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. Virtually all deaths occur in children under one year of age. 90% of all cases occur in developing countries. It is caused by certain species of the bacterium Bordetella - usually B. pertussis , but some cases are caused by B. parapertussis .
The disease was recognizably described as early as 1578, and B. 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 initially by mild respiratory infection symptoms such as cough, sneezing, and runny nose. After one to two 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. Coughing fits gradually diminish over one to two months. Other complications of the disease include pneumonia, encephalitis, pulmonary hypertension, and secondary bacterial superinfection.
The disease is spread by contact with airborne discharges from the mucous membranes of infected people. Treatment of the disease with antibiotics (often erythromycin , azithromycin, clarithromycin or trimethoprim-sulfamethoxazole) results in the person becoming less infectious but probably does not significantly alter the outcome of the disease. Close contacts who receive appropriate antibiotics, "chemoprophylaxis", during the 7-21 day incubation period may be protected from developing symptomatic disease.
Pertussis vaccines were initially formulated in 1926, most notable by Dr. Louis W. Sauer of Northwestern University, 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. Traditionally, Pertussis vaccines are not given after age seven, as the frequency of side effects associated with the immunization increased with age. The most serious side-effects of immunization are neurological: they include seizures and hypotonic episodes. An acellular vaccine preparation for older individuals is available in Canada and Europe and two such products are being evaluated for their safety in adolescents and adults in the US; an FDA decision is expected in 2005.
The disease is much milder in adults than in children and many cases go undiagnosed.
Bordetella pertussis elaborates several virulence factors, including: pertussis toxin, an adenylate cyclase toxin, filamentous hemagglutinin, a tracheal cytotoxin , fimbriae, and pertactin.