Every weekday at 7 a.m., a van drives slowly through the southeastern Brazilian city of Piracicaba carrying a precious cargo — mosquitoes. More than 100,000 of them are dumped from plastic containers out the van's window, and they fly off to find mates.
But these are not ordinary mosquitoes. They have been genetically engineered to pass a lethal gene to their offspring, which die before they can reach adulthood. In small tests, this approach has lowered mosquito populations by 80 percent or more.
The biotech bugs could become one of the newest weapons in the perennial battle between humans and mosquitoes, which kill hundreds of thousands of people a year by transmitting malaria, dengue fever and other devastating diseases and have been called the deadliest animal in the world.
"When it comes to killing humans, no other animal even comes close," Bill Gates, whose foundation fights disease globally, has written.
The battle has become more pressing by what the World Health Organization calls the "explosive" spread of the mosquito-borne Zika virus through Brazil and other parts of Latin America.
Experts say that new methods are needed because the standard practices — using insecticides and removing the standing water where mosquitoes breed — have not proved sufficient.
"After 30 years of this kind of fight, we had more than 2 million cases of dengue last year in Brazil," said Dr. Artur Timerman, an infectious disease expert in Sao Paulo. "New approaches are critically necessary."
But the new efforts have yet to be proved, and it would take some years to scale them up to a meaningful level. An alternative to mosquito control, a vaccine against Zika, is not expected to be available soon.
So for now, experts say, the best modes of prevention are to intensify use of the older methods of mosquito control and to lower the risk of being bitten using repellents and by wearing long sleeves.
Women are being advised to not get pregnant and to avoid infested areas if pregnant, since the virus is strongly suspected of causing babies to be born with abnormally small heads and damaged brains.
One old method that is not getting serious attention would be to use DDT, a pesticide that is banned in many countries because of the ecological damage documented in the 1962 book Silent Spring. Still, it is being mentioned a bit, and some experts defend its use for disease control.
"That concern about DDT has to be reconsidered in the public health context," said Dr. Lyle Petersen, director of the division of vector-borne diseases at the federal Centers for Disease Control and Prevention. He said the damage to fish and wildlife stemmed from widespread outdoor use of DDT in agriculture, not the use of small amounts on walls inside homes to kill mosquitoes.
Other experts say the old methods can work if applied diligently.