West Nile Virus

West Nile Virus is spread through infected mosquito bites. In Weld County, mosquitoes are primarily active from June through early September.

Mosquito surveillance (trapping) has started for 2025 and mosquito testing will begin soon as well.

Updated - July 25, 2025

Positive Mosquito Pools

Positive Raptors

• week of 6/23/2025 - one collected in Zone 2
• week of 7/7/2025 - two collected in Zone 1, two collected in Zone 2

Human Cases

• First case identified the week of 7/21/2025.

Prevention:

• Wear approved insect repellent when working outdoors or participating in outdoor activities.
• Wear long sleeved shirts, pants, and socks in active mosquito areas.
• Treat clothing and gear, such as tents, with insect repellent.
• Use screens on windows and doors, and repair any holes.
• Use air conditioning when possible.
• Check for water-holding containers both indoors and outdoors.
• Empty week-old water from tires, buckets, planters, toys, pools, or trash containers.
• Use larvicides to treat large containers of water that will not be used for drinking.

Repellents containing DEET, picaridin, IR3535, lemon eucalyptus oil, para-methane-diol, and 2-undecanone provide the best protection.

Is DEET Safe?

There is no reliable evidence that DEET causes cancer and DEET toxicity rarely occurs when it is used as directed. It is not recommended to spray your eyes, mouth, cuts, or irritated skin. For children older than 2 months old, it is recommended to spray repellent onto your hands and then apply to the child’s face. Mosquito netting is recommended by the CDC for infants younger than 2 months old.

Who can contract West Nile Virus?

Anyone can develop symptoms, but those most at risk for severe infection include individuals over the age of 60 and individuals with pre-existing conditions such as cancer, diabetes, hypertension, kidney disease, and individuals who received an organ transplant.

For more information:

Centers for Disease Control