Efficacy of oral afoxolaner (NexGard®) against natural infestations with Heterodoxus spiniger (Phthiraptera: Boopiidae) in dogs under field conditions

Abstract

Heterodoxus spiniger is a chewing louse of a diverse range of hosts, primarily Carnivora. Domestic dogs are considered a major host, and infestations can lead to pruritus, hair loss, or seborrhea. In the context of absence of clinical trials evaluating the efficacy of isoxazolines against H. spiniger, the study aimed to assess the effectiveness of a single oral dose of afoxolaner (NexGard®, Boehringer Ingelheim, Germany) under field conditions for the treatment of natural infestations in dogs, and to compare it with a topical contact ectoparasiticide registered in Europe for the chewing lice Trichodectes canis (Frontline Combo®, Boehringer Ingelheim, Germany) based on fipronil and (S)-methoprene. The study was a field, blinded, positive-control, single-site clinical efficacy study that was performed around Mount Ng'iro, Kenya. Between 30th January and 4th February 2025, 36 dogs infested with H. spiniger were included in the study when brought by owners for a regular rabies vaccination. For each included animal one adult H. spiniger was identified microscopically and collected in absolute ethanol. After inclusion, each infested dog was randomly assigned to one of the two groups: group 1 (investigational group treated with NexGard®) group 2 (positive control group treated with Frontline Combo®). Clinical assessments were performed at inclusion (day 0), then at day 15 (±2) and day 30 (±2) when scoring and evaluation of the skin lesions and symptoms was done. A grading system was also applied for scoring the presence of H. spiniger. Overall, 36 dogs were included (16 in group 1 and 20 in group 2). Four dogs did not complete the study. On days 15 (±2) and 30 (±2), all 32 dogs (from the 2 study groups) scored 0 for lice (i.e. no nits, no alive lice). The primary outcome was the complete eradication of lice by day 30 (±2). During the duration of the study, no reinfestation due to the hatching of eggs was observed. After treatment, a statistically significant decrease in degree of hair loss, pruritus, scaling, and lice score was noticed in the two groups at days 15 (±2) and 30 (±2) compared to day 0. The results show a clinical efficacy of 100 % for oral afoxolaner (NexGard®) against Heterodoxus spiniger, as well as of the control product (Frontline Combo®).