Bordetella(redirected from bordetellas)
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A genus of gram-negative bacteria which are coccobacilli and obligate aerobes, and fail to ferment carbohydrates. These bacteria are respiratory pathogens. Bordetella pertussis, B. parapertussis, and B. bronchiseptica share greater than 90% of their deoxyribonucleic acid (DNA) sequences and would not warrant separate species designations except that the distinctions are useful for clinical purposes. Bordetella pertussis is an obligate human pathogen and is the causative agent of whooping cough (pertussis). Bordetella parapertussis causes a milder form of disease in humans and also causes respiratory infections in sheep. Bordetella bronchiseptica has the broadest host range, causing disease in many mammalian species, but kennel cough in dogs and atrophic rhinitis, in which infected piglets develop deformed nasal passages, have the biggest economic impact. Bordetella avium is more distantly related to the other species. A pathogen of birds, it is of major economic importance to the poultry industry.
Infection by all four species is characterized by bacterial adherence to the ciliated cells that line the windpipe (trachea), B. pertussis releases massive amounts of peptidoglycan, causing an exaggerated immune response that is ultimately deleterious, resulting in self-induced death of the ciliated cells. Bordetella also produces protein toxins. The best-characterized is pertussis toxin, made only by B. pertussis. This toxin interferes with the mechanisms used by host cells to communicate with one another.
Bordetella pertussis is spread by coughing and has no environmental reservoir other than infected humans. Culturing the organism is difficult. Erythromycin is the antibiotic used most frequently to treat whooping cough. Unfortunately, antibiotic treatment improves the patient's condition only if given early, when the disease is most difficult to diagnose, and does not help after whooping has begun. This is consistent with the concept that the early symptoms of the disease result from bacterial damage to the respiratory tract and the later symptoms are due to toxins released by the bacteria. Antibiotics can eradicate the microorganisms but cannot reverse the effects of toxins, which can cause damage far from the site of bacterial growth.
Vaccines have been developed for whooping cough and kennel cough. Multicomponent pertussis vaccines consisting of inactivated pertussis toxin and various combinations of filamentous hemagglutinin, pertactin, and fimbriae are now replacing the older whole-cell vaccines consisting of killed bacteria, which were suspected but not proven to cause rare but serious side effects. Vaccination programs have greatly reduced the incidence of whooping cough in affluent nations, but worldwide nearly half a million deaths occur each year, most of which are vaccine-preventable. See Antibiotic, Medical bacteriology