Phylogenetic characterization of a highly attenuated strain of equine arteritis virus from the semen of a persistently infected Standardbred stallion

An avirulent, novel variant of equine arteritis virus (EAV; CA95G) was isol ated from the semen of a persistently infected Standardbred stallion. The C A95G virus caused subclinical infection and seroconversion in susceptible h orses, and virus was isolated only once from blood and nasal secretions col lected from 6 experimentally infected horses, Sequence analysis of genes en coding the known EAV structural proteins shows that this highly attenuated strain of EAV is genetically similar to virulent field strains of EAV and, in particular, to a strain of EAV that was isolated during an outbreak of e quine viral arteritis in western Canada in 1986. Not only is the carrier st allion the critical natural reservoir of EAV, but genetic diversity of the virus is generated in the course of persistent infection of carrier stallio ns. The subtle genetic changes that facilitate and maintain persistent EAV infection of the stallion's reproductive tract likely influence phenotypic properties of the virus such as virulence.