Nucleotide sequence of the capsid protein gene of two serotypes of San Miguel sea lion virus: identification of conserved and non-conserved amino acid sequences among calicivirus capsid proteins

Classification of genotypes based on the VP1 gene of feline calicivirus and study of cross-protection between different genotypes

Feline calicivirus (FCV) causes upper respiratory tract diseases and even death in cats, thereby acting as a great threat to feline animals. Currently, FCV prevention is mainly achieved through vaccination, but the effectiveness of vaccination is limited. In this study, 105 FCV strain VP1 sequences with clear backgrounds were downloaded from the NCBI and subjected to a maximum likelihood method for systematic evolutionary analysis. Based on the genetic analysis results, FCV-positive sera were prepared using SPF mice and Chinese field cats as target animals, followed by a cross-neutralization assay conducted on the different genotype strains and in vivo challenge tests were carried out to further verify with the strain with best cross-protection effect. The results revealed that FCV was mainly divided into two genotypes: GI and GII. The GI genotype strains are prevalent worldwide, but all GII genotype strains were isolated from Asia, indicating a clear geographical feature. This may form resistance to FCV prevention in Asia. The in vitro neutralization assay conducted using murine serum demonstrated that the cross-protection effect varied among strains. A strain with broad-spectrum neutralization properties, DL39, was screened. This strain could produce neutralizing titers (10 × 23.08-10 × 20.25) against all strains used in this study. The antibody titers against the GI strains were 10 × 23.08-10 × 20.5 and those against the GII strains were 10 × 20.75-10 × 20.25. Preliminary evidence suggested that the antibody titer of the DL39 strain against GI was higher than that against GII. Subsequent cross-neutralization assays with cat serum prepared with the DL39 strain and each strain simultaneously yielded results similar to those described above. In vivo challenge tests revealed that the DL39 strain-immunized cats outperformed the positive controls in all measures. The results of several trials demonstrated that strain DL39 can potentially be used as a vaccine strain. The study attempted to combine the genetic diversity and phylogenetic analysis of FCV with the discovery of potential vaccines, which is crucial for developing highly effective FCV vaccines.

Genetic Evolution and Biological Characteristics of Feline Caliciviruses Isolated from Dogs

Feline calicivirus (FCV) is a highly contagious pathogen associated with oral and upper respiratory tract diseases (URTD), and it is also possibly considered as an enteric pathogen. Some studies found FCV-like viruses in the enteric tract of dogs, but there was a lack of understanding regarding the epidemiology and biological properties of FCVs in dogs. In this study, 252 fecal/feces samples were collected from dogs, with or without diarrhea, from 2020 to 2021. There were 6 FCV-positive samples (2.41%, 6/252), from which only two FCVs were successfully isolated and the complete genome sequences obtained. Phylogenetic analysis showed that the two canine-origin FCV isolates belonged to genogroup I and formed a monophyletic cluster with previous FCV strains, sharing a common ancestor. However, there was genetic diversity when the nt identity of the VP1 proteins between the two canine-origin FCV isolates (77.4% nt identity) was compared. In particular, the genomic sequence of the canine/GXHC01-21 isolate showed evidence of recombination at the 3ʹ end of the ORF1 gene with sequence identity very similar to the FCV strain, GX2019, previously isolated from cats in Guangxi in 2019. A comparison of their replication properties indicated that the two isolates could not replicate efficiently in MDCK cells. This was also seen in the enteric FCV isolate, GXNN04-20. However, both displayed similar plaque phenotypes to the respiratory FCV isolate, GX01-13. In addition, it was found that sera from vaccinated cats had low cross-reactivity in a neutralizing antibody test against the two canine-origin FCV isolates. Moreover, high neutralizing antibody titers (≥1 : 128) against canine-origin FCV viruses were observed in the two canine serum samples. This confirmed that interspecies transmission had occurred between cats and dogs. Our results provided an in-depth understanding of the genetic evolution and characteristics of FCVs circulating in dogs.

Identification of amino acid substitutions escaping from a broadly neutralizing monoclonal antibody of feline calicivirus

Feline calicivirus (FCV) causes upper respiratory tract diseases in cats and has highly variable antigenicity for neutralization of each strain. Neutralizing epitopes of FCV are currently found in the hypervariable region (HVR) in the P2 domain of the major capsid protein VP1. Due to its unique ability to neutralize various FCV strains, 1D7 is a monoclonal antibody that may recognize a novel neutralizing epitope. While other neutralizing epitopes were characterized by producing neutralization-resistant variants, only 1D7-resistant variants could not be obtained, and its epitope has not been identified in the previous studies. In this study, we successfully generated these variants by multiple passaging of the FCV F4 strain in the presence of 1D7 and discovered that several amino acid substitutions (K638N, R662G, and T666I in the P1 domain of VP1) are involved in the decreased binding of 1D7. These substitution sites are also highly conserved among FCV strains compared with the substitution sites of other neutralization-resistant variants found in the HVR. Our results indicate that amino acid substitutions in the P1 domain, which are not responsible for direct interaction with the FCV receptor, are associated with neutralization escape. Since FCV can be conveniently cultured in vitro and the receptor required for infection is known, a detailed analysis of the 1D7 epitope could shed more light on the neutralization mechanism of the epitopes of viruses belonging to the Caliciviridae.

Bioinformatics analysis of capsid protein of different subtypes rabbit hemorrhagic disease virus

Background

Rabbit Hemorrhagic Disease Virus (RHDV) belongs to the Caliciviridae family, is a highly lethal pathogen to rabbits. Increasing numbers of studies have demonstrated the existence of antigenic variation in RHDV, leading to the emergence of a new RHDV isolate (RHDVb). However, the underlying factors determining the emergence of the new RHDV and its unpredictable epidemiology remain unclear. To investigate these issues, we selected more than 184 partial and/or complete genome sequences of RHDV from GenBank and analyzed their phylogenetic relationships, divergence, and predicted protein modification sites.

Results

Phylogenetic analysis showed that classic RHDV isolates, RHDVa, and RHDVb formed different clades. It’s interesting to note that RHDVa being more closely related to classic RHDV than RHDVb, while RHDVb had a closer genetic relationship to Rabbit Calicivirus (RCV) than to classic RHDV isolates. Moreover, divergence analysis suggested that the accumulation of amino acid (aa) changes might be a consequence of adaptive diversification of capsid protein (VP60) during the division between classical RHDV, RHDVa, RHDVb, and RCV. Notably, the prediction of N-glycosylation sites suggested that RHDVb subtypes had two unique N-glycosylation sites (aa 301, 362) but lacked three other N-glycosylation sites (aa 45, 308, 474) displayed in classic RHDV and RHDVa VP60 implying this divergence of N-glycosylation sites in RHDV might affect viral virulence. Analysis of phosphorylation sites also indicated that some phosphorylation sites in RHDVa and RHDVb differed from those in classic RHDV, potentially related to antigenic variation in RHDV.

