A long-lasting topical deltamethrin treatment to protect dogs against visceral leishmaniasis.
To develop long-lasting, topical pour-on insecticides for dogs to control zoonotic visceral leishmaniasis, two deltamethrin-based formulations (emulsifiable concentrate [EC] and suspension concentrate [SC]) were tested for their efficacy against the phlebotomine sandfly Lutzomyia longipalpis Lutz & Neiva (Diptera: Psychodidae), vector of Leishmania infantum Nicolle (Kinetoplastida: Trypanosomatidae). The entomological outcomes tested were anti-feeding effect (proportion of female sandflies unfed), lethal effect (24-h female sandfly mortality) and these two effects combined, and the insecticide persistence time at 50% (residual activity, RA50) and 80% (RA80) efficacy. On initial application, the proportions of female flies that demonstrated anti-feeding activity or were killed were similar for both formulations, at 0.93 (95% confidence interval [CI] 0.856-0.977) vs. 0.81 (95% CI 0.763-0.858) (anti-feeding) and 0.86 (95% CI 0.787-0.920) vs. 0.76 (95% CI 0.698-0.817) (24-h mortality) for EC and SC, respectively. The RA(50) rates for anti-feeding and mortality caused by the EC formulation were 4.7 months (95% CI 4.18-5.84) and 2.5 months (95% CI 2.25-2.90), respectively, compared with 1.1 months (95% CI 0.96-1.15) and 0.6 months (95% CI 0.50-0.61), respectively, for the SC formulation. The RA(50) for the combined anti-feeding and mortality effects of EC was 5.2 months (95% CI 4.73-5.96), compared with only 0.9 months (95% CI 0.85-1.00) for the SC formulation. The four- to six-fold superior residual activity of the EC formulation was attributed to the addition of a solvent-soluble resin in the formulation which improved fur adhesion and acted as a reservoir for the slow release of the active ingredient. These results identify the potential of such a low-cost formulation to reduce the inter-intervention interval to 5-6 months, similar to that recommended for deltamethrin-impregnated dog collars or for re-impregnation of conventional bednets, both of which are currently used to combat Leishmania transmission. Finally, a novel bioassay was developed in which sandflies were exposed to fur from treated dogs, revealing no detectable tolerance (24-h mortality) in wild-caught sandflies to the insecticide formulations up to 8 months after the initiation of communitywide application of the insecticides to dogs.
Courtenay
O
O
Populations and Disease Research Group, Department of Biological Sciences, University of Warwick, Coventry, UK. orin.courtenay@warwick.ac.uk
Kovacic
V
V
Gomes
P A F
PA
Garcez
L M
LM
Quinnell
R J
RJ
D000287:Administration, Topical; D000818:Animals; D001938:Brazil / Q000453:epidemiology; D004283:Dog Diseases / Q000469:parasitology* / Q000517:prevention & control; D004285:Dogs; D005260:Female; D006197:Hair / Q000469:parasitology; D006799:Housing, Animal; D006801:Humans; D007258:Informed Consent; D007306:Insecticides / Q000008:administration & dosage / Q000627:therapeutic use*; D007898:Leishmaniasis, Visceral / Q000453:epidemiology / Q000517:prevention & control* / Q000662:veterinary; D008297:Male; D009570:Nitriles / Q000008:administration & dosage / Q000627:therapeutic use*; D011576:Psychodidae; D011722:Pyrethrins / Q000008:administration & dosage / Q000627:therapeutic use*; D016032:Randomized Controlled Trials as Topic
D007306:Insecticides; D009570:Nitriles; D011722:Pyrethrins; C017180:decamethrin