What is a Diphtheria Toxin?

Diphtheria toxin is a chemical that is secreted by an infectious bacterium called Corynebacterium diphtheriae, or C. diphtheriae. When a person inhales C. diphtheriae spores, they imbed in the throat and respiratory tract and begin to release toxins. If the immune system is not strong enough to suppress the toxins, a potentially life-threatening infection occurs. Diphtheria has largely been eradicated in developed countries due to vaccination efforts, but the disease still affects thousands of people a year in poorer regions without access to quality health-care.

Extensive medical research has been performed on C. diphtheriae and the diphtheria toxin. The bacteria is found worldwide, and it is most prevalent in temperate climates. Most infections occur when pathogens become airborne and are inhaled by a host. Once inside the body, C. diphtheriae spores attach to the mucous membranes lining the lungs, airways, and throat. The bacteria is highly contagious, and an individual can contract it after being in close contact with an infected person.

Diphtheria toxin is not always released by C. diphtheriae, and non-active infections generally do not cause health problems. Certain strains of the bacteria can be activated by iron from the bloodstream, however, causing toxins to be excreted. Toxic effects are initially isolated to the original site of infection, and can result in a sore throat, cough, hoarseness, and breathing difficulties.

Over the course of several hours or days, diphtheria toxin begins to spread throughout the bloodstream to other parts of the body. A person may develop skin lesions, sinus congestion, and frequent bloody noses. If diphtheria toxin reaches the heart, it can cause severe inflammation and swelling that raises blood pressure and presents the risk of heart attack. Rarely, toxins in the nervous system can lead to partial or total muscle paralysis.

A person who shows possible symptoms of diphtheria should be evaluated by a doctor as soon as possible. Blood and sputum tests can confirm the presence of C. diphtheriae and indicate whether or not toxins have been released. A synthetic antitoxin can be injected directly into the bloodstream that cancels out the effects of the toxin. In addition, penicillin and other antibiotics are given to help prevent secondary infections. Patients in critical condition may need oxygen therapy and careful heart monitoring to prevent serious complications.

When antitoxin solutions are readily available, most cases of diphtheria can be cured. The best treatment, however, is preventing infection in the first place and minimizing the risks of an epidemic. A diluted form of diphtheria toxin is used as part of a routine childhood vaccination schedule in most countries. Adults who have never had diphtheria can also receive the vaccination.