Tetanus in horses is a bacterial infection, where the toxins produced attack the horse’s nervous system. The condition is also known as lockjaw because as the disease progresses, the mouth clamps shut so the animal cannot eat or drink. It is usually fatal. Once a horse is recumbent because of the disease, it is reported that almost 80% of these cases will die. Certainly, it is a far easier disease to prevent by vaccination than it to treat.
At least three different types of deadly toxins are released by the bacterium Clostridium tetani to cause tetanus. Spores of this bacterium are widespread and can be found in dust, manure and soil. These spores enter a wound and given the appropriate conditions, they will germinate into bacteria.
Perhaps surprisingly, a large, cleanish cut is a lower tetanus risk than a small puncture wound. The biggest danger is a deep, festering wound with dead tissue and pus, which is not exposed to fresh air.
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.
High-risk situations that are most likely to lead to a horse suffering from a tetanus infection include:
- Puncture wounds contaminated with soil, e.g. kicks
- Stake wounds, because they are often deep and heavily contaminated
- Umbilical infections in the foal
- Castration wounds
- Infections at foaling
Once the Tetanus infection takes hold, the deadly toxins migrate along the peripheral nerves to the brain affecting the nervous system.
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 tetanus infection is.Tetanus is not contagious, so it cannot be passed between horses or between horses and humans. However, the bacteria can infect humans directly.
Signs of tetanus in horses
The signs of this distressing disease are characterised by extreme sensitivity to stimuli, increasing stiffness and muscle spasms.
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
- 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
How is tetanus diagnosed?
Diagnosis is made on the history and the clinical signs. Sometimes additional conditions such as colic, pneumonia and laminitis can confuse the picture, but it is frequently all too obvious, with a visible dirty wound on an unvaccinated animal.
Treatment of tetanus in horses
If you see any signs that point towards tetanus, call your vet straight away. It is those cases that are caught early, that will have the best chance of survival. Their only chance is to undergo intensive and expensive treatment including large doses of tetanus antitoxin along with antibiotics, sedatives and muscle relaxants (see case study: https://secure.horseandhound.co.uk/news/pony-tetanus-beats-one-100-odds-survive-679964). 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
Tetanus can be easily prevented by a safe, effective and inexpensive vaccination that is readily available. Make sure all your horses and ponies are vaccinated following your vet’s advice. Humans should also be vaccinated.
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 can advise you.
Booster vaccinations in horses are usually administered only every two or three years, whereas 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, although this antitoxin which provided rapid protection is more costly. 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 vaccinations should be recorded in the horse’s passport.
https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1939-1676.1994.tb03210.x – Tetanus in the horse: a review of 20 cases (1970 to 1990).