Equine Protozoal Myeloencephalitis

Question 1

What causes equine protozoal myeloencephalitis? What is the definitive host? How do horses play into the life cycle?

Answer 1

Sarcocystis neurona

opossum

horses are aberrant (dead-end) hosts

Question 2

What is the lifecycle of Sarcocystis neurona like? How do horses play into is?

Answer 2

• opossum releases infective sporocysts into the food and water of IH (prey) hosts
• upon ingestion by the IH, sporocysts excyst and eventually enter skeletal muscle cells where they develop into sarcocysts
• life cycle is completed when the DH ingests the sarcosysts within the muscle of the IH

the horse is an aberrant (dead-end) host the ingests sporocysts

Question 3

What are the classical clinical signs associated with EPM? What are some other less common signs?

Answer 3

affected horse is bright and alert, but demonstrates ASSYMETRIC ATAXIA, weakness, and muscle ATROPHY (3 A’s)

• head tilt
• facial paralysis
• masseter muscle atrophy (brainstem involvement)

Question 4

What is the distinguishable feature of EPM when compared to cervical vertebral malformation?

Answer 4

asymmetry associated with EPM

Question 5

What are some supportive diagnostics for cases of EPM?

Answer 5

• positive Western blot analysis of CSF for S. neurona
• immunofluorescent antibody testing

(mostly by clinical signs –> asymmetry, ataxia, atrophy)

Question 6

What are the 3 primary treatments for EPM?

Answer 6

1. Trimethoprim-sulfonamide and pyrimethamine - blocks folate metabolism is protozoa
2. Ponazuril - anti-protozoal that targets plastid (organelle)
3. Nitazoxinade - inhibits electron transfer reactions essential for energy metabolism

Question 7

What is prognosis for equine protozoal myeloencephalitis like?

Answer 7

variable - some horses completely recover while others may have little to no improvement or have residual neurologic deficits

• neurologic signs may persist