Experimental infection of cotton rats with three naturally occurring Bartonella species

The kinetics of infection and humoral immune response of laboratory-bred co tton rats (Sigmodon hispidus) challenged with three Bartonella spp. recover ed from the blood of naturally infected cotton rats captured in Georgia (US A) are described. Bartonella spp. infection, as determined by bacteremia, o ccurred in all 18 cotton rats inoculated with live Bartonella of each speci es at either a low dose, 10(3) colony-forming units (CFU's), or high dose, 10(7) CFU. Cotton rats inoculated with lower doses of Bartonella spp, devel oped higher bacteremia that persisted for longer periods than in those inoc ulated with high doses. Peak bacteremia varied among Bartonella spp, rangin g from 10(4) to 10(6) CFUs per 1.0 mi of blood. Antibody measured by immuno fluorescence assays using species-specific antigens indicated more rapidly rising and higher antibody titers in cotton rats challenged with high doses vs. low doses and with inactivated bacteria vs. live bacteria. Each group of rats produced high IgG titers to the homologous challenge antigen; low o r unmeasurable cross-reactivity was detected to heterologous Bartonella ant igens. Exposure of cotton rats to a specific Bartonella sp. resulted in pro tection, as measured by detectable bacteremia, in eight of nine animals cha llenged with the same Bartonella sp. used initially; no evidence of resista nce to secondary challenge with different Bartonella spp. was obtained. Cro ss-protection between Bartonella spp., isolated from the same rodent specie s, may not occur.