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Equine Arteritis Virus: Fact vs Fiction

September 21, 2016

Equine arteritis virus is one of four respiratory-borne viruses of horses, the others being Influenza virus and equine herpesviruses 1& 4.  It is widely distributed geographically, being found in domestic horse populations in many countries around the world with the known exception of Japan, New Zealand and Iceland.  The USA is the only country that currently has no testing requirements on the importation of equine arteritis virus carrier stallions or semen that may be contaminated with the virus.

While all breeds of horses appear susceptible to infection, the percentage of those that test antibody positive can vary widely between breeds.  Although not life-threatening in otherwise healthy adult horses, the virus can cause abortion in pregnant mares, death in young foals, and give rise to a long-term carrier state in stallions and post-pubertal colts, but not in mares, geldings or sexually immature colts.

The carrier stallion in the primary reservoir of equine arteritis virus.  Its role is to disseminate the virus within any given breeding season and furthermore, ensure its perpetuation in equid populations from one year to the next.  The carrier stallion differs significantly from the acutely infected stallion, i.e. one that experiences infection with the virus for the first time, in one major respect, namely in how it can spread the virus.  Whereas the acutely infected stallion circulates the virus in its bloodstream, and sheds it into the respiratory tract, conjunctival secretions, urine, feces and semen for varying periods of time, the persistently infected carrier stallion only sheds the virus in its semen.  Therefore, the carrier stallion can only transmit the virus via venereal exposure through natural service or artificial insemination.  Accordingly, a carrier stallion does not represent a risk of transmission of equine arteritis virus through coming into direct contact with other horses, unless that is direct or indirect venereal contact.  As such, there is no scientific justification for preventing an equine arteritis virus stallion from competing at a show or keuring.

A great is known on how to manage a carrier stallion whether with reference to participating at a show or in a breeding setting.  Experience over many years has confirmed time and again that Equine Viral Arteritis is a “manageable disease.”


Peter Timoney