Equine viral arteritis

Equine viral arteritis

Changing Times Equine Viral Arteritis P. J. Timoney, DVM It has been almost 20 years since an extensive outbreak of equine viral arteritis (EVA) occu...

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Changing Times Equine Viral Arteritis P. J. Timoney, DVM

It has been almost 20 years since an extensive outbreak of equine viral arteritis (EVA) occurred on a considerable number of Thoroughbred breeding farms in Kentucky in 1984. Subsequent events have shown that this was a watershed event. That occurrence resulted in a dramatic increase in the significance with which this disease would henceforth be perceived by many horse industries worldwide. Greater awareness, surveillance, and improved diagnostic capability collectively have led to an increase in the number of reported outbreaks of EVA over the intervening years. Spread of this infection internationally can almost invariably be attributed to the movement of carrier stallions or shipment of virus-infective semen. The increase in number of confirmed outbreaks of the disease bears little relationship, however, to the known global distribution of the causal agent, equine arteritis virus (EAV). Based on the results of serosurveillance surveys and diagnostic testing, it would appear that the majority of cases of EAV infection continue to be asymptomatic. Where investigated, the virus has not been shown to be a significant cause of abortion or illness and death in young foals. Outbreaks at racetracks, sales yards, etc are very infrequent in occurrence.

Programs for the prevention and control of EVA have centered largely on restricting the spread of the virus on breeding farms. These have been predicated on identifying carrier stallions and controlling the commercial breeding of such individuals. Similar principles have been applied to the use of EAV-infective semen. Over the years, targeted vaccination of noncarrier breeding stallion populations and prepubertal colts has proven effective in preventing establishment of the carrier state and reducing the number of available carrier stallions. Extensive field use of a commercial modified live virus vaccine against EVA has confirmed its safety and immunogenicity for stallions and nonpregnant mares. Furthermore, an increasing number of European countries have approved the selective use of a commercial inactivated vaccine against the disease. A recent preliminary report would suggest that it may be possible to expedite spontaneous clearance of the carrier state in some stallions through down-regulation of testosterone levels. If efforts to achieve greater control over the international spread of EAV are to be successful, then countries need to ensure greater standardization of diagnostic testing for this infection, implement scientifically based programs for its prevention, and thereby greatly reduce the number of carrier stallions that are the primary reservoirs of the virus.

From Proceedings of the 8th Congress World Equine Veterinary Association. 0737-0806/$ - see front matter © 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.jevs.2004.07.004

Volume 24, Number 8

359