Zoom in on microorganisms

Germs that infect humans

Whooping cough

Whooping cough

© Illustration Bruno Laporte

Microorganism: the bacterium Bordetella pertussis.

Disease: whooping cough (also known as "pertussis").

Occurrence of the disease

Current situation: every year, approximately 100,000 people die from whooping cough around the world. In 1998, 4,850 cases of whooping cough were reported in Quebec, and 8,797 cases in Canada. In the United States, fewer than ten deaths are reported every year.

Mechanism of action of the microorganism: the bacteria enter the body through the respiratory tract, and attach themselves to the cells lining the lungs, where they produce toxic substances known as toxins. These toxins are responsible for the effects of the disease.

Symptoms of the disease: the initial symptoms resemble those of a cold, but a prolonged and persistent cough develops subsequently. Later effects include pneumonia, convulsions, and serious neurological complications.

Incubation period: seven to 14 days.

Contagious period: approximately three weeks from the onset of cough. Antibiotic therapy can reduce the contagious period to approximately five days from the onset of treatment.

Hosts: humans are probably the only hosts.

Transmission: inhalation of airborne bacteria in saliva droplets produced by infected individuals.

Discoverers of the microorganism: Bordet and Gengou in 1906.

Treatment of the disease: antibiotics such as erythromycin, tetracycline, and chloramphenicol.

Geographical distribution of the microorganism: worldwide. Over the last four decades, there has been a marked decline in the incidence of whooping cough in countries, such as Canada, that have instituted immunization programs.

Prevention: the DTP-Polio-Hib vaccine at two, four, six, and 18 months and the DTP-Polio vaccine at four and six years. These vaccines contain a diphtheria vaccine combined with other vaccines (the "P" in the name of the vaccine stands for "pertussis"). Several booster injections are necessary.

Vaccine: the vaccine contains dead whooping cough bacteria (Bordetella pertussis). After the five recommended boosters have been administered, the vaccine is effective in 85% of cases.

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. The incidence of side effects has dropped considerably since the introduction of an acellular vaccine in 1998.