Dr. Ellison (of the new ELISA peptide EPM test and new treatment protocol - see my EPM page for more about this) has a blog with occasional posts about her work and that of others on EPM - better understanding it and how to treat it effectively. In the most recent post, Pie and Drifter (and I) have our pictures included!
The post is about some technical things - that the primary disease mechanism may be inflamatory rather than central nervous system infection - but the take-away for me is that it is possible to detect very early symptoms of infection with the organism that causes EPM, and that many horses, regardless of the stage of infection, may be able to make a full recovery. Inflamed abdominal lymph nodes - like what Pie experienced and which probably caused his recurring colic - would be very consistent with this. Many of these very early symptoms are not the ataxia - poor coordination and lameness - that have traditionally been considered the markers of the disease - ataxia indicates that the disease is more advanced. It also makes the very good point that it's not the absolute level of antibodies, but changes in the antibody level over time that most clearly indicate the progression of the infection. EPM is a very scary disease, and it's good to know that infected horses have significant hope for full recovery. (Note to readers outside the Americas: EPM is transmitted to horses through contamination of water, hay or grass with opossum urine or feces - and opossums are a Western Hemisphere animal, so one thing the rest of you don't have to worry about - unless your horse has made a trip to the New World.)