Aerial spraying results for mosquitoes carrying the West Nile virus missed estimates given by Clarke, the company that provided the service, by at least 10 percent, but county officials don’t expect another round of spraying this year.
Following the aerial spraying that took place between Aug. 31 and Sept. 2, Clarke officials estimated a 70 percent to 90 percent mosquito kill. On Wednesday, Denton County Health Department officials reported a reduction of 56 percent of all mosquitoes and 60 percent of West Nile carriers.
“I had hoped to see higher numbers, but killing 56 percent of the mosquitoes in the spray area is still a very good result and killing 60 percent of the Culex mosquitoes is even better,” said Bing Burton, Denton County health director.
The figures are based on the number of mosquitoes trapped before and after the aerial spraying, Burton said.
The 56 percent was reported to the county by Clarke.
The 60 percent resulted from the sum of several traps that captured 81 mosquitoes before spraying and only 32 mosquitoes after.
“When we considered only the mosquitoes left in a trap and exposed to the spraying, over 90 percent were killed,” Burton said.
Several communities with the highest numbers of human cases of West Nile experienced the most dramatic reductions in mosquitoes as a result of aerial spraying, a county press release stated.
Bob Martinez, the county’s emergency preparedness coordinator, said some areas with the most West Nile cases had a 94 percent reduction.
County Judge Mary Horn declared a health emergency in mid-August after a number of county residents were diagnosed with West Nile virus. Spraying was conducted by state contractor Clarke in Denton County and for 26 of 44 municipalities.
The number of new cases of West Nile virus has decreased substantially since aerial spraying; however, it is premature to conclude that the results are solely attributable to aerial spraying, the county reported.
However, the county says aerial spraying significantly reduced the mosquito population.
The Centers for Disease Control and Prevention will release a comprehensive regional report on this year’s West Nile virus season in the fall.
As of Wednesday afternoon, the health department had reported 92 positive mosquito pools and two West Nile-related deaths among the 167 human cases of the virus — 118 of those cases were diagnosed as West Nile fever, which has milder symptoms, and 49 diagnosed as the more serious neuro-invasive disease.
JOHN D. HARDEN can be reached at 940-566-6882. His e-mail address is firstname.lastname@example.org .