DENVER (KDVR) — Boulder County Public Health and Weld County both confirmed within two days that there have been the first positive tests of West Nile virus in mosquitoes in those counties.

In a press release on Tuesday, the Boulder County health department said that the positive mosquitoes were collected last week from a trap site in Niwot East; however, there have been no other positive tests in other areas of the county thus far.

“We’ve seen low numbers of mosquitoes so far, but we expect them to increase as the season goes on,” said Marshall Lipps, environmental health specialist at Boulder County Public Health, in the release. “However, West Nile virus transmission risk still exists in Boulder County and surrounding areas, and we encourage the community to take personal precautions to prevent mosquito bites. Finding a positive mosquito in one location doesn’t mean the risk is limited to that area. West Nile virus can still be present anywhere across the county.”

Weld County said in a press release on Monday that following tests in three different zones, two of those zones found positive tests from mosquitoes. The two zones that tested positive included the municipalities of Greeley, Evans, Kersey, LaSalle, Johnstown, Milliken and Platteville.

“The increasing hot weather often leads to favorable conditions for the Culex mosquito that carries West Nile virus,” said Jason Chessher, executive director of the Weld County Health Department, in the release. “The public needs to be vigilant, because West Nile Virus has a permanent summer presence in Colorado.”

This comes after Larimer and Denver counties both confirmed in June first positive tests of mosquitoes with West Nile virus.

The West Nile virus spreads through infected mosquito bites, which can cause flu-like symptoms and even severe illness in people. Weld County noted that most people infected don’t experience any symptoms.

Both counties also remind residents of the four "D's" to prevent mosquito bites:

• DEET: Use insect repellent with DEET or other EPA-approved ingredients.
• Dress: Wear long sleeves and pants when outdoors.
• Dusk to Dawn: Limit outdoor activity during these peak mosquito hours.
• Drain: Remove standing water around your home where mosquitoes can breed.

Mosquito season in Colorado typically lasts from late April through mid-October, ending with the first fall freeze.