Equine Arteritis Virus

Since my appointment to the Frederick L. Van Lennep Chair in Equine Veterinary Science in 1988, my primary research interest has focused on aspects of the biology and epidemiology of equine arteritis virus, the causal agent of equine viral arteritis, with particular reference to occurrence of the carrier state.

Earlier studies in this department confirmed that establishment and persistence of equine arteritis virus in the horse is testosterone-dependent, which explains why the carrier state has only been recorded in intact, sexually mature colts or stallions. Based on field investigative studies over the past 20 years, frequency of the carrier state can vary from less than 10% to as high as 70% in naturally infected stallions. Furthermore, not all carrier stallions remain persistently infected for life. It is now widely accepted that the carrier stallion is the principal reservoir of equine arteritis virus in various equine populations worldwide.

There have been authenticated instances where global spread of equine arteritis virus has resulted from the international movement of persistently infected stallions or the shipment of infective semen. It is little wonder, then, that all the major horse breeding countries with the exception of the United States bar the importation of such animals or their semen, regardless of the genetic potential that they may represent. Aside from the significant economic repercussions that can result from restrictions on the international trade in carrier stallions or infective semen, most stallions suffer a major decline in commercial marketability and value domestically if they are confirmed virus carriers.

In view of the significance of the carrier stallion in the epidemiology of equine arteritis virus and the economic consequences arising therefrom, there is an obvious need to expand upon earlier studies of the carrier state, notwithstanding the availability of a safe and effective vaccine with which to protect against the infection. Current research is focused in several areas -- establishment of an in vitro model of viral persistence, investigation of host-related factors that play a role in defining whether equine arteritis virus persists in the reproductive tract of certain individual stallions and not others, elucidating the basis for spontaneous clearance of the carrier state in particular stallions, and determining whether viral pathogenicity can be modulated by long term persistence in the stallion.

Through increasing our understanding of the carrier state, hopefully, it will be possible to develop safe and reliable strategies for eliminating the virus without the risk of compromising the future fertility of these stallions. Successful treatment of stallions persistently infected with equine arteritis virus would have the major economic advantage of enhancing the commercial value and marketability of such animals and eliminating any impediment to their export to most countries in the world.

The significant contributions to past and current studies on the carrier state by various individuals over the years, most notably Dr. William McCollum, Professor Emeritus, University of Kentucky, and Drs. James MacLachlan and Udeni Balasuriya, University of California, Davis, is acknowledged with gratitude.

Dr. Peter Timoney, Frederick L. Van Lennep Chair in Equine Veterinary Science
(859) 257-4757, ptimoney@uky.edu
Maxwell H. Gluck Equine Research Center, University of Kentucky.