The West Nile debate: to spray or not to spray?

07/25/2014 5:16 PM

07/25/2014 5:17 PM

When a Benbrook mosquito trap became the first this year to test positive for the West Nile virus, city officials didn’t hesitate to ground spray.

Benbrook was following Tarrant County Public Health’s guidelines to spray after a positive mosquito trap test.

And when North Richland Hills officials were notified Friday of a positive sample at a trap in Northfield Park, they laid out a schedule to ground spray Friday, Saturday and Sunday nights in a radius around that trap for “maximum effectiveness,” said spokeswoman Mary Peters.

But it was a different story earlier this month in Colleyville and Bedford when those cities had positive samples. Both cities chose not to spray. This week, when that same Bedford trap tested positive twice and that same Colleyville trap tested positive once, they both stuck by their decision.

Bedford spokeswoman Natalalie Foster said the city “would discuss all options” if they had a human case but the preference would be to avoid spraying.

“Bedford has no plans, at this time, to spray,” Foster said via email. “We are focusing on preventative treatments with an emphasis on locations where a positive sample was discovered. The City is also concentrating on public/resident education and awareness to help combat mosquito breeding. We did spray in 2012 and received negative feedback from the community, both health and environmental concerns were raised.”

Colleyville’s policy doesn’t rule out spraying. The city might consider it if there is a cluster of human West Nile cases and positive mosquito samples in a targeted area. Any spraying would be done in conjunction with larvicide treatments.

No human cases in Tarrant

Anita Kurian, associate director of Environmental Health for Tarrant County Public Health, said the county can only make recommendations.

“We as a county can establish guidelines but it’s up to the city to decide for themselves,” Kurian said.

So far this year, Tarrant County has tested 2,135 samples with 12 testing positive. There have been no reports of humans being infected with West Nile in Tarrant County.

Dallas County has reported two human cases — one in Dallas and one in Coppell — with 13 traps testing positive around the county.

The debate over West Nile goes back to 2012 when North Texas was inundated with cases. Texas led the nation that year with 1,868 West Nile cases, including 89 deaths.

Last year, the number of cases plummeted with Dallas County having 16 cases and two deaths while Tarrant County had 10 cases and two deaths.

This year is looking more like 2013 but Kurian is watching for any surge in cases.

The spraying debate

While Tarrant County recommends spraying after samples test positive, Kurian said the data is far from conclusive on its effectiveness.

Spraying will reduce the number of adult mosquitoes but it isn’t clear yet how much it reduces the incidence of West Nile infections in humans.

“The surveillance data is changing year to year,” Kurian said. “It’s going to take several years before we can establish a trend.”

Dallas County Public Health Director Zachary Thompson is more adamant about ground spraying. While he acknowledges each city must decide on its own, he believes spraying does make a difference.

“If we see a lot of mosquitoes, if we got positive traps, that tells us we need to get our there immediately and do ground spraying,” Thompson said. “We need to eliminate those adult mosquitoes from spreading and prevent additional infections in that area.”

In Tarrant County, Fort Worth officials are reluctant to spray and would only consider targeted spraying in certain circumstances; Arlington’s policy is similar to Colleyville.

Studies inconclusive

Many residents oppose spraying for concerns about its possible harm to the environment and there are fears that it could impact pets and humans.

Joon Lee, an assistant professor of environmental and occupational health sciences, who oversees the sampling and testing program at the University of North Texas Health Science Center, said there are no clear-cut answers when it comes to spraying.

“An insecticide spraying would help decrease of mosquito numbers in a short period of time,” said Lee, who added that the “spraying effect on reduction of West Nile Virus activities couldn’t be scientifically measured unless West Nile Virus activities were high.”

A study published in the April 2014 edition of the American Journal of Tropical Medicine and Hygiene looked at the aerial aerial spraying in Tarrant, Dallas, Denton and Collin counties in 2012. The study found a 2.5 percent decrease in neuroinvasive cases, the most serious form of West Nile, in treated areas compared to untreated areas. But the study acknowledged that data was limited on the effects of ground spraying.

Kurian said they have received calls from residents suggesting alternative methods to combating mosquito populations and West Nile but Tarrant County Public Health will follow the guidelines recommended by the Centers for Disease Control and Prevention and the Environmental Protection Agency.

Bill Hanna, 817-390-7698

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