Genetic and phenotypic variation of the equine infectious anemia virus surface unit envelope glycoprotein during disease progression

Equine infectious anemia virus (EIAV) infection causes a variable disease course consisting of acute, chronic, and inapparent stages of disease. Previous studies have characterized genetic variation in the envelope during recurrent febrile episodes of the chronic period in EIAV infection, detecting the appearance of novel envelope variants with successive fever episodes. Recently, it has become apparent that virus replication continues during the inapparent stage of disease at higher titers than previously thought. Genetic and antigenic variation in the envelope is considered to play an important role in EIAV persistence; however, few studies have characterized variants isolated during the inapparent stage of disease. We undertook a longitudinal study of surface unit envelope glycoprotein (SU) variation in a pony experimentally inoculated with the virulent, wild1 Department of Veterinary Microbiology and Preventive Medicine, Iowa State University ^Department of Veterinary Microbiology and Pathology, Washington State University