Conclusion

The genetic relationship between RHDVb and RCV was closer than classic RHDV isolates. Moreover, compared to RHDV and RHDVa, RHDVb had two unique N-glycosylation sites but lacked three sites, which might affect the virulence of RHDV. These results may provide new clues for further investigations of the origin of new types of RHDV and the mechanisms of genetic variation in RHDV.

Bat Caliciviruses and Human Noroviruses Are Antigenically Similar and Have Overlapping Histo-Blood Group Antigen Binding Profiles

Emerging zoonotic viral diseases remain a challenge to global public health. Recent surveillance studies have implicated bats as potential reservoirs for a number of viral pathogens, including coronaviruses and Ebola viruses. Caliciviridae represent a major viral family contributing to emerging diseases in both human and animal populations and have been recently identified in bats. In this study, we blended metagenomics, phylogenetics, homology modeling, and in vitro assays to characterize two novel bat calicivirus (BtCalV) capsid sequences, corresponding to strain BtCalV/A10/USA/2009, identified in Perimyotis subflavus near Little Orleans, MD, and bat norovirus. We observed that bat norovirus formed virus-like particles and had epitopes and receptor-binding patterns similar to those of human noroviruses. To determine whether these observations stretch across multiple bat caliciviruses, we characterized a novel bat calicivirus, BtCalV/A10/USA/2009. Phylogenetic analysis revealed that BtCalV/A10/USA/2009 likely represents a novel Caliciviridae genus and is most closely related to "recoviruses." Homology modeling revealed that the capsid sequences of BtCalV/A10/USA/2009 and bat norovirus resembled human norovirus capsid sequences and retained host ligand binding within the receptor-binding domains similar to that seen with human noroviruses. Both caliciviruses bound histo-blood group antigens in patterns that overlapped those seen with human and animal noroviruses. Taken together, our results indicate the potential for bat caliciviruses to bind histo-blood group antigens and overcome a significant barrier to cross-species transmission. Additionally, we have shown that bat norovirus maintains antigenic epitopes similar to those seen with human noroviruses, providing further evidence of evolutionary descent. Our results reiterate the importance of surveillance of wild-animal populations, especially of bats, for novel viral pathogens.IMPORTANCE Caliciviruses are rapidly evolving viruses that cause pandemic outbreaks associated with significant morbidity and mortality globally. The animal reservoirs for human caliciviruses are unknown; bats represent critical reservoir species for several emerging and zoonotic diseases. Recent reports have identified several bat caliciviruses but have not characterized biological functions associated with disease risk, including their potential emergence in other mammalian populations. In this report, we identified a novel bat calicivirus that is most closely related to nonhuman primate caliciviruses. Using this new bat calicivirus and a second norovirus-like bat calicivirus capsid gene sequence, we generated virus-like particles that have host carbohydrate ligand binding patterns similar to those of human and animal noroviruses and that share antigens with human noroviruses. The similarities to human noroviruses with respect to binding patterns and antigenic epitopes illustrate the potential for bat caliciviruses to emerge in other species and the importance of pathogen surveillance in wild-animal populations.

Characterization of a Vesivirus Associated with an Outbreak of Acute Hemorrhagic Gastroenteritis in Domestic Dogs

Four of eleven affected dogs died despite aggressive treatment during a 2015 focal outbreak of hemorrhagic gastroenteritis following a stay in a pet housing facility. Routine diagnostic investigations failed to identify a specific cause. Virus isolation from fresh necropsy tissues yielded a calicivirus with sequence homology to a vesivirus within the group colloquially known as the vesivirus 2117 strains that were originally identified as contaminants in CHO cell bioreactors. In situ hybridization and reverse transcription-PCR assays of tissues from the four deceased dogs confirmed the presence of canine vesivirus (CaVV) nucleic acids that localized to endothelial cells of arterial and capillary blood vessels. CaVV nucleic acid corresponded to areas of necrosis and hemorrhage primarily in the intestinal tract, but also in the brain of one dog with nonsuppurative meningoencephalitis. This is the first report of an atypical disease association with a putative hypervirulent vesivirus strain in dogs, as all other known strains of CaVV appear to cause nonclinical infections or relatively mild disease. After identification of the CU-296 vesivirus strain from this outbreak, four additional CaVV strains were amplified from unrelated fecal specimens and archived stocks provided by other laboratories. Broader questions include the origins, reservoir(s), and potential for reemergence and spread of these related CaVVs.

Intranasal immunization with inactivated feline calicivirus particles confers robust protection against homologous virus and suppression against heterologous virus in cats

The protective efficacy of intranasal (IN) administration of inactivated feline calicivirus (FCV) vaccine against homologous or heterologous FCV infection was investigated. Groups of cats immunized with the experimental inactivated, non-adjuvanted FCV vaccine via either the IN or subcutaneous (SC) route were exposed to homologous or highly heterologous FCV. Both the IN and SC immunization protocols established robust protection against homologous FCV infection. Although neither immunization regimen conferred protection against the heterologous strain, clinical scores and virus titres of oral swabs were lower in cats in the IN group compared to those in the SC group, accompanying a faster neutralizing antibody response against the heterologous virus in cats in the IN group. The IN group secreted more IgA specific to FCV proteins in oral washes (lavage fluids from the oral cavity) than the SC group. IN immunization with an inactivated whole FCV particle, which protects cats from homologous virus exposure and shortens the period of heterologous virus shedding, may serve as a better platform for anti-FCV vaccine.

An in vivo system for directed experimental evolution of rabbit haemorrhagic disease virus

The calicivirus Rabbit haemorrhagic disease virus (RHDV) is widely used in Australia as a biocontrol agent to manage wild European rabbit (Oryctolagus cuniculus) populations. However, widespread herd immunity limits the effectiveness of the currently used strain, CAPM V-351. To overcome this, we developed an experimental platform for the selection and characterisation of novel RHDV strains. As RHDV does not replicate in cell culture, variant viruses were selected by serially passaging a highly virulent RHDV field isolate in immunologically naïve laboratory rabbits that were passively immunised 18–24 hours post-challenge with a neutralising monoclonal antibody. After seven passages, two amino acid substitutions in the P2 domain of the capsid protein became fixed within the virus population. Furthermore, a synonymous substitution within the coding sequence of the viral polymerase appeared and was also maintained in all subsequent passages. These findings demonstrate proof-of-concept that RHDV evolution can be experimentally manipulated to select for virus variants with altered phenotypes, in this case partial immune escape.

