HOUSTON — Public health officials fighting to stem the Zika virus in the United States have a problem on their hands beside the formidable mosquito: us.
Mosquitoes multiply in the trash that people toss and in the flower pots that dot gardens when water collects there. Crews sometimes run into resistance from the very people they’re trying to protect.
“Some people just don’t want government in their backyard, literally,” said Dr. Jeff Engel, executive director of the Council of State and Territorial Epidemiologists.
If Zika were to spread locally, experts say that aggressive, door-to-door canvassing will be critical to stomping out the breeding sites of the mosquito species, the furtive Aedes aegypti, that is responsible for propelling the virus throughout much of the Americas.
To curb the insects, inspectors sometimes go house to house, dumping water from containers, conducting targeted spraying of insecticides, and dropping larvicide in water that can’t be emptied.
Aedes aegypti thrives in cities and suburbs, laying eggs in man-made containers and discarded tires. They hunker in homes, hiding under beds and in closets. They hover low to the ground and don’t venture far, evading insecticide spraying from planes or trucks.
“Aegypti is just like this with humans,” Stanton Cope, the president of the American Mosquito Control Association, said as he interlocked his fingers. “They’re that tight.”
But some people can’t be bothered to clean up their garbage or cover rain barrels. Others fear the chemicals in mosquito treatments or mistrust any government program.
And in some places, “what these people are not going to want is someone from the feds coming down and telling them they’re living like pigs,” said Joseph Conlon, a retired Navy entomologist and technical advisor to the American Mosquito Control Association.
The good news is that a large majority of people seem happy to help with initiatives aimed at paring mosquito populations, say officials from state and local health and mosquito agencies, which handle most control and surveillance efforts.
Most experts also predict that any spread of the Zika virus in the continental United States will be limited, nothing like the outbreak that has exploded in most of Latin America and the Caribbean. In some places in the region, the virus has resulted in an increase in birth defects.
But even a few holdout homeowners pose a public health threat because Aedes aegypti reproduces so prolifically given the right conditions, experts say. In extreme cases, health and environmental agencies can get a court order or fine residents who refuse to clean up their properties or allow crews to come do so.
“If you don’t control breeding sites, all your efforts around that site are useless,” said Robert Eadie, the administrator of the health department in Monroe County, Fla., which has seen local transmission of dengue, another virus spread by Aedes aegypti.
Dr. Tom Frieden, director of the Centers for Disease Control and Prevention, alluded to such concerns at a Zika preparedness summit this month, mentioning the “hesitancy” that exists to control programs.
“Access to private property has been a persistent problem,” said Roger Nasci, a former top vector-borne diseases official at the CDC who is now the executive director of the North Shore Mosquito Abatement District in Illinois.
People in some areas might be more obstinate than others. A research team in New Jersey found people in urban Mercer County (home to Trenton) to be more responsive to their mosquito control initiatives than people in suburban Monmouth County, said Dina Fonseca, a Rutgers University evolutionary biologist who led the 2013 study. The large majority of people in Monmouth did enlist, but there was a noticeable difference.
In Trenton, “people were happy we were there, they would let us into their houses,” Fonseca said. “While in Monmouth, it was a bit more difficult to get access.”
Such opposition could be inhibiting what researchers can learn about the changing biology and behavior of Aedes mosquitoes.
Douglas Watts, a University of Texas at El Paso virologist, said one of his graduate students had to give up a project studying how Aedes aegypti acted in homes because he could not get enough people to participate.
“I think he maybe got permission from one house out of 10,” Watts said. “They don’t understand we’re trying to prevent diseases.”
A lack of cooperation from the public only complicates the already arduous task of controlling Aedes aegypti. They bite during the day, so people accustomed to protecting themselves at dawn and dusk need to be reeducated. In Puerto Rico, they are showing resistance to insecticides. Many states, counties, and cities lack the resources or expertise for full-fledged campaigns.
The most likely scenario for mosquito-borne transmission in the continental United States is that a mosquito contracts Zika after biting someone who was infected abroad. If it becomes infectious, that mosquito could then transmit the virus to other people it bites.
It’s more than just a theoretical scenario here in the Houston area, a hub for travelers to and from Latin America that has year-round populations of Aedes aegypti and has already seen a dozen travel-related cases of Zika.
“We just don’t know if it’s next week, or this summer, or next summer,” Dr. Umair Shah, the executive director of the Harris County Public Health and Environmental Services department, said about local transmission. “But it’s really a matter of when.”
On a recent day, in a neighborhood in the southeastern part of this city, garbage and tree clippings clogged an overgrown drainage ditch, hoarding that morning’s rainfall. Water shimmered in a Bud Light bottle, pooled on black trash bags, and filled an orange-and-white Styrofoam cup from Whataburger, the Texas fast food staple.
As Mustapha Debboun, director of mosquito control for Harris County, bent down to take a closer look, a burst of mosquitoes scattered. Then he saw them curled in the water in a tire packed into the trash pile: larvae.
The heap was a few arms’ lengths away from a gated driveway, beyond which lay a front yard scattered with watering cans and buckets where larvae could be growing.
“The problem is created by us,” Debboun said. “People need to help us help themselves.”
Across the street, another garbage pile sat in another drainage ditch in front of another house. Across from that, overgrown grass and weeds blanketed an empty lot, providing plenty of places for mosquitoes to hide.
“This is one little area,” Debboun said, “magnified by thousands.”