Megan Campbell, D.V.M.

Equine Viral Arteritis (EVA) is a disease widely talked about in the reproductive community.  Many EVA infections are subclinical, however, manifestations unclude fevers, upper respiratory/ocular disease, depression, limb edema and most importantly, abortions.

The virus is primarily spread through nasal and urinary secretions or via the venereal route.  Mares infected via the venereal route during breeding usually have no clinical signs associated with the disease, but do shed the virus through nasal/urinary secretions.  These mares usually go on to recover on their own and have no further reproductive consequences.  Diagnosing these subclinical mares can be done through paired serum titers.  Mares infected via nasal secretions later in gestation are at risk of aborting, with or without developing other clinical signs.  Natural EVA infections in mares produce long term immunity against the disease.

30-60% of stallions who contract the disease can go on to shed the virus in the semen for years to come.  EVA positive stallions do not have any other fertility problems associated with the infection.  EVA can be transmitted by fresh, fresh cooled, or frozen semen.

A vaccine for EVA does exist and does confer a fairly protective immune response.  All horses vaccinated for EVA should have a negative EVA titer prior to beginning the vaccination series.