Tetanus is a severe, frequently fatal disease caused by an exotoxin produced by Clostridium tetani, a bacterium that is found in the environment. Tetanus is not transmitted from person to person. Rather, Clostridium tetani enters the body through an open wound, including lacerations, abrasions and puncture wounds. The toxin causes neuromuscular dysfunction, with rigidity and spasms of skeletal muscles. The muscle spasms usually start in the jaw (which is why the disease is sometimes called "lockjaw") and neck and may spread to many other muscles, leading to generalized paralysis.