A couple of days ago, I reported about a deadly outbreak on a Queensland farm that had killed a significant number of horses. A definitive diagnosis has still not been made, but it is starting to look like botulism might be the cause. In my previous assessment, I said botulism was a potential cause of an outbreak like this, but that this particular disease has a pretty consistent clinical presentation so it was probably unlikely if no one was talking about it as a leading option. It looks like now they are, with the owner stating "I’ve been talking to vets all over Queensland and they’re saying the symptoms are spot-on for botulism." It’s unclear whether the first vet(s) didn’t consider it or whether there wasn’t much veterinary involvement at all initially. Regardless, botulism makes sense, particularly with the description of the type of illness that’s now being provided.

Botulism testing is underway, but it’s often hard to get a positive lab test for this disease in horses. Often, it’s a presumptive diagnosis made based on the clinical appearance and lack of any other identifiable cause. Botulism outbreaks on horse farms can be devastating, as in this case. They are often associated with feeding improperly fermented silage or haylage, but there are a variety of ways horses can ingest feed (or water) contaminated with the toxins produced Clostridium botulinum.

The good thing that comes out of this, if botulism is diagnosed, is that there’s not much risk to other horses in the region, or at least not any higher risk than is always present. Whenever a large number of horses die from an unknown cause, it’s always a concern that a new disease might be involved, something that fortunately does not seem to be likely here.

Image: Poor tongue tone is one of the classic signs of botulism in horses, which results in difficulty eating and drinking (click image for source).