Genetic relatedness of the caliciviruses: San Miguel sea lion and vesicular exanthema of swine viruses constitute a single genotype within the Caliciviridae

A systematic review on global zoonotic virus-associated mortality events in marine mammals

Marine mammals play a critical role as sentinels for tracking the spread of zoonotic diseases, with viruses being the primary causative factor behind infectious disease induced mortality events. A systematic review was conducted to document marine mammal mortality events attributed to zoonotic viral infections in published literature across the globe. This rigorous search strategy yielded 2883 studies with 88 meeting inclusion criteria. The studies spanned from 1989 to 2023, with a peak in publications observed in 2020. Most of the included studies were retrospective, providing valuable insights into historical trends. The United States (U.S.) reported the highest number of mortality events followed by Spain, Italy, Brazil and the United Kingdom. Harbor seals were the most impacted species, particularly in regions like Anholt, Denmark and the New England Coast, U.S. Analysis revealed six main viruses responsible for mortality events, with Morbillivirus causing the highest proportion of deaths. Notably, the occurrence of these viral events varied geographically, with distinct patterns observed in different regions. Immunohistochemistry emerged as the most employed detection method. This study underscores the importance of global surveillance efforts in understanding and mitigating the impact of viral infections on marine mammal populations, thereby emphasizing the necessity of collaborative One Health approaches to address emerging threats at the human-animal-environment interface. Additionally, the potential transfer of zoonotic viruses to aquatic organisms used in food production, such as fish and shellfish, highlights the broader implications for food safety, food security and public health.

Comparison of de novo assembly using long-read shotgun metagenomic sequencing of viruses in fecal and serum samples from marine mammals

Introduction

Viral diseases of marine mammals are difficult to study, and this has led to a limited knowledge on emerging known and unknown viruses which are ongoing threats to animal health. Viruses are the leading cause of infectious disease-induced mass mortality events among marine mammals.

Methods

In this study, we performed viral metagenomics in stool and serum samples from California sea lions (Zalophus californianus) and bottlenose dolphins (Tursiops truncates) using long-read nanopore sequencing. Two widely used long-read de novo assemblers, Canu and Metaflye, were evaluated to assemble viral metagenomic sequencing reads from marine mammals.

Results

Both Metaflye and Canu assembled similar viral contigs of vertebrates, such as Parvoviridae, and Poxviridae. Metaflye assembled viral contigs that aligned with one viral family that was not reproduced by Canu, while Canu assembled viral contigs that aligned with seven viral families that was not reproduced by Metaflye. Only Canu assembled viral contigs from dolphin and sea lion fecal samples that matched both protein and nucleotide RefSeq viral databases using BLASTx and BLASTn for Anelloviridae, Parvoviridae and Circoviridae families. Viral contigs assembled with Canu aligned with torque teno viruses and anelloviruses from vertebrate hosts. Viruses associated with invertebrate hosts including densoviruses, Ambidensovirus, and various Circoviridae isolates were also aligned. Some of the invertebrate and vertebrate viruses reported here are known to potentially cause mortality events and/or disease in different seals, sea stars, fish, and bivalve species.

Discussion

Canu performed better by producing the most viral contigs as compared to Metaflye with assemblies aligning to both protein and nucleotide databases. This study suggests that marine mammals can be used as important sentinels to surveil marine viruses that can potentially cause diseases in vertebrate and invertebrate hosts.

