the first to be affected and are affected most profoundly as these neurons are located superficially within the spinal cord. At various intervals the protozoa become active and feed off of the spinal tissue, grow and replicate, increasing the amount of inflammation and damage in the CNS. They then re-encyst and become dormant for a period.
EPM is only known to occur in
, and is seen most commonly in and Thoroughbreds. It is thought that many breeds of ponies are
resistant to EPM as they produce antibodies against S. neurona without clinical signs of disease. Animals that are kept at pasture, and those feed in pastures are at increased risk for EPM as they are more likely to ingest feed or water contaminated by opossums. of one or more limbs, ataxia, poor tail tone, knuckling over of the hind limb during exercise, asymmetric musculature of the hind quarters, poor performance, hyperflexion of the hind limb(s), excessive sweating, dysphagia, seizures and recumbency. The incubation period for EPM is one week to five years depending on the immune status of the horse and the activity level of the protozoa. Clinically EPM is seen as
Diagnosis of EPM is made through CSF analysis using the
test to determine
exposure to S. neurona , and through blood tests & clinical signs and symptoms.
Treatment of EPM is difficult and need constant repetition throughout the horse’s life. The protozoa are to most antimicrobial and antiprotozoal medications during the phase, making it difficult to eliminate the entire protozoa population from the CNS at one time. Repeated treatments with antiprotozoal products such as Baycox or Marquis reduce the clinical signs of disease while NSAID’s help to manage the inflammation of the spinal cord. DMSO may be helpful in allowing the medications to cross the blood-brain barrier and the meninges. Immunity boosting medications may be helpful in controlling the acute episodes of EPM, while immunosuppressants such as corticosteroids will aggravate the condition and make the clinical signs worse. It is thought that EPM can be prevented by enclosing feed and water so that there is no contamination. Controlling the opossum population may also reduce the risk of contamination. Prognosis depends on the severity, location of the ‘attack’ and the time between onset of signs & symptoms and the start of treatment. Horses treated aggressively & quickly show good prognosis and have significant or complete reversal of the clinical disease. Horses showing signs & symptoms 3 months after the start of treatment have a poorer prognosis as this means damage to the nervous tissue is permanent.
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