I've been fortunate in my horse life so far to have never had to deal with a horse with EPM - equine protozoal myeloencephalitis - one of the most difficult equine diseases to accurately diagnose and treat. First, a disclaimer - I'm not a vet, have no vet training, and I'm not in a position to advise people on how to deal with a horse who may have EPM - if you have a horse with EPM, do your own research and talk to your vet (who may or may know about this new protocol). What I'm describing in this post was told to me by our vet/chiropractor and is based on her personal knowledge of the research, her own experience and that of her clients and their horses. And here's a site which contains a lot of good information about EPM, including description of the current testing and treatment protocols and also the new research.
Here's the summary - there is new research on EPM that has led to the development of a new, much more accurate test to determine if your horse has EPM, and a new treatment protocol is also in research that is significantly less expensive (at least for now) than the current approved pharmaceutical treatment and which may be more effective. According to my vet/chiro, this new treatment protocol appears so far to be producing excellent results. Obviously, this is still research, but if you have a horse with EPM or suspected EPM, you may want to have your vet get in touch with the people doing the research (details later).
EPM has always been a difficult disease to diagnose and also treat. It's a disease caused by a protozoan, horses pick it up in the environment, and a fairly large proportion of horses in the U.S. have been exposed to it but exhibit no clinical signs. A small percentage of horses develop neurological signs - weakness, gait abnormalities and balance and postural problems - which can make them unrideable and even a danger to themselves and unsafe to be around. Part of the difficulty in diagnosis is that other neurological diseases can produce similar symptoms, and the symptoms of EPM can vary widely. The currently available tests are also not completely reliable. Apparently horses that are treated sometime relapse repeatedly, and the current approved treatment can be very expensive, which may lead people to not treat or euthanize horses with EPM or suspected EPM.
The research is being conducted by a vet in the Ocala area - Dr. Siobhan Ellison. The new test is an ELISA test. Since it's an ELISA test, the reliability is much higher, and it also can be done using a blood draw instead of a spinal tap (the Western blot test that is also currently used also does not have high reliability). One reason for the treatment failures may be that existing treatments may not be effective against all strains of EPM, and a horse may have only one of the two strains that can affect equines, and current tests cannot distinguish among strains. Here's a page which describes how you and your vet and your horse may participate in the research - it's pretty easy - submit a serum sample, and if that is positive there is an ongoing trial of the drug, Oroquin-10 (decoquimate, I'm told, although the web site doesn't say this - this is according to my vet/chiro), which is also fairly inexpensive, has been shown to be effective against protozoal disease in other species, and which is reportedly effective against three strains of EPM, including the two that have so far been detected in horses. The page mentions a short-course oral paste treatment of the drug, but my vet/chiro indicated that there is a also a feed top dressing that is available for treatment for a three-month course.
To summarize, I am not advocating or not advocating this new test and treatment, as I have no personal experience with it, and I'm not vouching for the accuracy of the information on any of these sites - do your own research. But I trust the judgment of our vet/chiro, and if I had a horse with EPM, I'd certainly be looking into it and you may wish to do the same - I thought it would be useful to put the information out there.