Reverse Genetics System for Rabbit vesivirus

Most caliciviruses are refractory to replication in cell culture and only a few members of the family propagate in vitro. Rabbit vesivirus (RaV) is unique due to its ability to grow to high titers in several animal and human cell lines. This outstanding feature makes RaV an ideal candidate for reverse genetics studies, an invaluable tool to understand the molecular basis of virus replication, the biological functions of viral genes and their roles in pathogenesis. The recovery of viruses from a cDNA clone is a prerequisite for reverse genetics studies. In this work, we constructed a RaV infectious cDNA clone using a plasmid expression vector, under the control of bacteriophage T7 RNA-polymerase promoter. The transfection of permissive cells with this plasmid DNA in the presence of T7 RNA-polymerase, provided in trans by a helper recombinant poxvirus, led to de novo synthesis of RNA transcripts that emulated the viral genome. The RaV progeny virus produced the typical virus-induced cytopathic effect after several passages of cell culture supernatants. Similarly, infectious RaV was recovered when the transcription step was performed in vitro, prior to transfection, provided that a 5′-cap structure was added to the 5′ end of synthetic genome-length RNAs. In this work, we report an efficient and consistent RaV rescue system based on a cDNA transcription vector, as a tool to investigate calicivirus biology through reverse genetics.

Calicivirus RNA-Dependent RNA Polymerases: Evolution, Structure, Protein Dynamics, and Function

The Caliciviridae are viruses with a positive-sense, single-stranded RNA genome that is packaged into an icosahedral, environmentally stable protein capsid. The family contains five genera (Norovirus, Nebovirus, Sapovirus, Lagovirus, and Vesivirus) that infect vertebrates including amphibians, reptiles, birds, and mammals. The RNA-dependent RNA polymerase (RdRp) replicates the genome of RNA viruses and can speed up evolution due to its error-prone nature. Studying calicivirus RdRps in the context of genuine virus replication is often hampered by a lack of suitable model systems. Enteric caliciviruses and RHDV in particular are notoriously difficult to propagate in cell culture; therefore, molecular studies of replication mechanisms are challenging. Nevertheless, research on recombinant proteins has revealed several unexpected characteristics of calicivirus RdRps. For example, the RdRps of RHDV and related lagoviruses possess the ability to expose a hydrophobic motif, to rearrange Golgi membranes, and to copy RNA at unusually high temperatures. This review is focused on the structural dynamics, biochemical properties, kinetics, and putative interaction partners of these RdRps. In addition, we discuss the possible existence of a conserved but as yet undescribed structural element that is shared amongst the RdRps of all caliciviruses.

Molecular Detection of Circovirus and Adenovirus in Feces of Fur Seals (Arctocephalus spp.)

In some regions, little is known about exposure to viruses in coastal marine mammals. The present study aimed to detect viral RNA or DNA in 23 free-ranging fur seals on the northern coastline of Rio Grande do Sul State, Brazil. Polymerase chain reaction was used to detect nucleic acids of circoviruses, adenoviruses, morbilliviruses, vesiviruses, and coronaviruses in the feces from twenty-one South American fur seals (Arctocephalus australis) and two Subantarctic fur seals (A. tropicalis). Adenovirus DNA fragments were detected in two South American fur seals; nucleotide sequences of these fragments revealed a high degree of similarity to human adenovirus type C. Circovirus DNA fragments were detected in six animals of the same species. Two were phylogenetically similar to the Circovirus genus, whereas the other four nucleotide fragments showed no similarity to any of the known genera within the family Circoviridae. RNA fragments indicating the presence of coronavirus, vesivirus, and morbillivirus were not detected. These findings suggest that adenoviruses and circoviruses are circulating in fur seal populations found along the coast of Rio Grande do Sul State, Brazil.

Senecavirus A

Senecavirus A (SVA) is the only member of the genus Senecavirus within the family Picornaviridae. This virus was discovered as a serendipitous finding in 2002 (and named Seneca Valley virus 001 [SVV-001]) while cultivating viral vectors in cell culture and has been proposed for use as an oncolytic virus to treat different types of human neoplasia. SVA was found in lesions in pigs affected by porcine idiopathic vesicular disease in Canada and the USA in 2008 and 2012, respectively. In 2014 and 2015, SVA infection was associated with outbreaks of vesicular disease in sows as well as neonatal pig mortality in Brazil and the USA. Phylogenetic analysis of the SVA VP1 indicates the existence of 3 clades of the virus. Clade I contains the historical strain SVV-001, clade II contains USA SVA strains identified between 1988 and 1997, and clade III contains global SVA strains from Brazil, Canada, China, and the USA identified between 2001 and 2015. The aim of this review is to draw the attention of veterinarians and researchers to a recently described infectious clinical-pathologic condition caused by a previously known agent (SVA). Apart from the intrinsic interest in a novel virus infecting pigs and causing economic losses, the major current concern is the similarity of the clinical picture to that of other swine diseases, because one of them-foot and mouth disease-is a World Organization for Animal Health-listed disease. Because the potential association of SVA with disease is rather new, there are still many questions to be resolved.

