Assessment of the insecticidal activity of afoxolaner against Aedes aegypti in dogs treated with NexGard®

Parasite, Oct 2017

Twelve healthy dogs were studied in this parallel group, blinded, randomised, and negative controlled efficacy study. On Day -1, the 12 dogs included were ranked within sex in descending order of individual pre-treatment (Day -5) fed mosquito counts and randomly allocated by blocks of two dogs to the untreated control group or the afoxolaner-treated group. NexGard® (Merial, now part of Boehringer Ingelheim Animal Health) was administered orally on Day 0 in accordance with the European label instructions. On Days 1, 7, 14, 21 and 28, all dogs were exposed for a duration of 1 hour to 50 ± 5 unfed Aedes aegypti females. After each exposure, mosquitoes were collected after 1 hour and assessed for viability during collection and at 24 ± 2 hours. The arithmetic (and geometric) mean values of live fed mosquito counts at 24 hours after the exposure periods for the negative control group ranged from 33.7 (32.3) to 49.8 (49.7), indicating that this was a vigorous mosquito strain. There was no significant difference between control and treated groups in the number of live and fed mosquitoes at each 1 hour post-exposure collection time. Based on arithmetic and geometric mean values at 24 hours after each exposure, significantly fewer live fed mosquitoes were recorded in the treated group, compared to the negative control group, throughout the study (p < 0.001). The afoxolaner insecticidal efficacy against A. aegypti varied from 98% (Day 2) to 75.3% (Day 29) based on arithmetic means, and 98.7% (Day 2) to 89.8% (Day 29) based on geometric means.

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Assessment of the insecticidal activity of afoxolaner against Aedes aegypti in dogs treated with NexGard®

Parasite Assessment of the insecticidal activity of afoxolaner against ® Aedes aegypti in dogs treated with NexGard Julian Liebenberg 1 Josephus Fourie 1 Wilfried Lebon 0 Diane Larsen 0 Lenaïg Halos 0 Frédéric Beugnet 0 0 Boehringer Ingelheim Animal Health , 29 avenue Tony Garnier, 69007 Lyon , France 1 Clinvet International (Pty) Ltd , PO Box 11186, 9321 Universitas , South Africa -Twelve healthy dogs were studied in this parallel group, blinded, randomised, and negative controlled efficacy study. On Day -1, the 12 dogs included were ranked within sex in descending order of individual pretreatment (Day -5) fed mosquito counts and randomly allocated by blocks of two dogs to the untreated control group or the afoxolaner-treated group. NexGard® (Merial, now part of Boehringer Ingelheim Animal Health) was administered orally on Day 0 in accordance with the European label instructions. On Days 1, 7, 14, 21 and 28, all dogs were exposed for a duration of 1 hour to 50 ± 5 unfed Aedes aegypti females. After each exposure, mosquitoes were collected after 1 hour and assessed for viability during collection and at 24 ± 2 hours. The arithmetic (and geometric) mean values of live fed mosquito counts at 24 hours after the exposure periods for the negative control group ranged from 33.7 (32.3) to 49.8 (49.7), indicating that this was a vigorous mosquito strain. There was no significant difference between control and treated groups in the number of live and fed mosquitoes at each 1 hour post-exposure collection time. Based on arithmetic and geometric mean values at 24 hours after each exposure, significantly fewer live fed mosquitoes were recorded in the treated group, compared to the negative control group, throughout the study (p < 0.001). The afoxolaner insecticidal efficacy against A. aegypti varied from 98% (Day 2) to 75.3% (Day 29) based on arithmetic means, and 98.7% (Day 2) to 89.8% (Day 29) based on geometric means. Aedes aegypti; insecticide; afoxolaner; NexGard®; dog Introduction Recently, a new class of insecticides/acaricides, the isoxazolines, have demonstrated very good efficacy against fleas and ticks [ 19 ]. Afoxolaner is an isoxazoline administered monthly to protect dogs against fleas and ticks (NexGard®, Merial, now part of Boehringer Ingelheim Animal Health) [ 2,3,8,10 ]. It is administered at a minimum dose of 2.5 mg/kg. Recent studies have demonstrated its activity against other arthropods, including Demodex canis, the agent of canine demodicosis, Sarcoptes scabiei var. canis and S. scabiei var. suis, the agent of sarcoptic mange in dogs and swine, respectively, as well as Otodectes cynotis, the agent of ear mange in dogs and cats [ 1,4,5 ]. After oral administration, afoxolaner is absorbed quickly, with peak plasma levels (Cmax) reached between 2 to 4 hours after administration [ 14,15 ]. Plasma protein binding is more than 99%, which explains the long half-life, 10–14 days on average [ 14,15 ]. Due to its strong binding to plasma proteins, its activity is systemic and exposure is related to the ingestion of blood or inflammatory fluids by the biting insect. In addition to its activity against well-known bloodfeeding ectoparasites like fleas and ticks, or resident ectoparasites like Demodex, Sarcoptes, and Otodectes, it is probable that afoxolaner would also have a certain level of insecticidal activity against other blood-feeding arthropods like mosquitoes. Insecticidal efficacy following a blood meal might not prevent pathogen transmission from the female mosquito, but it could have a further effect by killing the mosquitoes before a new bite, and/or by reducing the mosquito population in a restricted area like a household where treated dogs are living. It could therefore have an indirect action on the rate of vector-borne pathogen transmission within the household. Aedes aegypti mosquitoes are endemic in tropical areas around the globe, but have expanded into sub-tropical areas and even some warm temperate locations, although the species seems less adaptable to temperate climate than Aedes albopictus [ 13 ]. It is now found in many parts of the world including South and Central America, the southern USA, Africa, India, tropical islands, South-East Asia, Northern Australia, and sporadically in the Mediterranean zone [ 13 ]. A. aegypti is a major vector of several diseases of animals and/or humans, e.g. heartworm disease due to Dirofilaria immitis in dogs, equine encephalitis viruses, West Nile virus, Dengue virus, Chikungunya virus, Zika virus, and yellow fever virus [ 9,12 ]. The objective of this study was to assess the insecticidal activity that afoxolaner may have against A. aegypti mosquitoes. Materials and methods The design and conditions of this study were approved by the South African and ClinVet animal welfare ethics committees, and were performed in accordance with the Good Clinical Practices of the European Agency for the Evaluation of Veterinary Medicinal P (...truncated)


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Julian Liebenberg, Josephus Fourie, Wilfried Lebon, Diane Larsen, Lenaïg Halos, Frédéric Beugnet. Assessment of the insecticidal activity of afoxolaner against Aedes aegypti in dogs treated with NexGard®, Parasite, 2017, pp. 39, 24, DOI: 10.1051/parasite/2017042