Report: Aerial spraying for West Nile was effective

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Denton County Health Department officials are feeling pretty good about the decision to counter the West Nile outbreak with aerial spraying after seeing a Centers for Disease Control and Prevention report.

The report, released earlier this month, says the aerial spraying had a measureable impact in preventing the West Nile virus in areas covered.

“That’s everything we could hope for,” said Bing Burton, Denton County Health Department director. “That is their scientific explanation for, ‘Yep, the spraying was effective.’ I felt very good about the spraying that we did, and I am glad they concluded it was effective.”

Following earlier September reports, Burton had previously said he wished to see higher mosquito kill numbers but that any progress against the spread was good.

One bullet point in the report that concerned Burton was related to ground spraying — CDC officials were not able to assess the impact of ground spraying.

Marc Fischer, epidemiologist with the CDC, said there was so much ground spraying by mosquito control districts and then by municipalities in those districts before and at the same time as the aerial spraying that it was difficult to put a number on the effect of ground spraying.

Burton believes the ground tactic was effective.

Ken Banks, Denton’s director of environmental services, has been monitoring mosquitoes and West Nile virus for the city for years and has noted that an outbreak, when it occurs, has a natural rise and fall.

“There’s a huge number of variables that affect it,” Banks said. “When an outbreak declines, it depends on a lot of variables — the weather, the bird population, what people are doing.”

CDC officials factored natural decline into their results, according to Fischer.

The way the analysis was done, it compared the time period before and after the spray with the same time period for areas not sprayed.

“In areas where spraying did occur, the decline was about two and a half times greater than in areas that were not sprayed.” he said.

The impact of aerial spraying could have been greater had it been done earlier, Fischer said.

“Certainly, the earlier in an outbreak that you could do an intervention, the more likely you are to prevent cases,” he said. “It’s a difficult decision when you’re talking about something as large, costly and [that] impacts as many people as an aerial spraying. In those counties in North Texas, they were doing a lot of interventions early, [but] if [aerial spraying] had been done earlier, it may have prevented additional cases.”

The spray applications, which occurred on Aug. 31 and Sept. 2, did not cost the county anything — the cost was paid by state and federal dollars.

“I thought we were incredibly fortunate,” Burton said. “I don’t know if that opportunity would come about again. We will need to be better prepared next time.”

Officials will prepare by trapping mosquitoes this year in the unincorporated area of Denton County. Last year, several municipalities trapped within their city limits, but this year the county will be trapping in the unincorporated areas. The trapped mosquitoes will be shipped to the Department of State Health Services laboratory in Austin for testing.

County officials met earlier this month with Denton County municipalities to discuss information sharing and to identify ways to optimize communication and plan to expand educational programs, which will continue to focus on the common preventative measures and emphasize source reduction.

In addition, Denton is preparing for another bad year, Banks said. The city’s committee on the environment has updated the surveillance and response plan, and will likely increase some of its public education efforts, in addition to considering ground spraying.

Staff Writer Peggy Heinkel-Wolfe contributed to this report.

BJ LEWIS can be reached at 940-566-6875. His e-mail address is blewis@dentonrc.

com.

Evaluation of West Nile Virus Outbreak by larrymmcbride


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