WNV and Kentucky Abortions?

A question has been raised whether the increased number of West Nile virus (WNV) cases in Kentucky in late summer and fall 2002 contributed to a rise in fall abortions. A retrospective study by the University of Kentucky’s Livestock Disease and Diagnostic Center (LDDC), starting in July of 2002 and going through early 2003, looked at 400 equine abortions for evidence of WNV. Their findings were “surprising,” said Diagnostic Center head Lenn Harrison, VMD. Of those 400 examined, 35 (about 8.8%) had evidence of WNV identified on polymerase chain reaction (PCR) testing. This is the same test the laboratory uses to check for WNV in birds.

West Nile virus has not previously been associated with abortion, and researchers and veterinarians are not saying that is the case now. They have no evidence at this time that WNV caused the abortions; there are only saying that there was evidence of the virus in the aborted fetuses. The virus itself has not been isolated in the fetuses at this time.

Bill Bernard, DVM, Dipl. ACVIM, of Rood and Riddle Equine Hospital in Lexington, Ky., and president of the Kentucky Association of Equine Practitioners (KAEP), said, “There is evidence of virus in fetal tissues, but to take a jump to it causing abortion might be too big a jump.”

To determine the relationship between WNV and abortion, further testing and information gathering is ongoing, said Harrison. Vaccination and disease status of mares, review of histology on the fetuses, and study of normal mares and foals born during that time will continue.

“We’re working toward a goal of seeing if West Nile virus is significant (in the abortions), but we’re a diagnostic lab, and that might be a research question,” said Harrison.

There are no plans that either Harrison or Bernard know about on funding research into this question .

Vertical transmission of viruses (passage of a virus from mother to fetus) in horses is not unheard of, and Harrison noted that viruses that can cross the blood-brain barrier (go from the blood system into the central nervous system) usually can cross the placental barrier (from the dam to the fetus). He said he was aware of one human case where the mother had West Nile virus and the baby was born with neurologic signs because of West Nile virus (transplacental or vertical transmission of the virus).

One of the problems in determining whether the number of abortions is significant is that no one has even a good estimate of the number of foaling mares in Kentucky, said Bernard. Veterinarians in Central Kentucky are of the general opinion that abortion numbers are not up this year, said Bernard, even though the diagnostic lab is receiving more aborted fetuses than last year. “There seems to be more foaling mares now, and we have to consider population dynamics. Maybe there are more fetuses being submitted because of heightened awareness.

Harrison said that it is nearly impossible for researchers to answer questions on significance of numbers because they don’t know the number of mares in the area.

“The denominator of that equation is mission,” added Bernard.

Harrison pointed out that this has not been a Thoroughbred-specific abortion problem, just as West Nile virus has not been a Thoroughbred-specific disease.

A computer program to assist in data collection and sorting is being sought for the LDDC with help from Dr. Francois Elvinger, an epidemiologist from Virginia Tech. Set data from each abortion submission will be collected, and the computer program will allow researchers to seek specific details or collate information to answer specific questions.

This type of information has been collected in the past, but there was no good way to retrieve it to answer specific questions. This program also could be used to look at information on a variety of problems, not just abortions.

The problem is that one to two people will be needed to collect and enter information in the Equine Health Monitoring System, and there is a hiring freeze at the University of Kentucky because of budget constraints. The first phase of the monitoring system should be in place in the next couple of months, said Harrison.

In an aside about the abortions, Harrison said that only five cases of leptospirosis-caused abortions have been documented in 2003, which is lower than normal.

Florida Report
Maureen T. Long, DVM, PhD, assistant professor of large animal veterinary medicine at the University of Florida's College of Veterinary Medicine, has an active research program on the clinical aspects of WNV infection in horses. Thus far, very informal inquiries at this stage have not elicited evidence of increased abortions in Florida. But she says that the Florida Thoroughbred industry, Florida pleasure horse breeding groups, and the University of Florida are looking at breed registry information and fetal abortion submissions. Long will also work with Kentucky researchers to follow some farms affected by West Nile virus in terms of reproductive losses.

Leroy M. Coffman, DVM, Florida Department of Agriculture and Consumer Services, Director of the Division of Animal Industry, said they have not found any correlation of abortions to WNV infection. “However, there has been proven evidence of human fetal infection in individuals affected during pregnancy. The true impacts are not clear. All impacts are relative to the level of infection. With all the virus circulating this past year, especially in states like Kentucky, I am not surprised that they have identified WNV In fetal abortions. At this time we have no ability to determine any direct impact WNV infection has on abortions. In the absence of ‘abortion storms’ coincidental with WNV activity, I would have to say the impact is present, negligible, and directly related to general loss of condition and health due to WNV challenge.”

About the Author

Kimberly S. Brown

Kimberly S. Brown was the Publisher/Editor of The Horse: Your Guide To Equine Health Care from June 2008 to March 2010, and she served in various positions at Blood-Horse Publications since 1980.

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