The fecal viral flora of California sea lions

California sea lions are one of the major marine mammal species along the Pacific coast of North America. Sea lions are susceptible to a wide variety of viruses, some of which can be transmitted to or from terrestrial mammals. Using an unbiased viral metagenomic approach, we surveyed the fecal virome in California sea lions of different ages and health statuses. Averages of 1.6 and 2.5 distinct mammalian viral species were shed by pups and juvenile sea lions, respectively. Previously undescribed mammalian viruses from four RNA virus families (Astroviridae, Picornaviridae, Caliciviridae, and Reoviridae) and one DNA virus family (Parvoviridae) were characterized. The first complete or partial genomes of sapeloviruses, sapoviruses, noroviruses, and bocavirus in marine mammals are reported. Astroviruses and bocaviruses showed the highest prevalence and abundance in California sea lion feces. The diversity of bacteriophages was higher in unweaned sea lion pups than in juveniles and animals in rehabilitation, where the phage community consisted largely of phages related to the family Microviridae. This study increases our understanding of the viral diversity in marine mammals, highlights the high rate of enteric viral infections in these highly social carnivores, and may be used as a baseline viral survey for comparison with samples from California sea lions during unexplained disease outbreaks.

Genetic characterization of a novel calicivirus from a chicken

We describe the identification and genetic characterization of a novel enteric calicivirus, detected by transmission electron microscopy and RT-PCR in two clinically normal chickens and in a chicken with runting and stunting syndrome from different flocks in southern Germany. Positive findings were confirmed by sequencing. The complete nucleotide sequence and genome organization of one strain (Bavaria/04V0021) was determined. The genome of the Bavaria virus is 7,908 nt long and contains two coding open reading frames. Phylogenetic analysis of the deduced partial 2C helicase/NTPase, 3C cysteine protease, RNA-dependent RNA polymerase and complete VP1 capsid protein amino acid sequences showed that the virus is genetically related to but distinct from sapoviruses and lagoviruses. Morphologically, the Bavaria virus particles are 37-42 nm in diameter and exhibit characteristic cup-shaped surface depressions.

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.

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.

Bioinformatic and functional analysis of RNA secondary structure elements among different genera of human and animal caliciviruses

The mechanism and role of RNA structure elements in the replication and translation of Caliciviridae remains poorly understood. Several algorithmically independent methods were used to predict secondary structures within the Norovirus, Sapovirus, Vesivirus and Lagovirus genera. All showed profound suppression of synonymous site variability (SSSV) at genomic 5' ends and the start of the sub-genomic (sg) transcript, consistent with evolutionary constraints from underlying RNA structure. A newly developed thermodynamic scanning method predicted RNA folding mapping precisely to regions of SSSV and at the genomic 3' end. These regions contained several evolutionarily conserved RNA secondary structures, of variable size and positions. However, all caliciviruses contained 3' terminal hairpins, and stem-loops in the anti-genomic strand invariably six bases upstream of the sg transcript, indicating putative roles as sg promoters. Using the murine norovirus (MNV) reverse-genetics system, disruption of 5' end stem-loops produced approximately 15- to 20-fold infectivity reductions, while disruption of the RNA structure in the sg promoter region and at the 3' end entirely destroyed replication ability. Restoration of infectivity by repair mutations in the sg promoter region confirmed a functional role for the RNA secondary structure, not the sequence. This study provides comprehensive bioinformatic resources for future functional studies of MNV and other caliciviruses.

