Tetanus is an illness of the nervous system caused by infection with the bacterium Clostridium tetani. These bacteria live in the soil and cause infection when they contaminate dirt that gets into an open wound. If the tetanus is allowed to spread, the mortality rate is around 40 percent, even with medical intervention. In general, tetanus requires several weeks to run its course.
Due to childhood immunization, tetanus is rare in the United States; only about 50 cases per year are reported. Approximately one million infants in developing countries die of tetanus per year due to poor hygiene.
Bacterial spores that cause tetanus are found in cultivated soil, animal excrement, and contaminated heroin, among other places. If these spores enter a wound that extends deep beneath the skin, they germinate and infect the blood stream via a toxin called tetanospasmin. The spores can enter the body via animal bites, surgical wound, burns, and needle injection sites, among others. People should be especially careful of wounds caused by rusty or dirty objects.
Tetanospasmin moves through the bloodstream toward the spine at the speed of 10 inches a day. After one to three weeks, the toxin short-circuits nerve signals and obstructs muscle relaxation.