EQUINE VIRAL ARTERITIS

In August, 1993, an outbreak of equine viral arteritis (EVA) was diagnosed at the Arlington race track near Chicago.  It affected 190 horses in two barns.  The most common clini­cal signs recognized with this outbreak were elevated tempera­ture, swollen, edematous limbs and a skin rash.  Other signs often associated with EVA have been abortions at various stages of gestation, nasal dis­charge, conjunctivitis, weak­ness, depression and anorexia.

Diagnosis of EVA cannot be based only on clinical signs which are nonspecific.  Speci­mens for virus isolation from the live, acutely affected ani­mal include nasopharyngeal and conjunctival swabs, citrated or edta whole blood and, in some labs, semen.  At necropsy, iso­lations can be made from many tissues.  Tissues of choice are spleen, mesenteric lymph nodes, and lung.  In cases of abor­tion, specimens should include fetal thoracic fluid, lung, spleen, liver, kidney and pla­centa.  All specimens must be fresh, chilled, and sent to the lab without delay.  At the Pur-due ADDL, isolations may take up to 3 weeks to complete.

At the race track, treatments were limited to supportive therapy.  Most infected horses recovered naturally, with mini­mal treatments.  Occasionally, nonsteroidal, anti-inflammatory drugs were used to help control pyrexia.

In order to control the spread of EVA, a conscience effort must be made to isolate, quarantine and possibly vacci­nate.  Because EVA is known to be spread by aerosol droplets, venereal transmission and from fomites, affected animals at Arlington were placed on a strict quarantine for 21 days.

Presently, the only vaccine on the market is Fort Dodge Laboratory's ARVAC.  Vaccina­tion apparently limits trans­mission and prevents carrier stallions.  The normal vaccina­tion protocol is a yearly vac­cine for all mares and non breeding mares.  Breeding mares and stallions should be vacci­nated at least three weeks prior to breeding.  If a mare is pregnant or a foal is less than 6 weeks old, they should not be vaccinated.  The draw­back of vaccination is that the antibody titer from vaccination can not be differentiated from the antibody titer of the natu­ral disease.  This complication may prevent international export to some countries.

Dan Wilson.PUSVM'94 Dr. William VanAlstine Chief of Pathology-ADDL Dr. Charles Kanitz Chief of Virology-ADDL