Development of a real-time reverse transcription polymerase chain reaction assay for detection of marine caliciviruses (genus Vesivirus)

Marine caliciviruses form a distinct lineage within the genus Vesivirus (family Caliciviridae). This group includes vesicular exanthema of swine virus (VESV) and San Miguel sea lion virus (SMSV) and other related viruses which have been proposed to be marine in origin isolated from a variety of terrestrial and marine animals. Rapid and reliable detection of marine caliciviruses is important as these viruses appear to be widespread and can cause vesicular disease in a wide variety of susceptible hosts including pigs and experimentally infected cattle where clinical signs cannot be easily distinguished from foot-and-mouth disease (FMD), swine vesicular disease (SVD) and vesicular stomatitis (VS). A real-time RT-PCR assay targeting conserved nucleotide sequences in the RNA-dependent RNA polymerase (3D) region of the genome successfully detected cell culture-grown virus preparations of more than thirty marine calicivirus serotypes. Only the atypical SMSV serotypes 8 and 12 failed to be detected, which provided further indication of genetic divergence between these and the other calicivirus serotypes said to be marine in origin. The real-time RT-PCR assay also specifically amplified RNA from samples collected following experimental inoculation of pigs with VESV. No cross-reactivity was demonstrated when the assay was tested with RNA prepared from representative viruses of FMD, SVD and VS. The real-time RT-PCR assay described is a sensitive and specific tool for detection and differential diagnosis of these viruses from other vesicular-disease causing viruses.

Vesivirus viremia and seroprevalence in humans

Pathogenic caliciviruses of the genus Vesivirus circulate in oceanic ecosystems and spread to and among terrestrial mammals. Isolation of Vesivirus from natural and laboratory infections in humans led to this investigation of Vesivirus seroprevalence and viremia. Sera from four groups were tested for antibodies to Vesivirus as follows: blood donors whose units were cleared for donation, blood donors whose units were not accepted for donation solely because of elevated blood liver alanine aminotransferase (ALT) concentrations, patients with clinical hepatitis of unknown but suspected infectious cause, and patients with clinical hepatitis of unknown cause but associated with blood transfusion or dialysis. Additionally, sera were tested for Vesivirus genome by three methods: dot‐blot and two reverse transcription‐polymerase chain reaction (RT‐PCR) methods. The calculated seroprevalence against Vesivirus virions within these groups (N = 765) was 12%, 21%, 29%, and 47%, respectively (P < 0.001 for group differences). Additionally, 11 (9.8%) of 112 sera tested yielded RT‐PCR amplicons that by nucleotide sequence were distinct from each other and related to known Vesivirus. These data indicate that some blood donors in the population tested have serologic evidence of previous Vesivirus infection and some also have Vesivirus viremia. These results justify further investigation of an association between Vesivirus infection and illness in humans. J. Med. Virol. 78:693–701, 2006. © 2006 Wiley‐Liss, Inc.

Genomic characterization of the unclassified bovine enteric virus Newbury agent-1 (Newbury1) endorses a new genus in the family Caliciviridae

The pathogenic bovine enteric virus, Newbury agent-1 (Bo//Newbury1/1976/UK), first identified in 1976, was characterized as a possible calicivirus by morphology, buoyant density in CsCl and the presence of a single capsid protein but genomic sequence could not be obtained. In the present study, the complete genome sequence of Newbury1 was determined and classified Newbury1 in a new genus of the Caliciviridae. The Newbury1 genome, of 7454 nucleotides, had two predicted open reading frames (ORFs). ORF1 encoded the non-structural and contiguous capsid proteins. ORF2 encoded a basic protein characteristic of the family Caliciviridae. Compared to the 4 recognized Caliciviridae genera, Norovirus, Sapovirus, Lagovirus and Vesivirus, Newbury1 had less than 39% amino acid (47% nucleotide) identity in the complete 2C-helicase, 3C-protease, 3D-polymerase and capsid regions but had 89% to 98% amino acid (78% to 92% nucleotide) identity to the recently characterized NB virus in these regions. By phylogenetic analyses, Newbury1 and NB viruses formed a distinct clade independent of the 4 recognized genera. However, amino acid identities showed that Newbury1 and the NB virus were distinct polymerase types (90% amino acid identity), but their complete capsid proteins were almost identical (98% amino acid identity). Analyses of contemporary viruses showed that the two polymerase genotypes, Newbury1 and NB, were circulating in UK cattle and antibody to Newbury1-like viruses was common in cattle sera. The present study defined the existence of a new genus in the Caliciviridae that we propose be named Becovirus or Nabovirus to distinguish the new clade from bovine noroviruses.

