Type A Botulism in Horses in the United States: A Review of the past Ten Years (1998–2008)

This is the authors' abstract. We don't add key points for this paper.

The objective of the current retrospective study was to describe naturally occurring type A botulism in horses in the United States. In the past 10 years, the Botulism Laboratory at the University of Pennsylvania's School of Veterinary Medicine has identified 3 isolated cases and 8 outbreaks of type A botulism in horses via samples positive for Clostridium botulinum type A toxin or spores using the mouse bioassay test. Additional information was obtained by review of submission forms and by telephone or email interviews. Almost all type A cases and outbreaks occurred in the western United States, with Oregon and Idaho overrepresented. Type A toxin was identified in only 1 outbreak; all other identified cases and outbreaks were positive for spores but not preformed toxin. Reported clinical signs included progressive muscle weakness, recumbency, decreased tail and/or tongue tone, dysphagia, respiratory distress, and death. Isolated cases involved foals < or =1 month of age; outbreaks involved horses > or =11 months. One hundred and nineteen horses were potentially exposed to the toxin source; 54 out of 119 showed signs of botulism, and 49 out of 54 affected horses were confirmed dead. The number of horses affected per outbreak ranged from 2 to 24. The source of infection was confirmed to be hay or silage in 6 out of 8 outbreaks and was unknown in 2 out of 8 outbreaks. The present report is the first description of outbreaks of type A botulism in horses and has important implications for prevention and treatment. Based on these findings, type A botulism should be considered in suspect cases of equine botulism in the western United States.