Reproductive cells (spores) of Clostridium tetani are found in the soil and enter the body through a skin wound. Once the spores develop into mature bacteria, the bacteria produce tetanospasmin, a neurotoxin (a protein that poisons the body's nervous system) that causes muscle spasms. In fact, tetanus gets its nickname -- lockjaw -- because the toxin often attacks the muscles that control the jaw. Lockjaw is accompanied by difficulty swallowing and painful stiffness in the neck, shoulders and back. The spasms can then spread to the muscles of the abdomen, upper arms and thighs.
According to the CDC, tetanus is fatal in about 11 percent of cases, but fortunately, it can't be spread from person to person -- you need direct contact with C. tetani to contract the disease. Today, tetanus immunization is standard in the United States, but if you're injured in a way that increases tetanus risk (i.e. stepping on a rusty nail, cutting your hand with a knife or getting bitten by a dog), a booster shot may be necessary if it's been several years since your last tetanus shot.
According to the CDC, since the 1970s, only about 50 to 100 cases of tetanus are reported in the United States each year, mostly among people who have never been vaccinated or who did not get a booster shot. And WHO says that globally there were about 15,500 cases of tetanus in 2005. Read on to find out how the WHO and the CDC have nearly eradicated once-fatal diseases such as yellow fever and smallpox.