LEXINGTON, Ky. - Four non-Thoroughbred stallions in central Kentucky and three in Indiana have tested positive for an equine venereal disease, contagious equine metritis, which can cause temporary infertility and abortion in pregnant mares. But, so far, the disease has not been seen in the Thoroughbred population, and regulatory agencies in the affected states remain cautiously optimistic that the outbreak will be contained without affecting the Thoroughbred breeding season.\nThe traditional start date to the Thoroughbred breeding season is Feb. 15. In 1978, the first known outbreak of CEM in the United States wreaked havoc on Kentucky's breeding business when two stallions imported from France began infecting mares. That prompted the Kentucky Department of Agriculture to shut down the breeding season in March, a move later estimated to have cost the state's Thoroughbred industry up to $60 million.\nCEM is treatable and can be eradicated with antibiotics.\n"There has been no indication at all that the organism has been transmitted outside the populations we've identified," said Rusty Ford, equine programs manager at the Kentucky state veterinarian's office. "There's no evidence or suspicion of that."\nA stallion tested positive for CEM on Dec. 10, 2008, at DeGraff Stables in Midway, Ky., a Quarter Horse and American Paint breeding facility. Since then, four stallions there and three who shipped from DeGraff to Indiana have tested positive for the bacterial infection. A total of 32 other horses in Kentucky, including six stallions and 22 mares, have been exposed to the disease at DeGraff either through breeding or by being on the premises.\nAs of Jan. 5, the United States Department of Agriculture reported 92 other exposed horses and three CEM-positive stallions have been located outside of Kentucky. Those horses were either shipped from DeGraff or artificially inseminated with infected horses' semen. All have been quarantined or placed under hold orders to prevent their further movement and are undergoing testing and/or treatment.\nAccording to the USDA, the agency is now tracing at least 250 more horses in at least 27 states that authorities believe have been exposed to the disease.\nCEM can be transmitted only sexually or through shared breeding equipment, and it does not affect humans.\n"We have completed treatment for the four positive stallions here in Kentucky," Ford said. "The remaining six stallions that have cultured negative on two occasions now will start test breeding on Jan. 6. That will allow us to more definitively determine their disease status."\nBy test-breeding two mares to those stallions and then testing the mares for the bacterium that causes CEM, authorities can determine whether the stallions are in fact carrying the bacteria. Stallions can carry the bacteria, Taylorella equigenitalis, without showing symptoms, and both stallions and mares can become chronic carriers.\nThough the Thoroughbred population has not been affected by this outbreak, breeders are keeping an eye on potential export regulation changes that could hamper international movement of breeding stock by requiring longer quarantines, test breeding while in quarantine, or other precautions.