The USDA Animal and Plant Health Inspection Service (APHIS) has added the Republic of Korea to the list of regions considered affected with contagious equine metritis (CEM).

A notice will be published in the Jan. 23 Federal Register.

In a release on the USDA website APHIS said it “took this action because of the confirmation of CEM, a highly contagious venereal disease of horses and other equines caused by an infection from a bacterium, in the Republic of Korea. As a result, horses and other equines from the Republic of Korea are subject to APHIS import restrictions designed to mitigate risk of CEM introduction into the United States.”

The restrictions are effective retroactively to May 7, 2015.

The United States has been considered CEM-free since the mid-1980s, though sporadic outbreaks of the disease can occur on U.S. soil. The venereal disease is caused by Taylorella equigenitalis.

Infection causes vaginal discharge and infertility in mares, but there are no outward clinical signs of disease in infected stallions. Some mares are capable of clearing the infection on their own, but others remain infected long-term carriers. Stallions can carry and transmit the organism indefinitely until they are diagnosed and treated for the infection.

A complete list of CEM-affected regions is available on the APHIS website.