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Causes of Sudden Weakness, Lameness, Seizures and Vision Problems
If a horse suddenly develops weakness, lameness, has seizures and vision
problems, he may be infected with Sarcocystis neurona protozoa which
causes the fatal equine protozoal myeloencephalitis (EPM).
Horses ingest the protozoal sporocysts in contaminated feed and pastures. A
major source of infection is opossum feces, contaminating feed and pasture. The
protozoa invade the tissue of the central nervous system, causing fatal
neurologic damage. The initial signs are loss of appetite, fever, diarrhea,
which are quickly followed by incoordination and head-pressing.
The key to diagnosis is recognition of subtle changes in the horse's stance
and way of traveling: toe dragging when tired, mild lameness in the hind legs,
back soreness, choppiness of gait, or awkward stance. As the disease gets worse,
the ears or lips droop on one side, the head tilts, and the animal leans to one
side. Horses in early stages of the disease are more likely to respond to
treatment.
Sarcocystis neurona is a two-host parasite, the secondary hosts being
the armadillo, the skunk, the raccoon, and the cat with the horse as the end
host. Mainly, EPM occurs in horses under the age of 5. There are no licensed
vaccines available.
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