Preliminary study on the acaricidal efficacy of spinosad administered orally to dogs infested with the brown dog tick, Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae)

摘要

Spinosad is a novel mode of action insecticide and acaricide derived from a family of natural compounds produced from fermentation of the actinomycete, Saccharopolyspora spinosa. Although spinosad has been shown to have rapid knockdown and 1 month of residual efficacy against fleas (Ctenocephalides spp.) following oral administration in dogs, potential activity against ticks infesting dogs has not been determined. To address this possibility, a proof-of-concept laboratory efficacy study was conducted using dogs orally treated with spinosad and experimentally infested with the brown dog tick, Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae). In this randomized block (blocked by gender and pre-treatment tick counts), blinded, parallel-arm study, 12 dogs selected on health and ability to maintain pre-treatment tick populations were allocated equally among three groups: placebo-treated negative control, and spinosad in gelatin capsules at 50 and 100mg/kg administered per os. All treatments were administered once on Day 0. On days 6, 1, 7, 14, 21 and 28, each dog was infested with 50 unfed adult R. sanguineus, approximately 50% male and 50% female, obtained from the investigator's established tick colony. Tick comb counts were performed approximately 48h post-infestation by study personnel who were blinded to treatments. Compared to geometric mean live tick counts in the control group, tick counts in the 50 and 100mg/kg spinosad doses were significantly (P <0.05) reduced by 94.8 and 97.2%, respectively, within 24h of treatment. Compared to geometric mean live tick counts in the control group at Days 9, 16, 23 and 30 after treatment, the 50mg/kg spinosad treatment group demonstrated 67.8, 49.1, 52.1 and 5.0% reductions, while the 100mg/kg spinosad treatment group demonstrated 88.6, 70.6, 61.9 and 71.3% reductions, respectively. This pilot efficacy study demonstrated that a single oral treatment with technical spinosad in gelatin capsules, at 50 and 100mg/kg, provides high efficacy against existing R. sanguineus infestations within 24h of dosing, and suggests that there is some post-treatment residual tick control in dogs for up to 1 month.