Guest Editorial – Equine Viral Arteritis—An Emergent Threat to the Quarter Horse Industry

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The year 2006 saw a resurgence of equine viral arteritis (EVA) in the US, with evidence of infection confirmed in 10 states, all linked to a Quarter Horse (QH) breeding farm in New Mexico. This year's occurrence is significant not only because of the widespread dissemination of the causal agent, equine arteritis virus (EAV), to various states, but because it marked the first known major incursion of EVA into the QH population.

Prior to 2006, there was very little evidence of EAV infection in the breed (0.6% positive antibody rate), underscoring the immunological naïveté of the breed with respect to EAV. This year's multi-state occurrence of EVA illustrated the ease with which EAV can be widely disseminated through shipment of semen. Approximately 70% of direct exposures to infection resulted from the use of infective, fresh-cooled semen from a QH stallion. Additionally, movement of donor/recipient mares within and outside New Mexico contributed to dissemination of the virus. The widespread practice of embryo transfer, proliferation in the number of recipient mare farms, and the highly intensive systems of broodmare management in the QH industry, all had a significant impact on the epidemiology of the 2006 multi-state occurrence of EVA.

Lessons from this year's costly experience with EVA include the need for increased industry awareness of the importance of EAV as a cause of contagious abortion in mares and establishment of the carrier state in stallions. For many years, prophylactic vaccination of stallions and colts against EVA has been strongly advocated, but not commonly practiced, with the exception of Kentucky and New York Thoroughbreds. The QH industry should give serious consideration to adopting a more widespread program of immunization against EVA that would encompass not only stallions and sexually mature colts, but also mares that could be at risk of exposure to infection through the use of EAV infective semen and/or movement between premises.