EPM - Equine Protozoal Myelitis

This is a neurological disease caused by a protozoan.  I've found the most complete and up-to-date info on these 2 web sites:

http://prevmed.vet.ohio-state.edu/epm/index.htm 

http://www.cvm.missouri.edu/cvm/courses/epm/index.html 

Also, http://www.thehorse.com (excellent equine veterinary magazine and website)

A few comments taken overall from my reading and experience with 2 cases (Sam and Scotty):

I don't think you can prevent it, until they find a vaccine. I would certainly try to limit access of birds and rodents to the feed supply, but the organism can live for extended periods in "the environment", which means it could be in your hay. I think some horses are naturally more resistant to "bugs" than others, and something that reduces the horse's ability to resist microorganisms (illness and stress) may be enough to cause that horse to get sick. And the horse can carry it around for many months before getting sick. They know this because a few European horses have gotten it, all of which had come from the US several months earlier. Opossums don't exist in Europe, so it isn't a native disease there.

Diagnosis is still rather uncertain. The blood test just means the horse has been exposed, which about half of all US horses have. The spinal tap, while the best we can do, is also not 100%. If it gets contaminated with blood, it's useless. And we don't know how long it takes to develop measurable antibodies after exposure. It comes down to a neurological exam. They do several things to evaluate whether the horse has good control and perception of his legs, and rate him on a 0-5 scale. 0 is normal, 5 is unable to stand. Then you consider alternatives, such as possible neck injury. EPM is one of the few neurological diseases that can be treated, so at this point, you give the EPM meds and see if he improves. If yes, it's probably EPM. Not very satisfying (I'm a scientist, I like things to be clearer than that!). They also treat with anti-inflammatory meds. I think this is VERY important, and must be done very promptly. Inflammation itself can be the cause of a lot of the neurological symptoms, and the faster that is treated, the better the chances that the damage will not be permanent. I think the different outcomes of my 2 horses is due to having very prompt treatment with Scotty (who recovered quickly and completely), compared to Sam, with whom we delayed a few weeks because we didn't know what we were dealing with, nor did we understand how important timely treatment was. Sam is on the permanently disabled list. He is comfortable, has a good life, gets around OK, but is not rideable and never will be.

I also think it's important to treat for 4-5 months, at least. If you stop before the bugs are totally eradicated, it just comes back. It's very hard to decide when enough is enough. Some folks want to keep treating till a spinal tap is negative, but we don't know how long antibodies persist after the bugs are gone, so this is probably excessive.

I'm not sure if there is enough data on whether the newer type drugs work better than daraprim/SMZ that has been used for several years. Treatment period is shorter, total cost not much different. But in terms of success rate, I don't know if the newer meds are any better. The vet sites may have some recent info on that.

Just my opinion....

Gina Miner,   

01/22/03