaminated food or water can result in large-scale common-source outbreaks. Many basic features concerning the biology and replication of the human caliciviruses are not known because they have not yet been grown in cell culture and the virus does not appear to replicate in animal models other than the chimpanzee. Sequence analysis of RT-PCR-generated DNA fragments derived from serotypically distinct reference strains (such as the Norwalk, Hawaii, and Snow Mountain viruses) and other circulating strains associated with gastroenteritis has provided evidence for marked genetic diversity among these viruses. Moreover, analysis of the antigenic relationships among these viruses using paired sera from individuals infected with well-characterized reference strains or from animals immunized with recombinant "virus-like particles" (VLPs) suggests that several serotypes of these viruses are circulating worldwide. The availability of molecular techniques for the detection of these fastidious viruses has enabled epidemiologic studies that have strengthened the association of human caliciviruses with acute gastroenteritis and has demonstrated a potential role for antigenic diversity in the natural history of these pathogens.

Structural, antigenic and immunogenic relationships between European brown hare syndrome virus and rabbit haemorrhagic disease virus

The capsid protein of a French isolate of the European brown hare syndrome virus (EBHSV) was expressed in the baculovirus system. The recombinant EBHSV (rEBHSV) capsid protein was able to self-assemble into virus-like particles (VLPs). The VLPs were indistinguishable from the infectious EBHSV and displayed morphological characteristics similar to those we have described for the VLPs resulting from the expression of the capsid protein of rabbit haemorrhagic disease virus (RHDV), a closely related calicivirus. Cross-protection experiments showed that vaccination with rEBHSV particles did not protect rabbits against an RHDV challenge. A set of monoclonal antibodies (MAbs) was raised against rEBHSV capsid protein and used together with anti-RHDV and anti-EBHSV MAbs produced against native viruses to study the antigenic relationships between the two caliciviruses. All six anti-EBHSV MAbs delineated discontinuous epitopes; two of them reacted with specific surface epitopes and the remaining four reacted with internal epitopes which were also present in rRHDV. All anti-RHDV MAbs were monospecific; three reacted with surface linear epitope(s), two reacted with internal linear epitope(s) and one with a surface conformational epitope. On the basis of all these results, a classification of RHDV and EBHSV as two serotypes of a single serogroup is proposed.

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

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

Repeated physical and cytologic characterizations of subcutaneous postvaccinal reactions in cats

OBJECTIVES

To examine local reactions and short-term cytologic responses of cats to administration of rabies virus (RV); FeLV; and combined feline rhinotracheitis, calicivirus, and panleukopenia virus (FRCPV) vaccines.

ANIMALS

9 healthy 6- to 7-month-old specific-pathogen-free cats.

PROCEDURE

One-milliliter doses of the aforementioned vaccines were administered SC (at different sites) to healthy, specific-pathogen-free cats. Each cat also received 1 ml of sterile saline solution SC as a control. Injection sites were visually examined and palpated daily for 4 weeks. Palpable lesions were measured by use of calipers. Temperature of the vaccination sites was measured weekly by use of a thermocouple. Aspirates were taken from vaccination sites weekly, and smears were submitted for cytologic analysis.

RESULTS

There were no significant differences in lesion surface temperature among injection sites at any time. Injections of saline solution and FeLV vaccine resulted in no palpable lesions. The FRCPV vaccine elicited a minor reaction in 1 of the 9 cats. The RV vaccine caused palpable lesions in all cats. Smears of the aspirates from the sites of saline injection were poorly cellular. Cellularity of aspirates from the sites of FRCPV and FeLV vaccinations was moderate at week 1, and decreased with time. Inflammatory infiltrates were composed principally of lymphocytes, with fewer neutrophils and macrophages. In contrast, cellularity of aspirates from RV vaccination sites increased for 21 days and was characterized by increasing numbers of lymphocytes and macrophages.

CONCLUSIONS

RV vaccine used in this study induced palpable lesions in many cats. In contrast, FRCPV and FeLV vaccines elicited less severe lesions.

CLINICAL RELEVANCE

Subcutaneous administration of killed virus vaccines in cats may result in palpable lesions that are detected by clients or clinicians. Aspiration cytologic examination may reveal a different characteristic pattern of cells that is dependent on the individual vaccine and time elapsed from vaccination.

