Tetanus and tetanus immunization

Tetanus is a bacterial disease that affects the nervous system in humans. The disease is caused by the bacteria Clostridium tetani. This organism, which is a common inhabitant of soil, dust, and manure, can contaminate an abrasion in the skin. Small cuts and pinpoint wounds can be contaminated. Because the organism can survive and grow in the absence of oxygen, deep wounds, such as those caused by puncture with a nail or a deep cut by a knife, are especially susceptible to infections with Clostridium tetani. The disease cannot be transmitted from one person to another.

In addition to being able to grow in oxygen-free environments, such as is found in a deep wound, Clostridium tetani is able to hibernate in environments such as the soil. This is because the bacteria can convert from an actively growing and dividing state, when conditions are favorable for growth, to a dormant state, when growth conditions are more hostile. Dormancy is achieved by the conversion of the socalled vegetative cell to an endospore. Essentially, an endospore is an armored ball in which the genetic material of the organism can be stored, in a form that resists heat, dryness, and lack of nutrients. When conditions once again become favorable, such as in the nutrient-rich and warm environment of a wound, the dormant bacteria revive and begin to grow and divide once more.

Tetanus is also commonly known as lockjaw, in recognition of the stiffening of the jaw that occurs because of the severe muscle spasms triggered by the infecting bacteria. The muscle paralysis restricts swallowing, and may even lead to death by suffocation. The muscular stiffening of the jaw, along with a headache, are usually the first symptoms of infection. These typically begin about a week after infection has begun. Some people experience symptoms as early as three days or as late as three weeks following the start of an infection. Following the early symptoms, swallowing becomes difficult. Other symptoms include the stiffening of the abdominal muscles, muscle spasms, sweating, and fever.

The muscle contractions can be so severe that, in some cases, they have actually broken bones with which they are associated. Treatment can include drugs to stimulate muscle relaxation, neutralize toxin that has not yet had a chance to react with the nervous system, and the administration of antibiotics to fight the bacterial infection . In spite of these efforts, three of every 10 people who contract tetanus will die from the effects of the disease. As of 2001, 50–100 cases of tetanus occur each year, usually involving people who either have never taken protective measures against the disease or who have let this protection lapse. In the absence of the protective measures such as vaccination , many more people would develop tetanus.

Interestingly, another group who are susceptible to tetanus are heroin addicts who inject themselves with a compound called quinine. This compound is used to dilute the heroin. Available evidence indicates that quinine may actually promote the growth of Clostridium tetani, by an as yet unknown mechanism.

For those who survive tetanus, recovery can take months and is not an easy process. Muscle stiffness and weakness may persist.

The molecular basis of the effects of infection by Clostridium tetani is a very potent toxin produced and excreted from the bacteria. The toxin is a neurotoxin. That is, the toxin affects neurons that are involved in transmitting signals to and from the brain in order to make possible the myriad of functions of the body. Specifically, in tetanus the neurotoxin blocks the release of neurotransmitters.

Clostridium tetani neurotoxin is composed of two chains of protein that are linked together. An enzyme present in the microorganism cuts these chains apart, which makes the toxin capable of the neurotransmitter inhibitory activity. One of the chains is called tetanospasmin. It binds to the ends of neurons and blocks the transmission of impulses. This blockage results in the characteristic spasms of the infection. The other toxin chain is known as tetanolysin. This chain has a structure that allows it to insert itself into the membrane surrounding the neuron. The inserted protein actually forms a pore, or hole, through the membrane. Molecules can move freely back and forth through the hole, which disrupts the functioning of the membrane.

The devastating effects of tetanus are entirely preventable. Vaccination in childhood, and even in adulthood, can prevent an infection from developing if Clostridium tetani should subsequently gain entry to a wound. Indeed, in the United States, laws requiring children to be immunized against tetanus now exist in most states, and all states require children in day care facilities to be immunized against tetanus.

Tetanus vaccination involves the administration of what is called tetanus toxoid. In use since the 1920s, tetanus toxoid is inactivated tetanus toxin. Injection of the toxoid stimulates the production of antibodies that will act to neutralize the active toxin. The toxoid can be given on its own. But typically, the toxoid is administered in combination with vaccines against diphtheria and pertussis (diphtheria toxoid pertussis, or DTP, vaccine ). The DTP vaccine is given to children several times (two months after birth, four months, six months, 15 months, and between four and six years of age). Thereafter, a booster injection should be given every 10 years to maintain the immunity to tetanus. A lapse in the 10-year cycle of vaccination can leave a person susceptible to infection.

Tetanus toxoid will not provide protection to someone who has already been wounded. There is a substance called tetanus immune globulin that can provide immediate immunity.

The tetanus vaccination can produce side effects, ranging from slight fever and crankiness to severe, but non-lethal convulsions. Very rarely, brain damage has resulted from vaccination. Even though the possibility of the serious side effects is far outweighed by the health risks of foregoing vaccination, controversy exists over the wisdom of tetanus vaccination. Available evidence indicates that tetanus immunization is a wise measure.

See also Anaerobes and anaerobic infections