Comparative analysis of rabbit hemorrhagic disease virus strains originating from outbreaks in the Russian Federation

Since the first introduction of rabbit hemorrhagic disease (RHD) in 1986, disease outbreaks have been continuously reported in different regions of Russia. Despite extensive vaccination, sporadic RHD cases are still reported. Here, we examine eleven RHDV strains originating from disease outbreaks occurring between 2003 and 2012 and one widely used vaccine strain. Notable phenotypic and genetic heterogeneity among RHDV strains was observed. The RHDV strains Tambov-2010, Perm-2010, Manihino-09 showed different hemagglutinating activity (HA) at 4 °C and room temperature. While all RHDV field strains were identified as hemagglutinating virulent viruses of the RHDVa variant, the vaccine strain was assigned as a "classical" RHDV. These data indicate that since 2003, RHDVa has become the predominant variant circulating in Russia.

Production, Characterization, and Epitope Mapping of Monoclonal Antibodies Against Different Subtypes of Rabbit Hemorrhagic Disease Virus (RHDV)

In 2010, a new rabbit hemorrhagic disease virus (RHDV) variant, designated RHDV2, was identified for the first time in Italy. Studies have shown that RHDV2 differs from RHDV1 (traditional RHDV) in terms of its antigenic profile and genetic characteristics. The VP60 protein of RHDV is a structural protein that plays important roles in viral replication, assembly, and immunogenicity. In this study, we immunized BALB/c mice with recombinant VP60 proteins from different RHDV subtypes. After three rounds of subcloning, type-specific positive hybridoma clones of RHDV1 and RHDV2 were further identified by an enzyme-linked immunosorbent assay, Western blotting, and an indirect immunofluorescence assay. Finally, three monoclonal antibodies (MAbs) (1D6, 1H2, and 3F2) that only recognize RHDV1, and four MAbs (1G2, 2C1, 3B7, and 5D6) that only recognize RHDV2 were identified. The epitopes recognized by these MAbs were mapped by Western blotting. Sequence analysis showed that the epitope sequences recognized by 1D6, 1H2, and 3F2 are highly conserved (98%) among RHDV1 strains, whereas the epitope sequences recognized by 1G2, 2C1, 3B7, and 5D6 are 100% conserved among RHDV2 strains. The high conservation of the epitope sequence showed that the screened MAbs were type-specific, and that they could distinguish different RHDV subtypes.

Molecular evolution and antigenic variation of European brown hare syndrome virus (EBHSV)

European brown hare syndrome virus (EBHSV) is the aetiological agent of European brown hare syndrome (EBHS), a disease affecting Lepus europaeus and Lepus timidus first diagnosed in Sweden in 1980. To characterize EBHSV evolution we studied hare samples collected in Sweden between 1982 and 2008. Our molecular clock dating is compatible with EBHSV emergence in the 1970s. Phylogenetic analysis revealed two lineages: Group A persisted until 1989 when it apparently suffered extinction; Group B emerged in the mid-1980s and contains the most recent strains. Antigenic differences exist between groups, with loss of reactivity of some MAbs over time, which are associated with amino acid substitutions in recognized epitopes. A role for immune selection is also supported by the presence of positively selected codons in exposed regions of the capsid. Hence, EBHSV evolution is characterized by replacement of Group A by Group B viruses, suggesting that the latter possess a selective advantage.

Rabbit hemorrhagic disease virus detected in Pico, Azores, Portugal, revealed a unique endemic strain with more than 17 years of independent evolution

Rabbit hemorrhagic disease is caused by a calicivirus, rabbit hemorrhagic disease virus (RHDV), which is responsible for high mortality in domestic and wild European rabbits (Oryctolagus cuniculus). RHDV strains were sequenced from wild European rabbits (Oryctolagus cuniculus algirus) collected in the Azorean island of Pico, Portugal. Phylogenetic analyses showed that the Pico RHDV strains diverge from all of the others described so far, but cluster with the genogroups 1–5 (G1–G5). The genetic distance between the Pico RHDV sequences and each G1, G2 and G3–G5 genogroup (~0.08) is compatible with an RHDV introduction at least 17 years ago. Our results show that in Pico, RHDV is the outcome of an independent evolution from the original RHDV strain that appeared in its European rabbit population. These are the first sequences of RHDV obtained in the subspecies O. c. algirus, outside of its original region, the Iberian Peninsula. Furthermore, we discuss the risk of rabbit translocations from the Azores to the Iberian Peninsula, where the rabbit wild populations are suffering high mortalities.

Immunogenicity of different recombinant rabbit hemorrhagic disease virus-like particles carrying CD8+ T cell epitope from chicken ovalbumin (OVA)

To explore the capacity and immunogenicity of virus-like particles (VLPs) of rabbit hemorrhagic disease virus (RHDV) accommodating foreign amino acid sequences, integrations were performed at the following four locations of the structural protein VP60 of RHDV using the OVA257-264 CD8+ T cell epitope (SIINFEKL): (1) inserting at the N-terminus of the VP60 protein (N1); (2) replacing amino acid positions 2-14 of the VP60 protein (N2); (3) replacing amino acid positions 196-207 of the VP60 protein (I1); and (4) replacing amino acid positions 217-228 of the VP60 protein (I2). The recombinant proteins were expressed by baculovirus expression system. The ability to form RHDV-like particles was confirmed by electron microscopy. The immunogenicity of the four recombinant proteins (N1, N2, I1 and I2) was evaluated in mice without any adjuvants. The results indicated that the four recombinant proteins (N1, N2, I1 and I2) could assemble into VLPs. All of the recombinant proteins could induce a specific immune response. Recombinant proteins I1 and I2 were able to elicit both high levels of IFN-γ secretion and anti-VP60 specific immune responses in the murine model. The levels of the VP60-specific IgG antibody in groups I1 and I2 displayed higher optical density (OD) values than those of groups N1 and N2 (P<0.001, P<0.001). The number of IFN-γ-producing splenocytes in mice that were immunized with recombinant proteins I1 and I2 was also significantly greater compared with mice that were immunized with recombinant proteins N1 and N2 (P<0.01). All of these above mentioned results might be beneficial to the establishment of the RHDV-VLPs display system.

Molecular epidemiology of Rabbit Haemorrhagic Disease Virus in Australia: when one became many

Rabbit Haemorrhagic Disease Virus (RHDV) was introduced into Australia in 1995 as a biological control agent against the wild European rabbit (Oryctolagus cuniculus). We evaluated its evolution over a 16-year period (1995-2011) by examining 50 isolates collected throughout Australia, as well as the original inoculum strains. Phylogenetic analysis of capsid protein VP60 sequences of the Australian isolates, compared with those sampled globally, revealed that they form a monophyletic group with the inoculum strains (CAPM V-351 and RHDV351INOC). Strikingly, despite more than 3000 rereleases of RHDV351INOC since 1995, only a single viral lineage has sustained its transmission in the long-term, indicative of a major competitive advantage. In addition, we find evidence for widespread viral gene flow, in which multiple lineages entered individual geographic locations, resulting in a marked turnover of viral lineages with time, as well as a continual increase in viral genetic diversity. The rate of RHDV evolution recorded in Australia -4.0 (3.3-4.7) × 10(-3) nucleotide substitutions per site per year - was higher than previously observed in RHDV, and evidence for adaptive evolution was obtained at two VP60 residues. Finally, more intensive study of a single rabbit population (Turretfield) in South Australia provided no evidence for viral persistence between outbreaks, with genetic diversity instead generated by continual strain importation.

