Kim Conley’s running career stems from a variety of formative experiences in Northern California’s Sonoma County, home to a long and distinguished distance running tradition. (Carlos Javier Ortiz for The Washington Post)

It’s Wednesday, so Kim Conley will run 11 miles, pretty much like any other day, except that on Wednesdays, she runs depleted — meaning she’s eaten exactly nothing. The idea is to be tough, reach down, push herself even harder than every other day.

She chews up the miles along the American River in Sacramento to keep shaving off seconds to keep getting closer to Rio. Conley, 30, has been running toward this summer’s Olympic Games for nearly a decade. But she’d also like to have a baby someday.

Two things stand between Conley and what could well be her last chance to win an Olympic medal. One is the clock, and she knows she can beat it. She’s lopped seconds off her time every year since she started running seriously. The other is a blood-sucking critter named Aedes, a globe-trotting mosquito with a world-class bite.

Zika is the latest battle in a long war between humans and mosquitoes

By the millions, Aedes skeeters are feeding on people who carry an unpredictable virus named Zika, then flitting over to their next victim, chomping down and spreading the disease. The bug’s bites have transmitted the virus to people in more than 20 countries: to pregnant mothers, with devastating consequences for their unborn children; to thousands of other people, who end up with fairly minor aches; and quite possibly this summer, to the best athletes in the world, gathered in one vulnerable place, wearing very little clothing.

The scramble to solve the Zika puzzle requires scientists to figure out exactly what threat a hardy breed of mosquitoes poses to people along the virus’s jagged journey. Crossing four continents since the first major outbreak nine years ago, Zika’s painful path now touches an Olympic runner in California, and before her a nurse from Indiana, pregnant women in Colombia, a misshapen infant in Brazil, immunologists in Bethesda, Md., all the way back to the owner of a souvenir shop on a tiny island in the South Pacific, 1,100 miles southeast of the Philippines. The hunt to understand Zika is a race to the very edge of science’s frontier, a race against the ticking clock of myriad pregnancies.

Conley’s passion and training push her to keep running toward Rio, even as a mounting clamor of warnings urge her to consider a detour. On a cool, sunny California morning at the cusp of spring, she can run straight ahead or look instead at the destruction and anxiety that Zika has caused, anguishing expectant mothers from Brazil up into the Caribbean and now even in the United States.

This is the story of Zika’s path so far, from its leading edge today back to its first appearance on a Pacific island in 2007. As the virus’s inexorable march brings it our way, scientists and governments are issuing a stream of strongly worded alerts. The chief of the federal bureaucracy in Washington this month urgently warned government employees to think twice about going to Brazil and other countries where the virus is rampant. The World Health Organization and the U.S. military put out similar warnings. But the U.S. Olympic Committee, buffeted between its desire to give elite athletes their moment  and its responsibility to protect competitors and their fans, has held back, issuing no guidance, announcing only that it will seek counsel from medical advisers.

Conley tries not to think about Zika. Her team — manager, agent, sports psychologist, physiologist, sponsor — is all about confidence: Rio or bust. Conley is a planner. She used to think in units of a school year. Then, preparing to run middle- and long-distance events in the London Olympics four years ago, she learned that elite athletes think in “quads,” four-year cycles leading to the next Games. After Conley failed to get past the qualifying heats in London, she’s spent this quad entirely focused on next steps, to Rio, then Tokyo in 2020, then maybe coaching, or becoming a physical therapist, or having a baby. Zika and pregnancy

Her husband and coach, Drew Wartenburg, thinks shorter term. He’s forever nudging Kim to live in the moment. “I call myself more an actor than a planner,” he says.

The agonizing wait of an expectant mother with Zika: ‘Is my baby okay?’

They haven’t talked much about kids, except that a baby would fit into their lives after Kim finishes running competitively. Then they started hearing about newborns in Brazil with heads that came out too small and pregnant women who felt compelled to consider abortions when they wanted to be preparing to raise a child.

Now, Conley and Wartenburg have to think about it. They’ve talked about whether Conley’s 28-year-old sister, already at the point where she wants a baby, should travel to Rio to watch Kim run. “She’s someone who probably shouldn’t go,” Conley says. “For us, we just have to wait.”

