long-lasting topical deltamethrin treatment to protect dogs against visceral leishmaniasis

• Published in: Medical and veterinary entomology Vol. 23; no. 3; pp. 245 - 256
• Main Authors: COURTENAY, O, KOVACIC, V, GOMES, P.A.F, GARCEZ, L.M, QUINNELL, R.J
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.09.2009; Blackwell Publishing Ltd
• Subjects: Administration, Topical; Animals; antifeeding activity; biting rates; Brazil - epidemiology; control; deltamethrin; Diptera; disease prevention; Dog Diseases - parasitology; Dog Diseases - prevention & control; Dogs; Female; Hair - parasitology; Housing, Animal; Humans; Informed Consent; insect vectors; insecticide; Insecticides - administration & dosage; Insecticides - therapeutic use; Kinetoplastida; Leishmania; Leishmania infantum; Leishmaniasis, Visceral - epidemiology; Leishmaniasis, Visceral - prevention & control; Leishmaniasis, Visceral - veterinary; Lutzomyia longipalpis; Male; mortality; Nitriles - administration & dosage; Nitriles - therapeutic use; pesticide persistence; pour-on formulations; Psychodidae; Pyrethrins - administration & dosage; Pyrethrins - therapeutic use; pyrethroid; Randomized Controlled Trials as Topic; residual effects; sandfly; topical application; transmission; Trypanosomatidae; vector; vector control; visceral leishmaniasis; zoonosis; Brazil
• ISSN: 0269-283X; 1365-2915
• DOI: 10.1111/j.1365-2915.2009.00815.x

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 RA₅₀ 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 RA₅₀ 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.