Strains of Equine arteritis virus (EAV) differ in the severity of the disease that they induce in horses. Infectious cDNA clones are potentially useful for identification of genetic determinants of EAV virulence; to date, two clones have been derived from a cell culture-adapted variant of the original (Bucyrus) isolate of EAV, and it has previously been shown that recombinant virus derived from one of these (rEAV030) is attenuated in horses. A complete cDNA copy of the genome of the virulent Bucyrus strain of EAV has now been assembled into a plasmid vector. In contrast to rEAV030, recombinant progeny virus derived from this clone caused severe disease in horses, characterized by pyrexia, oedema, leukopenia, high-titre viraemia and substantial nasal shedding of virus. The availability of infectious cDNA clones that produce recombinant viruses of different virulence to horses will facilitate characterization of the virulence determinants of EAV through reverse genetics.
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