Tetanus in horses: understanding the danger

Every year, equine vets will see occasional cases of tetanus in horses. Very few of these cases will survive. But the disease is easily prevented by a safe, effective and inexpensive vaccination that is readily available, so there is really no excuse for not using it.

Tetanus is caused by toxins released by the bacterium Clostridium tetani. Spores of this bacterium are widespread and are found in dust, manure and soil. These spores enter a wound and if they find ideal conditions they will germinate into bacteria. Perhaps surprisingly, a large, dirty cut is a lower tetanus risk than a small puncture wound. The main danger is a deep, festering wound, which is not exposed to fresh air.

High-risk situations that are most likely to lead to a horse suffering from a tetanus infection include:

  • Puncture wounds contaminated with soil, eg kicks
  • Stake wounds
  • Umbilical infections in the foal
  • Castration wounds
  • Infections at foaling

Horses and ponies are the most susceptible domestic animal to tetanus. They are readily exposed to the spores while grazing and their predilection for wounds such as lacerations and punctures make them prime candidates for acquiring tetanus. Dogs very rarely develop tetanus and are not routinely vaccinated. Humans are susceptible and children in the UK are routinely vaccinated as babies.

What is tetanus?

The illness is also known as lockjaw. This is because, as the disease progresses, the mouth clamps shut, so the animal cannot eat or drink.

Tetanus infection produces at least three deadly toxins, which migrate along the peripheral nerves to the brain affecting the nervous system. This distressing disease is characterised by extreme sensitivity to stimuli, increasing stiffness and muscle spasms.

The incubation period depends on the distance the toxins have to travel from the wound to the brain and ranges from three days to several weeks. The clinical signs usually become apparent within one to two weeks. The shorter the incubation period, the more serious the infection.

Signs of tetanus in horses

Early signs of tetanus include:

  • Abnormal sensitivity to sound or touch
  • A stiff gait
  • Prolapse of the third eyelid, which may cover half the eye
  • Very rigid ears that stick up
  • The top of the tail sticks out
  • A worried expression, with retraction of the eyelids and flared nostrils due to muscle spasm
  • Inability to open the mouth due to spasm of the masseter (powerful chewing) muscles, hence the name lockjaw
  • Regurgitation of food and water from the nostrils and drooling of saliva from the mouth as swallowing becomes more difficult
  • Partially chewed hay may be held in the mouth
  • Colic

As the disease progresses, there are increasingly distressing muscle spasms and convulsions. These eventually lead to death from respiratory failure and dehydration.

Diagnosis is made on the history and the clinical signs. Sometimes additional signs such as colic, pneumonia and laminitis can confuse the picture, but unfortunately it is frequently all too obvious, due to a wound on an unvaccinated animal.

If you see any signs that point towards tetanus, call your vet straight away. About three-quarters of tetanus cases die. Those who do survive are caught early and have intensive and expensive treatment. If a tetanus case is unable to stand, it is kindest for the horse to be euthanised, since the chance of recovery is remote.

Prevention of tetanus in horses

Make sure all your horses and ponies are vaccinated regularly and ensure you are covered as well.

The primary vaccination course of tetanus toxoid includes two doses given four to six weeks apart. Regular boosters are given thereafter. The exact schedule may vary slightly according to the recommendations of different vaccine manufacturers and whether it is combined with vaccination against equine influenza. Your vet will advise you best. Booster vaccinations in horses are usually administered only every two or three years and most people only need booster immunisations every 10 years or even longer. Tetanus is more common in certain areas of the country, where it may be advisable to have more regular boosters.

Vaccinated pregnant mares should have a tetanus toxoid booster four to six weeks prior to foaling. This ensures the foal receives maximum protection from the antibodies in the colostrum (first milk). Foals usually begin their vaccination programme at approximately four months. Foals of unvaccinated mares or those who do not receive adequate colostrum for any reason should be given tetanus antitoxin at birth.

Horses who are unvaccinated or are of doubtful vaccination status should be given tetanus antitoxin if they have a wound or require surgery. A vaccination programme should be started straight away, as well as administering the antitoxin that provides immediate temporary protection for three to four weeks. Tetanus inoculations should be recorded in the horse’s passport.

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