Would You Recognize Botulism If You Saw It?

Most of us have probably heard that your horse should have a botulism vaccine if you feed round bales, but if you’re like me, you may have never actually seen or known a horse with the disease.  Just recently, we did have a patient with a confirmed diagnosis of botulism and we hope it will be helpful to detail the symptoms.  Of course, the best scenario is to avoid botulism in your horse, which is easily done by keeping your horse vaccinated against it.

We received a call from a client whose horse was just not himself:  lethargic, depressed, not cleaning up all of his feed, slight fever of 101 degrees, slightly loose stool with an occasional trip/mistep.  The horse had been ridden the day before and seemed fine.  The owner knew the horse well and was convinced something was just not right.  Bute had not seemed to make the horse more comfortable.  He was up to date on his Rabies vaccine only, lived with four other horses who remained well and had access to a round bale in his pasture.

When Dr. Hecking saw the horse, he displayed progressive depression and exhibited weakness, stumbling, and incoordination.  She gave the horse electrolyte paste, Banamine and pulled bloodwork, but was concerned enough about possible neurologic conditions, EHV or enchepalitis that she referred the horse to an equine hospital for evaluation.

Upon presentation at the hospital, temperature/pulse/respiration were normal.   A neurologic exam confirmed that he was very dull, had little to no sensation to the face, eyelid tone was reduced and he would not pull his tongue back into his mouth when it was pulled out.  Likewise, his tail tone was reduced and he had decreased resistance to tail pulls.  His bloodwork showed mild electrolyte abnormalities and increased fibrinogen consistent with inflammation and anorexia.

Based on his access to a round bale and his muscle weakness, a presumptive diagnosis of botulism was made.  Botulism is caused by a toxin produced by the bacteria Clostridium botulism, which can result in stimulated muscle contraction.  This can cause horses to develop a flaccid paralysis, usually starting in the facial muscles, moving to limb muscles and in severe cases, paralysis of the diaphragm.

In adult horses, intoxication usually comes from one or two sources:  contaminated hay or from a toxin produced within a wound infected with the bacteria.  Though this patient had a wound on his left hock, it was reported to be old and was not painful or hot on palpation, so the most likely source of infection was the round bale.

The patient received Botulism antitoxin plasma, IV fluids with electrolytes, DMSO and Banamine.  Within 24 hours, he appeared much brighter and his facial sensation was almost normal, with tongue, eyelid and tail tone significantly improved.  Cerebrospinal fluid was normal, making the botulism intoxication more likely than neurologic diseases like herpes, EEE, WEE or WNV.  A test for EPM was done, although his marked, quick response to treatment made EPM less likely.

Only three days after he was initially seen by Dr. Hecking, our patient was bright, alert, and responsive with a good appetite.  He is expected to make a full recovery, in large part due to his owner’s quick call to us the first day he noticed a departure from normal behavior.

To protect your horse against botulism, we do recommend the vaccine for all equines having access to round bales.  Initially, a series of three vaccines (three to four weeks apart) are necessary for full protection, with only an annual booster required thereafter.  Please call us (434)973-7947 or (540)460-5702 if we may be of help with your vaccine questions.