Detection of RHDVa on the Iberian Peninsula: isolation of an RHDVa strain from a Spanish rabbitry

Rabbit haemorrhagic disease virus (RHDV), genus Lagovirus, family Caliciviridae, causes a large number of deaths in wild and domestic adult European rabbits (Oryctolagus cuniculus). The first documented outbreak dates from 1984 in China, but the virus rapidly dispersed worldwide. In 1997, an antigenic variant was detected in Italy and designated RHDVa. Despite causing symptoms similar to those caused by classic RHDV strains, marked antigenic and genetic differences exist. In some parts of Europe, RHDVa is replacing classic strains. Here, we report the presence of RHDVa on the Iberian Peninsula, where this variant was thought not to contribute to viral diversity.

Variant rabbit hemorrhagic disease virus in young rabbits, Spain

Outbreaks of rabbit hemorrhagic disease have occurred recently in young rabbits on farms on the Iberian Peninsula where rabbits were previously vaccinated. Investigation identified a rabbit hemorrhagic disease virus variant genetically related to apathogenic rabbit caliciviruses. Improved antivirus strategies are needed to slow the spread of this pathogen.

Large-scale spatial and temporal genetic diversity of feline calicivirus

Feline calicivirus (FCV) is an important pathogen of domestic cats and a frequently used model of human caliciviruses. Here we use an epidemiologically rigorous sampling framework to describe for the first time the phylodynamics of a calicivirus at regional and national scales. A large number of FCV strains cocirculated in the United Kingdom at the national and community levels, with no strain comprising more than 5% and 14% of these populations, respectively. The majority of strains exhibited a relatively restricted geographical range, with only two strains (one field virus and one vaccine virus) spreading further than 100 km. None of the field strains were identified outside the United Kingdom. Temporally, while some strains persisted locally for the majority of the study, others may have become locally extinct. Evolutionary analysis revealed a radial phylogeny with little bootstrap support for nodes above the strain level. In most cases, spatially and temporally diverse strains intermingled in the phylogeny. Together, these data suggest that current FCV evolution is not associated with selective competition among strains. Rather, the genetic and antigenic landscape in each geographical location is highly complex, with many strains cocirculating. These variants likely exist at the community level by a combination of de novo evolution and occasional gene flow from the wider national population. This complexity provides a benchmark, for the first time, against which vaccine cross-protection at both local and national levels can be judged.

Rabbit haemorrhagic disease (RHD) and rabbit haemorrhagic disease virus (RHDV): a review

Rabbit haemorrhagic disease virus (RHDV) is a calicivirus of the genus Lagovirus that causes rabbit haemorrhagic disease (RHD) in adult European rabbits (Oryctolagus cuniculus). First described in China in 1984, the virus rapidly spread worldwide and is nowadays considered as endemic in several countries. In Australia and New Zealand where rabbits are pests, RHDV was purposely introduced for rabbit biocontrol. Factors that may have precipitated RHD emergence remain unclear, but non-pathogenic strains seem to pre-date the appearance of the pathogenic strains suggesting a key role for the comprehension of the virus origins. All pathogenic strains are classified within one single serotype, but two subtypes are recognised, RHDV and RHDVa. RHD causes high mortality in both domestic and wild adult animals, with individuals succumbing between 48-72 h post-infection. No other species has been reported to be fatally susceptible to RHD. The disease is characterised by acute necrotising hepatitis, but haemorrhages may also be found in other organs, in particular the lungs, heart, and kidneys due to disseminated intravascular coagulation. Resistance to the disease might be explained in part by genetically determined absence or weak expression of attachment factors, but humoral immunity is also important. Disease control in rabbitries relies mainly on vaccination and biosecurity measures. Such measures are difficult to be implemented in wild populations. More recent research has indicated that RHDV might be used as a molecular tool for therapeutic applications. Although the study of RHDV and RHD has been hampered by the lack of an appropriate cell culture system for the virus, several aspects of the replication, epizootology, epidemiology and evolution have been disclosed. This review provides a broad coverage and description of the current knowledge on the disease and the virus.

Characterisation of a non-pathogenic and non-protective infectious rabbit lagovirus related to RHDV

The existence of non-pathogenic RHDV strains was established when a non-lethal virus named rabbit calicivirus (RCV) was characterised in 1996 in Italy. Since then, different RNA sequences related to RHDV have been detected in apparently healthy domestic and wild rabbits, and recently a new lagovirus was identified in Australia. We have characterised from seropositive healthy domestic rabbits a non-lethal lagovirus that differs from RHDV in terms of pathogenicity, tissue tropism and capsid protein sequence. Phylogenetic analyses have revealed that it is close to the Ashington strain and to the RCV, but distinct. We proved experimentally that it is infectious but non-pathogenic and demonstrated that, contrary to the other described non-pathogenic lagoviruses, it induces antibodies that do not protect against RHDV. Our results indicate the existence of a gradient of cross-protection between circulating strains, from non-protective, partially protective to protective strains, and highlight the extent of diversity within the genus Lagovirus.

Immunological and genetic characterization of feline caliciviruses used in the development of a new trivalent inactivated vaccine in Japan

Although vaccination against feline calicivirus (FCV) infection is widespread in Japan, FCV-associated diseases are still a significant problem in cats. Thus, we developed a new trivalent inactivated vaccine, Kyoto Biken Feline-CPR, consisting of three FCV strains; one was the production strain of our previous vaccine, and the others were screened from 60 field isolates obtained between 1998 and 2000 based on cross-neutralization tests. In this report, the three FCV strains used for development of the new vaccine were antigenically and genetically characterized. The three strains were antigenically quite different, as revealed by cross-neutralization tests. Alignment of deduced amino acid sequences of capsid regions A to E revealed that there were marked differences between the strains in both the N- and C ends of region E. Antisera against the three vaccine strains, our new vaccine and 2 commercial vaccines were then evaluated for neutralization with 58 field isolates collected between 2003 and 2006. Rat antisera against the three vaccine strains and a mixture of the 3 strains neutralized 49, 37, 42 and 55 isolates, respectively. Cat antiserum against the new vaccine neutralized 50 (86.2%) isolates, whereas the numbers neutralized by cat antisera against 2 commercial vaccines were 37 (63.8%) and 25 (43.1%). In conclusion, the immunological and genetic properties of the 3 vaccine strains investigated varied widely, and the Kyoto Biken Feline-CPR vaccine may have more potential to meet the antigenic diversity of FCVs spreading throughout Japan.

