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Bordetella pertussis causes whooping cough (pertussis), an acute respiratory infection marked by severe, spasmodic coughing episodes during the paroxysmal phase. Leukocytosis with lymphocytosis is also common during this phase of the illness. Dangerous complications are bronchopneumonia and acute encephalopathy. Bordetella parapertussis can cause a milder form of pertussis.
The bordetellae are small, Gram-negative, aerobic coccobacilli. Bordetella pertussis produces a number of virulence factors, including pertussis toxin, adenylate cyclase toxin, filamentous hemagglutinin, and hemolysin. Agglutinogens and other outer membrane proteins are important antigens.
The genus Bordetella contains the species B pertussis and B parapertussis, which cause pertussis in humans. Other members of the genus are B bronchiseptica, causing respiratory disease in various animals and occasionally in humans, and B avium as well as B hinzii, which cause respiratory disease in poultry and are very rarely found in humans.
Bordetellae are characterized by culture characteristics, biochemical tests, and nucleic acid analysis. Some of them show reversible antigenic modulation under certain culture conditions, and they mutate through several antigenically distinct phases when grown on agar.
Transmission is by droplets. The bacteria colonize only ciliated cells of the respiratory mucosa, and they multiply rapidly.
Bacteremia does not occur. The roles of the various toxins in pathogenesis are unclear.
Infection induces substantial immunity, although the protective antigens have not been identified conclusively. Both nonspecific and specific defenses participate in the response to disease.
The human respiratory mucosa is the natural habitat for B pertussis and B parapertussis. Transmission is almost always directly from person to person. Patients are most infectious during the early, catarrhal phase of the disease and remain infectious for about 5 weeks. Pertussis is a common and dangerous childhood disease in unvaccinated populations.
B pertussis can be cultured on modified Bordet-Gengou medium, charcoal-horseblood agar (Regan-Lowe) or grown in supplement Stainer-Scholte broth. Bordetella DNA can also be detected by PCR. Circulating antibodies appear in week 3 of illness and peak in the eighth to tenth week. Antibodies can be demonstrated by an enzyme-linked immunosorbent assay. Detection of specific IgA provides evidence of natural infection.
Treatment with erythromycin does not alter the course of disease, but reduces the infectious period to 5 to 10 days. Inactivated whole-cell vaccines are highly effective, but occasionally cause toxic side effects. Acellular vaccines with fewer side effects have been licensed for booster vaccination and will possibly be also licensed for primary vaccination.
