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.

Transmission and Epidemiology of Zoonotic Protozoal Diseases of Companion Animals

“…Limitations in diagnostic sensitivity likely lead to false-negative diagnoses for a large number of asymptomatic dogs, delays between testing and dog removal increase the likelihood of transmission, and the financial and emotional costs of the policy implemented in Brazil are high (329,339,340). The use of permethrin or deltamethrin collars or topical applications has shown efficacy in reducing sandfly feeding and transmission in areas of endemicity (341,342). However, the cost and necessity for reapplication make these interventions more difficult to utilize in many regions of endemicity.…”

Lutzomyia longipalpis behavior and control at an urban visceral leishmaniasis focus in Argentina

“…longipalpis densities in the first seven days after intervention, but did not increase the dispersion of vector to the sprayed border areas. Although some studies reported deltamethrin residual effects up to 9-12 months inside houses 13,19 , strong anti-feeding effects when applied to dogs as collars or topically, and repellent effects in impregnated bednets 7,8,9 , and pyrethroids as lambdacyalothrin reducing impact on Lu. longipalpis sand fly captures after focal or indoor applications 14,18 , there are many reports about the short or transient effects of fenitrothion 14 , cypermethrin 12 and deltamethrin as peridomestic sprayed insecticide 1,13,22,36 .…”

Optimizing Insecticide Allocation Strategies Based on Houses and Livestock Shelters for Visceral Leishmaniasis Control in Bihar, India

“…For example, the model is capable of suggesting spraying intervention at only one of the two site types (either at houses or at cattle sheds). Even though insecticides have the dual effect of anti-feeding and of mortality, 21,31 this model only considers the mortality effect. In our future research, we plan to extend the framework by incorporating the above features as well as influences of an anti-feeding effect on the sprayed sites and dynamic variation in sandfly population as it changes due to seasonal conditions and reduces over time after insecticide intervention.…”

“…20 Moreover, the appropriate empirical studies were used to estimate P. argentipes' insecticide-induced mortality, 24 hours after spraying with DDT 12 and deltamethrin. 16 An insecticide's lethal effect is assumed to decay exponentially over time 21 as suggested in the literature. The decay rates inside houses 16 and cattle sheds 22 were then estimated using data from the literature (the procedure is shown in Supplemental Appendix S1).…”

“…21 Thus, the proportions of sandflies that die on the ζ th day after insecticide application inside houses and cattle sheds, respectively, are given by:…”