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1993 Newsletters

Horse Sickness
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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



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