Tetanus is caused by the toxin produced by the bacteria Clostridium tetani. This belongs to the family of bacteria which exist in the soil. Some of these produce powerful toxins causing the nervous diseases of botulism and tetanus. Others invade the tissues and produce gas gangrene infections, such as blackleg and pulpy kidney.
The tetanus organism does not multiply in the presence of air, and wounds that are open and washed clean do not lead to the disease. Wounds deep into the tissues which become secondarily infected by other bacteria are most liable to encourage the proliferation of the bacteria and the subsequent production of the toxin. It may take as long as three to four weeks for the first symptoms to develop after the initial introduction of the bacteria, and by this time the wound may have healed and be hard to find.
Of all species, horses are the most susceptible to the effects of tetanus toxin. Sheep are not so susceptible and cattle and pigs are rarely affected. Birds seem totally unaffected by the toxin. The amount of toxin per gram of body-weight required to kill a chicken is 350,000 times as great as it is for a horse. For the dog is 600 times as great.
The first symptoms of tetanus observed in the dog is usually difficulty in swallowing. The dog appears to walk stiffly and may have tremors of the muscles of the hind leg. Of course the possibility of tick paralysis or poisoning with snail baits must be eliminated at this time.
As the symptoms progress the dog has difficulty in walking and the muscle tremors may become so great that the dog falls over, particularly if excited. The muscles around the face become taut and the lips may be drawn apart to expose the teeth.
The base of the ears tend to be drawn together to give the dog an unnaturally alert appearance. The muscles of the eye lids are also contracted and the animal is unable to fully open the eyes. Often the third eyelid is partially drawn across the eye.
The dog has a much better chance of survival from tetanus than the horse and the sheep. If the symptoms are relatively slow in their onset and the dog is able to eat, the prognosis is quite favorable. Antibiotics are administered to control the infection from the initial wound. Some form of sedation is also given until all signs of the nervous spasm of muscles have subsided.
Prevention of the disease in the horse and sheep is of course recommended. Vaccination is given early in life and is repeated a month later, then again in a year. For most dogs, vaccination is probably not necessary.
However, dogs working where there are large numbers of horses are more at risk, as horse manure may contain large numbers of Clostridium tetani bacteria. Sheep dogs working in areas of the State where tetanus is common are often protected by vaccination.