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Vol. #2 No. 1, January 26, 2001
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We have received numerous requests for in-depth information on Equine Protozoal Myeloencephalitis (EPM). This often fatal neurological disease, caused by the Sarcocystis neurona parasite, costs horse owners millions of dollars each year in diagnostics and treatment. But perhaps the greatest toll taken by this insidious disease is the progressive debilitation suffered by afflicted horses, and the emotional pain and frustration faced by their unfortunate owners.
The EPM information below is taken with permission from the Ohio State University Department of Preventative Veterinary Medicine Website (http://prevmed.vet.ohio-state.edu/epm/). We have found this to be one of the most concise and complete sources of information on EPM. It's not the easiest reading (very scientific), so if you have any questions please give us a call (1-800-848-2359) and we'll be happy to help you decipher the "science speak." We also encourage you to visit and bookmark Ohio State’s very helpful site.
--------------- Equine Protozoal Myeloencephalitis (EPM) ----------
Reprinted, with permission, from http://prevmed.vet.ohio-state.edu/epm/epmshort.htm
EPM, The Disease
Equine Protozoal Myeloencephalitis (EPM) is a serious and often fatal neurologic disease of horses. The causative agent of EPM is Sarcocystis neurona, a protozoan parasite which appears to have a predilection for the central nervous system. The classic presentation of the disease is an asymmetrical ataxia with focal muscle atrophy. The disease may be focal or multifocal in nature with atypical manifestations such as head tilts, facial paralysis, and sometimes seizures. The horse is an aberrant host in that the asexual stage of S. neurona is the only stage of the parasite which has been detected. This is also confirmed by the inability to detect sarcocysts in the muscle of the horse.
Diagnosis
The only methods of definitive antemortem diagnosis presently available are the Western blot for detection of antibodies to S. neurona in cerebrospinal fluid (CSF) and the detection of species-specific DNA with the aid of polymerase chain reaction (PCR). Additional tests that are used to aid in diagnosis of EPM are called the CSF Indices. They help to determine whether the CSF sample was contaminated with serum at the time of collection or whether there is intrathecal production of antibody. These calculations along with the cytology of the sample and the Western blot analysis may help clarify the true disease status of the horse.
Treatment
The current method of treatment recommended is potentiated sulfonamides in combination with pyrimethamine, an antimalarial medication. The efficacy of the treatment as indicated by short term survival and response to therapy has been reported to only be 55% or 60%, although there are indications it may be higher.
In addition to the anti-protozoal medications, it is recommended that horses undergoing treatment for this disease be supplemented with Vitamin E up to 9,000 IU per day. We also recommend your horse's blood be checked monthly for folic acid levels and a CBC every other week to examine for signs of anemia. This is to attempt to prevent folic acid deficiency as both sulfonamides and pyrimethamine are anti-folate medications and may cause folic acid deficiency. Folic acid supplementation is not recommended at this time, particularly in pregnant mares with EPM.
Additional therapies are also being used by some clinicians. These therapies include the use of immune stimulants such as Eqstim, Equimune, alpha-interferon, or levamisole. These compounds may boost non-specific cell-mediated immunity. Cell-mediated immunity is necessary to rid the body of these parasites. The efficacy of these compounds has been established in humans with leishmaniasis.
A new therapy (Diclazuril) has been receiving a lot of press recently and has been under study by the University of Kentucky. This new compound is a triazine derivative that has been used as a coccidiostat in other countries for a number of years. The site at which these compounds exert their effect is called a chloroplast which do not exist in mammals. For this reason, the compound should not be toxic to mammals, however, the toxicity studies have not been completed to date. The efficacy of this compound is very similar to the standard therapy discussed above, however, the treatment period is much shorter (4 weeks) and therefore less costly. This compound has been used primarily in horses that have relapsed after the standard therapy with reasonably good success. This compound is available through the AAEP and the FDA by special permit. An additional triazine derivative (Toltrazuril) is available through the same sources as the Diclazuril. Current clinical trials are being performed at several sites throughout the US to establish efficacy against Sarcocystis neurona.
A new therapy called Nitazoxanide (NTZ) is being investigated by Blue Ridge Pharmaceuticals. NTZ is a thiazolide derivative that demonstrates a wide spectrum of activity against bacteria, protozoa, and intestinal helminths. The drug is in development for humans to treat parasitic infections that are common in developing countries and to treat immunocompromised patients afflicted with cryptosporidiosis.
Epidemiology
EPM has only recently been recognized in horses, and as a result our knowledge of the pathogenesis and epidemiology of this disease are limited. Available information suggests that EPM is a disease of the Americas but that there may be geographic differences in the prevalence of infection. There were reports of cases of this myeloencephalitis from Canada, California and Brazil. While cases were reported from England only horses born in the U.S. were affected. S. neurona was cultured from both the gray and white matter of the spinal cord of a horse born in Panama. Another case of EPM was reported from the Republic of South Africa in a young Arabian horse that was imported from the US a few months before onset of clinical signs.
It has been suggested that the distribution of EPM may be limited to North, Central and South America because of indigenous wildlife which likely serve as definitive and intermediate hosts. An organism that is very similar to S. neurona was found in the brain of 2 raccoons which led to some speculation that this host species may be involved in the life cycle of the disease. Reports on the disease indicated that the most likely species involved in the life cycle of S. neurona are skunks, raccoons, and opossums.
The skunk is the only species that has been serologically positive, but may be incidentally infected like the horse. In 1995, results of PCR analysis provided strong evidence that the opossum is the definitive host of Sarcocystis neurona. This study revealed a 99.89% homology with the opossum sporocyst, Sarcocystis falcatula. These results have been corroborated by others. Experimental induction of EPM has just been completed by investigators at the University of Kentucky, which further corroborates that the opossum is the definitive host for this organism. The opossum is indigenous to North, Central and South America which coincides with the fact that no cases of EPM have been reported in horses other than those born there.
Life Cycle
The life cycle was determined in 1995 when the research determined that the Opossum is likely the definitive host and the grackle and cowbird are putatively the natural intermediate hosts. In addition there are likely numerous other intermediate hosts which will hopefully be determined in the future. The issue of transport vectors is still undecided, however, there is speculation about cockroaches, birds and a potential for the orbatid mite.
More Epidemiology
A multi-center descriptive study indicated that there was not a preferred geographic location nor a breed predilection. The study involved ten centers throughout North America with follow-up periods ranging from three to eleven years. Another study from the University of Pennsylvania Veterinary Teaching Hospital suggested that the incidence was higher in Standardbreds and male horses. These two studies are the only epidemiologic studies undertaken but had conflicting conclusions and did not identify risk factors for disease which could be used to design control programs.
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We hope that this information helps you in your understanding of EPM. We would also like to suggest two of our products recommended for EPM. GlutaSyn (www.glutasyn.com), an all natural milk serum isolate, is an immunoenhancer that will help the body fight the deleterious effects of EPM. E-5000 (www.vita-flex.com/e5000.htm) delivers a minimum of 5000 IUs vitamin E per ounce. As stated in the article above, vitamin E is highly recommended for horses facing EPM. As always, consult your veterinarian with any specific problems or concerns about EPM or any other disease. We are also offering a special coupon on E-5000 this month. See below.
We encourage you to pass this newsletter on to friends and colleagues. Thanks!
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