Epidemiology of Norwalk-like virus infections in cattle in The Netherlands

"Norwalk-like viruses" (NLVs) are the most common cause of acute non-bacterial gastroenteritis in humans. Cattle may be a reservoir of NLVs although never bovine NLVs have been found in humans. To gain more insight into the epidemiology of NLV, infections in cattle in The Netherlands were studied. Individual faecal samples from a large dairy herd and 243 pooled samples from veal calf farms were analysed for NLV by RT-PCR. Calves under 3 months of age in the dairy herd were sampled three to five times with 3-week intervals, whereas dairy cattle were sampled twice with a 2-month interval. In 31.6% (77/243) of the veal calf farm samples and in 4.2% (13/312) of the individual dairy cattle samples NLV was detected. The mean age of virus positive dairy cattle was 2.5 months. The highest numbers of NLV positive veal calf farms in The Netherlands were found in the regions with the highest number of veal calf farms. NLV infected veal calf farms were detected in every month throughout the study period. Cattle appeared to be hosts of NLVs, and virus shedding was weakly associated with diarrhoea. Complete ORF2 sequences were obtained from two calf NLVs and phylogenetic analyses suggested that these strains belong to a distinct cluster (GGIII/2) in between GGI and GGII NLVs of humans. Overall, genetic variation between strains as determined by sequence analysis of the P1/P2 capsid region was limited to 14.6%. Our data shows that NLV is endemic in the cattle population in The Netherlands and genetically distinct from NLVs in humans.

Crystallization and preliminary crystallographic analysis of San Miguel sea lion virus: an animal calicivirus

The Caliciviridae is a family of nonenveloped, icosahedral, positive-sense single-stranded RNA viruses. This family of viruses consists of both animal and human pathogens. Adapting human caliciviruses to cell culture has not been successful, whereas some animal caliciviruses, including San Miguel sea lion virus, have been successfully propagated in vitro. Here we report the crystallization of San Miguel sea lion virus serotype 4 (SMSV4) and the preliminary X-ray crystallographic analysis of the crystals. SMSV4 have been crystallized using the hanging-drop method. These crystals diffracted to approximately 3A resolution using a synchrotron radiation source. A single crystal under cryo-conditions yielded a complete set of diffraction data. Data processing of the diffraction patterns showed that SMSV crystals belong to I23 space group with cell dimensions a=b=c=457 A. The crystallographic asymmetric unit includes five icosahedral asymmetric units, each consisting of three capsid protein subunits. In the space group I23, given the icosahedral symmetry and the size of the virus particle, the location of the particle is constrained to be at the point where the crystallographic 2- and 3-fold axes intersect. The orientation of the virus particle in the unit cell was ascertained by self-rotation function calculations.

Molecular characterization of bovine enteric caliciviruses: a distinct third genogroup of noroviruses (Norwalk-like viruses) unlikely to be of risk to humans

Bovine enteric caliciviruses (BoCVs) have been classified in the Norovirus (Norwalk-like virus) genus of the Caliciviridae, raising questions about zoonotic transmission and an animal reservoir for the human Norwalk-like viruses (NLVs), an important cause of nonbacterial gastroenteritis in humans. We examined the genetic relationship of human NLVs to BoCVs that were identified by using reverse transcription-PCR with primer pairs originally designed to detect human NLVs. Polymerase, capsid, and open reading frame 3 (ORF3) gene sequence analyses of BoCVs that were identified from 1976 to 2000 from throughout the United Kingdom showed that BoCVs formed a distinct third genogroup of closely related viruses distinct from the human genogroup I and II NLVs. Evidence was not obtained to support the concept that BoCVs are circulating in humans and pose a threat to human health.

