Tetanus in Horses

Filed Under: Horses, Diseases

Tetanus is caused by a neurotoxin produced by club-shaped bacteria, known as Clostridium tetani. In the presence of oxygen or other adverse environmental conditions such as cold or a lack of humidity, this bacterium will produce a single inactive spore. The spore is a defense mechanism by which the bacteria are able to survive conditions that would result in their death. When conditions become right and no oxygen is present, the bacterium will again be activated, metabolizing and reproducing until oxygen or other adverse environmental conditions occurs and the bacteria again finds it necessary to revert back to a spore. The fact that C. tetni cannot live actively in the presence of oxygen classifies it as an anaerobic bacteria. Spores are commonly found in the soil and are especially prevalent in warmer climates.

Horses, pot bellied pigs and man are particularly susceptible to tetanus. Dogs, cattle and especially cats seem much more resistant to the effects of tetanus; however, almost all mammals are susceptible to this disease. Tetanus characteristically results from the introduction of spores to the body via a particularly deep puncture wounds although spores may be ingested and passed through fecal material. A wound causes a suitable anaerobic environment through the creation of necrotic (dead) tissue. A high incidence of tetanus may occur in horses, pigs and lambs following surgical procedures such as castration. Dental procedures, such as trimming of the canine teeth, can also increase the risk of tetanus in pigs. The bacteria remain localized to the necrotic anaerobic environment were they divide and multiply. When the bacteria undergo autolysis (dies and disintegrate) a potent neurotoxin is released. It is actually the neurotoxin which causes the clinical signs associated with tetanus.

The incubation period or the time between infection and the onset of clinical signs takes from one to several weeks, but on average will run between 10 to 14 days following an injury. Initially reflexes will increase in intensity. As the effect of the neurotoxin increases, stiffness and difficulty swallowing develop. The pulse rate is increased. Breathing may become labored. Spasmodic contractions of the muscular system develop and they tend to extend muscles of the jaw, thus the term “lockjaw.” The head, neck and leg muscles will become extended due to muscle spasms causing the animal to assume a “sawhorse” stance. These animals may be unusually sensitive to light and heat. Sweating is common but an animal’s temperature is not usually elevated unless shortly before death. Death tends to occur in horses and cattle 5 to 10 days after the onset of clinical signs in untreated cases. Sheep and pigs will often die on the third or fourth day that clinical signs are present.

There are 2 ways of dealing with Tetanus medically. In animals and man who are especially susceptible to tetanus, it is common to vaccinate with what is called a Tetanus Toxoid on a regular interval. To manufacture tetanus toxoids, the tetanus toxin is detoxified, purified and concentrated to provide a vaccine. Horses, pigs, goats, cattle and sheep are usually vaccinated intramuscularly with an initial two doses 4 to 8 weeks apart. These animals are then revaccinated annually and again at the time of any injury. This vaccine provides protection against the tetanus toxin by stimulating the animal’s own immune system to inactivate the toxin. Toxoids are available from Fort Dodge Animal Health, Colorado Serum, Franklin and Professional Biological.

The second way of dealing with tetanus is through the use of Tetanus Antitoxin. Tetanus antitoxin is prepared from the serum of healthy horses that have been hyperimmunized with repeated doses of tetanus toxoid. The serum is concentrated and then injected when immediate short-term protection against tetanus neurotoxin is necessary. In animals already showing clinical signs of tetanus, massive and repeated doses of antitoxin may provide a cure, although a positive outcome cannot be guaranteed. Tetanus Antitoxin is available from Fort Dodge, Professional Biological, Rhone Merieux and EquilLabs.

Tetanus Toxoid cannot be used with Tetanus Antitoxin since the use of both products will cancel each other out with the antitoxin neutralizing the toxoid.

Topics: bacteria, tetanus

Symptoms: lockjaw, rapid pulse, sensitivity to light, stiffness

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