Equine botulism outbreak in Florida

news desk @bactiman63

Last week, the University of Florida (UF) Large Animal Hospital reported treating a number of horses suspected of botulism. Botulism is a disease caused by the ingestion of botulinum toxin, one of the most potent toxins known.


The Horse website reports that horses from several farms showed signs consistent with botulism.

Botulism affects all mammals, however, horses are one of the most susceptible species. Although botulism is not contagious between horses, it can affect multiple horses on the same property. Sources of botulinum toxin include round bales, alfalfa blocks, contaminated soil and grain.

Clinical signs of botulism include longer than normal elongation, difficulty eating, tremors, low head posture and, in many cases, death. Prompt treatment with botulinum antitoxin is critically important to the survival of affected horses, and any horse showing clinical signs consistent with botulism should be seen by its veterinarian immediately.

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UF officials say botulism is a disease caused by toxins produced by the bacteria Clostridium botulinum. There are 8 different types of botulism which produce toxins of varying potency. Types A, B, and C are the types that commonly affect horses. Horses can contract the disease in three different ways. The most common route is to eat foods that are already contaminated with toxins that have been released by bacteria. This can be from spoiled food or food contaminated by an animal carcass. They can also contract the disease by ingesting the bacteria which then sporulate in the gastrointestinal tract and release toxins inside the animal. This is more common in foals and is caused by type B toxin. Rarely, horses can contract botulism if a wound becomes contaminated with bacteria which then release a toxin. The toxin itself acts at the junction between the nerves and the muscles so that the muscles are not given the signal to contract when they should, hence “flaccid paralysis”.

How can I prevent my horse from getting botulism?

Do not feed obviously spoiled grain or food containing animal carcasses (rats, birds, squirrels, etc.). Also avoid feeding silage or haylage to horses as, if improperly fermented, it can harbor Clostridial organisms. Do not feed hay from plastic-wrapped bales if the plastic is torn. There is a vaccine against one type of botulism (Type B). This vaccine is given in certain geographic areas (central Kentucky, mid-Atlantic) to reduce the risk of “Shaker Foal Syndrome”. Mares should be vaccinated with a series of 3 doses during the last 3 months of gestation. Unfortunately, this vaccine is not effective against other types of botulism.

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