Characterization of an enteropathogenic bovine calicivirus representing a potentially new calicivirus genus

Bovine enteric caliciviruses (BEC) are associated with diarrhea in young calves. The BEC strains detected in Europe form a third genogroup within the genus "Norwalk-like viruses" (NLV) of the family Caliciviridae. In this report, we present sequence, clinical, and histological data characterizing a novel enteropathogenic BEC strain, NB, detected in fecal specimens from calves in the United States. The complete RNA genome of the NB virus is 7,453 bases long and is organized into two open reading frames (ORFs). ORF-1 is 2,210 amino acids long and encodes a large nonstructural polyprotein contiguous with the major capsid protein (VP1), similar to the lagoviruses and "Sapporo-like viruses" (SLV). The conserved calicivirus motifs were identified in the nonstructural proteins. ORF-2 is located at the 3' end of the genome and encodes a small basic protein (VP2) of 225 amino acids. The 5' and 3' untranslated regions are 74 and 67 bases long, respectively. Among caliciviruses, NB virus shows amino acid identities of 14.1 to 22.6% over the entire ORF-1 nonstructural-protein sequence with NLV, SLV, vesivirus, and lagovirus strains, while the overall sequence identity of the complete NB VP-1 with other caliciviruses is low, varying between 14.6 and 26.7%. Phylogenetic analysis of the complete VP1 protein, including strains from all four calicivirus genera, showed the closest grouping of NB virus to be with viruses in the genus Lagovirus, which cause liver infections and systemic hemorrhage in rabbits. In gnotobiotic calves, however, NB virus elicited only diarrhea and intestinal lesions that were most severe in the upper small intestine (duodenum and jejunum), similar to the NLV BEC strains. The tissues of major organs, including the lung, liver, kidney, and spleen, had no visible microscopic lesions.

Norwalk-like calicivirus genes in farm animals

Viruses closely related to Norwalk-like viruses (NLVs) were recently found in stored stool samples from two calves (United Kingdom and Germany) and four pigs (Japan), sparking discussions about the potential for zoonotic transmission. To investigate if NLVs are commonly present in farm animals, pooled stool samples from 100 pig farms, 48 chicken farms, 43 dairy cow herds, and 75 veal calf farms from the Netherlands were assayed by reverse transcription- polymerase chain reaction amplification, using primers specific for the detection of NLVs from humans. NLV RNA was detected in 33 (44%) of the specimens from veal calf farms and two (2%) specimens from pig farms. Our data show that NLV infections until recently thought to be restricted to humans occur often in calves and sometimes in pigs. While zoonotic transmission has not been proven, these findings suggest that calves and pigs may be reservoir hosts of NLVs.

Development of a reverse transcription polymerase chain reaction procedure for the detection of marine caliciviruses with potential application for nucleotide sequencing

A reverse transcription polymerase chain reaction (RT-PCR) procedure is described for the detection of marine caliciviruses including vesicular exanthema of swine virus (VESV), San Miguel sea lion virus (SMSV), bovine Tillamook virus (BCV Bos-1) and caliciviruses (CV) isolated from dolphin (Cetacean CV), gorilla (Primate CV) and rattlesnake (Reptile CV) using primers (1F and 1R) designed from the capsid-coding region of the viral genome. These primers were compared with those described by Neill, J.D. and Seal, B.S., 1995: Development of PCR primers for specific amplification of two distinct regions of the genomes of San Miguel sea lion and vesicular exanthema of swine viruses, Mol. Cell. Probes 9, 33-38 (Hel1/Hel2), which had been designed from the 2C-like region of the calicivirus genome. Both sets proved to be extremely useful diagnostic tools for all of the known marine calicivirus serotypes with the exception of three: SMSV-8 and -12 and mink CV suggesting that these three caliciviruses may belong to a different group. Neither of the two primer sets reacted with strains of the vesicular disease viruses of foot-and-mouth disease (FMD), swine vesicular disease (SVD) or vesicular stomatitis (VS) nor with two feline caliciviruses (FCV). The 1F/1R primer set has the advantage over the Hel1/Hel2 set in that it generates a larger PCR product for nucleotide sequence investigations and so provides greater opportunity for identifying molecular differences between the viruses.

