Mosquito Sample Tests Positive for West Nile Virus: Insecticide Spraying

Oct 19, 2016

mosquito-trap-500A mosquito trap sample collected last week on the north side of downtown Georgetown has tested positive for West Nile Virus. This testing is part of the City of Georgetown’s participation in the Williamson County and Cities Health District’s Integrated Mosquito Management program. The positive test was indicated in lab results received yesterday afternoon from the Texas Department of State Health Services lab in Austin.

The sample was collected from a trap on the north end of the downtown area on October 11. The species of mosquito that tested positive for West Nile Virus was Culex quinquefasciatus, also known as the Southern house mosquito. This species of mosquito has a flight range of about one mile.

Due to the number of children and adults who will be outside in the evening for Halloween activities over the weekend, the City is implementing insecticide spraying in the vicinity of the positive sample. In the late evening tonight, a City vehicle will use a pyrethrin-based insecticide along the street right-of-way and in public parks, weather permitting. Pyrethrin is a chemical that can be found in chrysanthemums.

mosquito-spraying-map-10-19-16A map is included showing the area where application of the insecticide is planned in the downtown area. The use of the insecticide will reduce the adult mosquito population in that area. Spraying will be done if the wind speed is less than 10 mph.

The City also continues to use larvicide tablets to treat standing water found on public property. “Residents have a key role in reducing mosquito breeding areas by draining pans and flower pots and putting larvicide disks in puddles or ponds on private property,” says Mark Miller, transportation services manager.

There are currently no reported human cases of West Nile Virus in Williamson County, and the County has not had any reported human cases since 2014.  West Nile Virus should not be confused with other mosquito-borne viruses.

What you can do

Mosquitoes breed in standing or stagnant water. Eliminating places where mosquitoes can breed and reducing the chances of mosquito bites are the most effective lines of defense against exposure to West Nile Virus.  As part of its Fight the Bite campaign the Health District recommends the 3 Ds of mosquito safety.

  • Drain standing water in flower pots, pet dishes, or clogged gutters so mosquitoes don’t have a place to breed and treat water that can’t be drained,
  • Defend by using an EPA-approved insect repellent, and
  • Dress in long sleeves and pants when outdoors.

For more information, go to the WCCHD website at or visit the Texas Department of State Health Services West Nile website at

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