Tetanus is an extremely serious bacterial disease affecting the nervous system. While it can occur in any animal (including humans), horses are one of the most vulnerable species. The disease is painful and fatal in more than 50% of cases.
Spores of the responsible organism, Clostridium tetani, are commonly found in soil and animal faeces and enter the body through fresh wounds. Clostridial bacteria are anaerobic – that is, they thrive where there are low oxygen levels – so puncture wounds and other deep lesions are most likely to create conditions for the tetanus spores to flourish and release the tetanus toxin. Sometimes the lesion is so small it goes unnoticed and heals over before symptoms of disease develop.
The toxin hits the nervous system, specifically the nerves controlling muscles, causing painful and progressively worsening muscle stiffness and spasm.
Above left: classic 'saw horse' stance with all four limbs planted apart, head and tail extended. Above right: third eyelid prolapse, nostrils flared, ears pricked and jaw muscles tight.
Symptoms
The characteristic signs of tetanus begin 3 to 21 days after infection. The affected horse becomes stiff and has difficulty moving and eating. Classic clinical signs include:
- the horse initially has a stiff gait and adopts a ‘saw horse’ stance, with all four limbs planted apart and the tail stretched out
- the head and neck become extended, nostrils flared, the ears pricked and the jaw is ‘locked’ ie jaw muscles become rigid, the horse can't eat and may drool because of difficulty swallowing
- the animal becomes hypersensitive to noise and touch
- spasm of the facial muscles produces the classic risus sardonicus, when the muscles of the lips are pulled back showing the teeth into a tight-lipped smile
- the third eyelids prolapse across the eyes as the disease progresses. Initially this may not be obvious but any movement around the head can cause the third eyelid to flash upwards.
In fatal cases, the horse eventually collapses with the worsening spasms, and death results from respiratory failure
Treatment
Treatment is difficult, intensive, expensive and often unsuccessful. Untreated horses will almost always die. Prompt administration of the tetanus antitoxin provides immediate but temporary immunity and the horse should be vaccinated at the same time. The antitoxin, made from the serum of horses that have been vaccinated against tetanus, acts to bind the toxins before they get to the spinal cord. If toxins are already in the central nervous system, while antitoxin can't stop the disease, it can neutralise any toxins that have not yet made it to the spinal cord.
If the wound can be found, it should be opened and cleaned out to reduce the anaerobic conditions. Antibiotics are essential and intravenous fluids will aid hydration while the horse is unable to eat and drink.
Sedatives and muscle relaxants minimise spasms and help keep the animal quiet. It’s important to move quietly and calmly around affected animals, avoid sudden movements and noise, and handle as little as possible. Putting the horse in a dark, quiet place can help lessen external stimuli and prevent triggering of spasms.
Prevention
Vaccination with tetanus toxoid is the only way to protect a horse from tetanus. CVH stocks all equine vaccines and, to protect against tetanus, we recommend the following vaccination schedule:
- foals between 3 to 6 months of age and unvaccinated adult horses require a course of 2 doses, 4 weeks apart, to achieve good initial immunity
- adults and young horses over 12 months of age should receive an annual booster after the initial 2 dose course, then 5 yearly or booster at the time of injury
- pregnant mares should be vaccinated during the last 4 weeks of pregnancy. This protects the foal for several months until the vaccination course begins
- vaccinated horses should receive a booster at the time of injury
- injured non-vaccinated horses or those with an unknown vaccination history should receive both the tetanus antitoxin and tetanus vaccination, with a follow up booster vaccination in 4 weeks.