The Zika virus is carried by Aedes aegypti mosquitoes. From the moment they arrived in the Americas on African slave ships, misery accompanied them: Wherever they appeared, disease followed. The breed likes warm, wet weather, and soon populated the entire midriff of the Western Hemisphere, from northern Argentina to the American south.

Aedes aegypti is not the only species to carry the disease, but it is likely the most efficient: It happily takes up residence in human dwellings, biting many people in a row. If it feeds on a sick person, the disease incubates in its belly, then migrates to its salivary glands. It is injected at the next bite.

Once a female has drunk enough blood, she seeks still water. She lays her eggs at water’s edge; the eggs stick to the container’s wet walls. Within days, they hatch into wormy larvae, which grow into spermy pupae, which sprout wings and fly away.

An estimated 80 percent of Aedes aegypti mosquitoes breed in water tanks.

Until recently, the two diseases associated with the Aedes were yellow fever and dengue. Now it brings new plagues: Zika and chikungunya. Both diseases were confined to the Eastern Hemisphere, but recently — no one knows precisely how — migrated to the West. In December 2013, chikungunya was found in the Caribbean. In May 2015, Zika virus was identified in Brazil. Industrious Aedes have since helped them spread.

The crisis has been met with ingenuity and urgency: The Zika virus now occupies petri dishes around the world, genetically modified mosquitoes have been released and vaccines have been fast-tracked.

The classic tools of mosquito eradication have also been deployed: Space-suited fumigation teams mist whole towns with pesticides. Merchants have made small fortunes selling bug spray. In Brazil, pervasive billboards and TV ads illustrate the art of avoiding mosquitoes.

Once upon a time, such tools worked. After World War II, Brazil’s military dictatorship crusaded against Aedes with the toxic pesticide DDT. In 1958, Brazil announced it had killed the last one. But as surveillance weakened and DDT was banned in most countries, the mosquitoes slipped back in, their eggs hitching rides in the puddled corners of container ships or the watery belly of a truck’s spare tire. Upon arrival, they found plenty of breeding sites.

As the mosquitoes returned, so did disease. After six dengue-free decades, Brazil had its first outbreak in 1981. The situation has deteriorated: Last year, 1.6 million people in Brazil were diagnosed with dengue, more than ever before. Chikungunya and Zika have infected hundreds of thousands more.

This time around, Brazil’s chief defense against mosquitoes isn’t pesticides. It’s people like George Wallenberg.

Biologist George Wallenberg conducts door-to-door inspections in the neighborhood of Alto José Bonifácio, where there are more mosquitoes than anywhere else in the city of Recife.

George, a 30-year-old biologist with an air of calm competence, is one of 46,500 environmental workers who engage in door-to-door combat with mosquitoes year round. Early this year, their ranks were supplemented by 220,000 soldiers — reported to be the largest military deployment in Brazil’s history — and another quarter-million community health workers. Teams were deployed to Brazil’s most disease-ridden cities, including Recife, which at 3.7 million is also one of the country’s largest metropolitan areas.

George wields two weapons against his tiny enemy: A canister of powdered larvicide, which, when sprinkled into standing water, kills baby mosquitoes, and a stack of educational leaflets. Each has its flaws: The larvicide only lasts a few weeks. The leaflets only help people who read.

So he talks his way through people’s front doors and then schools them on mosquito abatement. He scrutinizes their property for places a homemaking mosquito could lay her eggs: The crumpled can in a bush. The tray under a houseplant. A water tank with its lid ajar.

Every two months, George and his colleagues pause to assess their work. For each of Recife’s 94 neighborhoods, they calculate the percentage of homes where they found mosquito larvae. The more larvae, the higher the neighborhood ranks on the city’s mosquito index.

In the past two years, the neighborhood of Alto José Bonifácio, where Adriana lives, has regularly ranked highest.

Alto José

Bonifácio Recife Alto José Bonifácio Recife, Brazil Income One of the poorest neighborhoods in Recife, Brazil. Water Access Intermittent running water, houses need to store water. Mosquito Index 6.2 The highest mosquito index in the city.

Door-to-door work has counteracted the momentum of an outbreak before. Recife’s health secretary, Dr. Jailson Correia, said that the last time soldiers were called to bolster the city’s door-to-door efforts, in a 2015 fight against dengue, new cases of illness did not halt, but they did slow. Which is a lot better than nothing, he said.

So in early March, George and his team spent several days knocking on doors in Alto José Bonifácio. One morning their knock was answered by Crislene Feitosa, mother of three. Her doctors say her youngest, 10-month-old Jayane, was one of Recife’s first cases of Zika-related microcephaly.

Jayane was born in May 2015 — months before the surge in microcephaly cases was flagged by health officials. Crislene has remained skeptical that Zika caused the disorder because she had no symptoms during her pregnancy. But Jayane’s doctor, Dr. Ana van der Linden, noted that 80 percent of Zika cases are asymptomatic, and that Jayane’s brain malformations are identical to those seen in Zika-related cases.

Crislene Feitosa was told her daughter, Jayane, had microcephaly shortly after she was born. Doctors predict Jayane will have impaired sight, decreased mobility and cognitive abilities, and will need care for the rest of her life.

George wandered through Crislene’s home, inquiring about her habits: If she uses repellant; whether her yard collects garbage; how often she takes her kids to the doctor. She answered confidently: She keeps a repellant dispenser in her children’s room; she cleaned the yard just last week; she takes Jayane to at least two appointments a week.

When George asked where Crislene stores the family’s water, she led him to a plastic barrel in the kitchen pantry. He pointed to a slit between the tank and the lid. “They can get through this crack here,” he said. “My husband puts the lid on upside-down,” she said, flipping it over. George peered closer. “That’s worse,” he said.

George pulled out his clipboard and began lecturing: Every time you use water, immediately replace the lid. Check regularly for mosquito eggs. Once a week, empty the barrel and scrub it.

Later, sitting on her stoop, Crislene said none of his advice was new to her. “What he told us to do, I already do.”

Her husband, 26-year-old Wellington Santana da Silva, sometimes laughs at the futility of their efforts. “We use repellant, we protect ourselves,” he insisted. “They go away, but then they come back. When you kill one, there’s 10 more.”