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