(reprinted from the NCDC newsletter, May 1997; updated 3/12/00)
As some NCDC members know, I have a horse who was diagnosed in June 1995 with EPM. I thought the group might be interested in some general information about the disease as well as Sam's story. EPM is caused by a protozoan (microorganism) which is a normal parasite in opossums. Its normal life cycle involves opossums and birds, but horses can pick it up from eating grass or hay contaminated with feces. Most horses are not affected by it, but in a few cases, the organism penetrates into the spinal cord and causes inflammation and permanent nerve damage. No one knows what makes one horse susceptible while his stablemates are resistant. Horses cannot pass the organism on to any other animal, including other horses. The symptoms vary quite a lot, but in general, the horse becomes uncoordinated, most commonly involving the hindquarters. The problem is usually worse on one side than on the other. It can start as very subtle indications that the horse is just not quite right, or can be severe and appear suddenly, even to the point of the horse being OK one day and unable to stand the next. The nerves which are affected are the ones which communicate back to the horse’s brain information about where his legs are in space. It is not painful, except that the horse can get hurt by falling. The only way to definitively diagnose EPM is by doing a spinal tap and looking for antibodies and protozoal DNA in the spinal fluid. Treatment consists of a combination of antibiotic and antiprotozoal drugs given orally every day for 3-6 months, at a cost of around $300 per month. Opinions vary widely about recovery rates, but it appears that the total recuperation process takes years and I think most horses do not fully recover.
In Sam's case, the first thing we noticed was he walked out of the barn one day kind of wobbly behind. He would place his hind foot on the ground, then rotate the toe inward, and "break over" the outside of his ankle. He did this about one out of 3-4 strides, with both hind legs. Two days later, several times I saw him standing still grazing, and lose his balance. He leaned his hindquarters more and more to one side until he almost tipped over, then staggered to catch himself. It took some time to get him to UC Davis for a spinal tap and then to get the results back and start him on medication. (I now wish we had started treating right away, without waiting for definitive diagnosis. The sooner treatment starts, the better.)
During the first 2 months on medication, he really didn’t get better, and the symptoms are very scary. He would lose his balance just standing or walking slowly on smooth ground. I saw him fall against the wall of his stall, and another time, stagger nearly a complete circle trying to get his balance back. He dragged his hind toes when he walked and would trip, sometimes falling down. He learned not to try to trot or canter when turned out because he would trip and fall. He loves to roll, but for 2 months he didn’t because he had so much trouble getting up and down. He was very depressed, probably due to a combination of the medication and not understanding what was happening to him.
The first signs of improvement after about 2 months of treatment were that he lay down to roll and he could walk steadily, as long as he walked slowly. Over the next 2 months, he got to where he could jog steadily. If he trotted faster, he would hit his hind fetlock with the opposite foot every stride. He could only go about 30 feet before he had to stop and reestablish his balance. He does best if he can establish a rhythm, because he doesn’t really know where his feet are, but his muscles know how to walk and trot. After 5 months of medication, his progress seemed to have leveled off and we stopped medication. He was very thin – all his ribs showed, his hip bones stuck out, his spine protruded a couple of inches and he had no roundness to his hindquarters. I started lunging and ponying him and he slowly improved in his movement and put muscle back on. It is a very slow process, and he continues to improve, even after nearly 2 years since this started. His weight is back to normal, and the only visible signs are that he occasionally trips and his movement still looks a bit awkward. He is not considered safe to ride, but I have started riding him a bit. He can now canter on both leads, and feels very balanced. Recently, we have started getting stretches of trot that, for the first time, feels even. He even bucks when he’s feeling good!
Update, 3/12/00:
While Sam did improve to the point where he no longer falls down, he is still classified as Grade 2 on the neurological scale (obvious signs of impairment). He does not move by driving from his hindquarters, and consequently his back muscles are very weak. He gets around OK in pasture, but is not truly rideable.
Much to my horror, in June, 1998, my new standardbred gelding was diagnosed with EPM. See Scotty's story.
I have lots of information on EPM, if anyone is interested --
The Last Chapter Sept 27, 2000
For the last few months, Sam has had a bloody nose, which has gotten steadily worse. Bleeding was coming from inside his nose, not from his lungs. Blood tests done in August showed him to be very low in red blood cells. The vet did not believe the amount of bleeding could cause him to be this anemic, but rather that the bloody nose and anemia were both symptoms of something else. We tried a month of iron supplements, but the subsequent blood tests showed his red cell count had dropped even further. Best guess is he had a tumor somewhere, but it's only a guess. We have no way of knowing if this is in any way related to EPM. In any case, treatment was not a practical option, and we put him down.
Last updated 01/22/03