Botulism Outbreak In Wisconsin Horses
An outbreak of botulism has killed 5 horses on a farm in Wisconsin, and is apparently also affecting cattle in the area.
It is suspected that the spring melt played a role in this outbreak, as was reported in a review of Type A botulism cases in horses that I discussed the other day. Botulism occurs when the bacterium Clostridium botulinum grows and produces toxins. To grow, it needs an oxygen-free environment. Clostridium botulinum can live in the environment in its dormant spore form for years, waiting for the right conditions to start multiplying. With a spring melt, you can get accumulations of hay that are soaked in water and starting to decompose. That can create a nice moist, oxygen-free environment with a good bacterial food source - perfect conditions for C. botulinum. If horses eat hay that the bacteria are growing in, they can get botulism. Other possible sources include feed that is already contaminated with toxin, something that is of particularly concern with large bales of hay, haylage and silage. Horses are exquisitely susceptible to botulinum toxin and extremely small amounts can cause disease. Identifying the actual source can be tough, but hopefully efforts to do so are underway in Wisconsin.
Three of the 8 horses on this farm survived. They were all treated with anti-toxin, which is very expensive (thousands of dollars). It's hard to say whether the antitoxin worked or whether the surviving horses actually weren't exposed to the toxin as the others were, but treating all potentially exposed horses is the preferred approach if you have rapid access to antitoxin and can afford it.
Photo soucre: www.edu.gov.mb.ca
