Ride With the Mosquito Hunters Protecting the US Against Zika
Every summer, millions of mosquitos hatch along the Gulf Coast and set out on a quest for blood. It’s only February, but people are already worrying about mosquito season thanks to Zika, a mosquito-borne virus that may cause debilitating brain defects in babies and is currently racing through Latin America. The Gulf Coast is almost certainly next.
When the mosquito hordes do descend this summer, the front lines of the fight against Zika will not be in some high-tech lab, but in local mosquito control departments. A vaccine or cure for Zika is years away, so controlling Zika means controlling the vector that spreads the virus from person to person: the Aedes aegypti mosquito, whose range in the US follows the Gulf Coast.
Harris County’s mosquito control program is one of the more robust in the country—and it has to be. The third most populous county in the US includes Houston and a swath of Texas, where travel to Latin American is common and Aedes aegypti even more so. (The county has already had seven travelers return with Zika since January. In the thick of summer, some mosquito somewhere will pick up Zika and spread it. “It’s a matter of when, not if,” says Umair Shah, executive director of Harris County Public Health and Environmental Services.
This past month, Harris County public health officials began meeting to draft a plan for dealing with Zika. This is what the front lines of fighting a mosquito-borne disease will look like.
Of Trash and Mosquitoes
Harris County’s mosquito control division occupies two low-slung buildings behind the county probation office. The lobby boasts a large glass cabinet of pinned mosquitoes—several specimens each of the more than two dozen species in the county. Among the most prominent is A. aegypti, the interloper from Africa that’s already brought dengue, yellow fever, chikungunya with it to Texas. Zika will soon be on the list.
Like pretty much everyone in the world, Mustapha Debboun, the head of mosquito control, is only just getting to know Zika. But he is no stranger to A. aegypti and its habits. He knows, for example, that that A. aegypti likes to fly low, biting ankles and feet—too low to spray with pesticides from helicopters or trucks, unlike the high-flying mosquito species that transmit West Nile. And he knows they like to live indoors in dark, cool spaces like under the bed.
The most effective way to control A. aegypti is to get rid of the small—even tiny—bodies of water where they breed. “Jars, buckets, tires, plastic bottles,” says Debboun, “anything that holds water.” In the 1950s, Brazil eradicated A. aegypti, but it wasn’t pretty. The government sent inspectors door to door looking for mosquito-breeding containers and spraying DDT. (The mosquitos then came back because neighboring countries did not eradicate their populations, and mosquitos don’t exactly need passports.)
That can’t and won’t happen in the US in 2016. In Harris County, the mosquito control division is planning outreach—on social media and at community events like sports games and town halls—to teach people about A. aegypti. The hype around Zika could, for once, help that cause.
What the US has over Brazil then and even today in the fight against mosquitoes is widespread air conditioning and window screens. The best way to keep away from them is to keep them out. In the US, however, that means the poorest neighborhoods are at the highest risk for Zika. “The Gulf Coast is vulnerable because we have both mosquito vectors and poverty,” says Peter Hotez, chief of the Baylor College of Medicine National School of Tropical Medicine. “Poverty is an important risk factor because people live in poor quality housing with broken screens, poor garbage collection.” Neighborhoods in east Houston, where half of the population lives in poverty, are of the most concern.
Debboun’s mosquito control team of 55 people, which swells to 75 in the summer, does have a few other tricks up its sleeve. The division is currently growing elephant mosquitoes, whose larvae eat the larvae of other mosquito species. (Elephant mosquitoes don’t bite people, of course.) They can take foggers to breeding sites like abandoned pools. “You only use pesticides when you know where the mosquitoes are,” he says. “Otherwise you’re just dousing the environment with pesticides.” On the other hand, genetically modified male mosquitoes, which are sterile, aren’t yet approved in the US, and they’re too politically dicey right now.
In addition to controlling mosquitos, Harris County actively looks for viruses in mosquitoes and birds flying. Here, they’re actually in unfamiliar territory with Zika. The mosquito control division regularly sets out traps baited with dry ice (carbon dioxide, which attracts the bugs) that capture hundreds or even thousands of mosquitoes in the summer. Staff sort them by species, grind them up, and test them for dengue, chikungunya and West Nile. The protocol is easy: Companies sell readymade dipstick tests for those viruses.
Not so with Zika. Nobody has a reliable field test for it—not even in humans, which has been one stumbling block in the outbreak. Debboun is planning to shell out several thousand dollars for a real time PCR machine, which can amplify and detect the genetic material of viruses. It’s cumbersome and slow compared to a dipstick test, but Zika has become important enough to justify the expensive machine.
All this work—from the trapping to the spraying—is unsexy, tedious, and often underfunded. “In the US, our vector control programs are not very effective,” says Robert Tesh, a mosquito-borne disease expert at the University of Texas Medical Branch, who has collaborated with the Harris County mosquito control and cites it as one of the better ones. In 2010, an environmental health scientist with the Centers for Disease Control and Prevention lamented, “Where Have All the Vector Control Programs Gone,” noting widespread budget cuts to local programs.
Abatement might not be as exciting the developing new vaccines or genetically modifying mosquitos to fight the war for you, but it’s necessary work. Don’t do it, and it’ll come back to bite you in the end.