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OS PATIOS, Colombia — A stroll down two blocks of Avenida 1e here shows just how hard it will be for the world to catch up to the Zika virus.

Families keep open basins of water in their backyards for laundry. They stash water tanks on top of their homes. Both are perfect breeding sites for the mosquitoes that transmit the virus. Bits of trash on an empty lot also collect standing water — and mosquito eggs bloom in the soggy nooks.

Nearly every resident up and down this stretch of rural road believes they have been infected with Zika or another mosquito-borne illness, such as dengue or chikungunya. Yet few have gone to a doctor to have the diagnosis confirmed.

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These two blocks serve as a microcosm of the challenges that researchers and global health officials face in trying to arrest the spread of the Aedes aegypti, the mosquito that carries Zika and that thrives in just this type of environment. A day here on Avenida 1e sheds light on why Zika has been able to travel so quickly through most of Latin America and the Caribbean — and why the disease is so hard to track.

As the morning heat on a recent day marched into the 90s, with humidity to match, windows and doors were flung wide open to catch any hint of a breeze. There were no screens to block the insects.

“If I’m in the living room, the mosquitoes are there,” said Martha Sanchez, 41, who lives on Avenida 1e, a rural road in this hilly city in northeast Colombia. She pointed out the many mosquito bites dotting her 3-year-old grandson’s leg, the red dots like pushpins on a map.

“There are lots of mosquitoes in the dining room,” her 8-year-old granddaughter, Nicole Ordoñez Jaimes, chimed in.

Colombian Town Zika
Martha Sanchez looks at mosquito bites on her grandson, Santiago Zamudia Jaimes Dania Maxwell for STAT

Zika has hit harder in this region by the Venezuelan border than in any other part of the country.

But getting treatment means trekking to a clinic in the heart of Los Patios or the hospital in the nearby city of Cúcuta. That requires paying for a motorcycle ride or a taxi. And to see a doctor at the hospital, you have to travel there in person just to make an appointment — then return a few days later to see the doctor.

So most locals simply rely on their tried-and-true cure-all: acetaminophen.

“The powerful acetaminophen,” John Mejia, 26, called it.

Are you at risk for contracting Zika virus? Your level of risk depends in part on your living conditions. Alex Hogan/STAT

Zika, in particular, often brings mild enough symptoms — headache, fever, rash — that most locals have not seen any need to see a doctor or get an official diagnosis. And an estimated 80 percent of Zika infections don’t cause any symptoms at all.

That makes it all the harder for disease detectives to track the spread of Zika, predict its path, or monitor any related health problems. As a result, firm facts about the virus are sparse.

Colombian health officials have identified 25,000 cases of Zika in the country so far, but experts say that figure is likely way too low.

Meanwhile, scientists have not yet confirmed (though they strongly suspect) the most potent fears about Zika — that it can cause a temporary paralysis called Guillain-Barré syndrome and that it can lead to birth defects if a woman is infected during her pregnancy. Urgent investigations are underway to learn more.

But locals don’t focus so much on those global questions.

Here on Avenida 1e, they’re just trying to figure out how to get rid of all the mosquitoes.

There’s a huge puddle that stretches across the entire road, forcing cars, motorcycles, and bicycles to slow down and hug the uphill side of the street when passing. Residents said the puddle — which some refer to as “el lago,” or the lake — has been there for years, never disappearing no matter how dry the weather. One resident joked the puddle is so big and permanent you could put ducks in it.

Turns out, though, the lake isn’t really the problem. The Aedes aegypti mosquitoes prefer to breed in tree holes, man-made basins, and pools of water that collect in trash. They can make a breeding ground out of even an overturned plastic bottle cap. Their eggs can survive for months clinging to the surfaces, waiting for the water to cover them and then hatching into larvae that live and feed in the water.

Grecia Quintero, 32, who believes the rash and headaches she experienced last month came from Zika, scrubs the walls of her outdoor water basin more regularly now, trying to wipe out the eggs before they hatch.

She also has another strategy to avoid bites: shaking out the clothes in her closet before she changes. She said she has seen mosquitos fly out from items she was just about to put on.

“They like dark places,” she said.

Residents have also tried to cover their water tanks. Some have hung netting inside their homes.

Francisco Gutierrez, 49, who works at a local tire repair shop, said he changes the water in a barrel inside his open-air workshop two or three times a week to kill the mosquito larvae and pupae that live in it.

Colombian Town Zika
Francisco Gutierrez checks tires for holes with a tank of water in his shop on Avenida 1e. He frequently drizzles gasoline into the water to kill larvae. Dania Maxwell for STAT

On a recent morning, tiny, dark larvae could be seen along the surface of the water. But it wasn’t clear if they were alive or dead, especially after Gutierrez grabbed a squeeze bottle and doused them with gasoline, the fuel glistening on the surface of the water and casting a shimmering reflection off the small shop’s corrugated metal roof.

Outside the open-air workshop stood a tower of tires, which offer a shady cache for mosquitoes to breed. Gutierrez said he brought the tires inside when it rained, so as not to create more pools of standing water. “It’s the mosquitoes’ home,” he said.

Sanchez, the grandmother, has her own methods of insect control. She heats eucalyptus in a pot and carries it through her home, washing the walls and doorways with smoke. (Unlike an insecticide, the smoke won’t kill the mosquitoes, but it might provide some repellent power, experts say.)

Yet none of these methods seem to have halted the mosquitoes.

Standing in her backyard, not far from a basin filled with a few inches of water, Sanchez started to describe the many mosquito-borne illnesses she and her family had contracted. She was interrupted by a mosquito landing on her left thigh.

Smack.

She slapped her leg, the squashed bloodsucker sticking to her hand as she pulled it away. “I killed it,” she said.

Back to her story: She suspected that everyone in the household, except her husband, Ernesto Jaimes, has had cases of Zika. But it’s not like Jaimes had escaped unscathed.

“He is the only one who has not had Zika,” Sanchez said, “but he’s had dengue and chikungunya.”

Zika virus, which can be transmitted by mosquitoes, has exploded onto the world stage. Alex Hogan/STAT

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