Characterization of San Miguel sea lion virus populations using pyrosequencing-based methods

San Miguel Sea Lion Virus (SMSV) is a small RNA virus in the genus Vesivirus with an unusually broad host range. Three populations of SMSV were examined by PCR amplification of the capsid precursor and putative helicase genes, followed by pyrosequencing. The populations were nasal swabs from two SMSV infected California sea lions (Zalophus californianus) from two different years, and a virus isolate from the earlier swab that was passaged in cell culture five times. In the capsid precursor, extensive deletions were prevalent in the passaged virus but uncommon in the clinical samples. A greater prevalence of point mutations was seen in the capsid precursor gene than in the putative helicase gene. In culture, the minority sequence in the capsid precursor at nucleotide position 5826 rapidly shifted after five passages to become the majority sequence. Levels of diversity at individual sites showed much more similarity between the two clinical samples than between the earlier clinical sample and the passaged culture from the same sample. SMSV appears to behave as a quasispecies. Assessment of original patient samples is preferable for understanding clinical SMSV populations.

Expression and self-assembly of virus-like particles from two genotypes of marine vesiviruses and development of an ELISA for the detection of antibodies

Sequences encoding the major and minor capsid proteins (VP1 and VP2) from two marine vesivirus isolates (Steller sea lion viruses V810 and V1415) were engineered for expression of virus-like particles (VLPs) in the baculovirus system. The resulting VLPs were morphologically similar to native vesivirus virions. Purified VLPs were probed in immunoblots with pooled antisera specific for nine San Miguel sea lion virus (SMSV) types, and a predominant protein of approximately 60kDa was detected. An enzyme linked immunosorbent assay (ELISA) for the detection of antibodies was developed in which the VLPs served as antigen. The VLPs were adsorbed to the wells of a microplate, and the specificity of the ELISA was established with hyperimmune sera raised against 24 serotypes of the genus Vesivirus. The ELISA was used to screen for the presence of vesivirus specific antibodies in the sera of free-ranging Steller sea lions. The ELISA results demonstrated that Steller sea lions that inhabit the Pacific Ocean waters of southeast Alaska are widely exposed to antigenically related marine vesiviruses, while no previous exposure could be demonstrated using VLP antigens in 17 Steller sea lions from the Aleutian Islands. The broad reactivity of these VLPs and their non-infectious nature will facilitate global sero-epidemiological studies aimed at determining the incidence and prevalence of marine vesiviruses in mammals that inhabit the Pacific and Atlantic oceans as well as susceptible terrestrial animals.

A capsid gene-based real-time reverse transcription polymerase chain reaction assay for the detection of marine vesiviruses in the Caliciviridae

A real-time reverse transcription polymerase chain reaction (rtRT-PCR) assay was developed for the identification of marine vesiviruses. The primers were designed to target a 176-nucleotide fragment within a highly conserved region of the San Miguel sea lion viruses (SMSVs) capsid gene. The assay detected viral RNA from nine marine vesivirus serotypes described previously, including two serotypes (SMSV-8 and -12) not identified with presently available molecular assays, a highly related bovine vesivirus strain (Bos-1), a mink vesivirus strain (MCV), and two novel genotypes isolated recently from Steller sea lions (SSL V810 and V1415). The real-time assay did not amplify sequences from the corresponding genomic regions of feline calicivirus (also in the genus Vesivirus) and representative members of the genus Norovirus. The rtRT-PCR assay described below may prove useful as a diagnostic tool for the detection of currently circulating, emerging and previously described marine vesiviruses in clinical samples, especially when large numbers are screened in surveillance studies of these restricted viruses.

Detection of positive selection in the major capsid protein VP60 of the rabbit haemorrhagic disease virus (RHDV)

Mutations were analysed in the major capsid protein VP60 of the rabbit haemorrhagic disease virus (RHDV), a calicivirus responsible for high mortality rates in both wild and domestic European rabbits (Oryctolagus cuniculus). Likelihood of positive selection was estimated using the PAML software applied to 43 non-identical complete sequences of the major capsid protein. Three codons showed signs of positive selection (with posterior probabilities over 95%), one of them is located in the region containing the major antigenic determinants (region E). The presence of positively selected codons (PSCs) in other regions may suggest the existence of other antigenic regions on the major capsid protein that stimulate protective immune responses. At all the 3 PSCs, variation contributes to putative N-glycosylation sites of the protein. An N-glycosylation site is deleted in the non-pathogenic strain RCV. Some of the substitutions at PSCs may alter the polarity and the charge of the protein with possible implications in the protein structure and host interaction. The detection of PSCs should allow a better understanding of the interaction between RHDV and the rabbit immune system.

Genomic characterization of novel marine vesiviruses from Steller sea lions (Eumetopias jubatus) from Alaska

Marine vesiviruses were isolated in cell culture from oral and rectal swabs and vesicular fluid from Alaskan Steller sea lions (SSL; Eumetopias jubatus). Further characterization by RT-PCR, complete genomic sequencing, and phylogenetic analyses indicated that these viruses are most closely related to the marine vesiviruses, but are distinct viruses and represent two novel genotypes. The complete genome of these two SSL isolates was sequenced after cloning their viral cDNA. The genomes were found to be 8302 and 8305 nucleotides in length, organized in three open reading frames and contained 5' and 3' untranslated regions (UTR) of 19 and 180 nucleotides, respectively. The complete genomes of both SSL viruses were most closely related to each other and shared 83.0% nucleotide identity. Using the very limited number of complete genomic vesivirus sequences available in the NCBI database, these novel SSL vesiviruses seem most closely related to vesicular exanthema of swine virus-A48 and least related to rabbit vesivirus and walrus calicivirus. Specific antiserum against some evolutionary closer marine vesiviruses did not neutralize these isolates supporting the novel nature of these SSL viruses.

FCV-VBS isolated from cats with typical symptoms caused VSD in experimental cats

Commercially available vaccines have been used widely to prevent feline calicivirus infection (FCI). However, with their widespread use, field strains, which are weakly cross-reactive with the live-virus vaccine strain F9, have posed the problem of vaccine breakdown. Recently the existence of FCV--associated virulent systemic disease (VSD) has been published. But their molecular diversity, antigenic mutations and physicochemical property have not been sufficiently clarified. Thus, we experimentally gave the vaccine breakdown strain (VBS) H10 to cats that had been inoculated with an F9 live vaccine. After the administration of strain H10, vaccinated cats (1 through 4) had no respiratory symptoms, whereas the non-vaccinated cat 5 showed clinical symptoms such as a fever of over 40 degrees C, loss of vitality, decreased appetite, diarrhea, and nasal discharge after receiving strain H10, and died. Lethal FCV is rare, and may be a virulent systemic disease (VSD)--inducing strain. This is the initial report on VSD in Japan. It has been reported that symptoms of VSD were similar in vaccinated and nonvaccinated cats on experimental infection. However, no VSD-like symptoms developed, and the incidence of the disease varied depending on the presence or absence of vaccination, suggesting that there are two mechanisms of vaccine breakdown: one is associated with the vaccine immunity level, and the other is not. The characteristics of the VBS revealed were: (1) the duration of virus excretion was short when the originally carried antibody titer before virus challenge was high, (2) the excreted viral molecular species varied daily, not being limited to a specific species with time, and (3) the acquired physicochemical properties did not persist, and altered daily. FCV-VBS alters the molecular species and physicochemical properties daily due to the reduction of host immunity, which may lead to VSD.

