CEM outbreak source remains elusive despite painstaking search

National Report

-- With a nationwide outbreak of contagious equine metritis (CEM) now nearly four months old, state and federal investigators say they still can't draw any conclusions regarding the source of the treatable reproductive disease.

The process of tracing, locating and treating exposed and infected horses is long and painstaking, and it's possible the origin may never be known, says Donna Gilson, a spokesman for Wisconsin's Department of Agriculture, Trade and Consumer Protection. "It might not have come from a single horse; it's even possible there was more than one originally," she adds.

Wisconsin is one of six states with horses that have tested positive for Taylorella equigenitalis, the bacterium that causes CEM, a disease that unless treated can lead to abortions and infertility.

The USDA's National Veterinary Services Laboratory in Ames, Iowa, has identified 15 stallions and five mares as positive for CEM. The positive stallions include five in Wisconsin, four in Kentucky, three in Indiana and one each in Georgia, Texas and Illinois. The positive mares include two in California, two in Illinois and one in Wisconsin, according to the USDA's Animal and Plant Health Inspection Service (APHIS).

One of the two most recently identified positive stallions in Wisconsin, like those previously in the state, was exposed to infection at an artificial insemination center. Its infection dates to 2006 and possibly 2005. "While the source of the outbreak isn't known, some presumed that Nanning, the first CEM-positive horse in Wisconsin, was the original source. This (latest) result makes it clear (because of the infection date) that he was not," says Wisconsin State Veterinarian Dr. Robert Ehlenfeldt.

Since the first positive horse was found on a central Kentucky farm last Dec. 15, examiners have checked breeding records and movement history of each infected horse to find other exposed animals. At each step, the exposed horses are quarantined, tested and treated for a minimum of 21 days before being pronounced free of the disease. Owners are contacted by officials; there is no need for them to have their horses tested unless they are contacted.

In addition to the 15 positive stallions and five positive mares, the investigation has confirmed locations for 706 additional horses exposed to the disease. The total of 726 horses are in 46 states. There are 120 exposed or positive stallions in 19 states and 606 exposed or positive mares in 44 states.

CEM, transmitted by artificial insemination and natural breeding, poses no risk to human health or to horses in the general population, investigators say.