Zika Coming: Some of U.S. Lacks Mosquito Control

By Brenda Goodman, MA
WebMD Health News

Reviewed by Brunilda Nazario, MD

April 1, 2016 -- Mosquitoes carrying the Zika virus could be a problem in most states this year. At the same time, nearly half the country lacks any kind of mosquito control, health officials said Friday.

With warmer weather -- and mosquito season -- rapidly approaching, the CDC unveiled new maps painting a bleak picture of the issues facing states and counties as they prepare for local transmission of Zika.

The virus, which is primarily mosquito-borne, poses the biggest risk to pregnant women and their unborn babies. It's been linked to cases of microcephaly -- a serious, sometimes fatal condition in which the head and brain are smaller than normal -- in babies of infected women.

The first maps suggest Zika-carrying mosquitoes could show up in all but about 10 states in the U.S. this year, a much wider range than previously thought.

The second map, in stark black and white, shows how many counties lack even a single person whose job it is to tamp them down, a job called vector control.

About half of the U.S. doesn't have any vector control at all, including counties in areas expected to be at risk for local Zika outbreaks like southern Florida, Mississippi, Louisiana, and Texas.

"Really what we're dealing with is a patchwork of mosquito control operations in the country of varying quality," said Lyle Petersen, MD, director of the Division of Vector-Borne Diseases at the CDC and the man who is leading the agency's Zika response.

"There are many places around the country that have no vector control capacity at all," Petersen said.

"It's of real concern to me. We really have to put a concerted effort, rebuilding those programs that have eroded over the years," he said.

Peterson spoke at the CDC's Zika Summit, a meeting geared to helping state and local health officials get ready for the virus. More than 2,300 people participated, according to the CDC.

The new maps offer the CDC's best guess of where two different mosquito species that are known to be able to pass Zika to people may be this year.

They update maps created over a decade ago, which showed much smaller estimated U.S. ranges for these two species, Aedes aegypti, the "yellow fever" mosquito, and Aedes albopictus, the "Asian tiger" mosquito.

The older maps showed that these mosquitoes were concentrated in the Southeastern U.S., stretching only as far north as New York and as far west as Arizona. The new maps indicate that they might actually be found as far north as southern Maine and as far west as southern California.

The maps are based on the CDC's surveillance system, ArboNET, which tracks insect-borne diseases; medical studies; and an online survey of mosquito control districts in the U.S., as well as a surveillance system for insect-spread diseases run by Walter Reed Army Medical Center in Washington, DC.

Still, experts said, they are full of holes.

That's largely because the systems that track mosquitoes in the U.S. are set up to track culex mosquitos, which pass the West Nile virus, not the aedes species that pass Zika.

Christopher Taylor, executive director of the Cherokee County Health Department in northeast Texas, says he doesn't know whether his area even has Zika-carrying mosquitoes. "We don't trap or collect the mosquitoes," he says. Taylor says he has to look to neighboring areas that do collect mosquitoes to try to develop some prediction models to tell whether there is a heavier risk.

Trying to keep people safe in the rural area where he works "is daunting."

Even in areas that do have some kind of vector control, it is often geared more to controlling the nuisance of mosquito bites. It isn't usually connected to local health department efforts to control disease.

And even if an area has some kind of vector control, it might be very part time.

Paul Ettestad, the state public health officer for the New Mexico Department of Health, said the CDC's map of mosquito control districts tickled him.

"I had to kind of laugh because most of those colored-in areas is one guy in the county who drives a snow plow in the winter and does mosquito control in the summertime," Ettestad said.

What's more, even where areas do have well designed vector control, they might not be using poisons that actually kill the mosquitoes.

"We believe there's widespread insecticide resistance in many parts of the United States," Petersen said.

There is a real danger, he said, that counties might undertake an extensive spraying program for mosquitoes using a chemical that wouldn't kill the mosquitoes but might kill helpful insects, like bees.

"I'm really worried about that. There's always a balance of environmental and health benefits," he said. "If you're spraying something that's not effective, you're tipping that balance in the wrong direction."

But again, it would be up to these local programs to do the resistance testing to find out which insecticides would work.

"Unfortunately, it's not being done widely," he said.

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SOURCES: Lyle Petersen, MD, director, Division of Vector-Borne Diseases, CDC, Atlanta. Christopher Taylor, executive director, Cherokee County Health Department, Cherokee County, TX. Paul Ettestad, DVM, state public health officer, New Mexico Department of Health, Santa Fe, NM. Morbidity and Mortality Weekly Report, April 1, 2016. Zika Summit, CDC, April 1, 2016.

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