BUSIA, Kenya — Along hundreds of miles of Lake Victoria’s shoreline in Kenya, a squadron of young scientists and an army of volunteers are waging an all-out war on a creature that threatens the health of more people than any other on earth: the mosquito.

They are testing new insecticides and ingenious new ways to deliver them. They are peering in windows at night, watching for the mosquitoes that home in on sleeping people. They are collecting blood — from babies, from moto-taxi drivers, from goat herders and from their goats — to track the parasites the mosquitoes carry.

But Eric Ochomo, the entomologist leading this effort on the front lines of global public health, stood recently in the swampy grass, laptop in hand, and acknowledged a grim reality: “It seems as though the mosquitoes are winning.”

Less than a decade ago, it was the humans who appeared to have gained the clear edge in the fight — more than a century old — against the mosquito. But over the past few years, that progress has reversed.

The insecticides used since the 1970s, to spray in houses and on bed nets to protect sleeping children, have become less effective as mosquitoes have evolved to survive them. After declining to a historic low in 2015, malaria cases and deaths are rising.

Climate change has brought mosquitoes carrying viruses that cause dengue and chikungunya, excruciating and sometimes deadly fevers, to places where they have never been found before. Once a purely tropical disease, dengue is now being transmitted in Florida and France. This summer, the United States saw its first locally transmitted cases of malaria in 20 years, with nine cases reported in Texas, Florida and Maryland.

“The situation has become challenging in new ways in places that have historically had these mosquitoes, and also at the same time other places are going to face new threats because of climate and environmental factors,” Ochomo said.

Scientists around the world are pressing hard for new solutions, including novel technologies that Ochomo is testing. They have developed some promising approaches, including a new generation of tools that modifies mosquitoes biologically and genetically to block disease.

But such efforts have been stymied by cost and regulatory hurdles. The process for getting any of these tools to the places where children fall ill with each new season of rain involves years of testing and regulatory reviews that are slow and underfunded.

“It’s just ridiculous how much time we are wasting before we can get into the field and actually start saving lives,” said Bart Knols, a Dutch vector biologist who runs mosquito-borne disease elimination projects across Africa, Asia and the Caribbean.