When my colleague Stephanie Nolen began working on an article earlier this year about new technologies to fight mosquito-borne diseases, she assumed she would be writing a story of continued progress.

For much of the past two decades, those diseases have been receding, thanks to mosquito nets, insecticides and billions of dollars of funding from governments and philanthropies. Between 2000 and 2019, for example, global malaria deaths fell more than a third.

“But it only took a couple of calls to realize that there was way more going on in the world of mosquitoes than I had realized,” Stephanie told me this week. “I was a bit taken aback, as a global health reporter who has been writing about malaria for 25 years, to realize that the common public narrative of a straightforward trajectory of progress against the disease is inaccurate.”

Over the past year, she has traveled to six countries, studied data, waded through swamps in Kenya, crawled into goat sheds in Ethiopia and learned how to suck a mosquito into a glass vial — as researchers do so they can study it alive. The result is a series of alarming stories that The Times published this morning.

The mosquito already kills more people every year than any other creature does, and the toll is rising. Malaria deaths rose about 8 percent between 2019 and 2021, the first increases in decades.

Two big causes

The toll is rising for two main reasons. First, mosquitoes have evolved to elude strategies that were once working against them. The increasing use of bed nets has led to a decline in the population of mosquitoes that tend to live indoors — but mosquitoes that thrive outdoors have increased in number, and bed nets can’t fight them so easily. Mosquitoes have also evolved to become more resistant to current insecticides.

Second, climate change has expanded the areas where the weather is warm enough for the most dangerous species of mosquitoes — those that carry deadly diseases — to thrive. Dengue, which used to be a purely tropical disease, has moved into Florida and France. This past summer, a small number of malaria cases spread in Texas, Florida and Maryland, the first local transmissions of the disease in the U.S. in 20 years.

“It seems as though the mosquitoes are winning,” Eric Ochomo, a mosquito-fighting scientist in Kenya, told Stephanie.

One problem, many experts believe, is that the World Health Organization and other regulators are slow to approve new insecticides and other preventive measures. These agencies typically wait for years of evidence to accumulate before approving new mitigation strategies, but people are dying in the meantime. The situation reminds me of the C.D.C.’s struggles to provide timely, clear help during the Covid pandemic, be it with masks, tests or behavioral guidance. Public health crises don’t operate on the same timetable as academic journals.

You can read Stephanie’s overview here — as well as a second story about a new malaria-carrying mosquito that’s threatening some of Africa’s largest cities.

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