CEM Exposure: 17 Wisconsin Horses Quarantined

Seventeen horses on 11 different farms in Wisconsin have been quarantined and will be tested because they have been exposed to a highly contagious disease that can cause reproductive problems in mares.

However, Wisconsin State Veterinarian Robert Ehlenfeldt, DVM, of the Wisconsin Department of Agriculture, Trade and Consumer Protection said there is no risk to horses in the general population, and no human health risk.

Most of the horses are mares that were bred either naturally or by artificial insemination to one of seven stallions that have tested positive for contagious equine metritis, or CEM, in other states. The quarantine means the horses cannot leave their farms without department approval, and must be isolated from non-quarantined horses until they test negative. This is a process that may take several weeks or even months, Ehlenfeldt said.


Watch a video interview on contagious equine metritis with Dr. Peter Timoney.
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The Wisconsin quarantines are part of an investigation that involves at least 350 horses in 28 states, according to the U.S. Department of Agriculture. The investigation began in mid-December, when a quarter horse stallion on a Kentucky farm tested positive for the venereal disease during routine testing for international semen shipment. Ultimately, three more stallions in Kentucky and three in Indiana that had spent time on the original farm also tested positive.

"There is no risk to horses in the general population," Ehlenfeldt emphasized. "The risk is limited to horses that had some exposure to the infected stallions, either by breeding or being in the same facility and sharing equipment. It is possible that as the trace continues, we'll be notified of other Wisconsin horses that were exposed, but we've contacted the owners of all the exposed horses we are aware of. If you're a horse owner and you haven't heard from us, it's unlikely that you will."

CEM is a highly contagious bacterial infection that passes between mares and stallion during mating or in semen used in artificial insemination. It can also be transmitted on contaminated insemination equipment. Stallions do not suffer any symptoms, but the infection causes inflammation in the mare's uterine lining. This may prevent pregnancy or cause the mare to abort if she becomes pregnant. It is treatable. The disease was first reported in 1977 in Great Britain, and was found only twice previously in the United States: in 1979 and in 2006, when three Lipizzaner stallions imported into Wisconsin from eastern Europe tested positive after their arrival (read more). The infection was discovered before they had been used for breeding.

More than 20,500 premises with horses are registered in Wisconsin. Although the state is not a big player in the international equine export market, the USDA said that this outbreak could threaten the nation's $415 million annual trade in exporting horses, semen, and embryos. Movement restrictions, tracebacks, and increased testing could result in added costs both to owners and to public agencies.

Ehlenfeldt said, "The main thing is for horse owners to be aware that the disease is out there and as always, good biosecurity is the best medicine. Breeders need to understand that, too, and be sure to clean and disinfect AI equipment thoroughly between uses."

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