Bordetella pertussis is the causative agent of the disease pertussis, better known as whooping cough. Pertussis is primarily a disease found in unimmunized children, although adults may contract the disease and subsequently spread the infection. Pertussis is a disease that carries significant morbidity and mortality, greater than 350,000 deaths occur annually worldwide due to the disease. Most deaths occur in young infants, and neonates are especially susceptible to pertussis with potentially fatal consequences.
Pertussis is also a highly communicable disease with >90% of susceptible household contacts contracting the infection. Vaccines, made from killed, detoxified whole cell organisms, are available for pertussis. They have an efficacy rate of 80-90%, however they have been associated with a high rate of minor adverse effects. Acellular vaccines that are better tolerated have been developed recently, and have shown strong efficacy in recent clinical trials. The vaccine-induced immunity is relatively short lived, and naturally acquired immunity also fades over time. In the U.S., pertussis exists in an endemic state while in countries with low vaccination rates pertussis is epidemic. In the U.S., 40-50% of cases occur in young infants and 30% of cases occur in adults. In countries where vaccination is less common, most cases of pertussis are seen in children 2-5 years of age.
Microscopically, members of the genus Bordetella are small coccobacilli that stain Gram negative using the Gram Stain method. Members of this genus are strict aerobes, catalase positive, and have simple nutritional requirements. Carbohydrates are not utilized by Bordetella pertussis as a source for energy. Its growth is not supported on standard laboratory mediums, and specialized media must be used to recover the organism from clinical specimens. Diagnosis of pertussis can also be performed by direct fluorescent antibody testing, Polymerase Chain Reaction (PCR) tests, and through serological testing.
Bordetella
produces a variety of toxins and virulence factors that are involved in cell adherence and the clinical disease process. The toxins include pertussis toxin (PT), adenylate cyclase toxin (ACT), and tracheal cytotoxin (TCT). PT inhibits the coupling of G proteins to intracellular signal transduction pathways, leading to a variety of biological effects. ACT inhibits host cells, including immune effector cells. TCT plays a major role in the initial pathology of pertussis by causing inhibition of DNA synthesis and cell death. The pathogenesis of pertussis is initiated by the attachment of the organism to epithelial and immune effector cells and the secretion of toxins and virulence factors causes the clinical symptoms of the disease from the organism. Erythromycin is the chemotherapeutic agent of choice for both the treatment and chemoprophylaxis of pertussis.
Reference:
Murray, P.R., Baron, E.J., Pfaller, M.A., Tenover, F.C., & Yolken, R.H. (Eds.). (1999).
Manual of Clinical Microbiology.
Washington, D.C.: ASM Press.