Zika keeps poking its head into their plans. Friends and neighbors keep asking about it. Family, too. “You want them to be excited about your Olympic journey,” Conley says, “and they’re mostly concerned about the Zika virus, and that’s too bad.”

Wartenburg the coach uses the virus as a motivator. “This is about confronting obstacles,” he says. “Part of what makes athletes elite is not letting any obstacle stand in your way.”

Conley glances over at him, eyebrow cocked. It’s not clear she’s buying this as a motivational tool.

Wartenburg the husband tries another tack. “You can’t have thousands of different athletes making thousands of different decisions about ‘Do I wrap myself in mosquito nets, or what?’ That’s not a burden I want. We just have to trust that someone will assess the risk and that their thinking will trickle down to us.”

Conley is quiet. When she speaks, it’s in a small voice: “No one’s said, ‘Don’t go.’ ”

January 2016: A scary mask

Barbara Ihrke went with plenty of mosquito repellent. When Ihrke, a 61-year-old nurse, decided to travel from Indiana to Haiti in January to teach a seminar in transcultural nursing, she’d heard a bit about Zika but hadn’t paid much attention to the news from Brazil.

Despite slathering herself with repellent, Ihrke got a few bites. She thought nothing of it. She came home in late January, feeling fine.

Then, on her fifth day back in Marion, Ind., she got a low-grade headache. She felt tired, her joints swelled, and a rash spread over much of her body, including, for a couple of days, her face.

Zika, it turned out, was already in the Caribbean, and people such as Ihrke were bringing it home with them. Enough cases had popped up in Haiti that the Centers for Disease Control and Prevention called the island nation a place of extreme concern.

Want to avoid Zika? Stay more than a mile above sea level, CDC says

Two days after her symptoms hit, Ihrke, who works as vice president of academic affairs at Indiana Wesleyan University’s nursing school, called her school’s health center and said, “I think I have Zika.” She was matter-of-fact. Trained in tropical medicine, she reacted more calmly than a layman might have.

By the time she got to the clinic an hour later, the staff had printed out fact sheets from the CDC on Zika. Tests showed her white-blood-cell count had dropped by half. She stayed home that weekend and went to work the next Monday wearing a mask — not because she was putting anyone else at risk of infection, but for her own protection, because of her low blood count. What can be done to prevent Zika?

As casually as Ihrke reacted to the virus, those around her were more alarmed, especially during the eight days when she wore the mask. “People took a step back when they saw it,” she says.

When one man pulled away and announced that his wife was pregnant, Ihrke set him straight: “I can’t give this to you, and there are no mosquitoes in Indiana in February.”

That assurance wasn’t enough for some people. Ihrke can’t guarantee that the virus isn’t still active in her bloodstream, and some neighbors have told her they’re afraid to get too close.

Still, Ihrke felt it was important to identify herself as Indiana’s first Zika case, even though state health officials had assured her they’d keep her identity secret. “Part of my calling is to help us react to illnesses, so I decided I should self-identify because I have the ability to explain,” she says.

Ihrke’s professional detachment lets her see that for most victims, Zika is no big deal. Having lived and worked in Africa, she says, “knowing that thousands of people die every day from malaria and now seeing that we’re spending millions of dollars on Zika, well, at times we in the U.S. are not rational about what we decide is scariest. We’ve gone into the Ebola mentality, which is that the sky is falling. We invested so much money in making everybody in America Ebola-prepared, and for what, maybe 10 cases in the U.S.? In a year or two, we’ll hardly remember Zika.”

Less than two weeks after she first felt ill, Ihrke got the all-clear, a call from the health center telling her that her blood count was back to normal.

She’s ready to return to Haiti, proposing to study the incidence of birth defects there in the coming year. But she knows heading into Zika’s lair is not the right choice for some people. “For the Olympic athletes, it’s hard,” Ihrke says. “Anyone who wanted to be pregnant, I’d say, ‘Are you certain this is what you want to do?’ ”

November 2015: ‘I was five months pregnant’

Two Colombian teenagers, both eight months pregnant, stand outside a health clinic in Cartagena, waiting to know what Zika has done to their babies.

