The causative agent of tetanus is a bacterium (Clostridium tetani). It always lives in the horse's environment, is constantly present and infectious, and sadly, horses are the domestic animal species most susceptible to tetanus. Tetanus is not contagious and cannot be transmitted to or from humans.
Naming
The term tetanus describes the strong contraction of skeletal muscles, essentially a muscle spasm. This term describes the condition just as well as the colloquial term "lockjaw". The infection occurs through the bacterium entering wounds, resulting in severe muscle cramps.
Clinical course
The designation describes the clinical picture quite accurately:
The externally visible muscles are constantly and painfully contracted – the poor horses stand rigid and stiff. If Clostridium tetani enters an oxygen-poor environment (for example, in a wound that closes rapidly), it multiplies and releases the toxin tetanospasmin in particular.
Important: The wound causing the infection does not necessarily have to be found. The toxin is absorbed by nerve cells located in the immediate vicinity of the wound and transported within these to the spinal cord. There, it blocks the release of substances that normally lead to a weakening of reflexes and reactions to external stimuli. Thus, the tetanus toxin blocks precisely those nerve cells that normally inhibit the tension of the body's musculature.
The condition is the uncontrollable spasm of the skeletal muscles with full consciousness: the horses stand with their necks stiffly stretched forward and their legs splayed (like a sawhorse). Due to the severe tension of the chewing muscles, they cannot take in food, let alone chew and swallow.
Every noise or even the slightest hint of light is agony, as all external stimuli lead to even greater muscle tension. Affected horses eventually become so exhausted that they collapse on their sides, as they cannot bend their legs. Most horses die from paralysis of the respiratory muscles while fully conscious, meaning they suffocate. The illness is very often fatal.
Therapy
Even with today's intensive medical and nursing capabilities, only a very small percentage of horses can be saved once the first symptoms appear. Once the tetanus toxin has entered the nerve cells, its breakdown often takes weeks. Humans can be ventilated and fed by infusion during this time – for a horse, tetanus most often ends in death.
Prophylaxis
A treatment (which is in any case very costly) generally only has a chance of success if the disease is not fully developed. The protective vaccination against tetanus is one of the most effective protective vaccinations in equine medicine; every horse should be vaccinated against tetanus due to the permanent risk of infection. This protective vaccination is the only preventive measure to protect the horse from tetanus, which often has a fatal outcome. Therefore, a preventive (prophylactic) vaccination is absolutely necessary. For newborn foals that have not received sufficient colostrum, or that come from unvaccinated mares, passive vaccination with tetanus antitoxin is important. Passive vaccination is also urgently recommended for injured unvaccinated horses.
