MIAMI -- The mosquitoes spreading Zika in Miami are proving harder to eradicate than expected, the nation's top disease-fighter said Tuesday as authorities sprayed clouds of insecticide in the ground-zero neighbourhood, emptied kiddie pools and handed out cans of insect repellent to the homeless.
Dr. Tom Frieden, director of the Centers for Disease Control and Prevention, said the mosquito-control efforts in the bustling urban neighbourhood aren't achieving the hoped-for results, suggesting the pests are resistant to the insecticides or are still finding standing water in which to breed.
"We're not seeing the number of mosquitoes come down as rapidly as we would have liked," he said in an interview with The Associated Press.
Mosquito control experts said that's no surprise to them, describing the Aedes aegypti mosquito as a "little ninja" capable of hiding in tiny crevices, sneaking up on people's ankles, and breeding in just a bottle cap of standing water.
Fifteen people have become infected with Zika in Miami's Wynwood arts district, officials said Tuesday. These are believed to be the first mosquito-transmitted cases in the mainland U.S., which has been girding for months against the epidemic coursing through Latin America and the Caribbean.
On Monday, the CDC instructed pregnant women to avoid the neighbourhood, marking what is believed to be the first time in the agency's 70-year history that it warned people not to travel somewhere in the U.S. The Zika virus can cause severe brain-related defects, including disastrously small heads.
At the same time, U.S. health authorities have said they don't expect major outbreaks in this country, in part because of better sanitation and the use of air conditioners and window screens.
On Tuesday, Miami-Dade County mosquito control inspectors toting backpack blowers released white clouds of bug spray in Wynwood.
They also went door to door, handing out information, checking tires and other objects for standing water, and dipping cups to take water samples from vacant lots, building sites and backyards.
In one lush yard, an inspector tipped over a kiddie pool and a cooler full of water.
Daily aerial spraying for adult mosquitoes and larvae has been approved for the next four weeks over a 10-square-mile area around Wynwood, county officials said.
The city of Miami said it is running more street sweepers in Wynwood to remove the litter and stagnant water that can serve as breeding grounds, and police officers handed out 50 cans of bug spray to homeless people in the neighbourhood.
"Be sure that you use it," Officer James Bernat said as he gave repellent to several people who had been sleeping on the street.
Dozens of pregnant women streamed into Borinquen Medical Center, a clinic just outside Wynwood where doctors said they were getting more and more nervous requests for Zika testing.
On the sidewalk outside, eight-months-pregnant Gabriella Acevedo said she would rush back to her Wynwood home.
"I'm going to put the AC on blast and try not to go outside. I've been bitten by mosquitoes probably two weeks ago, but I don't feel sick," she said. "It's just really stressful to me."
Because of environmental regulations governing which chemicals can be used as insecticides, mosquito control authorities cannot easily switch to another compound if bugs prove resistant to it.
Nothing has worked to stop this mosquito elsewhere in the world except for the introduction of mosquitoes modified to pass on genes that kill their offspring, said Michael Doyle, executive director of the Florida Keys Mosquito Control District. And the Food and Drug Administration has not given approval to that approach in the U.S.
"We have to totally rethink mosquito control for Aedes aegypti," Doyle said. "It's like a little ninja. It's always hiding."
Frieden complained that in the U.S., "we really dismantled the mosquito monitoring and control infrastructure over the past few decades."
The result: "We have blind spots where we don't know where the mosquito populations are and what the susceptibility is to different insecticides," the CDC director said.
The U.S. government might have underestimated how difficult it would be to control Zika's spread, said University of Florida public health researcher Ira Longini.
But he also said there aren't enough of the disease-transmitting mosquitoes living in and around houses to cause long-term or widespread outbreaks in this country.
"In defence of the CDC and the government, it's a difficult problem to solve," he said.
