Saturday, April 01, 2006
Equine Protozoan Myeloencephalitis (EPM) 1
James Rooney, a recently retired Doctor of Veterinary medicine from the University of Kentucky, identified a mysterious neurologic condition in 1964 that later gained the name Equine Protozoan Myeloencephalitis. The name literally means Horse disease caused by a protozoan (organism) that affects the muscles of the central nervous tissue. Ten years later research teams recognized the protozoa and learned the extent of distribution of what was once thought a rare disease.
The organism, Sarcocystis neurona, a single celled animal, can cause a neurological disease in equines of any age, sex, and location throughout the USA. The parasite cycle involves two animals: birds eat both plants and other animals of prey that carry the sporocysts of the organism. The opossum, the host responsible for ultimately carrying the protozoan to the horse, eats birds killed by the effects of the disease. The organism reproduces sexually in the opossum and is passed out in the feces. The horse picks up the organism by eating opossum feces dropped in feed or hay. The horse is a dead-end host, meaning the horse is non-contagious.
A growing problem? Many scientists and veterinarians alike have come to a realistic idea that this disease has been present for longer than twenty years, while considering the rise of incidence. In the start of the infection horses will display asymmetric incoordination (or incoordination on one side of the horse or the other), and loss of proprioception (or loss of sense of awareness of the position of the limbs). People may confuse this with a lameness . Not all horses exposed to EPM will show signs and some may develop an immunity and fight off the disease. Variations of the clinical signs depends on how much tissue damage is done, and may include various levels of seizure, muscle atrophy (leading to loss of ability to use muscles), and facial paralysis.
Antiprotozoal drugs are used in treating EPM, which drugs which kill the protozoan. The most common is trimethoprim-sulfamethoxazole, an antimicrobial. Anti-inflammatory therapy is recommended and supplements of vitamins E and folic acid may aid in treatment. The prognosis is variable. Approximately 60% respond to the therapy. Some undesirable effects of treatment may occur, and depending on the amount of nerve tissue damage, there is no reversibility with treatment.
The best preventative to EPM is to control the contact between opossums and your horses in and around your barn. Keeping all food covered and out of range is an essential practice (especially if there is cat food around). Any person with a trained and precise eye should consider EPM when evaluating a lame horse. The key is to catch the disease early in order to effect a full recovery. There is also a higher incidence in stressed horses; for example, a race track may have an 80-90% occurrence rate. It is helpful to know that the disease takes a minimum of two weeks to two years from exposure to time it shows signs. There is presently no vaccine, and labs estimate 20 years before an effective vaccine is available.
