Tetanus: Poster Child for Preventive Medicine

 

True preventive medicine is an intervention that stops a disease from developing, not one which simply slows disease progress. The body’s immune system is the master of disease prevention and it is no accident that one of the first medical efforts at preventing disease stemmed from the observation in the late 1700s that suffering a mild infection like cowpox prevented a similar but more severe infection – smallpox. Immunization was born, and to this date is the single most effective form of prevention of lethal disease. In the current age of rejection of routine immunization by a significant number of people, the disease called tetanus and its prevention by immunization is a story worth reviewing.

What causes tetanus?

Tetanus a disease is caused by a type of bacteria called Clostridia tetani, a fragile little organism that can’t tolerate oxygen or high temperatures but which changes itself into a tough intermediate form called a spore to lie in wait for potential victims. C. tetani spores survive indefinitely, are common in soil, particularly manure rich soil, and are found in intestinal tracts of farm animal, cats, guinea pigs, rats and people. They can survive oxygen rich environments, the usual antiseptics and even the temperatures used to sterilize medical instruments. Once the spores gain entry into body tissues, they revert to fragile bacterial form, reproduce and begin to manufacture tetanospasmin, one of the most lethal toxins known to man and the substance responsible for the symptoms of the disease. Though farm animals and people are susceptible to tetanus infection, dogs and cats are not.

Development of symptoms

Tetanus infections are usually acquired when C. tetani spores enter the body through a deep wound in the skin that air does not reach. Contaminated batches of heroin are also sources of infection when the drug is injected under the skin or intravenously. In the first few days after C. tetani spores come to life inside the body, no symptoms or tests indicate anything amiss. As the toxin producing bacteria increase in number, and the toxin produced finds its way to the spaces between nerves and muscle and between motor nerve cells in the brain and spinal cord, profound muscle spasms begin. Tetanospasmin works by the blocking normal neurochemical signals that inhibit muscle tone and motor nerve excitability.
The time from infection to development of symptoms in any infection is known as the incubation period. In human tetanus, the closer the entrance point of the bacteria to the brain or spinal cord the shorter the incubation period. On average symptoms begin about a week after injury. Though localized forms of tetanus can occur, with muscle spasm limited to the area around the wound, most cases are general and symptoms begin in the muscles of the head and neck. Spasm of the powerful masseter muscles of the jaw is the origin of the term “lockjaw,” a commonly used name for tetanus infection. Vocal cord and respiratory muscle involvement can interfere with breathing. Abdominal, trunk and skeletal muscle involvement are extremely painful and spasms can be strong enough to fracture long bones and spinal vertebrae. Other complications arise from involvement of the central nervous system: fever, high blood pressure, heart rhythm abnormalities and seizures. Secondary complications like bladder infections, pneumonia and blood clots in the legs and lungs also contribute to the lethality of the disease. In the pre-immunization era, treatment was confined to supporting the patient through the four weeks it takes for the toxin’s effects to wane.

Making the immune system remember the disease

Unlike cow pox, in which the natural immune response directed against the cowpox virus prevents more cowpox episodes but also smallpox, a full-blown case of tetanus does not confer any immunity because the minute amounts of toxin that produce the symptoms are not sufficient to stimulate the immune system to make antibodies against it. Immunization to tetanus is accomplished by presenting the immune system with a much larger amount of a formaldehyde weakened version of the toxin, to which it will produce antibodies which will neutralize the real toxin should it ever appear. This process takes a few weeks and several doses are required over time to reach full potency of an antibody response.

Immunization programs have made tetanus rare enough for people to forget how terrible an illness it is. In the US, since routine, active immunization began in the 1940s, tetanus rates declined steadily and were at an all-time low of .01 cases per 100,000 people in 2009. In addition, with better supportive care, mortality rates declined from 30% in the mid-1900s to 10% in the first decade of the 21st C.

Borrowing someone else’s immunity

Nevertheless, tetanus infections still occur and may increase in frequency if immunization rates drop. Fortunately, another type of immunization helps when tetanus develops in people who have not been immunized – a passive immunization process that allows patients to borrow antibodies produced in the blood of other people who have been immunized against C.tetani. This “antitoxin” is a mixture of human gamma globulin from screened donors and antibodies in it that “recognize” tetanus toxin react with the toxin circulating in the tetanus victim’s body, neutralizing a lot of its potency.

Boosting weakened immunity

The antibody response to tetanus toxoid wanes over time, but a repeat injection brings it up to full speed quickly. Booster doses are recommended for all adults every 10 years and in the event of penetrating wounds, especially if immunization status is unknown. Awareness of the symptoms of tetanus and the status of immunization of anyone someone suffering from heroin addiction, a sad and growing problem, is crucial for anyone who cares for them. Tetanus is the poster child for preventive medicine and no one should have to suffer this disease. The earlier it is recognized, the better the outcome is likely to be.

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