Bordetella pertussis is the etiological agent for Pertussis (whooping cough), a highly contagious, acute and chronic upper respiratory disease. Though mostly seen in infants and young children a milder form is recognized in adults. Vaccination has greatly reduced disease incidence in many countries though outbreaks are now more frequent.
The disease begins with the catarrhal stage (like a common cold). Patients at this stage are most infectious because the bacterial load is at its highest and the disease normally unrecognised. After catarrhal disease begins the peroxysmal stage, characterised by the classic whooping cough paroxysms (repetitive coughs then rapid inspiration or whoop of air) up to 40 to 50 times/day. Then the disease enters convalescence when the number and severity of paroxysms diminish.
B. pertussis is a slow growing, gram negative coccobacillus. Successful isolation depends on the time between disease onset and sample collection and whether or not the patient is on antibiotics. Direct fluorescent antibody (DFA) testing on nasopharyngeal samples is not sufficiently sensitive.
Various serological procedures have been developed for the detection of antibody to B. pertussis. In an effort to improve sensitivity and especially specificity, more recent techniques measure antibody to B. pertussis virulence factors, especially pertussis toxin (PT) and filamentous hemagglutanin (FHA). PT is a bacterial exotoxin and FHA has been shown to play a major role in the attachment of B. pertussis to the (epithelium of the) upper respiratory tract of the host, the target site for establishment of infection. Antibodies to both PT and FHA develop as a result of infection with B. pertussis. It is believed that such antibodies confer humoral protection against infection. Due to cross reactivity of antibodies to FHA, in many countries the importance of FHA as an aid to diagnosis is under review.
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