DDT-based indoor residual spraying suboptimal for visceral leishmaniasis elimination in India

Abstract

Indoor residual spraying (IRS) is used to control visceral leishmaniasis (VL) in India, but it is poorly quality assured. Quality assurance was performed in eight VL endemic districts in Bihar State, India, in 2014. Residual dichlorodiphenyltrichloroethane (DDT) was sampled from walls using Bostik tape discs, and DDT concentrations [grams of active ingredient per square meter (g ai/m 2 )] were determined using HPLC. Pre-IRS surveys were performed in three districts, and post-IRS surveys were performed in eight districts. A 20% threshold above and below the target spray of 1.0 g ai/m 2 was defined as "in range." The entomological assessments were made in four districts in IRS and non-IRS villages. Vector densities were measured: pre-IRS and 1 and 3 mo post-IRS. Insecticide susceptibility to 4% DDT and 0.05% deltamethrin WHO-impregnated papers was determined with wild-caught sand flies. The majority (329 of 360, 91.3%) of pre-IRS samples had residual DDT concentrations of <0.1 g ai/m 2 . The mean residual concentration of DDT post-IRS was 0.37 g ai/m 2 ; 84.9% of walls were undersprayed, 7.4% were sprayed in range, and 7.6% were oversprayed. The abundance of sand flies in IRS and non-IRS villages was significantly different at 1 mo post-IRS only. Sand flies were highly resistant to DDT but susceptible to deltamethrin. The Stockholm Convention, ratified by India in 2006, calls for the complete phasing out of DDT as soon as practical, with limited use in the interim where no viable IRS alternatives exist. Given the poor quality of the DDT-based IRS, ready availability of pyrethroids, and susceptibility profile of Indian sand flies, the continued use of DDT in this IRS program is questionable.leishmaniasis | elimination |

Insecticide resistance in phlebotomine sandflies in Southeast Asia with emphasis on the Indian subcontinent

“…Recently, Coleman et al [53] reported spraying of DDT (1gm/m 2 ) on walls up to 84.9 % and concluded that DDT-based IRS is suboptimal for achieving the goal of VL elimination.…”

Progress in the Mathematical Modelling of Visceral Leishmaniasis

“…if asymptomatics are not responsible for maintaining transmission). It also potentially explains why current control programmes in the ISC have been successful despite the apparent ineffectiveness of vector control (Coleman et al, 2015). Results from this model suggest that a diagnostic test with only 50% sensitivity might result in a considerable reduction (halving) of R 0 and offer the potential for elimination.…”

“…In India, resistance of P. argentipes to DDT and pyrethroids is patchy (Ostyn et al, 2008;Dinesh et al, 2008b). The Indian and Nepalese routine IRS activities are considered suboptimal due to financial and logistical constraints, poor quality spraying practices and low community compliance (Chowdhury et al, 2011;Picado et al, 2012;Coleman et al, 2015). In Brazil, spraying lambda-cyhalothrin in animals sheds where the vector Lu.…”

Visceral Leishmaniasis Control and Elimination: Is There a Role for Vaccines in Achieving Regional and Global Goals?

“…However, there was slow reduction in vector density and development of resistance occurred in the targeted sandfly species due to substandard IRS spraying. 13 Personal protection methods, such as long-lasting insecticide-treated nets, N,N-diethyl-1, 3-methylbenzamide/neem oil, and chemical inhibition of feeding, resulted in up to 90% reduction in sandfly density. Control methods based on environmental management strategies included reduction in sandfly breeding sites and interruption of breeding using pheromone.…”