Efficacy of selamectin against experimentally induced and naturally acquired infections of Toxocara cati and Ancylostoma tubaeforme in cats

The efficacy of selamectin against experimentally induced and naturally acq uired infections of adult ascarids (Toxocara call) and adult hookworms (Anc ylostoma tubaeforme) was evaluated in five controlled studies in cats. Two studies evaluated the efficacy of selamectin against both ascarid (natural or induced) and hookworm (induced) infections; two studies evaluated the ef ficacy of selamectin against single natural infections of T. cati or A. tub aeforme; and the fifth study evaluated the efficacy of selamectin against i nduced infections of A. tubaeforme. Cats received selamectin topically in u nit doses designed to deliver a minimum of 6 mg kg(-1). Treatments were app lied to the skin on each animal's back at the base of the neck in front of the scapulae. For experimentally induced infections, cats were inoculated o rally with approximately 500 embryonated eggs of T. cati 56 days prior to t reatment and/or approximately 150-250 larvae (L-3) of A. tubaeforme 30 or 4 2 days prior to treatment. For both induced and naturally acquired infectio ns, cats were allocated randomly to treatments (6-12 cats per treatment) on the basis of fecal egg counts to receive either selamectin or a vehicle co ntaining the inert formulation ingredients. In all studies, adult worm coun ts were performed at necropsy 14 days after the last treatment administrati on. Against T. cati, a single application of selamectin provided a 100% red uction in the geometric mean number of adult worms for both experimentally induced and naturally acquired infections. Against A. tubaeforme, a single administration of selamectin provided a 99.4% reduction in the geometric me an number of adult worms in cats with natural infections, and an 84.7-99.7% reduction in adult worms in cats with induced infections. Two doses of selamectin administered at monthly intervals provided a 91.9% reduction in the geometric mean number of adult A. tubaeforme worms in cats with experimentally induced infections. The geometric mean numbers of adul t worms (T. cati and A. tubaeforme) from selamectin-treated eats were signi ficantly (P less than or equal to 0.0018) lower than for vehicle-treated ca ts in all studies. Thus, a single topical unit dosage providing a minimum d osage of 6 mg kg(-1) selamectin was highly effective in the treatment of na turally acquired and experimentally induced infections of T. cati and A. tu baeforme in cats. (C) 2000 Elsevier Science B.V. All rights reserved.