Control of Filaroides hirthi infections in Beagle dogs by ivermectin

The efficacy of ivermectin against Filaroides hirthi was evaluated in a series of three trials using Beagle dogs of a breeding colony known to be endemically infected with this lungworm. Ivermectin was subcutaneously given at a dosage of 1 mg kg-1 bodyweight once to 40 (group A) or, at a one week interval, twice to 32 dogs (group B) 14-15 weeks prior to necropsy; another 40 dogs (group C) remained untreated. All animals were necropsied and lungs were digested using the pepsin-hydrochloride method and qualitatively examined for Filaroides spp. stages. A 44.8% and 74.1% reduction of the prevalence of lungworm infection as well as a 87.5% and 94.8% reduction of the proportion of dogs harbouring first-stage Filaroides spp. larvae were found in groups A and B, respectively, as compared to group C. These results suggest that repeated treatments of breeding dogs with ivermectin might reduce the transmission of F. hirthi infection to their offspring.