Experimental Study of the Relationship between Bordetella pertussis and B. parapertussis Infections in Suckling Mice

Abstract

Bordetella parapertussis can occasionally be isolated in the late period of epidemic pertussis and even from the same patient infected with B. pertussis, thereby closely related to B. pertussis. Compared with B. pertussis, it is more frequently isolated from vaccinated individuals as well. Based on the findings, we carried out an experimental study to establish their interrelationship in mice infected with B. parapertussis alone or with both bacteria.
The total of 4 groups, each of which constituted ten 10-12 day-day-old mice were in this study. Each 10 mice from mothers which were either unimmunized or immunized with filamentous hemagglutinin-predominant pertussis vaccine were infected with either freshly isolated 1.2×10⁴ CFU strain 422 of B. parapertussis alone or mixed with 6×10³ CFU strain 18-323 of B.pertussis and 6×10³ CFU strain 422 of B. parapertussis transnasally. We then compared bacterial colonization 1, 2 and 3 weeks after challenge, using the numbers of bacteria in the lungs and peripheral white blood cell count.
In the B. parapertussis infection group, B. parapertussis could colonize neither the lungs regardless of pertussis antibodies. In the group infected with a mixture of B. pertussis and B. parapertussis, 10⁶ CFU of B. pertussis was primarily found in mice not given the pertussis antibodies, however, 10⁵ CFU of B. parapertussis was found in mice given the pertussis antibodies. These results suggest that B. pertussis helps B. parapertussis to colonize in the presence of the pertussis antibodies, thus explaining above the clinical findings.