Fighting Zika on the streets
South Florida has been battling mosquitoes since the first settlers swatted their way through the Everglades. Centuries later, we’re still at war.
Only now, the adversary is an insidious, exotic species. The Aedes aegypti, unlike Florida’s native mosquitoes that inhabit coastal mangroves and swampy marshes, is an urban mosquito, proficient at hiding in our midst, feeding on our blood and spreading disease like a dirty needle. The more people, the better. And since the 1960s, its distribution across the U.S. has only increased.
“Every person’s yard is where the mosquito districts have to fight the battle,” said Phil Koehler, a University of Florida urban entomologist.
While the agriculture industry has chalked up repeated wins against exotic pests — this past year, Florida quickly contained an outbreak of Oriental fruit fly in the Redlands — the fight against the mosquito spreading Zika in Miami’s Wynwood neighborhood remains far from settled.
Mosquito control on a massive scale remains challenged by politics, money, environmental ripple effects and weapons that haven’t changed much in decades. Spraying can knock back populations temporarily but not eliminate them and there are emerging concerns that some mosquitoes are developing resistance to the limited pesticides approved for use. New technology still has regulatory hurdles and public resistance to overcome — most notably, mosquitoes genetically modified to wipe out their own species, which have been proposed for testing in Key West.
Koehler, for instance, is working on a new pesticide to deal with resistant mosquitoes but said it and others remain unavailable.
“The bureaucracy has slowed down the availability of new tools,” he said. “Everyone’s hands are tied because there’s only so much one agency can do. So the CDC has to do their own thing. The EPA does their own thing and the Florida Department of Agriculture and everyone has their boxes they need to check off to get it done.”
Every person’s yard is where the mosquito districts have to fight the battle.
Phil Koehler, a University of Florida urban entomologist
This past week, after the number of confirmed local Zika cases jumped from four to 16, Miami-Dade County beefed up operations, expanding a staff of 12 inspectors to more than 100. Aerial spraying misted about 10-square miles with the insecticide Naled, an effort that will likely be repeated for the next three weeks.
But for now, experts say the best weapon also remains the most unreliable: residents of infected areas who need to wear repellents and dump containers — flower pots, overturned garbage can lids, broken fountains, saggy roof tarps or clogged gutters — where mosquitoes breed.
“In Brazil, they did a survey and found 91 percent of the population knows to get rid of containers, but only 55 percent are doing it. We have the same problem with people wearing repellents,” said entomologist Joseph Conlon, technical advisor for the American Mosquito Control Association. “What can I say? That really confounds control efforts.”
Mosquito programs can tend to fall victim to their own success. When mosquito numbers go down, so do diligence and funding. Miami-Dade County has cut its budget since 2014 and, in 2011, the state shut down its Panama City mosquito lab when lawmakers slashed its budget by 40 percent.
“And now we’re seeing the results of this,” Conlon said.
The Aedes aegypti, which appeared in Africa millions of years ago and likely made its way to the U.S. in the 17th century, poses a formidable enemy. Only females bite and transmit disease. But the mosquitoes are active during the day, which complicates spraying.
Over the years, pest control in agriculture has made huge leaps, from genetically modified insects to more efficient pesticides. But only five percent of pesticides in use are deployed to kill mosquitoes and other insects that pose public health threats, said Uli Bernier, a research chemist at the U.S. Department of Agriculture’s Research Service who has worked with the military to develop mosquito-resistant uniforms. For mosquitoes, most efforts have been aimed at improving the same old strategies: surveillance, education and eradication. But those efforts can be expensive and labor intensive.
In Houston, the Harris County mosquito control division employs about five times as many inspectors as Miami-Dade and also has its own virology lab, a perk that allows mosquitoes to be quickly tested so the county can rapidly zero in on diseased insects, said mosquito control director Mustapha Debboun.
You can’t just spray the whole county.
Harris County Mosquito Control Director Mustapha Debboun
“You can’t just spray the whole county,” he said. “These darn mosquitoes are very difficult to get the pesticides to hit them because, as you know, they hide in containers, in tires, or inside homes and in the gutters.”
Debboun said his agency prefers to use hand foggers, but even those have limits.
Only three insecticides — two organophosphates and one pyrethroid — are currently available in the U.S. to kill adult mosquitoes, Bernier said. The most effective, DDT, was banned in the 1970s after bald eagles, brown pelicans and other birds began to disappear.
