Contagious Disease: Care Not Fear

It never seems quite fair when "something" happens that doesn't directly involve you, but ends up affecting you. Vesicular stomatitis did that to many horse people in the last two years. Restrictions on movement of horses caused problems for people who had not been within 100 miles of an infected horse. It caused problems for some people who didn't live within hundreds of miles of an infected state!

In the most recent scenario, the culprit is CEM (contagious equine metritis), the problem is possible state, federal, and international travel and breeding restrictions, and the clincher is that it affects all of us.

But, that is only looking at it from the short-term perspective. CEM has caused serious problems in various parts of the world, including the United States, in the past 20 years, and it could be a problem again if we don't continue to be vigilant (see article on page 35). Prevention, in this case especially, is much better than cure.

Briefly, CEM is a highly contagious venereal disease that can affect all equids (horses, donkeys, mules, etc.) caused by the bacterium Taylorella equigenitalis. The infection can result in short-term infertility in mares that is sometimes associated with a vaginal discharge and rarely abortion. Foals born to mares with CEM can become infected while in the uterus (unusual in equines) or during parturition (birth). Mares can be inapparent carriers of the bacterium in their reproductive tracts, meaning they can appear perfectly normal, yet they shed the organism into their environment and transmit it through breeding.

Stallions don't develop clinical signs of disease after exposure to the bacterium that causes CEM. In the truest definition, they don't become "infected" following exposure to T. equigenitalis. They merely harbor the organism as a surface contaminant on their external genitalia.

It has been found in past outbreaks of CEM that the clinically inapparent carrier state can be established in a large percentage of exposed stallions. Such studs look normal, yet are capable of infecting your mare when bred (naturally or through AI). Your mare can in turn spread the bacterium to other mares or stallions back at her home farm, which then can spread it to other mares and stallions, and so on.

While there is no vaccine against CEM, there are ways to detect the organism's presence, and to rid stallions and mares of the bacterium. CEM is considered an "exotic" disease in the United States, which means it isn't found in the native equid population. There are at least 25 countries and/or territories where CEM exists, including a number of the member states of the European Union.

What This Means To Horse Owners

At the present time, there is an infected Mammoth jack in California that had been in that state his entire 11 yearse. He was discovered in late December to have a "CEM-like organism" when his semen was tested for export to Australia. The jack is in quarantine at UC Davis and epidemiologic studies are underway to see if any other horses directly or indirectly exposed to this animal are positive.

Laboratory investigations have determined that the organism is not identical to the cause of CEM, although it is a 97.5% match. There are some differences on DNA sequencing and a lesser reaction to the fluorescent antibody test than with the standard CEM organism.

The quesiton now is whether the organism found in this donkey (and other donkeys) is a CEM subset organism, whether it can be transmitted through breeding, and whether it can cause disease (in donkeys or horses).

In the case of the California native jack, there were jacks from another country (Mexico) residing on the property where the jack resided for most of his life.

Recently in New Jersey, a Warmblood stallion from Southern Europe was tested for CEM while in post-import quarantine. This involved test-breeding to two CEM-free mares. The first mare was negative for antibodies to the bacterium of CEM on the federally mandated 15-day post-breeding test, declared free of the infection, and released from quarantine. The second test mare, however, showed up positive on the blood test when sampled at 15 days. The first mare was retrieved immediately, re-tested, and found to be CEM-positive on the blood test. In light of this experience, Ernie Zirkle, DVM, Director of the Division of Animal Health, Department of Agriculture, in New Jersey, has changed the regulations for CEM testing on all imported stallions and mares in New Jersey, and he has recommended changes in the federal testing procedures for horses imported from known CEM-affected countries (see page 38).

In Kentucky (where a 1978 outbreak of CEM in Thoroughbreds traced to imported stallions shut down that breeding industry), two mares being qualified as "test" mares for imported stallions were blood tested routinely for CEM. They were both positive for antibodies to the CEM bacterium. They had been bred to a jack on the farm, and all three animals have since cultured positive for CEM. Epidemiologic studies are underway to find out where the CEM organism originated.

Also in Kentucky, a warmblood stallion from Germany was identified as carrying the CEM organism on post-entry examination. Officials now are waiting to see if he infected his test mares during breeding.

Tim Cordes, DVM, Senior Staff Veterinarian, Equine Programs, USDA-APHIS, said, "It is time to be cautious about CEM." He said USDA-APHIS Deputy Administrator Joan Arnoldi considers these incidents under each state's purview, and while the USDA is providing support by way of laboratory testing and federal personnel, it will not implement any federal controls at this time. However, that doesn't rule out a federal task force's being called in to investigate CEM if one is requested by a state or federal agency.

In summary, there is one incident involving an imported stallion which almost resulted in problems. It highlighted the need to extend the time of inspection of test-bred mares. There is the incident of a native jack in California having a "CEM-like organism" and not knowing how he became contaminated with this organism. Finally, in Kentucky there is the problem with two grade mares and a jack testing positive for CEM without indication of a source of infection and an imported stallion testing positive. These four separate incidents raise questions about current testing procedures, and concerns over the health status of our native equid population.

In this case, as with other contagious diseases, it is better to be safe than sorry. We should encourage our state and federal agencies to err on the side of caution in carrying out thorough epidemiologic studies to find out the answers to where these infections originated and ensure they are eradicated. We also should encourage additional research to determine if the CEM organism has changed in some manner that causes it to be missed in some horses under current testing protocols.

About the Author

Kimberly S. Brown

Kimberly S. Brown was the Publisher/Editor of The Horse: Your Guide To Equine Health Care from June 2008 to March 2010, and she served in various positions at Blood-Horse Publications since 1980.

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