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Why the Capital of India Is Flush with Mosquitoes

City residents have long resorted to low-cost, do-it-yourself remedies that may be harmful to human health.

As the sun began to set on Delhi, 45-year-old Rani hiked up her salwar pants, squatted next to the iron pan just outside her home, and lit a match. Plastic grocery bags were the first items to catch fire. Soon the cow-dung cakes ignited, their chocolate-brown edges glowing in the dusk. Rani coughed as smoke rose from the pan.

According to a recent survey conducted by the South Delhi Municipal Corporation, Delhi’s mosquito density was almost nine times higher than normal this past March and April, a 50 percent increase over the previous year. Yet local authorities did not mount a vigorous response because the insects belonged to the Culex genus, which is not known to transmit the well-known diseases — malaria, dengue, chikungunya — that are at the forefront of India’s public health initiatives.

When it comes to malaria, in particular, India has achieved success in reducing the disease. But even as malaria deaths are on the decline, the sheer number of mosquitoes, particularly in urban areas, has shot up. This is partly due to climate change, said Ramesh C Dhiman, an expert in malaria epidemiology who spent three decades as a government researcher at the Indian Council of Medical Research before becoming an independent consultant. Mosquito populations are on the rise in other countries, too, fueled not just by climate change, but by increased urbanization and the decay of residual DDT in the environment.

A spokesperson for Delhi’s municipal government told Undark that the local government has taken a number of actions to combat the problem.

These measures were temporary and did not address the severity of the issue, said a Delhi public health official, who asked not to be named for fear of retribution from his employer.

The mosquitoes in Rani’s neighborhood are so insufferable that children and adults struggle to sleep through the night. While not yet much of a problem in Delhi, residents could also face some risk of diseases that are transmitted by Culex mosquitoes, including West Nile and Japanese encephalitis. According to experts, this risk may increase as mosquitoes evolve in response to changing climatic conditions. For the moment, low-cost do-it-yourself remedies like smoke and insecticides offer some measure of relief. But researchers note that these approaches pose a risk to human health and fail to address the underlying problems that allowed the mosquitoes to flourish in the first place.

Delhi’s surge of Culex mosquitoes comes at a time when public health officials are declaring notable victories against other kinds of mosquitoes, including the Anopheles genus that transmits malaria. 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. And amid a changing climate, mosquitoes have found new niches to exploit, especially in urban areas.

Over the last few decades, malaria’s global footprints have diminished, thanks in part to interventions such as mosquito nets and insecticides used to target Anopheles. In India, such interventions have been implemented with the help of a government agency called the National Center for Vector Borne Diseases Control. The program’s efforts helped dramatically reduce malaria deaths in recent years.

A retired government official who worked in northeast India at the ICMR for nearly three decades, Vas Dev, said deforestation likely contributed to declining malaria rates in India, but it came at a cost. Increased urbanization creates more habitats for mosquitoes that prefer urban and suburban landscapes, including Culex and Aedes, the mosquito genus that transmits dengue, Zika, and chikungunya. Since 1970, dengue has spread dramatically in poor countries, killing thousands of people each year, mostly children.

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