As Zika skipped into Puerto Rico and then Florida this summer and threatened to spread northward, an uncoordinated patchwork of mosquito control offices — funded by state health departments, county governments and special tax districts — stretched their budgets in the campaign to track and eradicate mosquito breeding grounds. Though the populations of the two species of mosquito that transmit the Zika virus will thin out in the U.S. by mid-October in colder weather, according to tropical disease experts, they will likely return with a vengeance next year.
And, while this year’s crisis may be nearing its end, officials in the states that will form the first ring of protection to limit the disease’s future spread remain worried and underprepared.
The efforts in many areas have been stymied by years of diminishing local spending for mosquito control, lack of emergency funding from the federal government and too few workers to handle the problem. And public health officials say they may not truly know the full extent of the Zika outbreaks for months when perhaps babies affected by the virus are born.
“We have no sense of the transmission. Our knowledge base is essentially nothing,” said Peter Hotez, dean for the National School of Tropical Medicine at Baylor College of Medicine in Houston.
Mosquito control is generally a local prerogative, and many jurisdictions gave up robust efforts years ago since — unlike in more tropical countries — U.S. mosquitoes didn’t generally carry serious disease. That calculus has changed.
In Florida, some local mosquito control agencies with generous budgets have been beating back Aedes mosquitoes for years, while efforts in other areas were much more constrained. In the state’s northern neighbor, Georgia, one-third of the 159 counties lack mosquito control offices, according to an Associated Press survey. And in 2011, the North Carolina state legislature voted to end all funding for its mosquito control program.
“There is considerable room for long-term improvement” of mosquito control, said Dr. Oscar Alleyne, senior adviser for public health programs at the National Association of County and City Health Officials. “Whether or not surveillance is capturing locally acquired cases is a complex picture.”
Zika is spread by Aedes aegypti and Aedes albopictus mosquitoes. But they are difficult to destroy. Overhead spraying has a limited effect. Eradication efforts often involve visiting individual homes to identify and eliminate mosquito breeding grounds. That can mean time-consuming and mundane tasks such as emptying bird baths and garbage bins of standing water.
In lieu of active surveillance and insecticide sprays, mosquito control districts have beefed up citizen awareness campaigns with “tip and toss” messages encouraging residents to eliminate these small pools of water. They have also delivered door hangers for neighboring homes when a travel-related case is identified. In Charleston, S.C., interns were dispatched to 5,000 homes to educate families about Zika.
“Sometimes we’ll go out to one of these homes and they’ll have a dog dish with standing water in it, or a bunch of potted plants … one yard can affect the whole block,” said Ed Harne, lab technician with Charleston County Public Works.
Controlling Aedes is a cumbersome, property-by-property effort, said Kenn Fujioka, president of the Mosquito and Vector Control Association of California and manager of the San Gabriel Valley Mosquito & Vector Control District.
“I think vector control agencies could always use more resources, but we have a long history of managing with the resources we have,” he said.
Federal emergency dollars for Zika languished in Congress all summer, but $1.1 billion was included in a bipartisan budget bill that passed last month.
A substantial portion will go to local jurisdictions for their efforts but won’t reach those localities until December, Tom Frieden, director of the federal Centers for Disease Control and Prevention, said last week.
Longstanding mosquito collection methods differ and are usually not designed for Aedes. In Charleston, inspectors in the field track mosquitoes by counting how many land on their arms in one minute. In Mobile, Ala., flocks of sentinel chickens are placed in 13 sites around the surrounding county and blood tested. Efforts are further complicated because, according to some local officials, many jurisdictions had trouble purchasing state-of-the-art traps because the manufacturer can’t keep up with orders.
“There’s no way of telling” whether Zika outbreaks are going undetected, said Paul G. Folse, director of vector services at the health department for Mobile County, where before the Zika outbreak, Aedes mosquitos were considered a nuisance and not tracked. “We go into the neighborhoods looking for breeding sources, getting the word out to people, stepping up control efforts. Just like in Miami, we’re trying to limit the possibility of this expanding.”
The last time small mosquito districts saw a large investment in resources was in the early 2000s, when West Nile, spread by another species of mosquito, the Culex, first tore through the continental U.S., killing hundreds.
“Most jurisdictions are primarily organized around Culex,” said Alleyne. “Aedes is much closer to the home and likes to hang out in heavily populated places. … It has shown to be a very hardy insect.” Broad-based approaches like the application of insecticides designed to kill adult mosquitoes, he said, will not necessarily be effective.
To justify an aggressive mosquito control response against Aedes mosquitoes, Alleyne said, insecticide spraying often has to be localized to a specific neighborhood, or even a specific block. There must be “evidence there are human cases to warrant the policy,” Alleyne said.
The CDC said last month that the selective aerial spraying in the Miami neighborhood of Wynwood in August had proven effective in helping to stem the spread of Zika there.
In the likely event that the disease surfaces again next summer, surveilling the virus and collecting information will present many of the same challenges. “We basically have to start all over from ground zero,” Hotez said.