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New Delhi, August 11, 2024 – Spraying insecticide inside homes in Indian villages has been found to significantly reduce the population of sandflies, the vectors responsible for spreading visceral leishmaniasis, also known as kala-azar. According to a new study published in The Lancet Infectious Diseases, this intervention led to a 27% reduction in sandfly numbers between 2016 and 2022, while the spread of the disease could potentially be reduced by 6-40%.
The study, which included researchers from CARE India and All India Institute of Medical Sciences, Patna, focused on the effects of the insecticide alpha-cypermethrin when used in homes where visceral leishmaniasis cases were detected. Alpha-cypermethrin, an insecticide commonly used on crops such as cotton, cereals, and soybeans, was introduced into homes as part of an elimination program first initiated in 2015.
The international research team surveyed 900 homes across 50 villages in the Indian states of Bihar, Jharkhand, and West Bengal—regions where visceral leishmaniasis is endemic. The study highlights that indoor spraying of insecticides was encouraged as a key component of the kala-azar elimination strategy.
Visceral leishmaniasis is a severe vector-borne disease caused by infection with Leishmania parasites, which are transmitted through the bites of phlebotomine sandflies. The disease primarily affects internal organs such as the liver, bone marrow, and spleen. Common symptoms include irregular bouts of fever, weight loss, and anemia, and if left untreated, the condition can be fatal. The World Health Organization (WHO) notes that most cases of visceral leishmaniasis occur in Brazil, East Africa, and India.
The study also brought attention to the economic burden of kala-azar control. The cost of indoor spraying for visceral leishmaniasis accounts for 12.5% of the expenses directed at controlling vector-borne diseases in India, second only to malaria, which consumes 76% of the budget. Despite this substantial investment, the study’s authors emphasized that there is limited strong evidence supporting the cost-effectiveness of indoor insecticide spraying in reducing disease case numbers. Previous research in this area has largely relied on observational surveillance studies and circumstantial evidence.
For their analysis, the researchers utilized three datasets. The first dataset tracked sandfly numbers in the homes included in the study, with data collected biweekly from 2017 to 2022 using light traps provided by the U.S. Centers for Disease Control and Prevention (CDC). The traps captured nearly 230,000 sandflies. The second dataset contained quality-assurance data related to the indoor insecticide spraying, while the third dataset comprised monthly surveillance data on visceral leishmaniasis cases from January 2013 to December 2021, sourced from India’s Kala-Azar Management Information System (KAMIS).
“Our analysis suggested that, across the 11 villages in four blocks (of Bihar) in which indoor spraying was started or stopped during the study period, the activity was associated with an overall reduction in sandfly abundance of 27%,” the study authors reported.
The researchers’ model predicted that three years of indoor insecticide spraying would not only reduce sandfly numbers but also result in an earlier and stronger decline in new cases of visceral leishmaniasis and related deaths. Specifically, the model suggested that a 30% reduction in vector abundance due to indoor spraying could lead to a 17% reduction in the total number of new cases and a 9% reduction in visceral leishmaniasis-related deaths over the three-year period.
The findings underscore the importance of targeted vector control strategies in reducing the burden of visceral leishmaniasis in endemic regions. While challenges remain in assessing the cost-effectiveness of such interventions, the study provides valuable insights into the potential impact of indoor insecticide spraying on controlling this life-threatening disease.
