A Quarter Horse mare in Montana has been quarantined after exposure to contagious equine metritis (CEM), a highly contagious venereal disease of horses that can cause temporary infertility and spontaneous abortion.

The mare was exposed via a semen shipment from a stallion in Kentucky diagnosed with the disease. Originally confirmed as pregnant, the mare is now open.

“The mare in question has been quarantined and is being tested,” said state veterinarian Marty Zaluski, DVM. “At this point, it is the only known exposure we have here in Montana from the Kentucky cases, although we will continue to work with animal health officials from other states and USDA-APHIS to do trace-backs and complete our investigation.”

After a 30-year absence in the United States, the disease–which can only be transmitted during breeding or artificial insemination, and not by casual contact or shared boarding facilities–reappeared in Kentucky in mid-December. Since then, seven stallions–four in Kentucky and three in Indiana –have been diagnosed with the disease. The subsequent investigation now includes 38 states, with 95 exposed horses identified and approximately 300 potential exposures being traced.

No permit was obtained from the Montana Department of Livestock for the semen that caused the mare’s exposure, Zaluski said. Fortunately, records from the index farm in Kentucky documented the semen shipment to Montana.

“Even though we did not have a record of the imported semen, as required, on-farm records from Kentucky enabled us to quickly identify the mare and alert the owner of the potential animal health problem,” Zaluski said. “The lesson here is that there is a good reason for animal health permitting–health permits allow us to quickly identify potential problems.”

Responsibility for making sure the proper permits are in place, Zaluski said, is shared between all of the involved parties.

CEM-infected horses must be quarantined and treated with disinfectants and antibiotics over a period of several weeks. Following successful treatment and re-evaluation, horses may be certified CEM-negative and released from quarantine.

Because of the rapidly developing nature of the investigation, USDA-APHIS has set up a Web site to provide the latest information.