Bordetella pertussis Infection: Pathogenesis, Diagnosis, Management, and the Role of Protective Immunity

 Whooping cough is presently one of the ten most common causes of death from infectious disease worldwide. Despite a high vaccine uptake, resurgences of this disease have been observed in several countries. Virulence factors of Bordetella pertussis include agglutinogens, fimbriae, P.69/pertactin, pertussis toxin, filamentous haemagglutinin, adenylate cyclase, tracheal cytotoxin, dermonecrotic toxin, lipopolysaccharide, tracheal colonisation factor, serum resistance factor, and type III secretion. Virulence factor expression is regulated by the bvgAS locus, a two-component signal transduction system. The pathophysiologic sequence consists of attachment (fimbriae, P.69/pertactin, tracheal colonisation factor, pertussis toxin, filamentous haemagglutinin), evasion of host defence (adenylate cyclase, pertussis toxin, serum resistance factor), local effects (tracheal cytotoxin), and systemic effects (pertussis toxin). Bordetella pertussis is transmitted by respiratory droplets and causes disease only in humans. Various diagnostic methods are available, including culture, serological methods, and the polymerase chain reaction. Serotyping of isolates to detect agglutinogens 2 and 3 is useful because serotype 1,2 may be associated with higher mortality, and antibodies to these antigens (agglutinins) may be protective in both animals and humans. Immunisation using whole-cell vaccine is effective but is reactogenic. Acellular vaccines containing one to five components are being used increasingly in various countries. Protective immunity to pertussis correlates with high levels of antibody to each of pertactin, fimbriae, and pertussis toxin; however, doubt remains as to the relationship between agglutinogen 3 and fimbria 3, making results of trials investigating these virulence factors difficult to interpret.