Can scientists outsmart the mosquitoes carrying Zika virus?
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CALI, Colombia — In Clara Ocampo’s lab here in southwestern Colombia, a mosquito model dangles from the ceiling, framed insects decorate one wall, and, behind several protective layers blocking them from the outside world, dengue-infected Aedes aegypti mosquitoes buzz around in plastic tubs.

Ocampo, a scientist at an independent research center known by the acronym CIDEIM, studies how mosquitoes spread viruses like dengue and how they develop immunity to insecticides. With researchers around the world now scrambling to learn more about Zika virus, she is at work on a project focused less on understanding it than slowing its spread — specifically by helping local communities spot and stem small outbreaks before they ignite into larger ones.

The model is being built for dengue, but once ready, it could be used for Zika or whatever other pathogen emerges next.

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“This is what we think we could do,” Ocampo said.

Ocampo’s effort is one of many scientists have undertaken to help them identify a disease’s spread sooner. Such tools could enable governments to take steps to protect communities earlier, instead of having to scramble to respond to whatever new scourge pops up. That, in large part, is how health officials have been responding to Zika so far.

“It seems to be more reactive than proactive with these cases,” said Jorge Osorio, an infectious disease expert at the University of Wisconsin, who was part of the team of scientists who first identified the virus in Colombia.

Andrew Joseph/STATMosquitoes at Clara Ocampo’s lab in Cali, Colombia.

Zika caught so many health officials off guard because until now, it wasn’t widespread and hadn’t been thought of as a threat to human health. But once thousands of cases were reported in Brazil, and scientists warned the virus could be responsible for birth defects, other countries with Aedes aegypti mosquitoes could have moved faster to launch education initiatives and campaigns to eliminate breeding grounds.

“It was a matter of time before this would happen,” Osorio said.

In the US, officials in places such as Texas and Florida, which have populations of Aedes aegypti, have been ramping up their surveillance and prevention efforts ahead of the summer mosquito season, when experts expect to see some locally transmitted cases.

Ocampo’s project, called Vectos, would analyze entomological, epidemiological, and sociological data on the neighborhood level in an effort to identify what features make certain areas more likely to have higher rates of disease, enabling local authorities to respond faster than they can now.

The model, which is funded by the Colombian government, would also allow for historical comparisons so that if, for example, the number of severe dengue cases rose in one spot compared with the number of standard cases, local health officials would be tipped off that a new strain might have arrived.

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

Inspectors who already go around to homes a few times a year would feed data to Vectos using an app that Ocampo’s lab is also developing. For each home, the inspectors would submit information that could be used to assess the risk mosquitoes might spread: whether there are screens in the windows, what kind of water tanks exist, how many pupae are seen. Ocampo hopes analyzing the data could help researchers pinpoint which variables increase the risk of disease.

Her previous work has shown how important it is to isolate what she calls the most “productive” mosquito breeding sites. In one pilot project in the Colombian city of Buga, Ocampo’s team determined which catch basins — boxes that catch debris before it can enter the sewer system — provided the best areas for mosquitoes to reproduce. When researchers applied insecticide to just those boxes, Buga reported fewer cases of dengue compared with nearby cities for several months.

But Zika and Aedes aegypti mosquitoes both present particular challenges for researchers and health officials trying to stop the spread of the virus.

Dania Maxwell for STATThis road in Norte de Santander, Colombia, is a common site for people to dump their trash, which can collect water and provide a place for mosquitoes to breed.

Part of the problem is a lack of firm data. Researchers don’t know the rate at which the virus is spread from mosquitoes to humans or from humans back to mosquitoes, or if mosquitoes can transmit the virus to their offspring, said Alessandro Vespignani, a professor of computer science and public health at Northeastern University. Even accurate information about the number of people who have been infected in Brazil has been hard to come by.

“There are a still a lot of things which are fuzzy, so it will not be easy to get accurate modeling for what’s going on,” said Vespignani, who is trying nonetheless.

Scientists are also trying to figure out how many infected mosquitoes are needed to cause an outbreak, and how many become infected during an outbreak, said Megan Wise de Valdez, a biologist at Texas A&M University San Antonio. A good chunk of Aedes aegypti, for example, don’t contract dengue even if they absorb the virus during a blood meal, which means they can’t spread it to other people they bite.

“I don’t think we know the proportion of Aedes aegypti that are infected [with Zika] down in Brazil,” Wise de Valdez said.

Aedes aegypti also stand as a formidable foe. They only need a bit of water to breed, and lay their eggs in water basins, planters, and piles of garbage and tires that collect water. They bite during the day and like to hide in homes, meaning they can evade fumigating campaigns. The female mosquitoes, which are the ones who bite, also prefer to feed on people instead of animals.

“She’s just adapted really nicely to living in urban areas,” said Heidi Brown, an assistant professor of epidemiology and biostatistics at the University of Arizona. “It’s now optimized for disease transmission. She’s living in this environment preferentially biting this thing that she can be infected from and this thing she can infect.”

All of that points to why scientists are trying to improve their ability to detect outbreaks early: Once one starts, recovering ground against the already pervasive Aedes aegpyti amounts to a serious challenge.

“We will not eliminate the mosquito,” Ocampo said. “This is the reality.”

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