Haemophilus influenzae b bacteremia and meningitis in infant rabbits after intranasal inoculation

A suitable model of Haemophilus influenzae meningitis will facilitate better understanding of the pathophysiology, therapy, and prevention of the disease and its sequelae. Bacteremia and meningitis were induced in infant New Zealand white rabbits by intranasal inoculation of H. influenzae type b. Intranasal trypsin prior to challenge significantly increased (p = 0.002) the rate of bacteremia from 64% (7/11) to 100% (45/45). In the trypsin-treated group, H. influenzae b was isolated from the CSF of 89% (25/28) of 17- to 21-day-old rabbits and from 76% (13/17) of 23- to 30-day-old animals, p = 0.3; fatality rates were 88% and 31%, respectively, p = 0.001. Bacteremia developed within 24 hr of inoculation and meningitis within 96 hr. Death occurred 1 to 7 days after the development of meningitis. Histologic evidence of nasopharyngitis and meningitis was found at autopsy. The intranasal route of infection, the age-dependent outcome, the size of the animal, and its low cost and availability make the infant rabbit an appropriate model of H. influenzae b meningitis.