Update 8/18/2023

Weld County is continuing to see Culex mosquito numbers just slightly above the 5-year average. However, this week there was an increase in mosquito pools testing positive, personal precautions should continue to be taken.

Increased risk of West Nile Virus

Weld County Public Health has reported that mosquito pools have tested positive for West Nile Virus (WNV) in Weld County and there continues to be extremely high numbers of Culex mosquitoes for this time of year.  

A health department contractor monitors mosquito traps on a weekly basis in three zones of Weld County: the Greeley, Evans, Kersey, LaSalle area (Zone 1); the Johnstown, Milliken, and Platteville area (Zone 2); and the Firestone, Dacono and Fort Lupton area (Zone 3).  Mosquitoes trapped in all three zones have tested positive for WNV with a higher concentration in Zone 2.  

The West Nile virus is transmitted predominantly by Culex mosquitoes. Culex are medium-sized mosquitoes that are brown with whitish markings on the abdomen. They typically bite at dusk and after dark. By day they rest in and around structures and vegetation.

Adult Culex mosquitoes do not fly far from where they develop as larvae. And unlike other mosquitoes that die with the coming of the first hard frost in autumn, the house mosquito can “over-winter” in protected places like sewers, crawlspaces and basements.

Culex lay “rafts” of eggs on still water in a variety of natural and man-made containers, including tree holes, ditches, sewage and septic system water, catch basins (storm drains), non-chlorinated swimming and wading pools, decorative ponds, bird baths, flower pots, buckets, clogged gutters, abandoned tires, and water-retaining junk and debris of all sorts. They cannot develop in running water and water that is present less than a week.

Health officials recommend following the four “D’s” to prevent mosquito bites:

DRAIN standing water around your house weekly. Remember to drain water from tires, cans, flowerpots, clogged rain gutters, rain barrels, toys and puddles

DUSK and DAWN are when mosquitoes are most active. Limit outdoor activities and take precautions to prevent mosquito bites during these times.

DEET is an effective ingredient to look for in insect repellents. Other repellents containing picaridin, IR3535, oil of lemon eucalyptus, or para-menthane-diol are also effective against mosquitoes.  Always follow the product label instructions carefully.

DRESS in long sleeves and pants, and a hat, in areas where mosquitoes are active.

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