Use of enrofloxacin for treatment of large-form Haemobartonella felis in experimentally infected cats

Objective-To compare treatment with enrofloxacin and doxycycline with no treatment in cats experimentally infected with Haemobartonella felis. Design-Prospective case-control study. Animals-16 cats. Procedure-Cats were inoculated with large-form H felis from a chronically infected donor. Cats were assigned to 1 of 4 treatment groups: doxycycline (5 mg/kg [2.3 mg/lb], PO, q 12 h), low-dose enrofloxacin (5 mg/kg, PO, q 24 h), high-dose enrofloxacin (10 mg/kg [4.5 mg/lb], PO, q 24 h), and an untreated control group. Clinical signs, Hct, blood smears, and a polymerase chain reaction (PCR) assay were used to monitor progression of the infection. Results-All cats were confirmed to be infected with H felis via blood smear evaluations and PCR assay results. Treatment had no effect on Hct during the intratreatment period, but Hct values were significantly greater in the low-dose enrofloxacin group, compared with the control group, during the posttreatment period. During the intratreatment period, H felis organism counts per 1,000 RBC in the doxycycline treatment and the high-dose enrofloxacin treatment groups decreased at a significantly faster rate than those in the control group. In the posttreatment period, organism counts in the doxycycline treatment group and the low- and high-dose enrofloxacin groups decreased at significantly faster rates than counts in the control group. There was no significant effect of treatment on the number of positive PCR assay results. Two cats treated with enrofloxacin and 1 cat treated with doxycycline completely cleared the H felis organism despite presumed immunosuppression caused by glucocorticoids. Conclusions and Clinical Relevance-Results support the hypothesis that enrofloxacin has anti-H felis effects.