The investigations of recent Contagious Equine Metritis (CEM) outbreaks in the United States are now closed. CEM is a venereally transmitted disease of horses caused by the bacterium Taylorella equigenitalis. It is commonly transmitted directly during sexual intercourse between CEM-positive mares and stallions but can also occur indirectly by artificial insemination or contact with other objects such as hands, instruments or breeding phantoms contaminated with the disease causing bacterium.
The outbreak in 2008 involved 1,005 horses (278 stallions and 727 mares) in 48 states. Hawaii and Rhode Island were the only two states not affected. As of now, a total of 23 stallions (including one that is now a gelding) and five mares were confirmed as positive for T. equigenitalis. The source of the outbreak has not been indentified but it is believed a stallion imported more than 10 years ago may be the source. Overall, 966 (96% percent) of the 1,005 horses involved are now known to be free of T. equigenitalis.
In 2010 it was confirmed that an Arabian stallion in Southern California was positive for CEM. It was determined that the strain of bacterium did not match any T. equigenitalis strains previously found in the United States, indicating this case is not related to the CEM outbreak detected in December 2008. The stallion was imported into the US from a country not known to be affected by CEM. However, based upon epidemiologic findings it has been determined that he was likely infected prior to his arrival in the US. As a result, a total of 23 horses (5 stallions and 18 mares) in several states were involved in this outbreak.
CEM was previously considered an exotic animal disease to the United States. At this time it is unlikely that “CEM free” status will be reinstated to the US, therefore import restrictions from countries like Canada will continue into the 2011 breeding season.
For more information visit the USDA website.