Oregon State University (OSU) researchers announced on June 23 that they linked vesiviruses to abortions seen during Central Kentucky's bout with mare reproductive loss syndrome (MRLS) in 2001 and concluded that vesivirus-specific reagents should be included in the diagnostic panel for aborting mares. A University of Kentucky (UK) scientist disagrees with the findings, cautioning that a more causative relationship needs to be established before labs put tests in place.

Vesiviruses are a genus within the family Caliciviridae, and they are best known for causing a clinical disease in pigs, called vesicular exanthema of swine. The OSU scientists wanted to examine possible vesiviral involvement because these agents have been shown to cause abortion not only in swine, but in a variety of mammals including cats, and probably cattle and humans.

In two experiments described in the study published in the American Journal of Veterinary Research, Alvin W. Smith, DVM, PhD, Dipl. ACALM, a professor in OSU's College of Veterinary Medicine, and his colleagues reported "significant association" between seropositive status for vesivirus and abortion in mares. The first experiment showed that nearly 64% of mares from Central Kentucky farms with abortion problems were seropositive for vesivirus antibodies. Forty percent of a group of breeding-age control mares were seropositive. In the second experiment, mares that aborted during the experiment after exposure to Eastern tent caterpillars had an increase in seropositive status for vesivirus antibodies from 47.1% to 88.2%.

"What I would hesitate to do is say this is associated with MRLS," said Smith, although OSU's press release linked the virus to the 2001 abortion storm. "I think it (the vesivirus) is an agent that's active in the equine population and can be an additional cause of abortion." If given the opportunity, Smith would like to more conclusively link the abortions to vesivirus, and in the meantime, Smith would like to see horse owners and veterinarians test for vesivirus when mares abort.

Bruce Webb, PhD, a UK entomologist and MRLS researcher, provided many of the samples used in the OSU study. Studies at UK have shown little evidence of a virus causing MRLS, such as a fever in affected mares or evidence of direct disease transmission.

"In my view, the weight of the evidence, both experimental and practical, argues against vesiviruses having any role in MRLS," Webb said. "We are very comfortable with the results of our work and the recommendations that we have in place. Specifically, if farm managers and horse owners control exposure of pregnant mares to Eastern tent caterpillars, it is an effective means of preventing MRLS." For more information see www.TheHorse.com/emag.aspx?id=7179.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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