Updated on 09/17/2011 9:51AM

West Nile suspect in abortions

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LEXINGTON, Ky. - Researchers at the University of Kentucky's Livestock Disease Diagnostic Laboratory may have found a link between West Nile virus infection and some incidents of abortion in mares, according to preliminary data from a new equine health surveillance program.

If a link is confirmed, it would be the first time scientists have identified the West Nile virus as a possible cause of abortions in horses. West Nile virus, a mosquito-borne disease, first appeared in the United States in 1999 and has caused human and equine deaths as it has spread rapidly across the country. Previous studies found the virus could cause abortion in sheep.

West Nile virus is not considered to be a suspect in mare reproductive loss syndrome, which has caused thousands of early fetal losses and late-term abortions and whose cause has yet to be identified. But its involvement in other cases could shed light on some of the many undiagnosed abortion cases that occur every year.

Establishment of a possible link between West Nile virus and some abortions is the first discovery under a new equine health surveillance program based at the diagnostic lab. Dr. Bill Bernard, Lexington-based president of the Kentucky Association of Equine Practitioners, cautioned that researchers are still working to confirm the link through research that is expected to be completed this week. In the meantime, the association is communicating with the state's practicing veterinarians and farm managers to keep them informed.

"We suspect that there may have been a few West Nile virus abortions, based on very preliminary evidence," he said. "The type of testing we've done so far is not as precise and doesn't prove any link between the presence of the virus and actual disease."

Bernard said initial testing had shown that about 40 fetuses among 200 to 300 submitted to the lab since the summer contained possible evidence of West Nile virus. Researchers are attempting to culture virus from the fetal tissue and will look for evidence that the virus actually caused damage to the tissue and did not merely contaminate the sample.

"If there is a link, it's important to note that this is not a huge number of cases," Bernard said, "and the small number of [fetuses] were spread out over a period of five to six months. This is no more than the number we would see for other problems like herpes virus or leptospirosis" - two relatively common causes of abortion in mares.

Bernard said researchers decided to investigate a possible link between West Nile virus and abortion when a spate of summertime West Nile cases coincided with a slight increase in aborted fetuses arriving at the diagnostic lab.

Bernard said that it was not yet known whether any of the mares who may have aborted due to West Nile virus had been vaccinated for the disease. The Fort Dodge Animal Health company began selling a vaccine in 2001 under a conditional license granted by the United States Department of Agriculture.

"We certainly can not implicate the vaccine, and vaccination of horses against West Nile should continue until any evidence comes out that does implicate the vaccine," Bernard said.

"What's good about this finding is that a lot of abortions go undiagnosed, and this helps answer the question for why some of them may happen," Bernard said. "Under the equine reproductive health surveillance program, every fetus that comes into the diagnostic lab is going to have a certain number of tests done, and certain questions will be asked of the breeder or farm manager submitting every fetus. All of that information is put into a computer database so it's easily retrievable, and we have a full-time epidemiologist on staff to monitor that data."