CORVALLIS, Ore. A new study by veterinary researchers at Oregon State University has linked a major epidemic of abortion a few years ago in Kentucky Thoroughbred mares to infection with vesivirus, the first time the virus has been suggested to cause this type of problem in horses.
The findings, which were just published in the American Journal of Veterinary Research, add another concern to the health issues associated with this virus, which is a part of the Caliciviridae viral family that can infect and cause health problems in many animal species, including humans.
About five years ago, mares in Kentucky's billion dollar Thoroughbred industry were losing foals at an alarming rate, with abortions of unknown cause happening up to 10 times more than usual on some farms. The problem eventually dissipated, and researchers since then have worked to identify the cause.
Many agents known to cause abortion in horses were considered at the time and ultimately dismissed, but some studies suggested at least part of the problem might be exposure to toxins in Eastern tent caterpillars found on some farms.
One new study examined 112 horses, both normal and those that had suffered abortions. It found that 40 percent of the mares with no reported abortion problems tested positive for vesivirus antibodies, but 64 percent of those from areas with high rates of abortion, or that had aborted their foals, had vesivirus exposure. All male horses and younger females not of breeding age tested negative for vesivirus antibodies.
According to researchers, these data suggest that vesivirus must now be considered a pathogenic virus associated with abortion in mares. It indicates that broodmares are being commonly exposed to vesivirus from unknown sources, they said, and that vesiviruses should be added to the panel of diagnostic tests for horses that abort.