What reps need to know about the prevention and treatment of tetanus in horses.
Editor’s note: In an interview with Veterinary Advantage, Randall J. Berrier, DVM, senior vice president – of scientific affairs at Colorado Serum Company, discussed the leading causes, common symptoms, and effective treatment of tetanus in horses, along with the importance of vaccination.
Vet-Advantage: What causes tetanus?
Dr. Berrier: The bacteria Clostridium tetani causes tetanus. This bacterium is commonly part of the normal gut flora in cattle and horses, and so it is found in their feces and produces spores that can live in the soil for many years. When an animal gets a wound, especially a puncture wound, and the wound is contaminated with soil or feces, Clostridium tetani (if present) can proliferate in the anaerobic environment of the puncture wound. When the bacteria cells die, they release the exotoxin that then circulates in the bloodstream and produces the disease known as tetanus.
Tetanus occurs secondary to contamination of a wound. You cannot contract tetanus through ingestion, and it is not contagious. Vaccination for tetanus is usually very efficacious.
Vet-Advantage: What are the most common symptoms?
Dr. Berrier: Once the exotoxin is released into the circulation, the toxin will bind to the neuromuscular junction and block the transmission of nerve signals to the muscles, which results in the classic “tetany,” which are repeated muscle spasms caused by severe muscle contraction.
This will present early on as agitation, heightened sensitivity to external stimuli, protrusion of the third eyelid, generalized muscle stiffness with a saw-horse stance and can progress rapidly to severe muscle contractions, which will result in an inability to chew or swallow (the classic “lockjaw”), and an inability to stand.
As the disease progresses, the animal will become easily excited by sudden noises or any stimulation, which will set off more severe episodes of muscle spasms, and even seizures.
There is no test to definitively diagnose tetanus, so diagnosis is based solely on the classic clinical signs and usually a history of overdue or no tetanus vaccination. Once the animal is down and unable to swallow, the prognosis is terrible and usually ends in death from suffocation because of the inability to breathe due to tetany of the muscles used for respiration.
Vet-Advantage: Are horses more susceptible to tetanus than other animals?
Dr. Berrier: Horses are probably the most susceptible species to tetanus. Unvaccinated people are also highly susceptible to tetanus from untreated, contaminated wounds. Ruminants are also vulnerable. In contrast, other species, like dogs, cats, and carnivores in general, are more resistant to tetanus infection and much less likely to contract this horrible disease. We do occasionally see tetanus in dogs and cats, but it is very rare. Birds are very resistant to tetanus.
Vet-Advantage: How many cases does a typical equine vet treat in a given year?
Dr. Berrier: Fortunately, we don’t see tetanus very often in horses anymore due to good vaccination compliance in the equine community. I would say most equine practitioners will only see one case or no cases a year on average. Where we see it most commonly is in band-castrated ruminants who were not properly immunized prior to banding.
Vet-Advantage: When would a veterinarian need to administer an antitoxin?
Dr. Berrier: Tetanus antitoxin is meant to be used (along with antibiotics) for immediate passive immunity in non-immunized animals that are at risk of contracting tetanus from a wound or in wounded animals that are overdue (> 12 months) for their tetanus toxoid booster.
Tetanus antitoxin is also indicated (in much higher doses – see label) in cases where animals are currently suffering from tetanus disease. In a horse that is current on its tetanus vaccination, a tetanus toxoid booster is all that is needed if this animal suffers a wound. It does not require TAT.
Vet-Advantage: What are some questions reps can ask veterinarians to make sure they have the right products to treat horses with tetanus?
Dr. Berrier: Just asking or knowing what the indications of use for tetanus toxoid vs. tetanus antitoxin (TAT) is. I already mentioned the indications for use of TAT. Because of the difficulty with TAT availability, it is good to know that if proper vaccination is done, the need for TAT is very rare.
Tetanus toxoid is intended to be used to induce immunity in naïve healthy animals or boost immunity in previously vaccinated animals. In young horses from vaccinated mares, initial vaccination with tetanus toxoid is at 5 to 6 months of age, followed by a booster 3 to 5 weeks later and annual vaccination thereafter.
Pregnant mares should be given their annual tetanus toxoid booster approximately 1 month prior to foaling so that they will have high levels of antibodies to tetanus in their colostrum that will passively transfer to the foal, and this protects the foal for the first 5 to 6 months of life. Tetanus toxoid can be given alone as a monovalent vaccine or in a combination product like a Flu-EWT 4-way vaccine, for example.
Photo credit: istockphoto.com/SeventyFour