Do we have an obligation to our industry? Does our industry have an obligation to us? (Sounds a little Kennedyesque.) If your neighbor has a horse with strangles, would you expect him or her to tell you so you can protect your horses? If you had a contagious disease on your farm, would you tell your neighbors? If you had something that could help your neighbors' horses, and it really wouldn't cost you a thing to provide it to them, would you have an obligation to hand it over?

While these questions seem convoluted and turned upon themselves, there are valid reasons to raise them: CEM and EPM.

Contagious equine metritis (CEM) is a venereal disease that can reside in mares and stallions without causing symptoms, can be spread through the venereal route (breeding) and through improper hygiene and management, and in rare occasions can cause abortion. It is a highly regulated disease on the state, federal, and international levels. (For more information see The's CEM Update).

CEM is considered a foreign animal disease, but in recent months, researchers have discovered a possible "subspecies" of the organism residing in a few donkeys and mules in this country. These isolates have thus far been labeled "CEM-like" organisms. Maybe this organism does not cause disease--it just lives in the animals without causing any reproductive problems. Maybe not. No one knows at this point. Research is absolutely necessary to find out the answers.

Care must be taken when introducing new animals onto any farm, especially if the new animals are from a farm that has donkeys or mules in residence or the new animals are mares which have been bred to jacks. Nurse mares should be tested, especially if they have been bred to a jack. If blood is sampled to test for evidence of recent exposure to the CEM organism, this should be done between 20 and 30 days after breeding to allow adequate time for development of serum antibodies.

Another question posed with CEM is whether our testing protocols are stringent enough to protect our horses. There have been three occasions in recent months when a stallion has been brought into the United States and has been found positive for the CEM organism. Many of the stallions being imported today are Warmbloods or other athletic/performance breeds whose owners might not be knowledgeable about CEM and its potential consequences. Because of the Kentucky outbreak in 1978, Thoroughbred breeders are all too aware of the serious economic consequences of this disease.

Questions that have been raised by researchers and officials are whether the countries of origin are testing adequately for CEM and whether the right sites in the mare are being sampled to optimize isolation of this organism if it is present?

The "CEM-like" organism should be investigated for its potential to cause disease. Mares exposed to this organism should be studied by those with experience in the area of CEM. Testing protocols might have to be extended rather than shortened, in light of recent experiences.

In short, all breeding operations should be careful until more information becomes available and researchers are better able to establish the prevalence and significance of infection with this "CEM-like" organism.


Equine protozoal myeloencephalitis is thought to affect about 1% of the equine population in the United States. That is a far lower prevalence than many other diseases that affect horses. However, with an estimated 6.9 million horses in the United States, 1% would be almost 70,000 horses affected to some degree. Some in the industry think the incidence of disease is closer to 3-5% of the population (200,000-345,000 horses).

EPM is a disease that can be devastating, can strike one horse out of a herd without rhyme or reason, and is prevalent throughout most of the United States (with horses from high-incidence areas shipped throughout the world). It is difficult to diagnose in its mild form, and can be deadly in its most severe. It can be mistaken for many other neurologic problems, and the diagnosis of EPM can be misapplied when other causes of subtle lameness or attitude problems are ruled out. Current treatments, at best, work 60-80% of the time and are expensive, with relapses common (in about 20-40% of cases). There are limitations to the tests used to diagnose EPM in cerebrospinal fluid, and there are horses being treated which might never develop the disease.

While there hasn't been much "news" on the EPM front for a time, it doesn't mean that work hasn't been ongoing into this disease. From epidemiologic studies to drug sensitivity testing, universities and private pharmaceutical companies are searching for answers.

However, there is question as to whether there is too much emphasis being placed on treating a disease we don't fully understand. Why do most horses exposed to Sarcocystis neurona fight off the parasite and not develop disease? How do they fight it off? What contribution does stress make to susceptibility of a horse to EPM? How does the horse's neurologic immune system deal with a parasite in the spinal cord and brain? How much does inflammation in the central nervous system contribute to symptoms of this disease? Is a horse owner's money better spent treating a horse for EPM without investing in extensive diagnostics, or having a complete workup done on the horse to rule out other possible causes of problems before EPM is decided on as the culprit?

As noted in a preliminary report on Diclazuril and EPM by researchers at the Gluck Equine Research Center in Lexington, "Since standard treatment of EPM often includes broad-spectrum antimicrobials, rest, and/or non-steroidal anti-inflammatory drugs, diseases other than EPM can improve on this therapy. Because Diclazuril is believed to be selectively toxic for apicomplexans, clinical improvement should occur selectively in horses with EPM. A positive clinical response to Diclazuril may be a useful diagnostic aid." (See The Horse Interactive's EPM update for more information.)

While we need to find a treatment, or treatments, that can save our horses, at a reasonable cost, we also need to understand the hows and whys of this disease.

EPM research is ongoing at the University of Kentucky's Gluck Equine Research Center in Lexington; at the University of Pennsylvania's New Bolton Center in Kennett Square; at the University of Florida in Gainesville; at Cornell University in Ithaca, N.Y.; and at the University of California-Davis. If you have questions, these are the places to go for answers. If you have resources, these are the places that can put your donations to good use.

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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