EPM

Well I just looked it up in my vet book. The disease is caused by a protozoan called Sarcocystis neurona that invades the brain and spinal cord.This protozoan is a parasite of opossums. The organism is shed in the opossums feces and contaminates feed and water, or may be picked and distributed by birds. The horse is not a primary host, which helps to explain the wide variation in clinical signs.
EPM occurs most often in young TB's and SB's 1 to 6 yrs of age. The geographic distribution of the disease follows the natural range of opossums. Most cases are isolated. Out breaks have not been reported.

The ingested protozoans migrate randomly through the spinal cord and brain producing a variety of unexplained and high;y variable neurological signs. The horse often stumbles or falls repeatedly and make exhibit a head tilt. Over a period of days, weeks, or months. The horse develops weakness, lameness, and muscle wasting in one or more limbs, frequently on different sides of the body.The ataxia and muscle weakness are progressive.Finally the horse goes down and can't get back up.

Diagnosis is based on clinical suspicion and neurological findings. A diagnostic blood test using fluid from a spinal tap has recently became available. EPM mimics many neurological diseases. However it should be the number one consideration for any horse with unexplained neurological signs along with weakness, ataxia and muscle weakness.

Treatment. It is directed at stopping the progress of the disease. Good results have been obtained using a drug combination (trimethoprim and pyrimethamine) according to strict protocol. The drugs may need to be given for 2 to 3 months. Complications may require discontinuation. DMSO has been used intravenously to reduce inflammation and swelling of the brain and spinal cord. Corticosteroids ordinarily are not used because they lower the horse's immune response to the parasites. Recovery from neurological signs will depend on the amount of tissue damage cauued by the protozoans. Some horse have permanent neurological deficits.

Hope this helps you....  
There is also Parasitic Myeloencephalitis which is similar to EPM. but instead of a protozoan it is the larval stages of  Strongyles vulgaris, Habronema, and other worms that migrate aimlessly through the brain and spinal cord. Worm encephalopathy is less common than EPM, but the sysptoms are nearly indistinguishable. 
Treatment Ivermectin, thiabendazole in high doses, and febendazole are effective against the larve tissue stages of nematodes. Anti-inflammatory drugs reduce inflammation and swelling around the killed parasites. Corticosteroids are contraindicted. Improvement follows but neurological deficits may persist.

Great info Mingiz, thanks.
I worry about EPM often too, as opossum are everywhere
Scary stuff!!!

I knew I could count on you  what kind of vet book are you using.?
and it is a standard bred that is coming to retire. 8 years old, has a broken (cracked? leg) than dropped a suspensory is now crippled can not run. owner is doing right by this big money winner and sending him here.
also was treated for epm . 

Lipazzan this is what one looks like..
 

Yes Opossums are night creatures. They do remind me of a rat too..Yes if you have them on your horse property kill them!!! squirtgun

Thiabendazole is a drug used for the treatment of infections caused by parasites (mites and worms) and fungi (molds and yeasts).
Though most often used as a de-wormer in large animals, when combined with other drugs, thiabendazole is an effective treatment for certain ear conditions in dogs and cats. The drug kills ear mites and controls ear infections caused by the yeast Malassezia.
The product Tresaderm® contains thiabendazole combined with the antibiotic, neomycin and the steroid, dexamethasone. Neomycin is effective against a variety of bacteria (including Pseudomonas, Proteus and Staphylococcus), while dexamethasone offers relief from itching and reduces inflammation.
Thiabendazole is a prescription drug and can only be obtained from a veterinarian or by prescription from a veterinarian.

Beware!
www.thehorse.com/articles/34031/horse-owners-file-lawsuits-against-wickliffe-pharmacy?utm_source=Newsletter&utm_medium=welfare-industry&utm_campaign=06-12-2014

If we see any around here we shoot them.

hl..........

how is your new boarder doing that had this diagnosis? 

mingiz we go one further, we bait, and set live traps for them, and raccoons. now before anyone hates me, i have seen 2 walking horses slowly die from epm. they basically wasted away, got anorexic, weak, and dangerous to be near. we live IN the woods heavy with white pine, and oak trees perfect homes for opossums, and raccoons. our neighbors dog got after a raccoon that was in their garbage, and it rolled on its back, clawed the dogs stomach wide open basically gutting it. the dog was a 85+ pound lab., the vet said they see a lot of serious injuries between dogs, cats, and raccoons. cats mainly their front feet, and legs getting bitten completely through because they sit back, and swat at the coons faces.