Tuesday, April 3, 2012

Oppressed by Opossums (?!!)

Some of you may remember Pie's and Drifter's experiences with the infection that causes EPM in horses - take a look at the EPM page for all the details.  Both boys were diagnosed with the disease through a new blood test, after developing gait abnormalities and, in Pie's case, recurrent colic, and both completed treatment (a new treatment that's in clinical trials) and have made complete recoveries.  Since 4 horses at the old barn (out of 7) had symptoms and tested positive, the other horses were tested as a precaution.  At that time Dawn did not show a clinically significant antibody response to any of the three strains of the organism that causes EPM, and her response on all the neurological tests was completely normal.

Now, what about opossums?  They're a marsupial - one of the few in the Americas - that is very common in my part of the world - they eat a wide variety of foods and are also efficient scavengers.  The problem with opossums is that they're an intermediate host for the organism that causes EPM in horses.  If, as they move around the landscape, their urine or feces contaminates water, hay or grass, it's a source of infection for horses.  Here's one of the critters - they're not the most attractive animals, but perhaps my judgment is colored by their role in causing EPM:

In the past, diagnosis of EPM in horses often only occurred when symptoms were dramatic - horses falling down or walking as if drunk.  The tests for EPM that were used weren't that accurate, which also made diagnosis difficult - there are several other diseases/conditions that can produce symptoms like this.  Treatment was also often ineffective. With the new test, it's now possible to diagnose EPM at very early stages of infection, where treatment can be started before more serious neurological damage occurs, or when EPM can be ruled out as a cause, and the new treatment that's in clinical trials seems to be very effective - at least that's my experience.

Dawn's been feeling a bit odd to me under saddle for a week or so.  She's seemed heavy on the forehand and has been having trouble softening.  Her gaits, which are normally fairly engaged and springy, have felt flat and dull - she's still plenty forward but the sense of power and lift is missing.  Occasionally, she take a funny step - not tripping, but like when you put your foot down and the ground isn't as level as you thought and your foot shifts. And, the last time I put her on the lunge a few days ago, she showed me that cantering on the right lead wasn't something she was happy about, by kicking out - it wasn't a buck, it was a protest, which is very unusual for her - I suspected some sort of issue with the left hind leg.  And she's been shaking her head a lot after our rides, and doing a lot of yawning.  Her stance when standing on the cross ties has seemed a bit odd - front feet farther apart than normal - and she's been very slow to give me her feet for picking - normally she lifts them in turn as I walk around without my asking.  It's like her legs are glued to the ground, and when I pick the left hind and let it go, it just falls to the ground.

Now some or all of that could be due to other things - I've had the chiropractor out, the dentist is coming Monday and the farrier is due.  But a number of these things are similar to things that happened with the boys, which made me suspicious. So yesterday, I decided to do some simple neurological tests to see what I saw - I'm not a vet but did these the best I could.  And today I took some pictures as well.  Now, remember that when Dawn has done these tests in the past, her responses were completely normal.

If you take a horse's front leg, and pull it out to the side, a normal horse will resist and will pull it back to the normal position very quickly.  Not Dawn - she just stood there with her front leg splayed to the side, and gradually shifted her weight so she was standing with her front legs well apart.  Same thing with the other front leg.  Here's a couple of pictures to show you what I mean:

With the hind legs, I did the test where you pick up the leg and place the foot behind the other hind leg - a normal horse will generally resist putting the foot in that position or at the least will lift the foot immediately and put it back where it goes.  With the left hind (remember that problem with right lead canter), she was perfectly fine with leaving her hind legs crossed and made no effort to move the foot.  The right hind was a bit better - she did allow me to place it in the odd position, but slowly moved it back to the normal position.  Here's the left hind in the odd position:

This one is particularly interesting - you can see her off-center hind legs through through the front legs, with both hind legs offset to the left (sorry for the horizontal stripe - Blogger seems to be doing this lately)  -  also note the somewhat splayed front legs - this is not normal for her:

Then we did the turning test - I couldn't get photos of this since I was turning her.  She had obvious difficultly turning in a small circle, in both directions, and did not normally cross the inside hind in front of the outside hind with each step - her steps and foot placement were irregular and she was slightly dragging the left hind.  When I backed her in hand, she was lifting and placing the right hind toe first, which is normal, but dragged the left hind.  I didn't bother with the tail pull to the side test.

Uh oh - all of this is abnormal . . .  Our vet/chiro is coming with the dentist on Monday to do the sedation for the dental work, so she's going to draw blood so we can have another peptide antigen test for the EPM organism done by Dr. Ellison.  I'll be interested to see what the results are, but the good news is that, if it is early-stage EPM, the treatment that's in clinical trials seems to work very well for most horses.  It's quite likely that Dawn did have the EPM organism in her system at the time of our move to the new barn, since she used the same water sources and hay and grass as the other horses, but did not have an active infection - some horses never get infected even when exposed - and that the stress of the move, and the effect of stress on her immune system due to that and also possibly due to her recent vaccinations, allowed an active infection to develop.

I'll keep riding Dawn so long as she doesn't feel unsteady, but will only ask her for long and low or relaxed contact, will avoid sharp turns and won't do much if any cantering, particularly to the right.

Darn those opossums!

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