Inoculation of two genotypes of Hemobartonella felis (California and Ohio variants) to induce infection in cats and the response to treatment with azithromycin

Objectives-To describe clinical and laboratory findings associated with cat s experimentally infected by inoculation with the 2 recognized genotypes of Hemobartonella felis (small variant, Hfsm; large variant, Hflg) and to det ermine the response of cats to treatment with azithromycin. Animals-18 young adult domestic shorthair cats of both sexes. Procedures-Cats were inoculated with H felis and monitored weekly, using CB C counts and a polymerase chain reaction (PCR) designed to detect both gene tic variants of H felis. Beginning 26 days after inoculation, 11 cats were administered azithromycin (15 mg/kg of body weight, PO, q 12 h, for 7 days) . Results-Inoculation resulted in coinfection with Hflg and Hfsm, and both va riants were detected by PCR. Clinical abnormalities and anemia were most se vere in Hflg- and dual-infected cats. Results of PCR and CBC were positive for H felis in 112/112 (100%) and 42/112 (37.5%), respectively, samples col lected after inoculation. Administration of azithromycin had little effect on clinical variables, including anemia. All cats, regardless of treatment with azithromycin, had positive results for the PCR a? the end of the study period. Conclusions and Clinical Relevance-In these cats, Hflg was more pathogenic than Hfsm, and coinfection with both variants was detected. Results of the PCR were superior to results of CBC for detecting infection with H felis. A zithromycin administered at the dose and duration reported here was not eff icacious for the treatment of cats with hemobartonellosis.