Haemophilus influenzae b infection in rats: effect of splenectomy on bloodstream and meningeal invasion after intravenous and intranasal inoculations.

We investigated the effect of splenectomy on the susceptibility of rats to intravenous or intranasal inoculation of Haemophilus influenzae, type b. The 50% lethal dose for asplenic rats inoculated either by intravenous (i.v.) (10(4.7)) or intranasal (i.n.) (10(4.6)) injection was similar, but significantly lower than the 50% lethal dose value in sham-operated rats (10(8.6) i.v. and 10(9.0) i.n.). Mean survival time was significantly longer for asplenic rats inoculated i.n. (49.3 h) compared to asplenic rats inoculated i.v. (24.4h). Similarly, sham-operated rats inoculated i.n. survived significantly longer after i.n. challenge (mean survival time, 171.4 h) than after i.v. challenge (34.7 h). Bacteremia was detected in 100% of asplenic rats and in 80% of sham-operated rats. The geometric mean number of bacteria in the blood of asplenic rats (10(4.90) per ml) was significantly greater than in sham-operated rats (10(3.29) per ml). Meningitis was detected in 7 of 15 randomly sacrificed asplenic rats, whereas none of 15 sham-operated rats had evidence of meningeal invasion. Thus, the asplenic rat was more susceptible to experimentally induced H. influenzae bacteremia, meningitis, and fatal sepsis and offers a biologically relevant experimental model for investigating the role of the spleen in defense against infection with encapsulated bacteria.