Etiology and Epidemiology

C. tetani is an obligate anerobe, a spore-forming, gram-positive motile rod. The terminal spore caused the organism to be called the "drumstick" rod. The protein toxin, tetanospasmin, blocks acetylcholine release at the motor end-plates. The toxin travels up the nerve trunks, as well as fixing directly on nerve cells. The spinal cord is the primary target organ, with chromatolysis of the motor neurons and inhibi tion of antagonists accounting for the spasm and rigidity that characterize the disease. Toxin fixation to central nervous system neurons may lead to seizures; involvement of the sympathetic nervous system may evoke vascular irregularities.

Humans may be considered accidental interveners in the life cycle of the organism, which is a soil saprophyte and a harmless inhabitant of the intestines of many herbivores. The organism requires a wound to invade mammals. Traumatic, surgical, dental, umbilical, burn, and cosmetic wounds are the most common causes of infection in humans. "Skin popping" of addictive drugs, insect bites, and nonmedical abortions are less common causes of infection. As an obligate anaerobe, the organism can reproduce and produce toxin only when local oxidation-reduction processes reduce tissue oxygen to near zero; deep, infected wounds are thus ideal culture media.

There may be 300,000 to 500,000 cases of tetanus a year worldwide, with perhaps 120,000 of those being neonates whose umbilical wounds become infected. The United States reported 101 cases in 1987 and 1988.

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