Of all the vaccines designated as “core” by the American Association of Equine Practitioners, vaccination against tetanus is considered the most basic for all horses, whether they are athletic competitors, companions, retired, young or old. Why is this?
What is Tetanus?
Tetanus is caused by the anaerobic bacterium Clostridium tetani. The bacterium lives in the gut of horses and many other animals, and is passed in the manure so the organism is abundant and ubiquitous in soil. Spores of C. tetani can live in the environment for many years. The disease is not transmitted from animal to animal, rather the bacterium can enter the body through cuts (especially of the foot or muscle), punctures, surgical incisions, or the umbilical cord of a newborn foal. Once inside the body, C. tetani very rapidly produces a potent toxin that attacks the nervous system, causing muscle spasms and ultimately paralysis. These muscle spasms are what gives the disease the common name of “lockjaw.” The progression of the disease is usually very quick, and it is very painful, and as many as 50% of all affected horses die. Once the toxin is bound to the nervous system, it cannot be dislodged. Therefore prevention and very early detection is key.
In this video, the horse with tetanus demonstrates the muscle rigidity and tremors, as well as the distress typical of the disease. If you look closely, you can see the abnormal movement of the third eyelid. The horse is choking because the muscles that allow him to swallow are also affected.
Horses are very sensitive to tetanus, among the most sensitive of all animals. Although tetanus is often believed to be more common in deep wounds and punctures, even superficial wounds have resulted in clinical cases of tetanus in horses. Therefore, the severity of the wound does NOT predict the risk for development of tetanus.
WARNING: The following video is of a severely affected horse. Some people may find it difficult to watch. Again, muscle tremors and rigidity characterize the disease.
Although the vaccine is not perfect (there have been rare cases of tetanus reported in vaccinated horses), it is a very good vaccine and survival of horses with tetanus is strongly associated with proper vaccination.
Why is tetanus vaccination yearly in horses, whereas in humans it is every 5-10 years?
Horses seem to be very susceptible to tetanus, much more so than humans. There have been reported cases of tetanus in horses vaccinated even 6 months previously, so diligent vaccination against the disease seems prudent. We recommend yearly vaccination against tetanus, however if a horse sustains a wound that puts him or her at additional risk and they not been vaccinated in the past six months, we will often booster the vaccination at that time.