Tarrant County mulls West Nile aerial spraying: 5 things to know

During the height of the 2012 West Nile virus outbreak, Dallas and Denton counties used aerial spraying to fight the virus, while Tarrant and Collin counties did not.

This year, Tarrant County Public Health Director Vinny Taneja is asking Tarrant County commissioners for the authority to use aerial spraying. The commissioners could make a decision at Tuesday’s meeting.

“The plan is to get the authorization and be ready,” Taneja said. “We also need to have a better conversation with our city partners about who’s willing to participate and who can’t.”

If he gets approval to move forward, aerial spraying wouldn’t happen right away, but the county would be ready if there is another increase in positive traps and the number of mosquitoes testing positive for West Nile. Dallas County Health and Human Services got approval in July but has not sprayed from the air this year.

Here are five things you need to know.

What type of mosquito carries West Nile?

The Culex mosquito carries West Nile virus and bites at night. The mosquito usually gets the virus from biting infected birds. The Zika virus is carried by the Aedes mosquito, which bites in daytime.

Is aerial spraying effective?

Depends on whom you ask. Public health officials say it can reach Culex mosquitoes up in the trees, helping reduce the risk of humans getting bit by infected mosquitoes. A 2014 study in the American Journal of Tropical Medicine and Hygiene of the 2012 aerial spraying in Dallas and Denton counties found that the incidence of neuroinvasive disease, the most serious form of West Nile, dropped from 7.31 per 100,000 people to 0.45. Dallas County has discussed aerial spraying for Zika if it starts having locally transmitted cases. Spraying for Zika would have to take place in the daytime.

Would every city take part?

No. Taneja said some Tarrant County cities have already said they couldn’t help pay for the spraying. Some cities may also oppose aerial spraying or believe that West Nile hasn’t reached a high enough threshold in their community. The recent cool, rainy weather could also influence whether to spray. The break from 100-degree heat should slow down mosquito activity, but Taneja said it could be a “blip in the data” before activity surges again.

“It doesn't really change the overall argument that we need to get into a position to respond,” Taneja said.

How much will it cost and who will pay for it?

The cost to spray the entire county one time by air would be about $1 million. Targeted spraying would cost $350,000 to $400,000 each time. The county and participating cities would share the costs.

What type of pesticide would be used?

Typically, the aerial spray companies use Duet, a pyrethroid that is effective against adult mosquitoes and is low in toxicity to mammals and birds. Duet contains sumithrin and prallethrin.

There have been concerns about its impact on beneficial insects such as bees. Mike Merchant, a Texas A&M AgriLife urban entomologist, said it “should not be a major impact on bee colonies” since it is sprayed at night in low doses when bees are not active. But in a 2012 report, Merchant said that “insecticides used in mosquito control programs are toxic to honey bees. Left unprotected, some bee colonies will suffer some mortality from aerial sprays, particularly those bees that cluster outside hives at night.”

Some environmentalists including Luke Metzger of Environment Texas argue that aerial spraying should never be used: “We can best protect public health and wildlife through common-sense measures like eliminating standing water or targeted ground spraying if necessary.”

Taneja says that ground spraying and getting rid of breeding sites have been used and that the number of infected mosquitoes continues to climb.

“We need another tool in the toolbox,” Taneja said.

This story was originally published August 19, 2016 at 3:55 PM with the headline "Tarrant County mulls West Nile aerial spraying: 5 things to know."