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[RC] newest research on EPM - Laurie Durgin

Since I'd posted today about Rascal's progress , 10 months post epm, we got this today, on the newest research notes on EPM.Thought I'd pass it on. Laurie/Rascal/Honey and Scout

Dr Furr gave his talk on EPM last night and I hope I can understand my scribbled notes well enough so that this information does not become distorted before it gets to your eyes!! Many of the"veteran EPM moms and dads" already know alot of what follows but for those that are new-- here is a summary of what was said : (excuse any mixup I may have made on scientific terminolgy)
EPM is disease of neuro system resulting in wide variety of neurological abnormalities caused by unicellular parasite (S. neurona and sometimes neospora hugesi is found in horses with EPM). Lives in the lining of the bowel of the opposum, sporocysts are shed in possum feces which are then eaten by intermediate host(which can be many- well documented intermediate hosts are 9 banded armidillo, skunk, raccoon and possibly cat-with jury out on cat and said Dr McKay says that perhaps anything that eats it has possibility of becoming intermediate host). After being ingested by intermediate host it is absorbed into bloodstream and travels to tissues and forms sarcocysts in skeletal muscles where it remains dormant until death of intermediate host. The sarcosysts do NOT cause the death of intermediate host and it is important to remember that it remains completely dormant in intermediate host until the animal is dead. When opposum eats the dead muscle tissue of infected intermediate host it then sheds sporocysts which are consumed by horses

After sporocysts are ingested by horses it is absorbed through bowel into blood stream. Blood flows to every part of body and horses' bodies are adept at ridding it in muscle but not so efficient of ridding it once in central nervous system.
It divides and expands inside neurons causing inflammation in nerve nerve cell which leads to swelling and possible nerve cell death or necrosis of spinal cord which result in neuro deficits. Clinical signs are wholy dependent on where in central nervous system organism "lands".
The disease has widespread exposure of 40 to 60% in horses in North and South America. It has never been found in native horses outside the Americas that have NEVER lived in the Americas. Dr Furr did state one vet in France thinks he may have seen one case but it has never been proven.
All breeds are affected with ponies being rarely affected. Most common age is 4 to 5 years of age but any age can be affected- it could be that age 4-5 is more noticable because of start of serious training, etc. Cases conform to range of opposum- not as common in Canada and AZ. Very heavy in FL and heavy in eastern seaboard. Further north you travel- less prevalent.
Any neurological sign can present-- most typical being ataxia, asymetrical deficits, abnormal leg placemement, muscle wasting. A bit not as common are abnormal swallowing, head tilt, head pressing, etc and rarer are seizures, blindness, etc.
The disease usually progresses slowly over weeks but acute cases do exist with exception being long term muscle atrophy(nerve to muscle dies).
Diagnostic criteria are not easy-can't be 100% sure in live horse. Only post mortem examination can defintiely provide 100%.
Diagnosis based on:
1)consistant clinical signs which show neurological disease
2)cerebral spinal fluid analysis-Western Blot
3)exclusion of other neuro disorders-neck xrays to rule out cervical vertebral disorders, testing for encephalitis, WN, herpes and checling of serum VIT E levels

CSF is collected from lumbar-sacral junction checking for antibodies of s neurona. As few as 8 red blood cells(RBCs) in one micro liter of CSFcan contaminate tap resulting in false positive. Consequently less than 10 RBCs per microliter are considered relatively clean , and over 50 RBCs per microliter of CSF result in a tap which is meaningless. In between 10 and 50 is questionable.
Dr Furr's treament of choice is ponazuril-marquis(Bayer). It is given for 28days at 5mg/kg BW. In studies after 28 days treatment at that dosage, treatment was stopped no matter how much improvement was seen and all horses were evaluated 90 post treatment. 60-70%(actually closer to 69%) of all horses in study showed improvement. There is essentually NO toxicity with marquis- it is as safe as you can get. Way back in time organism was related to blue green algae and S.n retains chlorophyll receptors. Ponazuril which was developed in 50's as herbicide shuts down chlorophyll receptors, hence killing organism. People and horses have no chlorophyll receptors so ponazuril has no place to bind hence it is completely safe for horses-pregnant mares and breeding stallions included. The actual killing of tha parasite is based on time-therefore extended treatment time would be more effective than increasing dosage. Some horses need to be treated 2 months. Adding 2 ounces of corn oil increases blood levels 25% so Dr Furr recommends supplememting with corn oil to increase absorption into blood stream.
Sulfadiazine pyrimethamine needs minimum of 4 to 6 mos of dosing with preferable minimum of 6 to 7 months dosing. Side affects that might occur are anemia, diarrhea. Fetal abnormailites and abortion can occur.
Nitazoxanide-NTZ(Navigator) is an antimicrobial, antiparasitic drug. Success rates are a bit higher but there is element of toxicity. Fever, of 102, 103, even 104, diarrhea, off feed etc sometimes occur during first week. Dosing is 22.72 mg/lb BW and manufacturer is now suggesting dosing with half that amount for first five days(11.36 mg/lb for days 1 thru 5 and then 22.72 mg/lb for days 6 thru 28) This seems to help with toxicity. It is imperative that directions be followed to the letter. Death can occur from overdosing. It may be a logical alternative for relapse cases or when other drugs do not work.
Diclazuril (Scherring) is very similar to ponazuril and will be approved shortly and cost will be similar to marquis. Success rates are similar as well.
DMSO, NSAIDs(bute/banamine) are good for treatment crisis which sometimes appear 5-7 days after start of treatment. Some give NSAIDs routinely to fend off treatment crisis.
Around 70% of affected horses willimprove and about 1/3 of those 70% will return to 100% normal whereas many of others will return to useful state but maybe not back to 100%.
To help prevent-- do NOT feed off of ground, keep feed locked up. Un of Fl has a test area in Gainsville("swimming in opposums") and all horses sero convert within 2 wks once put into that area-- but by running electric fence 10 inches off ground sero conversion was slowed dramatically. Dr Furr also showed picture of "opposum heaven"-- grass clearing surrounded by thick brush-said opposums travel out 75 to 100 yards from brush at night, do their thing and then head back into thick brush and said although not always practical to keep pasture fences away from thick brush and woods. It is believed that about 1/4 of opposums carry this.
This was news to me-- but in Dr Furr's words-- "as we speak" EPM vaccine is part of challenge studies at Ohio State under Bill Saville. OSU has been able to produce EPM in horses in controlled setting and vaccinated horses are now being challenged. Within a few months we will know for sure if vaccine is effective and it will either be marketed or pulled from the market . He says Fort Dodge has been very accommodating and has worked very hard to get to this end. Dr Furr explained the conditional vs full licensure-saying 48 of 50 states have approved conditionally . Vaccine is proven safe and has reasonable expectancy of efficacy(as opposed to say sterile water which is safe but no expectancy of efficacy).
Marquis kills but takes time-a time dependent effect-increasing treatment duration is more effective than increasing dosage amount.
He said 40% of us(people) have toxiplasm(????don't know what that is or how to spell it??) in our brains-- just sitting there quietly. An immunesuppressive event or getting ill can set it off and similar thing is with EPM and horses. It "can sit" in horses for a long time and later activate in 1 1/2 % of horses.
Dr Furr explained neural plasticity where nerves can "learn" functions of other nerves. Said this is age dependent-- meaning younger horses have greater ability to retrain nerves.


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