“You got it, too?” Yisleth Luna Cardenas, 18, asks Darley Martinez Cabarcas, who is 17.

“When I was five months pregnant,” Darley says, recalling the headaches and fever she had in November. “I see the news. I see the babies being born with big problems. Aren’t you worried?”

Yisleth dealt with Zika anxiety by focusing not on possible birth defects, but on delivering her first baby: “Will it be a Caesarean section? How painful will the labor be?”

Darley cracks a smile, enjoying a rare shared moment in what she calls the “solitude of being pregnant with Zika.”

“I know everyone is worried — men, too — but so much falls to the women,” she says. “We carry the babies, and then we will raise the babies.” A pause. “My boyfriend wanted me to abort.”

A Catholic, Darley says it is wrong to have an abortion. She is no longer in touch with the baby’s father.

Now, in March, she waits. She knows the virus has been linked to severe birth defects, including microcephaly, the interrupted development of the skull that leads to abnormally small heads and brain damage. The virus has been active in Colombia long enough to have infected thousands of pregnant women, but not yet long enough to reveal whether the defects that have become rampant in Brazil will happen here. What is microcephaly?

Zika’s aches subside quickly; the real pain sets in when the women are strong enough to start worrying about what the virus may have done to the baby inside them. “It’s a lonely time,” Darley says. Being pregnant with Zika is not something you can talk to your mother about, because it’s so new. “I can’t wait to have the baby in my arms, to see with my own eyes that he is okay.”

At the Juan Felipe Gomez Escobar Foundation, a nonprofit serving low-income, teenage mothers, Darley and Yisleth attend job skill classes and get sonograms.

The scans show no sign of microcephaly. But the doctors also say that developmental and neurological problems linked to Zika might not show up on a scan.

Darley goes home to wait with her mother, sister and grandmother — her father no longer lives with the family. “Women have it hard,” she says.

October 2015: A tiny skull

While Darley and Yisleth wait, Zika’s impact is already clear 3,000 miles to the southeast, where a mother and a physical therapist try to soothe an agitated, bent baby boy named Arthur. The therapist places Arthur face-down on a yellow exercise ball. He immediately begins to cry. The way his 5-month-old body is shaped, shoulders hunched, arms and legs perpetually bent and clenched — typical for microcephalic babies — doing anything on his stomach feels uncomfortable.

The therapist rubs his back while his mother, Rozilene Ferreira de Mesquita, puts a pacifier in his mouth.

“Calm down,” she whispers.

Arthur has appointments lined up for visual testing, motor-skill development and auditory stimulation at the Altino Ventura Foundation hospital in the Brazilian city of Recife. On Thursdays, dozens of mothers of babies with abnormally small heads gather here for therapy sessions, group talks and one-month birthday celebrations. Of 6,671 suspected microcephaly cases in Brazil, 1,819 of them are in this state, Pernambuco, the highest proportion in the country.

Recife, the ‘ground zero’ of the zika virus

Thousands of parents now spend their days visiting doctors who X-ray, scan, probe, bend and measure their babies to try to understand what Zika has done. Just three days into March, de Mesquita has already filled a piece of notebook paper with 25 doctors’ visits Arthur must make at eight hospitals over the course of the month.

She refuses to miss an appointment. Once her maternity leave ended, she resorted to doctors’ notes to explain her absence from work. She expects to lose her job. Then the family will subsist on her husband’s minimum-wage salary of $220 per month.

“I work for my son now,” she says. “My son is my boss, and he’s a picky boss.”

De Mesquita, 39, contracted Zika last March, the second month of her pregnancy, after a mosquito-swarmed Friday on the beach in Suape, a town south of Recife where her husband worked as a hotel security guard.

The next weekend, she woke feeling achy, with a rash on her arms and torso, and an infuriating itch. Recife was not yet known as the epicenter of a hemisphere-wide outbreak. There were as yet no billboards along the highways warning about microcephaly. In the hallways of the state health ministry, where de Mesquita worked as a cleaner, she’d never heard the name Zika.