Isolation and identification of a non-haemagglutinating strain of rabbit hemorrhagic disease virus from China and sequence analysis for the VP60 Gene

A variant strain of rabbit hemorrhagic disease virus, designated "whn-1", was isolated and identified in China. The virus lacked haemagglutinating activity at 25, 37 and 4 degrees C, respectively, and gave negative results in the HAT after two passages in experimentally infected rabbits, but gave positive results in Agar Diffusion Reaction (ADR) and Counter Immunoelectrophoresis (CIE). Using electron microscopy, negatively stained particles of the RHDV isolate showed that the virions was approximately 35 nm in diameter. The capsid protein VP60 gene of whn-1 strain was cloned into pMD18-T vector by RT-PCR assays and sequenced. The obtained VP60 gene sequence has been submitted to GenBank with the accession number: DQ069280. The whole VP60 gene of whn-1 was 1740 nt in size and encodes 579 aa. Alignment with other 16 strains of RHDV in the world, including such "RHDVa" strains as France 99-05, France-Reu-00, Germany-Triptis and ChinaTP, in addition to RCV and EBHSV, showed that the homology of RHDV strains were 90.0-98.0% for nucleotide sequence, 94.3-99.0% for amino acid sequence, respectively. The results indicated that the sequences of VP60 gene of different RHDV isolates, including non-haemagglutinating whn-1 strain and low-haemagglutinating Rainham strain, were relatively highly homologous, and the major variant amino acid were located within region C (301-328 aa) and region E(344-434 aa), which were specific to "RHDVa" strains. Moreover, the molecular characterisation of VP60 protein of RHDV whn-1 strain, such as Hydrophilicity plot, Flexible regions, Antigenic index, etc., were compared with reference RHDV strains of Spanish-AST/89, France-99-5 and UK-Rainham in this article. From the experiment, it's concluded that, the "whn-1" strain is probably an antigenic variant of "RHDVa", and the 3 amino acids of Phe (304), Ala (305), Ser (309), and 5 amino acids of Gly (359), Asn (365), Ala (369), Ala (370), Asn (386), located in P2 region in the VP60 protein, probably played an important role in the haemagglutination activity.

Longitudinal molecular epidemiological analysis of feline calicivirus infection in an animal shelter: a model for investigating calicivirus transmission within high-density, high-turnover populations

The control of outbreaks of calicivirus infection in high-density, high-throughput populations is a challenge to both human and veterinary medicine. In such populations, the prevalence of infection is, in part, dependent on the levels of biosecurity and how this affects virus transmission. Here we show how longitudinal analysis of feline calicivirus (FCV) infection in an animal rescue shelter can be used as a model to examine the dynamics of calicivirus transmission and evolution in such environments. FCV was isolated from 33 of 116 cats sampled over a 15-month period (overall prevalence, 28%). Sequence analysis of the immunodominant variable regions of the viral capsid gene identified 16 strains circulating in the shelter, with no single strain appearing to predominate. The majority of these strains were introduced into the shelter from the community and did not appear to be transmitted within the population. However, for three of these strains, putative transmission events within the shelter were identified. The rates of evolution within hypervariable regions of the FCV capsid gene in individual cats ranged from 0.05 to 1.4% per week, with the highest rates generally being found in animals that either acquired the virus while in the shelter or were undergoing acute infection. These data suggest that despite the high prevalence and presence of multiple strains of FCV within the shelter, the spread of such pathogens may be restricted by various control measures, including good hygiene and biosecurity.

Molecular and antigenic characterization of rabbit hemorrhagic disease virus isolated in Cuba indicates a distinct antigenic subtype

Phylogenetic analyses conducted on isolates of rabbit hemorrhagic disease virus (RHDV) from throughout the world have shown well-defined genogroups comprising representative strains of the virus and antigenic variants. In this work, we have isolated and characterized RHDV from the major epizootic that occurred in Cuba in 2004-2005. Sequence analysis of the capsid protein gene and antigenic characterization of this strain has allowed its inclusion as a member of the distinct RHDVa subtype. We also found that specific antibodies directed against RHDV reference strains bound to the Cuban isolate in a competition ELISA and inhibited virus hemagglutination in vitro. This is the second report on the molecular characterization of RHDVa circulating in the American region.

Persistence of viral RNA in rabbits which overcome an experimental RHDV infection detected by a highly sensitive multiplex real-time RT-PCR

An internally controlled multiplex real-time RT-PCR using TaqMan probes and external standards for absolute RNA quantification was developed as a new diagnostic tool for the detection of rabbit haemorrhagic disease virus (RHDV). The test revealed a specificity of 100%, an analytical sensitivity of 10 copies/well and a linearity over a range from 10(1) to 10(10) copies. The viral loads in organs, leukocytes, sera and excretions of seropositive, convalescent rabbits which were overcoming an experimental infection with RHDV were determined using the validated assay. As a result, viral RNA was demonstrated and quantified for at least 15 weeks. Thus, a persistence of viral RNA after experimental infection of rabbits could be shown for the first time. In contrast, neither antigen nor infectious virus could be detected by antigen-ELISA, immunohistochemistry or experimental transmission. Therefore, further experiments are necessary to prove that the persistence of RNA is linked with the persistence of infectious virus particles.

