Tetanus is caused by the bacteria Clostridium tetani, which is commonly found in manure and soil. When this organism gains entry into the body to an area low in oxygen – such as a puncture wound – it produces a toxin, which migrates to the central nervous system. It can take 5 – 21 days for signs of an infection to occur and is not uncommon for the initial wound to be small and completely healed when signs occur.
Affected horses initially appear stiff, reluctant to move and have difficulty opening their mouth and therefore can not eat. The neck and head then stretch out and the tail may be slightly elevated. As the disease progresses they are unable to swallow and so drool saliva.
The third eye-lid comes across the eye – initially in spasms and later permanently. The horse becomes hypersensitive to sound and will go into rigid spasms when disturbed and may even appear to have convulsions or fits. Eventually the respiratory muscles are affected making breathing difficult; the horse becomes progressively exhausted, collapses and dies.
Treatment is possible in very early / mild cases but is prolonged and therefore expensive. It involves use of surgical drainage of wound if found, muscle relaxants, sedatives, analgesics and antibiotics. The horse must be kept in a very quiet environment for many months – often 6 months in a dark quiet stable before it may be turned out in a paddock and 12+ months before training / exercise may resume. Some horses may survive but not return to normal performance. Advanced cases require euthanasia to prevent a very painful death. A recent study reported that there is still a very high mortality rate in tetanus cases and only horses that had previously been vaccinated [but not recently] recovered.
This disease may be prevented in two ways. Because the initial wound may be small and go unnoticed – vaccination is the recommended method.
Vaccination gives year-round protection and requires two injections a month apart followed by yearly boosters. It was previously thought that vaccination should last 5 years. However, cases have occurred in horses within this time span so yearly boosters are advised. As all animals are individuals immunity wanes at different times after vaccination so yearly boosters offers optimal protection for all.
Unvaccinated horses that are wounded may be treated with a short-acting “anti-toxin” that will give protection for 2-3 weeks only and then vaccination may be started. Mares should receive their annual booster 1-2 months before foaling to ensure high antibody levels in her colostrum to protect the foal in the first 2-3 months of life. Foals from vaccinated mares may be vaccinated from 3 months of age. Foals from unvaccinated mares should be given tetanus anti-toxin at birth and then vaccinated from 6 weeks of age.
Should an unvaccinated horse be lucky enough to survive infection and recover from the disease this does not infer future immunity. Such horses should be vaccinated once stable during the recovery phase.
For more information on vaccination visit www.csl.com.