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.

The study was supported by the Special Programme for Research and Training in Tropical Diseases (WHO/TDR) in Geneva, Switzerland. The authors thank Drs S. N. Sharma (National Vector Borne Disease Control Programme, New Delhi), F. H. M. Nurunnabi Chowdhury (Directorate General of Health Services, Dhaka) and G. D. Thakur (Epidemiology and Disease Control Division, Kathmandu, Nepal) for their continuous support and advice. They are also very grateful to Dr N. Rao (Indian Institute of Chemical Technology, Hyderabad) for analysis of the filter‐paper samples, and the staff of the Centre Wallon de Recherches Agronomiques (Gembloux, Belgium) for the validation of chemical tests. Important co‐workers in the study teams at the Rajendra Memorial Research Institute of Medical Sciences (N. Kumar Sinha, M. Prasad, S. A. Khan and S. Kumar), Tribhuvan University’s Institute of Medicine (Professor C. K. Gurung, K. Raj Pant and S. Raj Adhikari), B. P. Koirala Institute of Health Sciences (Professor S. Rijal and L. Roy), the Bangladeshi National Institute of Preventive and Social Medicine (N. Maheswary and S. Faria), and the International Centre for Diarrhoeal Disease Research (S. Alam) are also thanked. Finally, the authors are grateful to the populations in the study villages, for their patience and support in many research activities.