Horses in Arkansas may have been exposed to a contagious disease called contagious equine metritis or CEM, according to the Jeremy Powell, Extension veterinarian for the University of Arkansas Division of Agriculture.

Arkansas is one of nearly 40 states being investigated for the disease. So far, the investigation has involved more than 300 horses in those states.

According to the USDA, the state of Kentucky confirmed a case of CEM in a quarter horse stallion in mid-December during a routine test for international semen shipment.

Pat Badley, Arkansas state veterinarian, indicated that two mares in Arkansas may have been exposed and have been placed under quarantine pending further testing for the disease. Currently, no known positive infections exist in Arkansas.

“Contagious equine metritis is a venereal disease among horses caused by a bacteria Taylorella equigenitalis. It’s only spread during breeding or artificial insemination, and cannot be spread by casual contact or shared boarding facilities,” he said.

CEM is not known to affect humans.

The disease leads to temporary infertility in infected mares causing an inflammation of the uterine lining. Up to 40 percent of affected mares may also exhibit vaginal discharge. Stallions typically exhibit no clinical signs of the disease, which may allow them to inadvertently spread the infection. CEM is not known to affect humans.

“Both stallions and mares can become chronic carriers of CEM, and act as a reservoir for future outbreaks,” Powell said. The transmission rate is relatively high when natural mating occurs with an infected individual. Semen collected for artificial insemination and other breeding equipment may also be indirect sources for infection.

According to the USDA, as of Jan. 15, nine stallions have been confirmed as positive for CEM. Four infected stallions are in Kentucky, three in Indiana and one each in Wisconsin and Texas.

The Texas-born quarter horse had spent the 2008 breeding season in Kentucky, where CEM was detected in a stallion during routine testing in mid-December. State and federal authorities are seeking the infection source.

All of the infected stallions have epidemiological links to one or more CEM-infected equine during the 2007 or 2008 breeding season.

A horse is considered “exposed” when it has been bred, naturally or through artificial insemination, to a CEM-positive horse, or it has been epidemiologically linked to a CEM-positive horse, as determined by state or federal veterinary health officials.

“Once horses have been identified as exposed, they’re quarantined, and further testing protocols are enforced,” Powell said.

The disease was first detected in the U.S. in 1978, and again in 1979. In both instances, the outbreaks were eradicated.

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