A strain of calicivirus isolated from lions with vesicular lesions on tongue and snout

In December 1992, 17 African lions and 7 Siberian tigers in a Safari park in Japan became sick with characteristic clinical symptoms of acute vesicular formations on tongue and snout. The disease was highly contagious since all of these animals showed similar symptoms within two days after the onset of the first case. Swabs were taken from affected animals in rubbing tongues, snouts and some from rectums. Cytopathic viruses were isolated on CRFK cell culture by virological tests. The physicochemical property of a representative virus strain, named Arthur/L, isolated from a male lion was identified as a member of Caliciviridae. However, seroneutralization test indicated that this virus strain was antigenically distinct from Japanese isolates of feline caliciviruses used for comparison. Viral capsid proteins of the present isolate, Arthur/L, and of a feline calicivirus, strain FC7, were compared in an electrophoresis in SDS-PAGE gel. The major viral capsid polypeptide of them were proved to be significantly different in molecular weight. The polypeptide of FC7 was estimated to be ca. 63 KDa whereas that of Arthur/L consisted of 2 components of ca. 65 and 62 KDa. The viral proteins of these two strains were also proved to be distinct by an immunoblotting test.

Identification of canine calicivirus capsid protein and its immunoreactivity in western blotting

A canine calicivirus (CaCV) isolated in Japan, designated as CaCV No. 48 strain, was propagated in MDCK cells and purified by CsCl equilibrium gradient centrifugation. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of the purified samples revealed the presence of only one major species of viral protein of about 60 kilodaltons after Coomassie staining. The same band, presumably that of the capsid protein, was detected by western blotting using a mouse hyperimmune serum. This capsid protein was synthesized in MDCK cells as early as 2 hr post-inoculation. Experimental infection of dogs resulted in the production of anti-CaCV antibodies which were detected by microneutralization test and western blotting. Likewise, serosurvey revealed not only the presence of neutralizing antibodies but also reactivity of the field sera against the capsid protein of the purified virus. These results indicate that the capsid protein of CaCV No. 48 strain is immunogenic and could be detected by antibodies in western blotting.

Human calicivirus genogroup II capsid sequence diversity revealed by analyses of the prototype Snow Mountain agent

The Snow Mountain agent (SMA) is the prototype genogroup II and serotype 3 human calicivirus responsible for epidemic outbreaks of acute gastroenteritis. We have cloned the region of the SMA genome that encodes the single capsid protein. The predicted amino acid sequence of the capsid protein is distinct from other calicivirus strains that have been termed SMA-like based on sequence similarity between the RNA polymerase regions and IEM reactivity. In a previous report, a high sequence similarity in a small region of the RNA polymerase between SMA and another strain, OTH-25, suggested that the capsid proteins of OTH-25 and SMA would be very similar. In this report, we show that the capsid proteins of OTH-25 and SMA are more distinct than was predicted by similarity in the RNA polymerase. In addition, phylogenetic analysis of a region of the RNA polymerase and of the N-terminal conserved domain of the capsid protein of 12 human caliciviruses resulted in trees with different topologies, suggesting that recombination has occurred within this group of viruses. Molecular characterization of the prototype calicivirus strains is important in determining the relationships between capsid similarity at the amino acid level, genetic grouping by sequence comparison, and antigenic reactivity.

Isolation of a calicivirus antigenically related to feline caliciviruses from feces of a dog with diarrhea

A CPE-producing agent was recovered in feline cell cultures from feces of a male dog suffering from intermittent watery diarrhea. Antigenic analysis of this isolate, Sapporo/283, was performed using the plaque reduction neutralization and complement fixation assays and it was neutralized by antisera against feline calicivirus (FCV) but not against canine calicivirus (CaCV). Likewise, it showed common CF antigenicity with the other FCV strains included in the experiments. These findings revealed that the isolate was more closely related antigenically to FCV than CaCV, indicating the possibility of interspecies transmission. It was also suggested that the isolate was a respiratory type calicivirus. Epizootiological results suggested, however, that FCV seldom infects dogs under natural condition.

Study on occurrence of human calicivirus (Mexico strain) as cause of sporadic cases and outbreaks of calicivirus-associated diarrhoea in the United Kingdom, 1983-1995

The use of a recently developed EIA using antisera raised against purified baculovirus expressed recombinant Mexico virus (rMx) capsid protein is described for screening for human calicivirus in stools. The results show that MX-like viruses have been circulating in the UK periodically since 1983 and were an occasional cause of sporadic cases of diarrhoea in infants and outbreaks of infection among elderly patients in hospitals and old people's homes. Further evidence is presented that some strains of caliciviruses with characteristic surface morphology (HuCVs) and some with an indistinct appearance, small round structured viruses (SRSVs) are antigenically related to MxV. Tests on SRSVs from four unrelated outbreaks typed as UK3 failed to react in the Mx EIA or recombinant Norwalk virus (rNV) EIA. A 2-month survey of 206 children treated in two London hospitals for diarrhoea showed that only one was positive for MxV, a child known to be infected with HIV-1. None of the samples reacted in the rNV EIA.

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.