Here's a quote from the EPM/Lyme page, with Pie's results from last fall:
Antigen A - Negative.Antigen C - Negative.Antigen F - 1,726 (cut off for active infection is 1,250). This is a positive result, although many horses with Lyme have much higher titers. This indicates an active, chronic Lyme infection that is more than 5 months old. Our vet believes that some of the acute symptoms Pie experienced in the summer and fall of 2011, including an episode of laminitis, severe muscle pain/soreness, acute sensitivity to touch, severe grumpiness - to the point of biting, and his continuing muscle tightness and unusual visual reactivity to movement may have been/be Lyme related.Pie was treating using oral doxycycline, using a new protocol that dosed once a day at a higher dosage, in an attempt to kill the critters when they were most vulnerable - Lyme can be a bear to treat. He finished treatment in November 2012 and has been symptom-free for Lyme since.
Both Red and Dawn have had minor neurological flare ups of unknown cause, and have continued to test negative for EPM, and made complete recoveries on their own. Pie also had a minor occurrence of neurological symptoms in May, 2013 and was retested and showed a slightly elevated EPM titer, where before his titers had been negative. As a precaution, he was treated for 10 days using decoquinate, which is one element of the EPM protocol that is in clinical trials. He has been symptom-free since - although Lyme and EPM can have some overlap in clinical symptoms since they are both neurological, in my personal experience with Red, Dawn and Pie the symptoms of EPM and Lyme were quite different.
This month, he was tested again for EPM, to see if the treatment made a change in the antibody levels - it did - he was back to negative status again. We don't know if he cleared the possible new infection on his own - persistence of immunity after treatment is still not known - or if the treatment did the trick. At the same time, he was retested for Lyme - it's necessary to wait for at least 6 months after completion of treatment for antibody counts to decline. We were delighted to hear that Pie is below the threshold for active infection for all three Lyme antigens. Dawn and Red were not tested for Lyme as they are asymptomatic - and I keep a very close eye on them for any Lyme-related symptoms. I am aware of other horses with Lyme whose treatments have not been as effective - my vet says the level of antibodies and length the horse has had the disease, as well as the treatment protocol, can affect how successful treatment is.
The EPM/Lyme page will have more specific details about Pie's test results for those interested in those technical details (once I update it).
Pie's quite the Pie, to have come through two episodes of EPM as well as Lyme so well - I told him today (well, I do every day) what a fine Pie horse he is (and we had a lovely ride in the much cooler weather).