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

Abstract

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.

• Authors: O Courtenay, V Kovacic, P A F Gomes, L M Garcez, R J Quinnell
• Journal: Medical and veterinary entomology (Med Vet Entomol) Vol. 23 Issue 3 Pg. 245-56 (Sep 2009) ISSN: 1365-2915 [Electronic] England
• PMID: 19712155 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Insecticides
• Nitriles
• Pyrethrins
• decamethrin

Topics

• Administration, Topical
• Animals
• Brazil (epidemiology)
• Dog Diseases (parasitology, prevention & control)
• Dogs
• Female
• Hair (parasitology)
• Housing, Animal
• Humans
• Informed Consent
• Insecticides (administration & dosage, therapeutic use)
• Leishmaniasis, Visceral (epidemiology, prevention & control, veterinary)
• Male
• Nitriles (administration & dosage, therapeutic use)
• Psychodidae
• Pyrethrins (administration & dosage, therapeutic use)
• Randomized Controlled Trials as Topic