What is Tetanus?
Tetanus is a disease caused by the bacteria Clostridium tetani that causes paralysis, rigidity, and sometimes death in horses. Compared to other animals, the horse is particularly sensitive to the toxins produced by the bacteria, which are commonly present in soil and are normally found in the intestinal tract of people and animals. Horses are also especially likely to acquire the types of wounds that permit growth of these organisms. In the soil, Clostridia bacteria are present as spores, which protect the organisms from adverse environmental conditions meaning it can survive in the environment for a long time. When these bacteria are introduced into deep wounds, they encounter favourable conditions that allow them to reproduce and produce toxins. These favourable conditions are the absence of oxygen and damaged/dead tissue. Wounds commonly involved in the development of tetanus include puncture wounds in the sole of the hoof, castration incisions, bone fractures, umbilical cord severance, and obstetrical trauma.
Signs of tetanus become apparent within several days to several weeks, depending on how close the contaminated wound is to the central nervous system. The extensor muscles of the jaw are often affected, leading to the common name of this disease, lockjaw. Saliva may drip from the horse’s mouth, and attempts to eat or drink may cause regurgitation of food or water from the nostrils. Paralysis and rigidity then progress to the face, neck, trunk, and legs. The third eyelid may be prolapsed, the ears may be held erect and rigid and the nostrils may be flared. Once the limbs become affected, the horse stands with all four legs stiff, in a characteristic “sawhorse stance.” The affected animal reacts violently to external stimuli, such as loud noises or sudden light, and may go into convulsions. Other possible signs of tetanus include profuse sweating, colic, and difficulty in walking and breathing. Laminitis and pneumonia may develop as secondary complications. After treatment has begun, clinical signs may persist for up to six weeks, and muscle spasms may occur for weeks to months before full recovery. If death occurs, it is usually due to respiratory failure. Unfortunately, about 80% of affected horses die or have to be euthanased.
Clinical signs, a history of a recent wound, and the horse’s lack of current vaccination history are usually diagnostic for tetanus. Bacteriologic cultures, along with specific serology testing, may also be used to support the clinical diagnosis.
Unfortunately, most cases of tetanus ultimately result in death of the affected animal. If diagnosed early, treatment is aimed at destroying the bacteria so that no more toxin is produced and reducing the effects of the toxin that has already been produced. Tetanus antitoxin (preformed antibodies against tetanus toxin) and tetanus toxoid (vaccination to elicit antibody production by the horse’s immune system) are given as soon as tetanus is suspected. Antitoxin and toxoid injections are repeated as prescribed by the veterinarian. Antibiotics are also given to kill the bacteria. Thorough cleansing of wounds and surgical removal of necrotic tissue or of any foreign bodies should be done promptly. Sedatives, tranquilizers, and muscle relaxants may be used to minimise rigidity, spasms, or convulsions, but their use may increase the risk of respiratory failure.Supportive nursing care is essential and intense. An affected horse should be kept in a quiet, dark stall to minimise external stimulation. Thick bedding and padding will help reduce injuries from falling or convulsing. Intravenous fluid and tube feeding may be necessary to maintain electrolyte balance and nutritional status. If the horse is unable to stand for a prolonged time, a sling or bales of hay may be necessary to prop up the animal. Urine and faeces may need to be removed by catheter and by hand respectively. If respiratory paralysis occurs, ventilation must be provided. Secondary complications, such as pneumonia, are likely and must be managed.
**PREVENTION IS KEY!!**
Tetanus toxoid should be given to all horses, beginning at 10 to 12 weeks of age with a primary course of 2 injections 4 weeks apart. The third injection needs to be administered one year after the second primary injection has been given. All adult horses should receive annual toxoid vaccinations, and brood mares should be given a booster during the last 4-6 weeks of pregnancy to ensure optimum passive transfer of tetanus antibodies to the foal. Antitoxin should be given to foals at birth.Please make sure your horses are up to date with vaccination for tetanus!