Experimental meningococcal meningitis in the infant rat.

Experimental infection of the infant rat could be established with intraperitoneal challenge with strains of all three meningococcal groups A, B, and C tested. 5-day-old rats were challenged with 3 different doses (10(2), 10(4), and 10(6) bacteria/animal) and the development of peritonitis, bacteraemia and meningitis detected as a function of time at 3, 6, and 9 h. Mortality was followed up to 24 h. Group B strains caused a rapidly developing and sustained high level bacteraemia and meningitis with all challenge doses. Bacteraemia and meningitis following challenge with MenA and MenC were of somewhat shorter duration and reached lower peak levels. Repeated 'rat passages' of meningococcal strains that had been kept stored for long periods markedly increased their virulence. This study shows that the infant rat model can be applied for studying pathogenesis of meningococcal bacteraemia and meningitis. Previous work from this laboratory has shown it to be suited also for studying antibody-mediated protection from this disease.