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