Tuesday, October 25, 2011

News Alert! - Now I Get to Learn About EPM . . .

Several weeks ago, Pie received a thorough neurological evaluation from our vet/chiropractor - I had her out when he seemed (incorrectly) to be over his repeated colic attacks, in the hopes that she could work on his continued body stiffness and lack of free movement.  I also had mentioned that he seemed to be having trouble when I picked his right hind - he didn't want to keep it up, which probably meant that he didn't want to continue weighting his left hind.  And he had several small interference injuries, where he had stepped on the inside of his left hind with his right hind when moving around the pasture, which meant the left hind wasn't getting out of the way quickly enough. When she did the neurological exam - which was very thorough - she found some anomalies in his cranial nerve responses and and also his spinal nerve reflexes - these tests involved using a pen to press on various points on the face to see his responses/reflexes, and running a pen down both sides from poll to tail to see what responses were triggered.  His backing and the tests involving turning in a small circle were pretty normal, but one of his foot placement tests - where the foot is moved to an unusual position to see if the horse moves it back - was highly abnormal - if she placed his left hind behind his right hind, he would just stand there for a very long time - I had noticed this before and in fact one time he actually caught his left hind behind his right hind and had a lot of difficulty disentangling himself.  She did only a little chiro work on him - to make him feel happy about her visit - since she thought it wasn't a chiro problem and I would just be wasting my money.

She suspected the early stages of EPM - here's a site with a lot of good information about it - and sent blood off for the new, much more accurate ELISA test that's in clinical trials - here's some information about the test and new treatment.  And it came back positive for all three antigen strains that occur in horses, but the positive numbers were only just into the range of likely active infection, and then we were off to U. Wisconsin to deal with Pie's repeated colic attacks.  I decided to wait until his liver enzyme numbers were pretty much back to normal in order to do a retest - one of the clearest signs of active EPM infection is a significant increase in the titer - a doubling or more.

I did a post a while ago about EPM, and the new test and treatment protocol that are in clinical trials.  EPM is a disease which horses get by consuming hay or grass, or drinking water, that are contaminated by the urine or feces of infected opossums.  Horses do not show clinical signs until the organism passes the blood/brain barrier, when it infects the central nervous system.  Some horses are exposed and never become infected.  Until recently, the only definitive test for it has been a spinal tap, and many horses have developed severe symptoms - falling, tripping, severe gait abnormalities, muscle wasting and/or difficulty chewing and swallowing - before being diagnosed.  There are other diseases/conditions that can cause similar neurological symptoms.  The older tests, other than the spinal tap, could not distinguish between exposure and active infection.  Until recently, there were few available treatments, and the most recent approved treatment that was available is very expensive and possibly not effective against all strains of EPM that infect horses.

I had our vet/chiropractor come back about two weeks after Pie's previous test to retest him - his liver enzymes had normalized.  In the interim, he had gotten better about picking up his right hind, but now the right front was a big problem for him - he clearly didn't want to stand with that foot off the ground.  When she evaluated Pie again, his hind foot placement tests were now abnormal for both hinds. And I had asked her to do some chiropractic work on Drifter - he'd started feeling "funky" behind - not off, precisely, but as if the "push" wasn't quite there.  I suspected the left hind based on how it felt and rode.  It was very subtle, but something wasn't quite right.  We observed him trotting at liberty in the paddock, and as I suspected, it was the left hind.  It was so subtle that it didn't even qualify as "off" and certainly not as lame, but it was there - he would bring the left hind forward normally, but then the backwards push was just slightly weak - that's what I'd been feeling.  She did a full neurological exam on him, and everything was normal, except for his backing - he tended to drag his toes behind (in fact he does this sometimes when moving forwards), and his hind foot placement test - he had difficulty correcting incorrect foot placement with both hinds.  We decided to send his blood in for the EPM test - the signs were very subtle but he clearly had no soft tissue issues going - no swelling or heat and the "offness" was extremely subtle - and his recent hock x-rays were completely normal.  As with Pie the last time she visited, she didn't do a full chiro treatment on Drifter as she felt it would have been a waste of time and my money.

Since Dawn was handy, we did a neuro exam on her too, and to quote my vet/chiro, Dawn was "appallingly normal".  So we didn't bother to do a blood test on her.  Opossums are very common in our part of the world - I see them often at night - but so far Dawn seems to have escaped, which is surprising, considering her propensity to strange diseases/conditions.

The results of the blood tests were interesting:  Pie's original results were phenotype SAG1-20, SAG5-20 and SAG6-40.  One, 5 and 6 are the three strains that infect horses.  The SAG6 story is complicated - focus on the SAG1 and 5 results.  Pie's second test - about two weeks later - SAG1-8,  SAG5-40 and SAG6-40.  Drifter's only results:  SAG1- 4, SAG5-40 and SAG6-40.  The cutoff for active infections is 16, and a doubling of a titer between two tests two to four weeks apart is highly indicative of an active infection.

Both Pie and Drifter have active EPM infections with strain 5, and Pie's is accelerating as shown by the doubling of the strain 5 titer.  If Pie was exposed to strain 1 - this may even have happened before I got him - he may have cleared the infection on his own as shown by the reduced titer - this is good news as strain 1 tends to have the worst symptoms.

The good news is that both horses can be treated, using the new trial treatments - which have very low toxicity and have produced good results in almost 200 horses so far - and the results of treatment should be to clear all infection.  I'll be calling the pharmacy tomorrow to confirm the orders our vet/chiro called in today, and we'll be off on our treatment path.  Drifter will get the trial 10-day paste treatment of Oroquin-10 followed by a 90-day feed treatment as a follow-up.  Oroquin-10 is a compound of a higher dose of decoquinate plus an immune stimulant. Because we're concerned that Pie's immune system may already be somewhat compromised as evidenced by his reaction to his vaccinations and the lumps in his abdomen, which may be enlarged lymph nodes, he'll be on only the 90-day treatment - decoquinate without the immune stimulant - where the medicine is added to his feed.

With the benefit of hindsight, some of Pie's other symptoms/behaviors may be related to EPM as well - his constant yawning and moving his jaw from side to side, the odd gulping noises he would make from time to time - effects on chewing and swallowing are common with EPM - his sluggishness and reluctance to move freely, and some recent head shaking and head rubbing that may indicate head discomfort.  We're hoping, perhaps against hope, that his digestive problems and the abdominal lumps may be related to his immune response to EPM and not to something more sinister, but only time will tell with that.

When they're in treatment, I can keep riding both Pie and Drifter provided they don't show dangerous gait or balance abnormalities.  I'm to avoid any steep hills either up or down, and also any cantering - it's a faster gait and there are times when only one foot on the ground, so in a horse with potential limb weakness or balance issues, cantering is inadvisable.  I have to be especially careful at certain periods in their treatment when symptoms may worsen due to the organisms being killed off - days 3 to 5 for Drifter and starting at about day 14 for Pie - and should probably avoid riding them at that time.

Sometimes I feel that my karma is to learn about lots of horse diseases, perhaps as punishment for my not having gone to vet school . . .

No comments:

Post a Comment