Definition: rare but usually fatal disease of horses caused by toxins produced by the Clostridium tetani bacterium. C. tetani spores, found in soil and manure, germinate beneath the skin of a closed wound, releasing neurotoxins that attack the nervous system, causing muscle spasms and contraction. Progressive paralysis associated with tetanus often leads to death.

Causes: wounds contaminated with C. tetani, particularly punctures that close over quickly. A foal may contract tetanus through its umbilical cord and a mare may develop the disease after a difficult delivery. Surgery —particularly procedures involving the abdomen or castrations—can lead to postoperative tetanus in unvaccinated horses.

Signs: gait stiffness, muscle spasms, rigidity, protrusion of the third eyelid and hypersensitivity to sound. Stiffness typically begins three days after infection and peaks around Day 10.

Treatment: Tetanus antitoxin can bind to circulating toxin, preventing further paralysis, but it cannot reverse the damage by toxin that has already bound to the nervous system. Beyond that, supportive care may keep a horse alive until neural pathways are able to heal over the course of several weeks.