Eleven stallions recently tested positive for CEM in the US, raising fears about imported horses and semen here, writes Dr Mac.
Contagious Equine Metritis(CEM) causes a severe, purulent discharge from the vagina in breeding mares, which results in infertility. It’s greyish and watery and occurs within 10 to 14 days after mating, but the mare usually looks well and continues eating. Some mares have no discharge, but come into season seven to eight weeks later because the embryo has died. Stallions never show any symptoms, but an infected stallion will transmit the disease to almost 100% of mares he mates with. Even teaser stallions can transmit CEM when they smell the vulva of an infected mare and then a susceptible mare.
Although it’s not fatal and mares can recover and breed again, it’s highly infectious. Infected stallions can be treated but mares usually remain carriers and a source of infection their whole lives. A recent US outbreak has raised fears that we could inadvertently import CEM in semen or infected breeding stock. It’s a notifiable disease in South Africa and a stud that becomes infected would probably be forced to close down due to the expense of eradicating the disease. Valuable bloodlines could easily be lost as a result.
The disease was first described in England in 1977 at the National Thoroughbred Stud in Newmarket, when the discharge was noticed in some mares. It resulted in a serious decrease in fertility as the infection also affected the uterus. Routine bacteriological cultures failed to show any growth and the new disease was named contagious equine metritis. It was only when the Public Health Laboratory in Cambridge used media designed for isolating human strains of gonococcus that a new, slow-growing organism was isolated. It was a new species, and named Taylorella equigenitalis after the scientist who made the discovery, Dr Eddie Taylor. By the time the organism was identified, over 100 mares were positive and showing symptoms, while 20 stallions had been identified as probable carriers. Some mares had been infected through specula used by vets during examinations.
Within a year, cases were confirmed in Thoroughbreds in the US, Europe and Australasia. The Thoroughbred breeding industry suffered significant financial losses due to the reduced fertility of mares, quarantine and the time it took for mares to be swabbed and certified either clean or infected before breeding. The Horse Race Betting Board developed stringent control measures and a protocol for diagnosis. Internationally, a voluntary code of practice was put in place in the Thoroughbred industry. It emphasised routine testing of all breeding mares, stallions and teasers, as well as stringent biosecurity by vets involved in breeding. Unfortunately, other breeds didn’t adopt the code and although CEM was eliminated from the racing industry, it lingered in sport horses, particularly in Europe.
In 1978, CEM was diagnosed in Kentucky, US, in a mare imported from Europe. It was quickly eradicated, but in December 2008, 30 years later, it was diagnosed in a Quarter Horse stallion, at a stud also in Kentucky. The disease has spread widely since it was first detected and so far this year 11 stallions and three mares have been diagnosed as positive. The positive stallions were in four states – three in Indiana, four in Kentucky, one in Texas and three in Wisconsin. The three positive mares are in California, Illinois and Wisconsin. Dr Becky Brewer, a state vet in the US, has said that artificial insemination equipment is believed to be the main cause of this outbreak. Canadian horse breeders are alarmed and have increased the biosecurity precautions for semen and horses imported from the US.
Like Canada, South Africa is free of CEM and all imported horses and semen must be tested. In addition , they must come from a country that’s been free of CEM for a year. The US no longer qualifies, so all imported breeding animals must be tested.
Because stallions show no symptoms, it’s difficult to certify them free of the disease until they’ve mated with susceptible mares, which have to be tested by swabbing and culture. The outbreak in the US is likely to have a negative effect on breeders who are currently importing semen or breeding stock. E-mail Dr Mac c/o
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