Abstract
BackgroundVesiviruses (family Caliciviridae) had been shown capable of invading a variety of host species, raising concern of their zoonotic potential. Since the 1980’s, several canine caliciviruses (CaCV) isolates have been reported and are phylogenetically related to the vesiviruses with features distinct from both Vesicular exanthema of swine virus (VESV) and Feline calicivirus (FCV) species in phylogeny, serology and cell culture specificities. Etiological studies of canine diseases in dogs used for military services and laboratory studies were conducted in 1963–1978 at the Walter Reed Army Institute of Research. Multiple known and unknown viral pathogens including caliciviruses were recovered.MethodsFour unidentified isolates were recovered in Walter Reed Canine Cells (WRCC) from respiratory, fecal and penile specimens. Physicochemical tests, electron microscopy, viral cultivation in human and animal cells, antibody neutralization assays, and recently the genome sequencing were used to characterize the isolates. Sera from these dogs and their cohorts were tested with the isolates to determine origin and prevalence of the infections.ResultsThe viral isolates were small non-enveloped spherical RNA virions, 27 to 42 nm in diameter with cup-like structures, indicating they are caliciviruses. They propagated in WRCC and MDCK cells, not in either other canine cells or human and other animal cells. Each isolate is antigenically distinct and react with dog sera in respective cohorts. The genomes have nucleotide identities ranging from 70.3% to 90.7% and encode the non-structural polyprotein (1810 amino acids), major capsid protein (691 amino acids) and minor structural protein (134 amino acids). They belong to two different phylogenetic clades in Vesivirus genus with close relation with canine calicivirus (CaCV).ConclusionsThese CaCV isolates have restricted cell tropism, antigenic diversity and genetic variation. Further investigation will shed light on antigenic relation to other vesiviruses, and its pathogenicity for dogs and potential infectivity to other animals. Together with the previously reported CaCV strains provides significant evidence to support the formation of a new CaCV species in the Vesivirus genus.
Highlights
Vesiviruses had been shown capable of invading a variety of host species, raising concern of their zoonotic potential
The CaCV isolates A128T and L198 T are close to type I strain 48, while isolates 3–68 and W191R are close to type II strain 2117. These results showed that these CaCVs phylogenetically belong to genus vesivirus with clear separation from species Feline calicivirus (FCV) and Vesicular exanthema of swine virus (VESV)
The initial physical and chemical studies and electron microscopic observations clearly indicate the isolates are caliciviruses. These characteristics are highly consistent with the few reports since 1985 that establish canine calicivirus as a new virus belonging to the vesivirus genus but distinct from FCV and VESV species [28,29,30,31]
Summary
Vesiviruses (family Caliciviridae) had been shown capable of invading a variety of host species, raising concern of their zoonotic potential. Since the 1980’s, several canine caliciviruses (CaCV) isolates have been reported and are phylogenetically related to the vesiviruses with features distinct from both Vesicular exanthema of swine virus (VESV) and Feline calicivirus (FCV) species in phylogeny, serology and cell culture specificities. There are five recognized genera, i.e., Norovirus, Sapovirus, Lagovirus, Vesivirus, and Nebovirus with several additional candidate genera or species proposed and under evaluation by the International Committee on Taxonomy of Viruses (ICTV) [1, 2] (http://www.caliciviridae.com/unclassified/unclassified.htm). In the Vesivirus genus, Vesicular exanthema of swine virus (VESV) and Feline calicivirus (FCV) are two species currently approved by ICTV. Several canine caliciviruses (CaCV) isolates have been identified and shown to be phylogenetically related to vesiviruses with features distinct from both VESV and FCV in phylogeny, serology and cell culture specificities. It is still unclassified to date and the evidence presented should facilitate the classification and acceptance of CaCV as a species of vesivirus
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