PATHOGENESIS AND DIAGNOSIS OF PERTUSSIS
Bordetella Pertussis is causative agent of pertussis, or whooping cough. It infects only humans by binding to the ciliated cells on respiratory epithelium. Once bound, it can exhibit the effects of its toxin. Importantly, the toxin of Bordetella pertussis is an AB toxin, which works by ADP-ribosylating G proteins that are responsible for the regulation of adenylate cyclase. In turn this allows for a great increase in cAMP levels, and an opening of chloride channels within cell membranes. Ultimately, excess mucus production results.
The organism exhibits 3 specific stages of pathogenesis - the catarrhal stage, paroxsymal stage and the convalescent stage. Within the catarrhal stage the infected host experiences mild symptoms that are not unlike the experiences with the flu. At this point, the host is still actively shedding organisms, and this period last about 1 to 2 weeks. After this, the onset of the typical whooping cough can be seen and indicates that the host is experiencing the paroxysmal stage of the disease. Cyanosis and fever are seen, but of particular note, infants are at great risk of seizures, brain damage and even death. Finally, in the convalescent stage of the disease the host begins the healing process.
Diagnosis of Bordetella pertussis is relatively simple by obtaining a patient nasopharyngeal swab and plating this to media specific for bordetella identification. media such as Bordet-Gengou agar is particularly effective and the colonies that appear on this plate are distinctive and look like droplets of mercury. Furthermore, a gram stain could be performed, where the organism would be identified as a gram negative coccobacilli. To differentiate the organism from other bordetella, catalase, oxidase, motility and macconkey growth could also be examined. The results of the catalase test are variable, but the oxidase test returns a positive result. The organism is non motile and does not grown on MacConkey agar.
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