Genogrouping of Vaccine Breakdown Strains (VBS) of Feline Calicivirus in Japan

Although prevention of feline calcivirus (FCV) infection by vaccination has been attempted, and isolation of FCV, development of the disease, and a few fatal cases in vaccinated cats have been reported. Fifteen FCV strains isolated from cats that had been vaccinated with commercially available FCV vaccines (F9, FCV-255, and FC-7) were genogrouped. Molecular analysis of viral genomes involved the construction of a phylogenetic tree of capsid genes using the NJ method. Cat anti-F9 serum and rabbit anti-FCV-255 serum were used for virus neutralization tests. Molecular phylogenetic analysis of the amino acid sequences of 15 virus isolates and those of the previously published and GenBank-deposited 9 global and 14 Japanese strains showed that 8 (53%) of the 15 virus isolates as well as the vaccine strains F9 and FCV-255 belonged to genogroup I (G(A)I), and 7 (47%) belonged to genogroup II (G(A)II). Of the 8 G(A)I strains, 2 were isolated from cats that had been vaccinated with an F9 strain live vaccine, 5 from cats vaccinated with an FCV-255-derived vaccine, and 1 from a cat vaccinated with an FC-7-derived vaccine. Of the 7 GAll strains, 5 were isolated from cats that had been vaccinated with the F9 strain live vaccine, 1 from a cat vaccinated with the FCV-255-derived vaccine, and 1 from a cat vaccinated with the FC-7-derived vaccine. These results indicate that more vaccine breakdown strains isolated from the cats vaccinated with the F9 strain-derived vaccine belong to G(A)II than to G(A)I, whereas more vaccine breakdown strains isolated from the cats vaccinated with the FCV-255 strain-derived vaccine belong to G(A)I than to G(A)II, and that when the FC-7 strain-derived vaccine is used, the vaccine breakdown strains belong almost equally to G(A)I and G(A)II. Thus, the genogroups of virus isolates varied with the vaccine strain used (p < 0.05). On the other hand, the neutralizing titres of feline anti-F9 serum and rabbit anti-FCV-255 serum against the 15 isolates were very low, showing no relationships between neutralizing antibody titres and genogroups. The DNA sequence identities between the virus isolates and the vaccine strains were low, at 70.6-82.9%, and no strains were found to have sequences derived from the vaccine strains. Alignment of amino acid sequences showed that the G(A)I or G(A)II virus isolates from the F9-vaccinated cats differed at position 428 of the 5' hypervariable region (HVR) of capsid region of the F9 strain, whereas those from the FCV-255-vaccinated cats differed at positions 438, 453, and 460 of the 5'HVR of capsid region E of the F9 strain. We speculate that these differences influence genogrouping. The amino acid changes within the F9 linear epitopes common to G(A)I and G(A)II were noted at positions 450, 451, 457 of 5'HVR of the capsid region E in the isolates from F9-derived vaccine-treated cats, and 449, 450, and 451 of 5'HVR of capsid region E in the isolates from FCV-255-derived vaccine-treated cats, suggesting that these amino acid changes are involved in escapes. These results suggest that alternate vaccination with the F9 and FCV-255 strains or the use of a polyvalent vaccine containing GAll strains serves to inhibit development.

Evolutionary mechanisms of persistence and diversification of a calicivirus within endemically infected natural host populations

In order to understand the evolutionary mechanisms of persistence and diversification within the Caliciviridae, we have been exploiting endemic infection of feline calicivirus within five geographically distinct household groups of cats. By sequencing immunodominant and variable regions of the capsid gene, we identified the relative contribution of the different evolutionary processes employed by the virus to ensure its long-term survival in the host population. Such strategies included progressive evolution of a given variant of a strain through mutation accumulation within an individual, sequential reinfection with either a variant of the same strain or with a different strain, and mixed infection. Recombination between different strains in this study has been reported in detail elsewhere (K. P. Coyne et al., J. Gen. Virol. 87:921-926, 2006). Here, we provide evidence to suggest that true long-term persistent infection in individuals is relatively rare, with the majority of apparent viral carriers undergoing a combination of progressive evolution and cyclical reinfection. Progressive evolution at the individual level and variant reinfection at both the individual and population levels were associated with positive selection. Two measures of evolution rate were determined; for a virus progressively evolving within an individual (1.32 x 10(-2) to 2.64 x 10(-2) substitutions per nucleotide per year, i.e., no transmission) and for a strain circulating within a population (3.84 x 10(-2) to 4.56 x 10(-2) substitutions per nucleotide per year, i.e., including transmission). Reiteration of both progressive evolution and variant reinfection appeared to lead to a gradual increase in the diversity of a given strain of virus, both in the individual and in the population, until eventually new strains emerged.

Long-term analysis of feline calicivirus prevalence and viral shedding patterns in naturally infected colonies of domestic cats

Feline calicivirus (FCV) is a highly infectious respiratory pathogen of domestic cats. The prevalence of FCV in the general cat population is high, particularly in multi-cat households, largely because many clinically recovered cats remain persistently infected carriers. In order to assess how FCV circulates in such groups and to assess the contribution that each individual animal makes to the epidemiology of the disease, we have carried out the first detailed analysis of long-term shedding patterns of FCV in individual cats within naturally infected colonies. The prevalence of FCV in each of the groups on individual sampling occasions ranged from 0% to 91%, with averages for the individual colonies ranging from 6% to 75%. Within each of the colonies, one to three distinct strains of FCV were identified. Individual cats showed a spectrum of FCV shedding patterns over the sampling period which broadly grouped into three categories: those that shed virus relatively consistently, those that shed virus intermittently, and those that appeared never to shed virus. This is the first report identifying non-shedder cats that appear resistant to FCV infection over long periods of time, despite being continually exposed to virus. Such resistance appeared to be age related, which may have been immune-mediated, although by analogy with other caliciviruses, factors such as host genetic resistance may play a role. Given that a proportion of the population appears to be resistant to infection, clearly the cohort of cats that consistently shed virus are likely to provide an important mechanism whereby infection can be maintained in small populations.

Detection and molecular characterization of porcine enteric calicivirus in Korea, genetically related to sapoviruses

Porcine enteric calicivirus (PECV) shares morphological and genetical similarities with Sapoviruses (SVs), which are the leading cause of epidemic, non‐bacterial gastroenteritis in children worldwide. The aim of this study was to identify the prevalence of PECV infection in pig farms in Korea, and to compare the evolutionary inter‐relationships between Korean PECVs and other caliciviruses. Among 102 diarrhoeic faecal samples of sucking (n = 50) and weaned (n = 52) piglets from 31 different farms in Korea, five samples (4.9%) were detected positive by reverse‐transcriptase polymerase chain reaction (PCR), but nine (8.8%) by nested‐PCR. Furthermore, we found that Korean PECVs are closely related to SVs.

Recombination of Feline calicivirus within an endemically infected cat colony

To understand the evolution of the family Caliciviridae, the persistence of Feline calicivirus (FCV) was studied within an endemically infected cat colony. Polymerase and capsid sequences were analysed for 34 FCV isolates obtained over a 4 year period. Initially, the colony was infected with one strain of virus, but a second distinct strain was later identified. Subsequently, the emergence of a recombinant virus was observed, containing elements of both of the strains circulating within the colony. The recombination event mapped close to the ORF1/ORF2 junction. This is consistent with recombination in other caliciviruses, suggesting a common mechanism within this family. This is the first report of recombination within the genus Vesivirus in the family Caliciviridae and the first time that a recombination event has been observed where the parental strains have also been identified.

