It might be more than a sore leg
The Associated Press
Jan 25, 2009
SOURCE: The Telegraph Herald
Dear Dr. Mundt:Â
I have a mare that became lame in her right rear leg three weeks ago. She now drags her toe when she walks, and her muscles are shrinking in that leg. She has trouble stepping over things in her way. I am really concerned that this isn't just a sore leg. -- Cameron
Dear Cameron:Â
It sounds like your mare might be having some neurological problems. You should have your veterinarian out as soon as possible, because the most common neurological disease of horses is called equine protozoal myeloencephalitis, or EPM. EPM is caused by a parasite called sarcocystis neurona. Horses are exposed to the parasite when they consume feed or water that is contaminated with opossum feces. The parasite then reproduces in the horses tissues and can travel to the brain or spinal cord.
Horses with EPM develop a wide variety of neurological symptoms depending on where the parasite infects. When the parasite affects the spinal cord, the horse can appear uncoordinated, weak, or lame, especially on one side of the body.
If sarcocystis parasitizes the brain, the symptoms can include depression, seizures, behavior changes, paralysis of face nerves and so on. Without treatment, the symptoms continue to progress until the horse can eventually not get up. Diagnosis of EPM is not easy. An antibody blood test is done first and it is better for telling us the horse doesn't have EPM than it is at telling us they do. A positive blood test only tells us that the horse has been exposed to sarcocystis, but many horses are exposed and don't develop the disease.
This tells us that most horses are able to mount an immune response against the organism before it reaches the nervous system. Testing spinal fluid collected with a spinal tap was thought to be more accurate, but studies over the last few years have also shown this test may not be any more accurate then using blood.
Many newer tests are currently being studied. Diagnosis is therefore made based on combination of test and physical exam results.
EPM is typically treated with ponazuril or nitazoxanide for 28 days. The older treatment involved using two drugs daily for a minimum of three months. Preventing EPM involves keeping hay, grain, and water sources free from opossum feces. A vaccine for EPM exists, but so far hasn't been very effective.
Mundt is an equine specialist at Pet Med Animal Hospital in Dubuque. E-mail her at rrmundt@hotmail.com.
