Results from a study into the risks of transmission of Equine Viral Arteritis (EVA) via embryo transfer will be known later this year.

Oklahoma State University's Center for Veterinary Health Sciences researcher Reed Holyoak, DVM, Ph.D., DACT, has received a grant of more than $106,000 from the American Quarter Horse Foundation. He is looking to determine if the equine arteritis virus (EAV) can be carried by an embryo when flushed from an infected embryo donor mare and transferred to the embryo's new surrogate mother, thereby infecting her with the disease (EVA).

"It was a very competitive grant. Oklahoma State University received the grant because we are in the heart of the quarter horse industry and I'm lucky enough to be here at the right time," said Dr Holyoak, associate professor of Theriogenology and Bullock Professorship in Equine Theriogenology.

Equine Viral Arteritis (EVA) is a serious concern for horse breeders. The disease comes in two forms. One form causes abortions in mares; the other form causes respiratory tract infections. The latter form looks like a cold - watery eyes, running nose and possible swelling of the limbs.

In both forms, the equine arteritis virus (EAV) attacks small blood vessels, especially arteries. It causes severe damage to arteries and the leaking of plasma tissue swelling. The most common signs are fever and red eyes, which resemble pink eye. Often horses have a very mild infection. Unless someone was taking the horse's temperature daily, it could go unnoticed. The virus can be spread from horse to horse and via infected semen.

"It can be smoldering and people don't recognize it until it is too late," says Dr Holyoak. "By the time they do, a mare may have been bred with infected semen and even embryos could have been transferred that may be infected. These events could cause a disease outbreak with associated abortions."

Dr. Holyoak is not alone in this quest for answers on EVA. He collaborates with the University of Kentucky Gluck Equine Research Center (Gluck). Gluck is completing the virus isolation portion of the project. Dr. Holyoak did the live sampling in Oklahoma.

According to Holyoak, in the early days of veterinary medicine, the disease was referred to as pink eye. In 1812 in Great Britain, an infected stallion caused an outbreak. Each mare bred to the stallion developed pink eye, which people thought was unusual.

In 1984, an EVA outbreak occurred in Kentucky. The virus reservoir was found to be the persistently infected stallion. Once infected, a stallion may continue to shed the virus in his semen for a long time after he has apparently recovered from the illness. The Kentucky outbreak caused a great deal of concern in the Thoroughbred horse industry, but not in the American Quarter Horse industry.

More recent outbreaks occurred in 2006 involving a Quarter Horse farm in New Mexico, spreading to multiple states in the US and in 2007 at the National Stud located in the Normandy region of France. Both were associated with shipment of semen for artificial insemination in mares and subsequent abortion in associated pregnant mares.

"The outbreak among the Quarter Horse population marked the first time that this disease had appeared in this breed," explains Holyoak. "The American Quarter Horse Association wanted to know more about the disease and the risks associated with embryo transfer."

In the study, there were two groups of mares. One group had never been vaccinated and had never been infected with the disease. The second group had been vaccinated but had never been exposed to infected semen. Both groups were exposed to the virus through infected semen.

Both groups were bred with semen from a persistently infected stallion from an outbreak in New Mexico. The semen was shipped and artificially inseminated to breed the mares. For the mares that had been vaccinated, the first time they were bred after vaccination, they became mildly infected and still shed virus in body secretions.

"Seven days after being bred, we flushed embryos from the mares and washed the embryos according to the guidelines of the International Embryo Transfer Society," continues Holyoak. "We then transferred those embryos into recipients that had never been vaccinated or exposed to the virus. The embryos went through a 10 wash series. After each wash, samples were taken to determine if the virus was there and when it may have been washed off.

"We monitored the recipient mares to see if the transferred embryos infected them. We took blood samples, nasal samples, and urine samples. We also took samples from the embryo donors."

According to Holyoak, there are about 1000 samples in total that are now being analyzed by the University of Kentucky. The group anticipates that the results will be available in the summer of 2008.

"Our goal is to assess the risk of embryo transfer in disease transmission so that we can avoid the transmission of this disease from an unapparent infected mare to an unsuspecting population of mares," says Holyoak. "We want to avoid illness in adult horses, persistent infections in stallions, pneumonia in neonatal foals, and abortions in pregnant mares caused by EVA."

The Oklahoma State Center for Veterinary Health Sciences is one of 28 veterinary colleges in the United States and is fully accredited by the Council on Education of the American Veterinary Medical Association.