She went to her neighborhood clinic, already packed with people with the same symptoms. Doctors treated her for an allergic reaction, which didn’t help, then tested her for dengue fever and rubella.

“I was so happy when they came out negative,” she says. “But it turned out that this was worse.”

Arthur Ferreira da Conceicao was born on Oct. 1 after a relatively painless two hours of labor, far easier than her first son, 15 years earlier. But Arthur’s body felt cold, and his skull was tiny, just 11 inches in circumference. The forehead was foreshortened. The back of his head was flat, with wrinkled skin. Within minutes, a doctor informed her there was a problem: Arthur had microcephaly. De Mesquita hadn’t heard the term.

“It’s weird, “ the doctor told her, “we already have seven other babies at the hospital with that right now.”

Zika: More than 2,500 babies born with microcephaly in Brazil, WHO predicts

Arthur couldn’t leave the hospital for 27 days. As he has grown, his problems have deepened. His body seems frozen in a rictus of tension.

His mother writes lists of questions for the doctors: Can he see or hear? Will he ever walk, talk, read, go to school? The answers are always the same: “I don’t know.”

In her small concrete house in a hillside slum, de Mesquita has filled Arthur’s crib with toys the therapists recommend. She built a rattle out of a water bottle filled with black beans, to test his hearing. She made a paddle with black and white stripes that she shines with a flashlight to encourage visual perception. On the wall of Arthur’s room, bug repellent mists from a plug-in dispenser.

To get to their first appointment, de Mesquita wakes at 4 a.m., tidies up, does the laundry, and feeds Arthur. She kisses her husband goodbye and walks into a warm, drizzling morning as insects trill and roosters crow. She is resigned to another trying commute.

“People are always staring,” de Mesquita says. “I know people are thinking, ‘What a small head.’ They’re not thinking, ‘Oh, that baby’s beautiful.’ ”

She transfers from the bus to a packed subway car. Passengers crowded around her stare at Arthur. A woman in a yellow tank top speaks loudly to de Mesquita, and others turn to look: “Did you have Zika? You had that thing?”

De Mesquita ignores the passengers and tries to soothe Arthur, who is sobbing, heaving, his face contorted in anguish.

“Calma,” she says, rubbing his head.

Her days unspool in waiting rooms on rows of hard plastic chairs bolted in place. Her hours slip by in a numbing drift of chitchat with other microcephaly moms. The moms started a WhatsApp group — more than 120 women strong — to share child-care tips for microcephaly kids.

Poor Brazilian mothers join hands, turn to social media amid microcephaly crisis

De Mesquita arrives at 6:45 a.m. at this morning’s hospital, the Association for the Assistance of Children with Deficiencies. She takes a number, 300, and waits for a doctor, who undresses Arthur, claps next to each ear, blows on his eyes, testing his sensations. Arthur’s body at rest is clenched and rigid, his hands in fists, his legs crossed. As the doctor pulls Arthur’s shoulders back, stretching his chest, the baby screams.

“Don’t cry,” de Mesquita whispers.

Five hours later, she walks back to the bus station and opens her umbrella to protect Arthur from the blazing sun.

A woman comes up to de Mesquita. “Jesus only gives children like this to people who are really strong, who are warriors,” the woman says. “You have the capacity to care for him. Someone without faith can’t do it, but you have faith.”

De Mesquita stands up, hefting Arthur onto her hip.

“That’s my bus,” she says.

As the Zika virus continues to spread, scientists in Recife, Brazil, are searching for a quicker, less expensive test to detect the virus. (Video: Whitney Leaming, Zoeann Murphy, Matt McClain/The Washington Post)

July 2015: A new mystery

Wing-Pui Kong opens a white mini-freezer, the size found in many a dorm room, and slides out a box labeled “Zik V DNA Vaccine.” He lifts the cover and removes one of about a dozen tiny vials of DNA plasmas that he and his colleagues at the Vaccine Research Center in Bethesda, Md., have synthesized to see if they can prompt cells to protect against the Zika virus. Countries that have the Zika virus

“Time is important,” Kong says. “When you see the pictures of the babies. . . . ” He stops himself. “I don’t really want to look at those pictures. I can’t imagine being those parents.”

