Immunisation gives long-term tetanus protection

8 February, 2006

Those of us unlucky enough to turn up to the doctor with a nasty cut will nearly always be asked about the status of our tetanus immunisation. There's a fair chance you'll face the joy of a booster jab in your arm.

It therefore seems strange that so few horse owners immunise their horses against this disease, especially given that equines are so susceptible to it. Not only that, but horses spend their days hanging out around the tetanus spore's natural habitat - the soil.

It's a very serious disease that kills about 80 per cent of horses it infects. A veterinarian turning up to treat a wound will usually give the horse an injection providing protection for about three weeks - enough time for the risk of tetanus infection from that particular injury to pass.

However, for long-lasting protection, the horse needs to be vaccinated. The initial shot requires a follow-up jab a month later, and a booster is recommended after a year. After this, a booster every five years is considered adequate.

Tetanus is caused by a naturally occurring bacteria called Clostridium tetani. This rod-shaped organism hangs out in the soil, tending to do best when it's warm and the soil is heavily cultivated. It needs only a small amount of soil moisture to survive, so is likely to be more prevalent in heavier soils as opposed to lighter types that dry out completely in the summer.

The tetanus bacteria is ingested by horses and can be found in their gut and their droppings. The spores themselves are not toxic to the animals. What they need are ideal growing conditions, and the source of an infection is nearly always through a wound. The wound may in some cases be so small that the source injury can no longer be found once a vet is called. It can also infect the horse through injuries to a mucus membrane.

The ideal growing conditions require an absence of oxygen (the spores are anaerobic), so penetrating foot injuries or puncture wounds carry greater risk of infection.

The multiplying spores produce a toxin which is what does the damage. The toxin attacks and binds itself to the nerve tissue of the infected animal and is carried throughout the body through the blood and lymphatic system. The symptoms can take anywhere from three days to a month to show, usually starting with a stiffness around the head and neck, and a lack of control in the third eyelid. If the third eyelid flicks across the eye when you bring a hand up sharply under the jaw, this is a clear indicator of tetanus.

The hind legs will become stiff, as well as the muscles around the wound area. The horse's reflexes will become exaggerated and spasms in the jaw will make ingestion of food and water very hard. This gives rise to the other common name of tetanus - lockjaw.

An infected horse will typically poke its head forward and its nostrils will be flared. The tail will most likely be raised and the horse will have a wide-legged stance. It will move stiffly. As the disease advances the horse becomes very excited and may develop breathing difficulties, which will often kill the horse.

There is little that can be done in advanced cases except euthanise the horse. Your vet will assess the best course, depending on the severity of the case.

A vet who gives a horse a fighting chance will prescribe antibiotics to kill the bacteria, but, remember, it is the toxins that are doing the damage. If a horse survives beyond 10 days and is still able to eat and drink, it stands a reasonable chance of survival. However, an owner may well be resorting to feeding through a stomach tube or giving fluids intravenously, and enemas and catheterisation may be required. Sedation and muscle relaxants will probably be prescribed.

Milder cases will require less intervention, but sedatives are usually recommended.

Administering the anti-toxin once symptoms are apparent is usually of little or no benefit. It will, however, deal with any toxins which have yet to bind to nerve tissue.

Immunisation is the best form of defence. If a horse does develop the infection, early veterinary intervention provides the best chance for the horse's survival, but the mortality rate is not encouraging.