Contagious Equine Metritis - USA Outbreak
In December 2008, an outbreak of contagious equine metritis (CEM) was reported in Kentucky. The index case was a healthy stallion that underwent routine testing for exportation of semen and the causative agent, Taylorella equigenitalis, was isolated by cutlure on December 15. By the end of the month, three more stallions on the same farm were also identified as infected. At the moment, it is estimated that there are 28 horses in Kentucky and another 156 horses outside Kentucky that have been exposed. Another 250 horses are being traced across 27 states. The last outbreak of CEM in the USA was in 1979 in Missouri, although a few sporadic cases have been identified in the country in the last three decades. It is a reportable disease in both the USA and Canada, and there are strict import (and export) regulations for horses entering the USA and Canada from CEM-positive countries.
CEM is a venereal disease of horses. It is spread by stallions who can carry the bacteria on their external genitalia without any noticeable clinical signs, as well as by infected mares, during breeding. The bacterium can also be transmitted through artificial insemination, particularly on contaminated equipment. The diseases causes temporary infertility in mares. Typically mares do not conceive when they are first infected, but if a mare does become pregnant she may abort, or the foal may be born a carrier. Some mares develop a heavy purulent vaginal discharge (pus) for up to two weeks after breeding, but others may only have a shortened heat cycle. Some mares will clear the infection on their own, but in some cases a mare may become a chronic carrier of T. equigenitalis and transmit the bacteria to stallions during breeding. The organism does not cause any clinical signs in stallions, so the only way to detect the bacteria in males is to culture it. However, T. equigenitalis is notoriously difficult to grow in a laboratory, so false-negative results can occur. Therefore adjunctive tests are also used, and additional testing methodologies (including molecular techniques such as PCR) are being developed for the detection and study of this organism.
The good news is that infected horses can be treated, and T. equigenitalis is typically susceptible to most common antibiotics. Local treatment and repeated flushing of the external genitalia of infected horses is also part of the treatment regimen. Compared to other diseases, the spread of CEM is also relatively easy to control, because it is only transmitted by breeding (either live cover or artificial insemination). The major problem is that this disease is also one that can easily “fly under the radar” for some time before it is discovered, because carrier animals show no clinical signs of infection, and stallions in particular, as in this case, may expose many mares before the bacterium is discovered. Hopefully this outbreak will be brought rapidly under control so that the equine industry in the USA can avoid devastating economic loses due to the presence of this disease.
