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Germs that infect humans

Corynebacterium diphteriae

Corynebacterium diphteriae

© Dennis Kunkel Microscopy, Inc.

Microorganism: the bacterium Corynebacterium diphteriae.

Disease: diphtheria

Occurrence of the disease

Current situation: in Canada, no cases of diphtheria have been reported for some years. In the United States, fewer than 100 cases of diphtheria are recorded annually, and most of the reported cases occur in individuals who have not been vaccinated.

Projections: in theory, it should be possible to completely eradicate this disease, as humans are the only host.

Mechanism of action of the microorganism: the bacteria enter the respiratory system and excrete a toxin that causes tiny membranes to form in the throat. Diphtheria toxin may also enter the blood and result in the destruction of heart, kidney, and nervous tissue.

Symptoms of the disease: diphtheria affects the throat, usually causing pharyngitis or laryngitis. Other symptoms include high fever, nasal discharge containing pus, and weakness.

Diphtheria may also occur in a cutaneous form. Most cases of cutaneous diphtheria occur in tropical regions in individuals who are older than 30 years and have a weakened immune system.

Incubation period: two to five days.

Contagious period: as long as there are lesions: usually two weeks, but in rare cases, more than four weeks.

Hosts: humans.

Transmission: direct contact with airborne droplets. The disease is highly contagious and has a mortality rate of five to ten per cent.

Discoverers of the microorganism: Klebs and Loeffler in 1883-1884.

Treatment of the disease: initially, diphtheria antitoxin, which destroys diphtheria toxin. This is followed by treatment of the infection with antibiotics such as penicillin or erythromycin.

Geographical distribution of the microorganism: worldwide.

Prevention: In all cases, the diphtheria vaccine is combined with other vaccines (the "D" in the name of the vaccine stands for "diphtheria"). Several injections are necessary in order to ensure that the immune system continues to recognize the diphtheria bacterium (vaccination with DTP-Polio-Hib vaccine at two, four, six, and 18 months old, DTP-Polio vaccine at four and six years and d2T5 vaccine at 14-15 years and at ten-year intervals thereafter).

Vaccine: the vaccine contains attenuated diphtheria toxin (diphtheria anatoxin) and is more than 90% effective.

Side effects of the vaccine: sixty per cent of children experience some pain at the site of injection, and 50% experience fever within 48 hours of the injection.