Infection hazard
Details
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Event title
United States - First mosquito sample tests positive for West Nile virus in Denver
Source
Severity
Low
Event date (UTC)
2025-07-04 09:09:14
Last update (UTC)
2025-07-04 09:09:14
Area range
Local event
Address/Affected area(s)
Denver, CO
The first trace of the West Nile virus this season was found in Denver through a positive mosquito sample.On Thursday, the Denver Department of Public Health & Environment announced that the virus was found through routine mosquito sample testing. This marks the first detection of the season for the city.The virus has been detected in other parts of Colorado. The West Nile virus was detected in Larimer County in late June through a mosquito sample. In previous years, there have been reported human cases. Last year, the human case of the season was found in Denver in August.If contracted, the department said it can cause common symptoms like fever, extreme fatigue, headache and body aches. In some cases, it can also cause rashes and swollen lymph nodes. Severe cases can lead to inflammation of the brain or meningitis, which can cause loss of vision, paralysis, coma, tremors, convulsions and even death. These symptoms usually appear three to 14 days after being bitten.The department said the virus usually spreads through birds and mosquitoes, but can spread to humans through infected mosquito bites. It can be transmitted anytime mosquitoes are active, which is usually between May through the first hard freeze, around October or November, in Colorado.People over 50 years old or with weakened immune systems are at higher risk of developing serious illness, but everyone can contract the virus. However, there are precautions you can take.
Precautions against West Nile virus
The department said to remember the “4Ds” to avoid infection:
Defend: Use insect repellent when you are outdoors, particularly repellants that contain DEET, picaridin, IR3535 and oil of lemon eucalyptus.
Dress: Wear closed-toe shoes, long sleeves and pants to cover as much exposed skin as possible.
Drain: Drain any standing water around your property at least once a week to eliminate mosquito breeding grounds.
Dusk and Dawn: Mosquito activity typically peaks at dusk and dawn. To reduce your exposure to mosquitoes, limit any outdoor activities at these times.
Denver is also testing mosquito samples each week and taking proactive measures, like reducing breeding sites, to stop the spread.
The department said anyone with symptoms should talk to a doctor and get tested.