Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

First Advisor

Charles J. Issel


Three Shetland ponies (A, B and C) were inoculated with plasma from a pony with clinical signs of equine infectious anemia (EIA) and observed for 165 to 440 days. Clinical signs of EIA marked by high fever (39.5$\sp\circ$C) lasting 2-4 days were observed 2-3 weeks after infection and one to four such episodes occurred in each pony. EIAV was reisolated from plasma by end-point dilution in fetal equine kidney (FEK) cells and a plasma viremia 10$\sp{3.5}$ TCID$\sb{50}$/ml was observed during each episode. A total of seven virus isolates were recovered. Cross-neutralization tests with sequential serum samples showed that four viruses isolated from pony A during febrile episodes 4-5 weeks apart were serologically different. Tryptic peptide map analysis of these isolates revealed additions or deletions between each isolate and its immediate predecessor. Western blot analysis of all the isolates with a panel of monoclonal antibodies confirmed antigenic variation in both gp90 and gp45. Conserved and variable epitopes were identified in each glycoprotein with the greatest variation being in gp90. Analysis with MAbs confirmed similar antigenic variation in a neutralization escape variant of EIAV generated in cell culture. Antibody responses to EIAV were monitored by AGID, Western blots and a novel single-step immunoblot devised in this study for rapid assay of EIAV antibodies and antigens, respectively. Specific IgG directed against determinants of EIAV gp90, gp45 and p26 in homologous and heterologous virus isolates was detectable within one month after infection. The group-specific determinants in gp90 and gp45 were more antigenic than those in p26. Neutralizing antibodies first detectable within two months after infection were type-specific but became broadly reactive later during the course of infection regardless of the number of clinical episodes. Our data showed that rapid antigenic variation occurred during persistent infection with EIAV in ponies and in cell culture in the presence of immune serum and the neutralizing antibody response broadened during the course of EIA. The conserved antigenic determinants of EIAV gp90 and gp45 identified in this and previous studies will be useful in diagnostic procedures and may have potential for vaccines against EIA.