Efficacy of a novel topical combination of fipronil, (S)-methoprene, eprinomectin and praziquantel against larval and adult stages of the cat lungworm, Aelurostrongylus abstrusus

Abstract The efficacy of a novel topical combination of fipronil 8.3% w/v, (S)-methoprene 10% w/v, eprinomectin 0.4% w/v, and praziquantel 8.3% w/v (BROADLINE ® , 1 Merial) against larval and adult Aelurostrongylus abstrusus lungworms in cats was assessed in a controlled laboratory study. The study included 48 purpose-bred, short-haired cats which were each inoculated with 225 infective A. abstrusus larvae. The cats were formed into eight blocks based on pre-treatment bodyweight and were then, within each block, randomly allocated to one of six treatment groups: untreated control; treated once when A. abstrusus were expected to be third-stage larvae (4 days post inoculation [dpi]), fourth-stage larvae (7 dpi), immature adults (14 dpi) or adult nematodes (32 dpi), or treated twice, once when A. abstrusus were expected to be third-stage larval and once again when A. abstrusus were expected to be adult nematodes (4 dpi + 32 dpi). Cats weighing ≥0.8–2.5 kg received one 0.3 mL applicator and cats weighing >2.5–7.5 kg received one 0.9 mL applicator. For determination of the efficacy of treatments, lungworm larval counts were established on faecal samples collected from all cats 32, 39, 46, 53 and 60 dpi. At each occasion from 46 dpi on, cats treated with fipronil, (S)-methoprene, eprinomectin and praziquantel had significantly lower A. abstrusus larval counts than the untreated controls with percentage reductions of 91.6% (cats treated 14 dpi; P  = 0.012), ≥98.9% (cats treated either 4 dpi, 7 dpi or 32 dpi; P 99.9% (cats treated 4 dpi + 32 dpi; P A. abstrusus lungworm infection in cats.