The surge in Delhi of Culex mosquitoes is being introduced at a moment when health authorities are celebrating notable successes against Anopheles mosquitoes. While those gains have saved lives, the situation, mosquito experts say, is complicated: The very changes that have reduced Anopheles’ numbers may be allowing other species to thrive. In an ever-changing climate, the mosquitoes are finding new ways to thrive, particularly in urban environments.
Over the past few decades, malaria’s global footprints have diminished, thanks in part to interventions such as mosquito nets and insecticides used to target Anopheles. These interventions were implemented in India by the National Center for Vector Borne Diseases Control, a government agency. The program’s efforts helped dramatically reduce malaria deaths in recent years.
Vas Dev is a retired official from the government who spent nearly 30 years working in northeast India for the ICMR. He said that although deforestation may have helped to reduce India’s malaria rate, it was also a costly decision. Urbanization has led to more mosquito habitats for the mosquito genus Culex, which transmits Zika and dengue. Dengue spread rapidly in the poorest countries since 1970 and has killed thousands every year.
Scientists work to understand the impact of climate change on mosquito populations. The climate change that has occurred in Delhi already extends the breeding season. It brings temperatures higher to areas previously too cool to reproduce. The mosquito population has been fueled by untimely rainfalls, which have increased humidity and created standing water. Dhiman said that areas once experiencing a 1-month-long mosquito season now have seasons lasting six to eight more months.
It is known that the insects can adapt rapidly to changing environments. Anopheles mosquitoes provide an interesting example, said Karthikeyan Chandrasegaran, a postdoctoral researcher at Virginia Tech who has expertise in evolutionary ecology and mosquito biology. Public health organisations working in sub-Saharan Africa purchased bed nets because the malaria-transmitting insects bite between dusk- and dawn. Although these measures were effective initially, the number of cases increased within 10 years. It turned out the mosquitoes were feeding in the early morning—after people had gotten out of bed. The resistance of mosquitoes to insecticides is also possible.
Chandrasegaran said that city dwellers will likely suffer the most from any problem. The insects thrive on poor waste management and lack of sanitation. In some cities like Delhi, water is scarce. This has made it possible for residents to keep a lot of supplies and use them as breeding areas. Rural areas are more vulnerable to these conditions, as they have higher numbers of predators like certain fishes and frogs.
However, rural areas face many challenges as well, such as a lack of infrastructure or awareness regarding vector-borne illnesses and limited healthcare. “So, you’ll have to probably tailor your solution differently to urban areas, tailor your solution differently to suburban areas, rural areas, forested areas,” said Chandrasegaran. “If you do not identify the pain points exactly, you are going to spend a lot of time and effort and money trying to implement one scheme across the entire country, which is going to waste a lot of things.”