Molecular characterization of a bovine enteric calicivirus: relationship to the Norwalk-like viruses

Jena virus (JV) is a noncultivatable bovine enteric calicivirus associated with diarrhea in calves and was first described in Jena, Germany. The virus was serially passaged 11 times in colostrum-deprived newborn calves and caused diarrheal disease symptoms at each passage. The complete JV genome sequence was determined by using cDNA made from partially purified virus obtained from a single stool sample. JV has a positive-sense single-stranded RNA genome which is 7,338 nucleotides in length, excluding the poly(A) tail. JV genome organization is similar to that of the human Norwalk-like viruses (NLVs), with three separate open reading frames (ORFs) and a 24-nucleotide sequence motif located at the 5' terminus of the genome and at the start of ORF 2. The polyprotein (ORF 1) consists of 1,680 amino acids and has the characteristic 2C helicase, 3C protease, and 3D RNA polymerase motifs also found in the NLVs. However, comparison of the N-terminal 100 amino acids of the JV polyprotein with those of the group 1 and group 2 NLVs showed a considerable divergence in sequence. The capsid protein (ORF 2) at 519 amino acids is smaller than that of all other caliciviruses. JV ORF 2 was translated in vitro to produce a 55-kDa protein that reacted with postinfection serum but not preinfection serum. Phylogenetic studies based on partial RNA polymerase sequences indicate that within the Caliciviridae JV is most closely related to the group 1 NLVs.

A further step in the evolution of rabbit hemorrhagic disease virus: the appearance of the first consistent antigenic variant

Rabbit hemorrhagic disease virus (RHDV) is a noncultivable calicivirus that infects rabbits (Oryctolagus cuniculus) and causes epidemics of an acute fatal hepatitis. In 1997 we identified two RHDV isolates from geographically distant Italian regions, which differed antigenically from the reference strain RHDV.Bs89. In fact, they were not reactive with mAb 1H8, that is able to protect rabbits from RHD and showed a low reactivity with the rabbit convalescent serum raised against RHDV.Bs89. Experimental infection of rabbits with either RHDV isolates confirmed their high pathogenicity and their peculiar antigenic profile; nevertheless, rabbits vaccinated with the current vaccine were protected against challenge infection with these isolates. Sequence comparison definitely demonstrated that the two isolates originated from the same RHDV variant and that the similarity of their structural protein (VP60) sequences with the RHDV.Bs89 is equal to 93%. This variant was named RHDVa since shows consistent genetic and antigenic differences from the wild-type RHDV. In particular, 44% of amino acid substitutions in RHDVa VP60 were located between amino acids 344 and 370, where the similarity with RHDV.Bs89 drops to 70%, suggesting that this region probably contains the epitope recognized by mAb 1H8. In addition, this paper presents preliminary data concerning the amino acids of VP60 involved in the hemagglutination site of the virus.

The capsid protein of vesicular exanthema of swine virus serotype A48: relationship to the capsid protein of other animal caliciviruses

