The clinical efficacy of topical and systemic therapy for the treatment of feline ocular chlamydiosis

Twenty-four specific-pathogen-free-derived cats aged four to 11 months were challenged by ocular application of a field isolate of Chlamydia psittaci to evaluate the effect of topical and systemic therapy on the course of disease. The cats were monitored for 35 days post-challenge, with severity of clinical signs being measured using a scoring system, and ocular shedding of the organism monitored by culture of conjunctival swabs. All cats developed active C psittaci infection, and after 7 days the cats were randomly assigned to one of four treatment groups: Group P (placebo) was given twice-daily ophthalmic tear-replacement ointment; group F was given twice-daily topical 1% fusidic acid ophthalmic viscous drops; group C was given twice-daily topical 1% chlortetracycline ophthalmic ointment; and group D was given doxycycline at 10 mg/kg daily per os in addition to twice-daily topical 1% fusidic acid ophthalmic ointment. Within 24 h of commencement of therapy, group D had significantly lower median clinical scores than group P, and with the exception of day 16, this trend was maintained throughout the observation period. Median clinical scores of cats in group F were not appreciably different to those in group P, whereas the median scores of cats in group C generally fell between those of groups P and D. The median duration of C psittaci shedding was 10 and 15 days for groups D and C respectively, but four of the six cats in groups F and P were still shedding organisms at the end of the study (day 35). In this study, systemic therapy with doxycycline proved superior to topical therapy in the treatment of feline chlamydiosis.