Detection of Feline calicivirus (FCV) from Vaccinated Cats and Phylogenetic Analysis of its Capsid Genes

We analysed genogroups of four feline calcivirus (FCV) isolates (FCV-S, H10, Ao198-1 and ML89) obtained from cats that experienced FCV infection after having been vaccinated against FCV. New PCR primer sets (8F/8R, Ao-S/Ao-A, cp-S/cp-A) were also designed, since the conventional Seal primer failed to amplify the target sequences in two samples. The genogroups of the four isolates as well as eight global and 17 domestic strains were determined by phylogenetic analysis of their amino acid sequences. One out of the four strains (25%) isolated in this study, H10, was grouped into genogroup I, along with the vaccine strains F9 and FCV-255. The other three isolates (75%) belonged to genogroup II. Thus, there were more isolates in genogroup II than in genogroup I. However, the antibody values of the four isolates against cat anti-F9 antisera were significantly decreased. There may be no relationship between the neutralizing antibody titre and genogroup. Amino acid sequence alignment of the four isolates showed that only a single amino acid in region C, which is involved in neutralization epitopes, was different in ML89 strain from that of F9. The other three strains, H10, Ao198-1 and FCV-B, shared the same amino acid sequence with F9. Alignment of amino acids for linear epitopes in the F9 strain, which are located at regions D and E, showed variations in 5' hypervariable region (HVR) of E, whereas D and conE had only synonymous substitutions i.e. no change in the amino acid sequence. This mutation in 5' HVR of region E suggested a vaccine breakdown, as the region is known to be essential for antigenicity. The genogroup II FCV is likely to be the cause of the FCV infection in this study, while the vaccine strains belong to genogroup I. Thus, the existing vaccine may need reevaluation for its effectiveness.

Phylogenetic analysis of rabbit haemorrhagic disease virus (RHDV) strains isolated between 1988 and 2003 in eastern Hungary

To define the genetic variability of RHDV strains collected in eastern Hungary, liver samples from rabbits that had died of RHD were collected between 1988 and 2003. The phylogenetic analysis of a 528-nucleotide-long portion of the gene encoding the VP60 capsid protein assigned the strains into three genogroups. The first group contained viruses from 1988-1993, and a second group comprised isolates from 1994-2002. A third group comprised all of the tested representatives of the RHDVa subtype and a Hungarian isolate from 2003. These findings were supported by the alignments of the deduced amino acid sequences of the VP60 gene and strongly suggest the presence of the RHDVa subtype in Hungary.

Capsid protein genetic analysis and viral spread to the spinal cord in cats experimentally infected with feline calicivirus (FCV)

We investigated primitively the molecular basis of the neural spread of a feline calcivirus isolate (FCV-S) from the spinal cord of a cat that died after manifesting excitation. Experimental infections of cats with three clones from parent virus isolate FCV-S, isolated based on plaque size, were performed, and virus recovery from the spinal cord and the nucleotide and predicted amino acid sequences of the viral capsid protein region (ORF2) were compared. In the experimental infection with the one-time cloned virus (C1L1) isolated from a large plaque, the C1L1 was recovered from the spinal cord. In contrast, seven-times cloned C6L7 (from large plaque) and five-times cloned C5S2 (isolated from small plaque) were not recovered from the spinal cord. Genetic analysis of the capsid protein gene of the three viral clones revealed that four bases were different and two amino acids were different at positions 34 (Val in C6L7 and Ala in C1L1 and C5S2) and 46 (Leu in C6L7 and Pro in C1L1 and C5S2) between C6L7 (with large plaque) and C5S2 (with small plaque). The amino acid at position 434 of C1L1 was different from those of C6L7 and C5S2 (Gly in C1L1, D (Asp) in C6L7 and C5S2). From these results, the plaque size seemed not to be related to the spread of virus to the spinal cord. Clone C1L1, which spread to the spinal cord, had a difference of one amino acid from the other two clones, which may be related to the ability to spread to the spinal cord.

Potential for broad-spectrum protection against feline calicivirus using an attenuated myxoma virus expressing a chimeric FCV capsid protein

It has previously been demonstrated that recombinant myxoma viruses expressing FCV capsid protein are capable of eliciting protective responses against virulent FCV challenge, following vaccination, in cats. An attempt was made to produce a bivalent myxoma recombinant expressing the capsid protein genes of both FCV strains F9 and LS015. The FCV capsid protein genes were inserted into the myxoma growth factor gene (MGF) locus, and the serine protease inhibitor (SERP 2) gene locus. Subsequent recombination between myxoma-FCV viruses resulted in a recombinant expressing a chimeric form of the capsid protein. Nonetheless, cats immunised with this myxoma-FCV recombinant demonstrate high levels of serum neutralising antibodies against both F9 and LS015 strains. Such a chimeric vaccine may provide effective protection against a wide range of FCV strains.

A novel nested PCR for the diagnosis of calicivirus infections in the cat

A novel nested PCR (nPCR) assay is reported on the diagnosis of the feline calicivirus (FCV) infection. The test was performed on 47 ocular and 40 pharyngeal swabs collected from 47 cats with respiratory syndrome; among the 87 samples examined, 18 ocular and 23 pharyngeal swabs were positive in nPCR. The nPCR sensitivity was compared to other diagnostic techniques such as virus isolation on cell culture and reverse transcriptase-polymerase chain reaction (RT-PCR). The nPCR was more sensitive than the virus isolation and RT-PCR; therefore, it can be used for calicivirosis diagnosis in cats.

Inter- and intragenus structural variations in caliciviruses and their functional implications

The family Caliciviridae is divided into four genera and consists of single-stranded RNA viruses with hosts ranging from humans to a wide variety of animals. Human caliciviruses are the major cause of outbreaks of acute nonbacterial gastroenteritis, whereas animal caliciviruses cause various host-dependent illnesses with a documented potential for zoonoses. To investigate inter- and intragenus structural variations and to provide a better understanding of the structural basis of host specificity and strain diversity, we performed structural studies of the recombinant capsid of Grimsby virus, the recombinant capsid of Parkville virus, and San Miguel sea lion virus serotype 4 (SMSV4), which are representative of the genera Norovirus (genogroup 2), Sapovirus, and Vesivirus, respectively. A comparative analysis of these structures was performed with that of the recombinant capsid of Norwalk virus, a prototype member of Norovirus genogroup 1. Although these capsids share a common architectural framework of 90 dimers of the capsid protein arranged on a T=3 icosahedral lattice with a modular domain organization of the subunit consisting of a shell (S) domain and a protrusion (P) domain, they exhibit distinct differences. The distally located P2 subdomain of P shows the most prominent differences both in shape and in size, in accordance with the observed sequence variability. Another major difference is in the relative orientation between the S and P domains, particularly between those of noroviruses and other caliciviruses. Despite being a human pathogen, the Parkville virus capsid shows more structural similarity to SMSV4, an animal calicivirus, suggesting a closer relationship between sapoviruses and animal caliciviruses. These comparative structural studies of caliciviruses provide a functional rationale for the unique modular domain organization of the capsid protein with an embedded flexibility reminiscent of an antibody structure. The highly conserved S domain functions to provide an icosahedral scaffold; the hypervariable P2 subdomain may function as a replaceable module to confer host specificity and strain diversity; and the P1 subdomain, located between S and P2, provides additional fine-tuning to position the P2 subdomain.