Bordetella

Bordetella Pertussis

Bordetella is a family of small gram-negative bacterial pathogens that cause respiratory tract infections in humans and animals.¹ Nine species of Bordetella have been identified to date, but Bordetella pertussis causes most of the human disease and only three additional members, B. bronchiseptica, B. parapertussis, and B. holmesii have been associated with respiratory infections in humans. B. pertussis causes whooping cough, a highly contagious respiratory tract infection with characteristic severe coughing episodes. The incubation period is on average 7-10 days and the disease follows a prolonged course consisting of three stages: (1) persistent runny nose (2) paroxysmal coughing, and (3) convalescence.²

Pertussis toxin (PT) is the major virulence factor of B. pertussis. PT acts via a complex mechanism of action involving entry into cells of the respiratory tract, modification of critical signaling pathways and disruption of cell regulatory mechanisms.¹ Along with other bacterial toxins, PT causes damage to the respiratory epithelium which results in most of the symptoms of infection such as severe coughing.³

Transmission

Whooping cough (pertussis) is highly contagious, and transmission is thought to occur via respiratory droplets.^{1, 2} Since B. pertussis has no known animal or environmental reservoir, all human infections occur via human-to-human transmission.³ Pertussis does not have a seasonal pattern. Secondary spread in families, schools, and hospitals is rapid. Vaccination has produced a dramatic reduction in disease, but outbreaks persist.¹

Prevention ^{2, 3}

Vaccination for B. pertussis is available via the diphtheria, tetanus, pertussis (DTP) vaccine and the recently developed acellular vaccine (DTaP), which is less reactogenic than DTP vaccines. DTP vaccine is generally used in most developed countries, and has had a significant impact on reducing whooping cough infections. The whooping cough booster vaccine for adolescents and adults is called Tdap.

Diagnosis⁴

When pertussis is suspected clinically, the diagnosis can be confirmed by isolation of B. pertussis on special culture media using nasopharyngeal secretions or swabs but not throat swabs. Culture is more likely to be positive early in the course of disease, but the diagnosis is frequently not considered until paroxysmal coughing has been present for some time. A direct immunofluorescent antibody (DFA) technique of nasopharyngeal smears is used for rapid diagnosis of pertussis, but nucleic acid amplification tests are replacing both culture and DFA and are highly sensitive.

Treatment ²

Antibacterial treatment is effective during the earlier stages of pertussis and can reduce spread to others. Several types of antibiotics are active against B. pertussis, but macrolides are preferred for both treatment and prophylaxis. Erythromycin has the greatest clinical experience but azithromycin and clarithromycin are equally effective.

References

¹ Mattoo, S. and Cherry, JD. Molecular Pathogenesis, Epidemiology, and Clinical Manofestations of Respiratory Infections Due to Bordetella pertussis and Other Bordetella Subspecies.  Clin Microbiol Rev. Apr 2005; 18(2): 326–382.           

² http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5414a1.htm

³ http://www.cdc.gov/vaccines/vpd-vac/pertussis/default.html#vacc

⁴ http://www.cdc.gov/pertussis/clinical/diagnostic-testing/diagnosis-confirmation.html