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.

Keywords: DDT; IRS; India; elimination; leishmaniasis.

Fig. 1.

Map of the Indian subcontinent showing VL-endemic countries. VL-endemic countries are labeled. (Inset) Eight study districts in Bihar, where 1 = Paschim Champaran, 2 = Gopalganj, 3 = Purbi Champaran, 4 = Patna, 5 = Samastipur, 6 = Begusarai, 7 = Khagaria, and 8 = Saharsa. Smaller divisions within districts indicate study PHC boundaries; green indicates PHCs where only IRS QA was performed, and red indicates PHCs where IRS QA and entomological assessments were performed.

Fig. 2.

Average DDT concentrations on walls, per household, following the first round of IRS in 2014. DDT concentrations on walls in 560 households, using average household results. The orange line represents the upper limit of in-target quantification (1.2 g ai/m²), and the red line represents the lower limit of in-target quantification (0.8 g ai/m²). Bostik tape discs were used to remove the insecticide from walls, and all samples were measured using HPLC.

Fig. 3.

Trends in insecticide resistance in Bihar State, 1978–2014. Combined historical and current data show insecticide resistance to 4% DDT, 5% malathion, and 0.05% deltamethrin WHO-impregnated papers in P. argentipes. Red diamonds represent DDT susceptibility, green diamonds represent malathion, and blue squares represent deltamethrin. There is a general trend of decreasing susceptibility to DDT.