SAN ANTONIO — A few days each week, students and volunteers from Texas A&M University-San Antonio stroll into the front yards of homes across this city, pull a black sticky trap from a bucket and carefully peer at the mosquitoes glued there.
The researchers are tracking travel patterns of the Aedes aegypti, the tiny human-feeding mosquito and main carrier of the Zika virus. Much is known about the Aedes aegypti, including how it prefers human blood and lives in close proximity to humans. But frustratingly little is known about the insects’ day-to-day movements and precise locations, said Megan Wise de Valdez, an associate professor of biology at Texas A&M-San Antonio leading the study.
“What’s novel about this research this summer is that we are using these (traps) across the seventh largest city in the United States,” she said. “We’re looking at distribution of Aedes aegypti across the city and we are sharing these data with our metropolitan health districts.”.
As Zika continues to spread both in and out of the USA, any intel about its carrier’s whereabouts is increasingly valuable.
Health officials fear Zika, which can cause devastating birth defects, could spread quickly in cities with large populations of foreigners, such as Houston, San Antonio or Miami. Miami’s Wynwood neighborhood has been dealing with a Zika outbreak and, on Friday, Florida health officials announced a new batch of cases in touristy Miami Beach.
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Around 2,200 Zika cases have been reported in the continental U.S. And more than 13,000 in Puerto Rico, according to the Centers for Disease Control and Prevention. Most of the cases within the continental U.S. Involved individuals who contracted the virus while traveling in another country, while most of the Puerto Rico cases were locally acquired, according to the CDC.
Though the Aedes aegypti is found in abundance in Gulf Coast states and resides alongside humans, little is known about its movements because it tends to reside on private property, said Kacey Ernst, an epidemiologist at the University of Arizona. Besides Zika, this species of mosquito is known to spread dengue, chikungunya and yellow fever.
“In the United States, we don’t know precisely where it is,” she said of the mosquito, adding the San Antonio study is “really valuable.”.
Tracking and studying the mosquito in the U.S. has been mostly left up to local municipalities, said Joe Conlonof the American Mosquito Control Association. Past global efforts to corral the virus involved mass government interventions.
In the late 1950s, health officials in South America eradicated the Aedes aegypti and the diseases they carried in 21 countries through a widespread program that included going onto people’s property and uprooting nesting areas, he said. Cuban officials, in the early 1980s, deployed military troops into neighborhoods to help stem a dengue outbreak by the mosquito after more than 300,000 cases were reported on the island, he said.
Those obtrusive measures, however, wouldn’t be particularly popular or even allowed in the U.S., Conlon said. “(Controlling Zika) can be done, but it takes a lot of manpower and government coercion to do it,” he said.
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For now, the task of stemming and studying Zika’s spread is falling to local officials and researchers like Wise de Valdez. Her team of researchers have so far counted more than 15,000 mosquitoes.
Ferried to the U.S. On slave ships 500 years ago, the Aedes aegypti prefers human environments and human blood and has populated the southern Gulf States, she said.
Wise de Valdez launched her study in June but needed permission to place the traps on private property. She went on local TV asking for volunteers: 420 homeowners called in offering their front lawns. She placed traps on 120 of those yards and dispatched research students to start tracking them.
One thing the study has shown: the Aedes aegypti doesn’t care much for the traps used in the research, known as “autocidal gravid ovitraps.” The traps consist of a length of sticky paper inside a bucket with water-logged hay, to lure pregnant females, and were given to Wise de Valdez free of charge by the CDC. The traps are widely used in Puerto Rico.
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Instead, the Zika-carrying mosquitoes much prefer the BG Sentinel traps, which are battery-operated and omit a human-like scent to draw hungry Aedes aegypti. Those are costlier, scarcer and more labor-intensive, she said. “The big take-home message I’m seeing is that trap type really matters,” Wise de Valdez said.
As classes start this month, the research project will likely scale back to 60 homes and conclude in September, she said. She’ll be sharing the results of the study at the Society for Vector Ecology meeting in Alaska next month and hopes the tracking methods are picked up across the country.
“This was a grass-roots thing. This fell in our lap and we just said, ‘Hey we’re going to go for it,’ ” she said. “I think it’s going to be easy to replicate anywhere.”.