“It did a great job of controlling mosquitoes but unfortunately there were other effects,” he said. “Nowadays, we do effective mosquito control but the mosquito control we do is integrated.”
But spraying might have diminishing returns. Resistance to the chemicals is also increasingly causing problems. Mosquitoes in California, Mexico and many of Central American and Caribbean countries are “more or less resistant to the insecticides used currently,” said Florence Fouque, a team leader for the World Health Organization’s Special Programme for Research and Training in Tropical Diseases. About 20 municipalities in Puerto Rico have documented resistance, according to the Centers for Disease Control.
CDC director Dr. Thomas Frieden last week worried that Miami mosquitoes might also be resistant. But testing has so far shown the use of pyrethrin in ground foggers to be effective, said Chalmers Vasquez, Miami-Dade County’s mosquito control manager. The county will continue testing and also plans on rotating insecticides and larvicides to keep mosquitoes from building up a tolerance, he said.
In situations like Puerto Rico, and now Miami, aerial spraying with Naled can quickly knock down populations. But the insecticide can also harm bees, butterflies, bats and other wildlife and isn’t always efficient at reaching the mosquitoes that don’t fly more than about 10 feet off the ground. Wind and temperature conditions have to be just right to deliver a fine mist that contains a minute amount of Naled, less than an ounce for 346,000 cubic feet of air, Conlon said.
But despite widespread use since the 1950s — Florida sprays an average of six million acres yearly, CDC officials said this week — fears over health effects remain. In July, a federal recommendation to spray Naled in Puerto Rico triggered protests. Florida environmentalists who have long objected to aerial spraying are also raising questions about this week’s spraying.
When you fly those airplanes, that stuff goes everywhere. It’s not carpet bombing. It’s like World War I, throwing hand grenades from camels.
American Butterfly Association Miami chapter board member Dennis Olle
“When you fly those airplanes, that stuff goes everywhere. It’s not carpet bombing. It’s like World War I, throwing hand grenades from camels,” said attorney Dennis Olle, a board member for the Miami Chapter of the North American Butterfly Association.
There are promising advances, but regulatory hurdles can be high. As Zika spread to the U.S. this year, the CDC said it would allow the use of a new trap still being tested called In2Care. The trap, which looks like a plastic bucket with a weird lid, lures females, killing their eggs, and then coats part of the female with a larvicide she spreads. But the agency would only approve use after a local case was confirmed, which some in Florida’s mosquito control ranks considered an unnecessary delay.
Koehler, the UF urban entomologist, said he also began warning state officials and Florida’s congressional representatives in July that more steps needed to be taken to prepare. He trained pest companies in Orlando and Palm Coast on the best treatment methods, hoping to have them ready if necessary, an approach that he said could be used around the state.
“We have one company that could put 1,500 technicians in the field tomorrow,” he said.
Among the efforts getting the most attention are genetically modified mosquitoes — a strategy using mosquitoes to fight mosquitoes. On Friday, the FDA cleared the way for Oxitec to field test mosquitoes in the Florida Keys but that effort still faces an uncertain public referendum. The company plans on manufacturing sterile males to mate with wild females, who then produce offspring that quickly die. Early tests in Brazil show mosquito populations reduced by up to 90 percent. Within the last month, a study also found dengue cases dropped by 90 percent in an area of 5,000 people when the mosquitoes were used, compared to a 40 percent with normal mosquito control measures, said Oxitec CEO Hadyn Parry.
What you’re trying to do is what everyone has always wanted to do, which is get rid of the mosquitoes.
Oxitec CEO Hadyn Parry
“What you’re trying to do is what everyone has always wanted to do, which is get rid of the mosquitoes,” Parry said.
Another technique under work produces mosquitoes infected with a bacteria, a “gonad-chomping parasite” that attacks the insect’s reproductive system. The mosquitoes are now being field-tested in California.
For some, the efforts provide a better alternative to producing more pesticides, which come with environmental consequences. The best approach, almost everyone agrees, combines a little of everything: improve surveillance, have an emergency response plan ready when a disease hits, and then be ready to wage strategic guerrilla warfare.
“There’s no one silver bullet,” Conlon said. “In the short term, Gov. Scott’s $16 million for mosquito control districts in the state, that’s definitely filling the breach. But for the long term, they need to figure out something else that keeps the money going or it will whither on the vine and 15 years down the road we’ll be dealing with another mosquito.”