Tetanus is a serious and often fatal disease caused by the neurotoxin tetanospasmin which is produced by the gram positive obligate anaerobic bacterium Clostridium tetani. Infections begins when the bacteria are introduced into an open injury or wound where they produce tetanospasmin toxin which blocks messages from the spinal cord to the muscles, forcing muscles to go into severe spasm. Deep puncture wound or those with devitalized (dead) tissue are particularly prone to tetanus infection because the bacillus thrives in an anaerobic environment. Tetanus often begins with mild spasm in the jaw muscles (hence called lock jaw or trismus), neck muscles and facial muscles. Stiffness rapidly develops in the chest, back and abdominal muscles. Immunization against tetanus can prevent the disease. Therefore a person who has received a cut and is bleeding needs to given antitetanus treatment. Antitetanus immunoglobin gives passive immunity. Tetanus is best prevented by active immunization with tetanus toxoid which stimulates the production of protective antitoxin.