Veterinary researchers at Oregon State University (OSU) announced today that they have linked a major abortion epidemic in Central Kentucky mares in 2001 to vesivirus infection. This marks 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, in spring 2001, 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, dubbed mare reproductive loss syndrome (MRLS) eventually dissipated, and researchers have been working to identify the cause ever since.

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