Equine Botulism

Equine botulism is clinically defined as a gradually progressive myasthenia characterized initially by mild dysphagia, decreased tongue muscle tone and strength, mild mydriasis, and decreased tail tone leading to recumbency. The rate of progression of clinical signs of botulism is toxin dose-dependent. Ingestion of massive amounts of toxin may lead to recumbency and death within 24 hours, whereas very modest doses of toxin may not result in clinical signs until 10 to 15 days following ingestion. Typical field cases show evidence of dysphagia and weakness over 2 to 3 days and become recumbent on day 3 or 4 following initial detection of clinical signs. Definitive diagnosis is often impossible in single cases. Treatment should include botulinum antitoxin, complete stall rest, and supportive therapy with oral fluids and nutrition. Prognosis for recovery is excellent, if the horse is standing when treated with antitoxin. Vaccination with type B botulinum toxoid provides excellent protection.