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Summary. Phase I strains 18-323, Tohama and L-84 of Bordetella pertussis produced paroxysmal coughing when encased in agarose beads and administered intrabronchially to adult Sprague-Dawley rats. In contrast, the Phase IV variant of strain L-84 was inactive in cough induction, as was strain BP 357, a transposon-insertion mutant which is deficient only in pertussis toxin (PT). Strain BPM 1809, which lacks only the heat-labile toxin, was similar to the unmodified Phase I strains for cough induction, indicating that this toxin is not needed to induce coughing. B. parapertussis also was inactive as a cough inducer. These results indicate that PT, present in Phase I strains of B. pertussis, and absent from Phase IV strains, strain BP 357 and B. parapertussis, is essential for the induction of paroxysmal coughlng in this rat model of whooping cough. Prior injection of DTP (whole-cell) vaccine greatly reduced the incidence of coughing in rats challenged subsequently with Phase I B. pertussis. Serological responses were monitored after intrabronchial infection with the various bacterial strains and after vaccination and challenge. The PT-positive or -negative status of the strains in uiuo was confirmed by the appropriate presence or absence of anti-PT IgG in the convalescent sera.

Summary. Adult Sprague-Dawley rats infected intrabronchially with Bordetella pertussis strain 18-323 encased in agarose beads (BP-beads), developed a paroxysmal cough and leucocytosis, both of which peaked at around day 10. When animals were exposed to ether for 2 min after delivery of the beads, there was an enhancement of the number of subsequent coughing episodes. Inclusion of carrageenan in the beads also enhanced coughing. Control rats, given sterile beads or left untreated, showed only a low level of coughing or no coughing, depending upon their source. Rats challenged by the same route with heat-killed B. pertussis in beads, or with live organisms in suspension (without beads) showed no cough induction or leucocytosis. However, intranasal delivery of B. pertussis suspension gave rise to a moderate amount of coughing and leucocytosis. Serum IgG responses to B. pertussis antigens were greatest in rats infected with BP-beads and antibodies against both pertussis toxin and filamentous haemagglutinin were detected. Since the rat is the only conveniently accessible laboratory animal species in which B. pertussis induces an intermittent paroxysmal cough, as in man, it merits further study for determining the mechanisms of pathogenesis and immunity in pertussis.

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Four strains of rats were each infected intrabronchially with approximately 10 8 CFU of Bordetella pertussis 18-323 encased in fine agarose beads. After 8 days, Sprague-Dawley rats developed the highest incidence of coughing paroxysms, as monitored with voice-activated tape recorders; Brown Norway, Lewis, and Hooded Lister rats coughed significantly less frequently. Marked leukocytosis, with counts up to four times the normal levels, and retardation of normal weight gain occurred in all four rat strains. Both coughing and leukocytosis were greater in animals that were infected at 4 weeks of age than in those infected at 6 weeks of age. Total serum immunoglobulin E (IgE) rose in all four rat strains 9-to 244-fold by day 8 after infection and returned to near preinfection levels at 6 weeks. Sprague-Dawley and Lewis rats, which had the lowest basal levels of total IgE in serum, showed the greatest degrees of elevation. All four rat strains had IgG to B. pertussis whole-cell sonicate and to filamentous hemagglutinin in 6-week-postinfection sera. However, the strains differed in production of IgG to pertussis toxin, with Sprague-Dawley rats having the highest titers and Hooded Lister and Lewis rats being nonresponders. These studies highlight the importance of rat strain as a variable in the coughing-rat model of pertussis and validate the choice of the Sprague-Dawley rats in previous studies.