Pertussis

Pertussis, also known as whooping cough, is a highly contagious disease that is one of the leading causes of vaccine-preventable deaths. There are 30-50 million cases per year, and about 300,000 deaths per year. 90% of all cases occur in developing countries.

The disease was recognizably described as early as 1578, and its causative organism, Bordetella pertussis, was isolated in pure culture in 1906 by Jules Bordet and Octave Gengou[?]. The complete B. pertussis genome of 4,086,186 base pairs was sequenced in 2002.

The disease is characterized by a cough, fever, sneezing, and runny nose. After several weeks the cough changes character, with paroxysms of coughing followed by an inspiratory "whooping" sound. Coughing fits may be followed by vomiting, which in severe cases leads to malnutrition. Other complications of the disease include pneumonia and encephalitis.

The disease is spread by contact with airborne discharges from the mucous membranes of infected people. Treatment of the disease with antibiotics (often erythromycin or chloramphenicol) results in the person becoming less infectious but probably does not significantly alter the outcome of the disease.

Pertussis vaccines were initially formulated as whole-cell preparations but are now available as acellular preparations, which cause fewer side effects. They offer protection for only a few years, and are given so that immunity lasts through childhood, the time of greatest exposure and greatest risk. The immunizations are often given in combination with tetanus and diphtheria immunizations, at ages 2, 4, and 6 months, and later at 15-18 months and 4-6 years. The vaccines are not given after age seven, as the frequency of side effects of the immunization increase with age. The most serious side-effects of immunization are neurological: they include seizures and hypotonic episodes.

Most human cases of pertussis are caused by B. pertussis, initially thought to be the only cause of human pertussis: some cases, however, are caused by a related bacterium, B. parapertussis. Similar syndromes are caused in animals by B. bronchiseptica and in birds by B. avium and B. hinzii.

Bordetella pertussis elaborates several virulence factors. Though the exact mechanism of "whooping" has still not been clarified, it is thought to be related to one of these, which include pertussis toxin, an adenylate cyclase toxin, a hemagglutinin[?], and a tracheal cytotoxin.