Large-scale spatial and temporal genetic diversity of feline calicivirus.
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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. (+info)
The feline calicivirus leader of the capsid protein is associated with cytopathic effect.
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Analysis of feline calicivirus capsid protein genes: identification of variable antigenic determinant regions of the protein.
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Three isolates of feline calicivirus (FCV) designated NADC, KCD and CFI/68 were compared for biochemical, serological and genetic variation within the capsid protein gene. The M(r) of the capsid protein from purified virions was approximately 66,000 for the NADC virus isolate, which differed slightly from the relative mobilities of the purified capsid proteins of the KCD and CFI/68 isolates. Polyclonal antisera from either cats infected or rabbits hyperimmunized with the CFI/68 isolate cross-reacted with all three isolates by Western blot analysis. However, these polyclonal antisera to CFI/68 varied considerably in their virus-neutralization titres to the KCD and NADC isolates. Nucleotide sequence data confirmed the genetic variability among these FCV isolates. Comparison of the predicted amino acid sequence of the capsid protein among isolates revealed two regions of sequence divergence that probably contain the antigenically variable determinants. These hypervariable regions may vary by as much as 55% among isolates of FCV. The amino acid sequence diversity in the hypervariable regions of the KCD and NADC isolates correlated well with the virus-neutralization data and suggests that polyvalent vaccines may be more protective than the commonly used monovalent vaccines. (+info)
RNA transcripts derived from a cloned full-length copy of the feline calicivirus genome do not require VpG for infectivity.
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Feline calicivirus (FCV) is a positive-strand, nonenveloped RNA virus in the family Caliciviridae. A cDNA library of the Urbana (URB) strain of FCV was generated and the sequence of the genome was determined from overlapping clones except for 13 bases from the 5'-end. The 5'-end sequence was identified by analysis of clones derived by RT-PCR across the ligated 5'- and 3'-ends of the RNA genome. A full-length cDNA clone of the RNA genome of the URB strain was constructed and placed downstream of the T7 RNA polymerase promoter and RNA transcripts generated in vitro from this clone were infectious when introduced into feline kidney cells. A virus-encoded genome-linked protein, VpG, which is considered to be essential for infectivity of wild-type genomic FCV RNA, was not required for the initiation of FCV infection by the synthetic transcripts. However, the addition of a cap structure analog (m7G(5')ppp(5')G) during in vitro transcription of the synthetic RNA was necessary for successful virus recovery. Two silent mutations engineered into the full-length clone were identified in the genomic RNA from recovered progeny virus. This system of introducing site-specific genetic changes into the genome of feline calicivirus and the recovery of infectious mutant viruses will enable studies related to the molecular basis for replication, growth restriction, and pathogenicity of this and other members of the Caliciviridae. (+info)
Detection of the ORF3 polypeptide of feline calicivirus in infected cells and evidence for its expression from a single, functionally bicistronic, subgenomic mRNA.
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Feline calicivirus (FCV) is a small positive-stranded RNA virus within the family Caliciviridae. Its genome is 7690 nucleotides in length and encodes three open reading frames (ORFs). The smallest, ORF3, is located at the extreme 3' end of the genome and can potentially encode a polypeptide of approximately 12 kDa. In this paper, we report the identification of an ORF3-encoded polypeptide in FCV-infected cells using an antiserum raised against a bacterially-expressed bacteriophage T7 gene 10-ORF3 fusion protein. Although a small mRNA of 0-5 kb, which could potentially encode ORF3, has been described, reports on the number and size of FCV subgenomic RNAs have varied considerably. To clarify the situation, RNAs from FCV-infected cells were labelled in vivo using [32P]orthophosphate, an approach which provided definitive data. Only two RNA species were detected, the genomic RNA and a subgenomic mRNA of 2.4 kb. The 5' end of the subgenomic mRNA was mapped to position 5227 on the genomic RNA using RNA sequencing and primer extension methods. RNA isolated from FCV-infected cells in which no subgenomic RNA smaller than 2.4 kb was detectable directed the synthesis in rabbit reticulocyte lysate of the ORF3-encoded polypeptide. Furthermore, a synthetic RNA copy of the 2-4 kb subgenomic mRNA of FCV, containing both ORF2 and ORF3 polypeptides in the in vitro translation system. These data strongly suggest that ORF3 is expressed from the 2-4 kb subgenomic RNA and that this RNA is functionally bicistronic. The possible mechanisms by which ORF3 is expressed are discussed. (+info)
Prevalence of antibodies to feline parvovirus, calicivirus, herpesvirus, coronavirus, and immunodeficiency virus and of feline leukemia virus antigen and the interrelationship of these viral infections in free-ranging lions in east Africa.
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While viral infections and their impact are well studied in domestic cats, only limited information is available on their occurrence in free-ranging lions. The goals of the present study were (i) to investigate the prevalence of antibodies to feline calicivirus (FCV), herpesvirus (FHV), coronavirus (FCoV), parvovirus (FPV), and immunodeficiency virus (FIV) and of feline leukemia virus (FeLV) antigen in 311 serum samples collected between 1984 and 1991 from lions inhabiting Tanzania's national parks and (ii) to evaluate the possible biological importance and the interrelationship of these viral infections. Antibodies to FCV, never reported previously in free-ranging lions, were detected in 70% of the sera. In addition, a much higher prevalence of antibodies to FCoV (57%) was found than was previously reported in Etosha National Park and Kruger National Park. Titers ranged from 25 to 400. FeLV antigen was not detectable in any of the serum samples. FCoV, FCV, FHV, and FIV were endemic in the Serengeti, while a transient elevation of FPV titers pointed to an outbreak of FPV infection between 1985 and 1987. Antibody titers to FPV and FCV were highly prevalent in the Serengeti (FPV, 75%; FCV, 67%) but not in Ngorongoro Crater (FPV, 27%; FCV, 2%). These differences could be explained by the different habitats and biological histories of the two populations and by the well-documented absence of immigration of lions from the Serengeti plains into Ngorongoro Crater after 1965. These observations indicate that, although the pathological potential of these viral infections seemed not to be very high in free-ranging lions, relocation of seropositive animals by humans to seronegative lion populations must be considered very carefully. (+info)
Mapping of antigenic sites involved in neutralization on the capsid protein of feline calicivirus.
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In order to locate amino acid residues involved in the formation of feline calicivirus (FCV) neutralizing epitopes, we analysed the capsid protein gene of monoclonal antibody neutralization-resistant variants of FCV. Amino acid substitutions in the variants were identified in the two hypervariable regions of the capsid protein. Four linear and two conformational epitopes were located in the regions from residues 426 to 460 and 490 to 520, respectively. The relative positions of individual epitopes agreed with our previous antigenic analysis. Two antigenic sites composed of the neutralizing epitopes were mapped in the hypervariable regions of the capsid protein, demonstrating that a relationship exists between the genetic variability and antigenic differences in the neutralization of FCV. (+info)