A new study by RGHI partner Erasmus MC has revealed that indoor residual spraying (IRS) with insecticides has been instrumental in curbing the spread of visceral leishmaniasis in India by significantly reducing the population of sandflies responsible for transmitting the disease.
Visceral leishmaniasis, known locally as kala-azar, remains a major cause of morbidity and mortality in India and has long been a target of public health initiatives. It is a severe parasitic disease caused by Leishmania parasites, which are transmitted through the bites of infected female sandflies. It primarily affects the internal organs like the spleen, liver, and bone marrow, leading to serious health complications if left untreated.
This study is the first to quantify the long-term impact of IRS interventions on sandfly populations and disease transmission in India. Published in Lancet Infectious Diseases, is the most comprehensive of its kind. It was carried out by RGHI member Luc Coffeng at Erasmus MC Rotterdam, in collaboration with the Liverpool School of Tropical Medicine and the All India Institute of Medical Science Patna.
The researchers demonstrate that large-scale IRS with the insecticide alphacypermethrin reduced the abundance of sandflies by 27%. The study also confirmed that a village-wide IRS response to newly detected cases of visceral leishmaniasis could reduce the number new cases by up to 40%. These findings are based on a comprehensive dataset collected from 50 villages across eight endemic regions in India over ten years. It includes unique entomological, epidemiological, and operational indicators, providing a robust foundation for evaluating the effectiveness of vector control measures.
Despite the success of IRS, the study also highlights the need for ongoing vigilance and adaptation of vector control strategies (methods used to reduce or eliminate the populations of organisms that transmit diseases to humans). Notably, operational research in 2013 identified resistance to existing pesticides, prompting a switch to alpha-cypermethrin, a fast-acting insecticide, causing paralysis and death by disrupting the nervous system of insects. This shows that while Indoor Residual Spraying remains a vital tool, its effectiveness must be continually assessed alongside improvements in disease detection and treatment.
With over 70% of India’s visceral leishmaniasis elimination budget allocated to vector-control activities, the research provides critical evidence to guide future public health strategies as part of a broader, integrated approach to disease elimination.
About the Author
Dr. Luc Coffeng is infectious disease modeler and epidemiologist with a medical background (MD). Luc’s research mainly focuses on informing global guidelines and policy for the control of neglected tropical diseases (NTDs) such as soil-transmitted helminths, onchocerciasis, lymphatic filariasis, and visceral leishmaniasis. He is an active member of several international consortia (NTD Modelling Consortium, CENTD) and has held international fellowship positions (University of Washington, Australian National University, University of New South Wales). Luc further acts as a consultant on applied statistics, modelling, and study design and is a member of the WHO Diagnostic Technical Advisory Committee on neglected tropical diseases.
- More information
Read the full article about visceral leishmaniasis in India.
