A bacterial disease, tetanus can affect most animals but horses are particularly susceptible because of the environment they live in and their tendency to incur injuries. Tetanus is caused by the bacterium Clostridium tetanii which is found in soil and droppings. It’s found everywhere and survives in the environment for long periods.
The bacterium enters the body through wounds, particularly puncture wounds, and especially if the wound is dirty. Puncture wounds on the sole of the horse’s foot are common sites of infection. Animals can also be infected via the intestines after eating contaminated soil or droppings, or through gastric or intestinal ulcers.
In foals, infection can be transmitted via the umbilicus (navel). The tetanus bacteria are classified as ‘anaerobic’ bacteria, meaning they do not need oxygen to survive and multiply rapidly in the damaged tissues at the site of the injury. The bacterium produce a potent neurotoxin (tetanus toxin) which causes the classical signs of tetanus.
Tetanus toxin attacks the nerves controlling the muscles of the body, causeing progressively worsening muscular stiffness and spasm. An affected horse will become stiff and have difficulty moving and eating.
The third eyelid (membrana nictitans, a membrane which can be easily seen at the inner corner of the eye) will begin to protrude across the eye, particularly if the horse is startled. The tail is often held out straight and the horse develops an anxious facial expression because of facial muscle spasm. Any stimulus such as a loud noise, bright light or touch can exacerbate the signs. The horse may sweat. In advanced cases the horse will collapse, showing spasms, convulsions. Death will usually result from respiratory failure.
Sadly, we cannot do much for a horse with infected with tetanus bacteria. Most cases of tetanus will result in the death of the affected animal. Diagnosed early enough, treatment is targeted at destroying the bacteria so that no more toxin is produced, and reducing the effects of the toxin that has already been produced. Large doses of antibiotics, usually penicillin, are used in conjunction with Tetanus Antitoxin injected usually intravenously and intramuscularly.
If the horse is able to eat, food should be offered at a height where it can easily reach it. In severe cases, slinging may be necessary. Intravenous fluids and/or catheterization of the bladder may also be necessary. Unfortunately, the chances of recovery are extremely poor if such measures are necessary and euthanasia on humane grounds is usually more appropriate.
Can tetanus be prevented?
The good news is that Tetanus is an easily preventable disease, with a readily available vaccine. Vaccination with ‘tetanus toxoid’ should be used for all horses and ponies. The initial course consists of two injections given approximately four to six weeks apart, with booster shots at two-year intervals.
Foals cannot respond to vaccine given before approximately four months of age but they should start a course of vaccine very soon after reaching this age. As protection before this age foals usually receive tetanus antitoxin soon after birth. They also receive some protection via colostrum (first milk) if the mare is well vaccinated.
Good first aid can also help prevent tetanus. Wounds should be cleaned as soon as they occur and steps should be taken to encourage drainage of deeper injuries. Paddocks, stables and stable yards should be kept safe, clean and clear of dangerous items such as old tractor parts, corrugated iron sheets and building materials that may cause injury.