Ever since last July, when a Brazilian physician pulled aside one of the Vaccine Research Center’s top scientists at a conference in Rockville, Md., warning him about a disturbing, rampant virus, Kong’s lab on the campus of the National Institutes of Health has been transformed into an anti-Zika war room. Rows of scientists painstakingly design and test dozens of different sequences of DNA, searching for those that might prompt creation of the perfect protein.

Around the country, scientists are studying cells isolated from people recovering from Zika. They need to learn how the virus works on people, why symptoms show up as they have, and how to make the human body defend itself. The goal is a vaccine, produced in the millions of doses, to be given to young children, ideally a one-time, lifelong immunization.

On the fourth floor of the Vaccine Research Center, created 16 years ago to develop protection against HIV, the best candidates for a vaccine will be injected into lab mice to see if they become immunized.

“The first round of mouse immunizations have not been the best,” says Barney Graham, the virologist who runs the Viral Pathogenesis Laboratory. “So we continue. Every week, there’s another mouse experiment.”

At the moment, the freezer contains 29 bacterial recipes. The goal is to begin testing vaccines this fall.

Zika has been linked to birth defects. Now it may be causing paralysis.

In lab after lab in their modern glass-and-concrete building, people who’d been working on HIV, Middle East respiratory syndrome or flu vaccines have shifted gears and launched a full-on drive against Zika. They still think mostly in timelines composed of years and decades, but that’s changing. In the past eight years, thanks mainly to research conducted toward an HIV vaccine, the process has sped up as researchers map the atomic structures of a virus and identify antibodies that lead toward a vaccine. Starting in 2003, it took 20 months to develop a vaccine to be tested against SARS. When avian flu hit a couple of years later, the process was slimmed down to 11 months. And in 2009’s H5N1 virus outbreak, the lab got its development work done in four months.

If all goes well in Bethesda, a vaccine could be ready for distribution in 2018.

“We’re always in a hurry here,” Graham says. “We’re still in a hurry on HIV even though it’s been 15 years. But we’re seeing more and more of these emerging, disruptive viruses now — it’s a sign of changes in ecology, as the ecosystems change from climate shifts or increased mobility.”

Last July, two years after a big outbreak of chikungunya virus in South America, the National Institute of Allergy and Infectious Diseases held a conference in Rockville on “Gaps and Opportunities in Chikungunya Research.” In a hallway during a break, a physician from Brazil, Roberto Jose da Silva Badaro, made it his business to find Graham. Chikungunya was indeed rampant and troublesome, Badaro said, but something new had cropped up in his region. Chikungunya and dengue fever in Brazil

All spring, patients in Bahia and neighboring Brazilian states had been coming down with rash and mild fever, but the symptoms were not quite the same as those from other mosquito-borne viruses. Brazilian doctors wondered if they were seeing measles, rubella, West Nile, Mayaro virus or an adverse reaction to some vaccine.

By late spring, the number of Zika cases in Bahia was tripling every week. At neighborhood clinics, people waited for hours to see a doctor.

A medical team led by a virologist at the Federal University of Bahia, Gubio Soares, isolated the Zika virus. They rushed to tell authorities, including Badaro, Bahia’s vice minister of health.

Over the summer, doctors began to see a spike in Guillain-Barré syndrome, a condition marked by temporary paralysis. In the second half of last year, the state recorded nearly 140 cases, seven times higher than normal. Hospitals scrambled to find enough intensive-care beds for all the patients.

“It was a war,” Badaro says.

The battle continues: Some pregnant women have left Brazil, heading for colder climates in Europe and the United States. Women have sought out illicit abortions, illegal in Brazil under almost all circumstances. Vendors in a downtown Rio market said Cytotec, a banned medication for stomach ulcers, is in high demand for home abortions. Some pregnant women choose to become virtual prisoners, refusing to leave home except for emergencies.

“You guys are discussing something that’s really in the past,” Badaro told U.S. researchers. “What’s coming is the Zika virus.”

Bahia, he told them, had already seen 63,000 Zika cases.

