The Indian and Nepalese programmes of indoor residual spraying for the elimination of visceral leishmaniasis: performance and effectiveness

Abstract

Although, when applied under controlled conditions in India and Nepal, indoor residual spraying (IRS) has been found to reduce sandfly densities significantly, it is not known if IRS will be as effective when applied generally in these countries, via the national programmes for the elimination of visceral leishmaniasis. The potential benefits and limitations of national IRS programmes for the control of sandflies were therefore evaluated in the districts of Vaishali (in the Indian state of Bihar), Sarlahi (in Nepal) and Sunsari (also in Nepal). The use of technical guidelines, levels of knowledge and skills related to spraying operations, insecticide bio-availability on the sprayed surfaces, concentrations of the insecticide on the walls of sprayed houses, insecticide resistance, and the effectiveness of spraying, in terms of reducing sandfly densities within sprayed houses (compared with those found in unsprayed sentinel houses or control villages) were all explored. It was observed that IRS programme managers, at district and subdistrict levels in India and Nepal, used the relevant technical guidelines and were familiar with the procedures for IRS operation. The performance of the spraying activities, however, showed important deficiencies. The results of bio-assays and the chemical analysis of samples from sprayed walls indicated substandard spraying and suboptimal concentrations of insecticide on sprayed surfaces. This was particularly obvious at one of the Nepali study sites (Sunsari district), where no significant vector reduction was achieved. Sandfly resistance to the insecticide used in India (DDT) was widespread but the potential vectors in Nepal remained very susceptible towards a pyrethroid similar to the one used there. The overall short-term effectiveness of IRS was found to be satisfactory in two of the three study sites (in terms of reduction in the densities of the sandfly vectors). Unfortunately, the medium-term evaluation, conducted 5 months after spraying, was probably made invalid by flooding or lime plastering in the study areas. Preparation for, and the monitoring of, the IRS operations against sandfly populations in India and Nepal need to be improved.Human visceral leishmaniasis (VL) or kalaazar, an often fatal disease if untreated, is usually caused by the parasite Leishmania

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

“…Chowdhury et al [49] while reviewing the performance of IRS in India and Nepal in the context of VL elimination found that after two weeks, four weeks and 5–6 months of DDT spraying in India (Vaishali district) and Nepal (Sunsari district), the percentage mortality of P. argentipes in cone bioassay on wall surfaces revealed 70 versus 100 %, 50 versus 55 % and 20 versus 25 % mortality in India and Nepal respectively.…”

Progress in the Mathematical Modelling of Visceral Leishmaniasis

“…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.…”

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

“…Given that effective prevention through vector control and rapid diagnosis and treatment methodologies exist (7,16), elimination of VL in this region should therefore be technically feasible. However, in order for the predicted outcomes of IRS to become a reality, the IRS itself must be of sufficient quality to achieve an impact (17,18).…”