University of Kentucky MRLS studies have shown little evidence of a virus being the cause of MRLS, such as a fever in affected mares or evidence of direct transmission of the disease between mares. "There is no direct evidence that vesiviruses have caused a single case of MRLS," Webb said."In my view, the weight of the evidence, both experimental and practical, argues against vesiviruses having any role in MRLS," Webb said. "So, I think that I speak for all of us (at the University of Kentucky) in saying that 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."
University of Kentucky researchers studying Mare Reproductive Loss Syndrome are concerned that the results of a study by Oregon State University linking vesiviruses, which can affect a wide variety of mammals, to MRLS can be misconstrued. Bruce Webb, PhD, a University of Kentucky entomologist and MRLS researcher who provided many of the samples used in the Oregon study, said the OSU report describes a correlation, not a cause, and that the link of vesiviruses to MRLS is premature.The Oregon researchers reported a "significant association" between finding antibodies in blood samples for vesivirus and abortion in mares. See Oregon State Study Links Kentucky Abortions to Virus.