Graham had heard of Zika — he knew it had been discovered in Africa in the 1940s, and that there’d been an outbreak in the South Pacific a few years ago, but he’d not heard of it causing alarming symptoms.

Graham and his colleagues soon started grabbing researchers off other projects.

“When we see a virus spreading like that, we take notice,” Graham says. “People like Dr. Badaro are the sentinel. He was looking for chikungunya, and he found Zika.”

Spring 2007: A spreading rash

For hours each night, the “nonstop Micronesian beat” of V6AI, the only radio station in the island state of Yap, transmits an endless loop of public service announcements warning residents to “sleep under insecticide-treated bed nets” and empty open containers where mosquitoes might breed.

Mosquito bites used to be just a nuisance, a small price to pay for living in South Pacific paradise. But in 2007, Zika hit Yap with a powerhouse punch — an alien virus zapping an isolated population in a place with few defenses against the bug.

But in little more than a year after it first hit Yap in spring of 2007, Zika — named after the forest in Uganda where the virus was discovered in 1947 — infected about 7,000 of the island’s 11,000 residents. Most people had mild symptoms or none at all. Doctors thought they were seeing dengue, but the symptoms weren’t quite right. They called in tropical-disease experts from the CDC and WHO. Lab tests determined the culprit: Zika.

“We probably didn’t pick it up till the third or fourth week,” says James Edilyong, a Yap native who is chief of staff at Yap State Hospital. People streamed into the hospital, but “really, we had nothing we could do for them.”

Andy Choor, 32, thought he had a cold, maybe a light flu. His temperature flared, his appetite waned. Everywhere around him, “people were going down. You almost knew who had it because they were down for three or four days, and you just didn’t see them,” he recalls.

Choor, who owns a souvenir and crafts shop, felt Zika’s impact at the cash register: Tourists — lifeblood of the island’s economy — became scarce. Life on the island changed. People who had never really cared about bug bites were now staying inside more. Things seemed quieter, more subdued.

“It was alarming, and people are still concerned,” he says, even though the virus has largely vanished from the island.

How a tiny mosquito became one of the world’s ‘most efficient killers’

Edilyong, 48, was among the first in Yap to get Zika. “I’ve had the privilege to have both Zika and dengue, and dengue was much worse,” he says. His Zika rash lasted only a few hours; the aches resolved themselves within a day.

From Yap, Zika made its way 5,000 miles east to French Polynesia in 2013 and on to Japan the next year.

After so many microcephalic babies were born in Brazil, doctors in the Pacific islands went back to see if they had missed a spike in birth defects. The results are inconclusive — in Polynesia, there had been an unusual number of malformations of the central nervous system in babies and miscarried fetuses, but the numbers were not large enough to cause alarm, and a connection to Zika remains unproven.

Yap saw no such cluster of defects, Edilyong says: “Whatever happened to Zika to cause the defects in Brazil hadn’t happened when the virus was active here.”

In Yap and Polynesia, Zika seemed to burn through in less than a year. No cases have been reported since the outbreak faded, doctors said.

How human-made environmental factors help spread Zika and other diseases

The fear hasn’t gone away, but the hope that life can be normal again has returned. “We never had a panic about it,” Edilyong says. “But people became more anxious after other countries got the outbreak, after we heard about the birth defects. We get the word out about what to do, how to help prevent the spread. We talk to the chiefs, and the message goes right to the villages. And we get people to clean up their yards and empty water containers. We’re okay, we watch out for each other.”

March 2016: Race against risk

Kim Conley runs to get to Rio. She runs for the satisfaction of knowing that she’s given it her all. “Really, it’s for the afterglow,” she says, “the feeling of the effort.”

She feels a fire, a will that is evident in her steely blue eyes, her zest for the daily punishment she endures, and now in her willingness to take a chance. Until someone in authority tells her otherwise, she’s determined to outrun the danger. She has to believe she can beat an opponent named Zika.

Fisher reported from Sacramento and Washington; Partlow from Brazil; and Jordan from Colombia. Julie Tate in Washington and Anna Kaiser in Brazil contributed to this report.

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