Vaccination is the only way to provide long-term protection against tetanus and is generally recommended yearly. It should be remembered that the horse is the most susceptible animal to tetanus. This susceptibility is largely due to the environment in which horses live. Tetanus occurs when a wound becomes infected with bacterial spores of Clostridium tetani. These spores germinate, multiply and produce a very powerful poison that affects the muscles. Some cases of tetanus occur from wounds that are so small they are not noticed. Persistent spores can be found in the soil (it is more prevalent in cultivated than uncultivated soils), and organisms are routinely isolated from the access of many domestic animals, including the dog and cat, and also from humans.
Vaccination is the only way to provide safe, effective long-term protection against tetanus. If an unvaccinated horse is injured, tetanus antitoxin should be administered to provide immediate but short-term (3 weeks) protection. At the same time, a vaccination program should be commenced to develop long-lasting immunity. The tetanus vaccine may be administered intramuscularly on one side of the neck.
Tetanus vaccine alone provides long-lasting protection, but immunity takes 7-10 days to develop, and an injured horse may develop tetanus before protection is achieved. Tetanus antitoxin alone provides protection in 2-3 hours, but it only lasts for 3 weeks. Horses given tetanus antitoxin can develop tetanus once the levels of antitoxin have dropped below the protective level. It is extremely risky if owners are relying on the use of tetanus antitoxin given to horses, after a wound, to protect them against tetanus, as some cases of tetanus occur from wounds that are so small they are not noticed.
For all horses and foals three months of age and above, the primary vaccination course consists of two injections of tetanus vaccine, four weeks apart, followed up by a booster dose one year later. Boosters after this can be given every five years, but it is recommended to give a booster every year. The antibodies remain active in the horse's system, but probably not as long as in humans. Again, horses live in an environment where they are more susceptible to the bacteria; therefore, they need a higher level of protection.