Vesicular exanthema of swine virus (VESV), the prototype calicivirus, is the etiologic agent of the porcine disease vesicular exanthema of swine (VES). VES is characterized by vesicle formation on the extremities, mouth and snout and causes abortions and stillbirths if infection occurs during pregnancy. VESV is considered an exotic agent in the US, following its eradication in 1956. The single capsid protein gene of VESV serotype A48 was cloned and sequenced. The capsid amino acid sequence was 69% similar to the San Miguel sea lion virus serotype 1 (SMSV 1) and 89% similar to the SMSV serotype 4 (SMSV 4) capsid proteins. The six functional regions (A-F) previously identified in SMSV 1, SMSV 4, feline calicivirus and rabbit hemorrhagic disease virus capsid proteins were present in VESV A48. Two sets of PCR primers were designed which directed amplification of the 5' end (A region) and the hypervariable (E region) sequences of the capsid protein precursor gene of these viruses, as well as seven additional SMSV serotypes. Alignment and phylogenetic analysis of the N-terminal sequences demonstrated the close relationship of these viruses. Alignment of the hypervariable region amino acid sequences of the ten viruses confirmed that a great variety of sequence exists in this region; however, a consensus sequence (NxT(N/H)F(K/R)GxYI(C/M)GxLx(T/R)) was derived which is also present in the feline calicivirus capsid protein. Comparison of the E region sequences provides further evidence that this area of animal calicivirus capsid protein may contain the major antigenic determinants.

Viral zoonoses and food of animal origin: caliciviruses and human disease

Caliciviruses are important veterinary and human pathogens. The viruses gain their name from characteristic cup-shaped structures seen on the virion surface by negative stain electron microscopy. In humans caliciviruses are a major cause of diarrhoeal disease. There are two fundamentally different genome structures amongst human caliciviruses. The Norwalk-like or small round structured viruses (SRSVs) are viruses that have an amorphous structure when viewed by EM, they have a genome composed of 3 major open reading frames (ORFs). These viruses cause epidemic gastroenteritis amongst all age groups. In contrast, the 'classic' human caliciviruses (HuCVs) display the typical calicivirus surface structure and have their capsid ORF fused to and contiguous with the non structural proteins forming one giant polyprotein. HuCVs are predominantly associated with paediatric infections and are only a minor cause of disease in humans. Spread of disease for both SRSVs and HuCVs is usually by faecal oral transmission. SRSVs are a major cause of foodborne gastroenteritis especially linked to the consumption of sewage-contaminated shellfish. However, there is no evidence that these viruses replicate in shellfish or that they originate from an animal source.

Phylogenetic analysis of the Caliciviruses

A phylogenetic portrait of the genus Calicivirus in the family Caliciviridae was developed based upon published sequences and newly characterized calicivirus (CV) strains, including additional Sapporo-like HuCV strains in pediatric diarrhea stool specimens from South Africa, the United Kingdom, and the United States. Distance and parsimony methods were applied to nucleotide and amino acid sequences of human and animal calicivirus 3D RNA-dependent RNA polymerase (approximately 470nt) and capsid hypervariable regions (approximately 1,200nt) to generate phylogenetic trees. Pairwise amino acid identity in the 3D region among the Sapporo-like strains ranged from 61% to 100%. Human and animal caliciviruses (HuCVs and AnCVs) separated into five genogroups: small round-structured viruses (SRSV), Sapporo-like, and hepatitis E virus (HEV)-like HuCVs and rabbit-, and vesicular exanthema of swine virus (VESV)-like AnCVs, each with a distinct genome organization. Each genogroup, including the Sapporo-like HuCVs, subdivided further into subgenogroups. The capsid region trees had higher levels of confidence than the 3D region trees and limited conclusions about genogroups could be drawn from the 3D region analyses. This analysis suggested that CVs include five potential virus subfamilies.

Microheterogeneity of p60 capsid protein and the encoding gene among contemporary isolates of rabbit hemorrhagic disease virus

The gene encoding the p60 capsid protein from a Spanish isolate of the rabbit hemorrhagic disease virus (RHDV) has been cloned and sequenced. Both cDNA and the derived protein sequences have been compared with those from several contemporary European RHDV isolates. Genetic heterogeneity among co-circulating viruses is nearly constant along the p60-encoding gene, around 0.034 substitutions per nucleotide, and it does not allow prediction of the preferential regions for long-term fixation of mutations. However, sequence comparisons with the more distant, but phylogenetically closely related calicivirus, the European brown hare syndrome virus (EBHSV), reveal a great extent of genetic variability within both a segment of p60 gene (nucleotides 900-1300) and the encoded polypeptide, suggesting the existence of strong selective pressures acting over this region of the capsid protein.