🦟 West Nile Virus

West Nile virus is most commonly spread by infected mosquitoes and has been regularly reported in Colorado since 2002. The greatest risk to humans occurs from June through early September, when mosquitoes are most active. Reports may continue through October until colder weather causes mosquitoes to go dormant.

How West Nile Virus Spreads

• Most people are infected through the bite of a mosquito carrying the virus.
• Mosquitoes become infected after feeding on birds carrying the virus.
• Infected mosquitoes can spread the virus to humans, birds, and other animals (such as horses).

Who Is at Risk?

• Everyone can be infected if bitten by an infected mosquito.
• Highest risk: People over age 60, those who spend significant time outdoors, and people with health conditions such as cancer, diabetes, hypertension, kidney disease, or weakened immune systems (including organ transplant recipients).

Symptoms

• Most people infected do not develop symptoms.
• About 1 in 5 infected people may develop mild illness such as: headache, muscle or joint pain, rash, or gastrointestinal symptoms.
• Severe cases (rare) may cause serious brain infections such as meningitis or encephalitis, with symptoms including: sudden high fever, severe headache, stiff neck, confusion, tremors, or coma.
• Severe cases can result in permanent brain damage or death, especially in older adults.

Timeframe: Symptoms usually begin 2–6 days after a mosquito bite, but can take up to 14 days to appear.

Treatment

• There is no specific treatment for West Nile virus.
• Mild illness usually improves on its own with rest, fluids, and over-the-counter pain relievers.
• If you experience severe headaches, confusion, or other serious symptoms, contact a health care provider immediately.

Prevention Tips

• ✅ Use insect repellent when outdoors. Products containing DEET, picaridin, IR3535, oil of lemon eucalyptus, or para-menthane-diol are most effective. (Learn more from the EPA)
• ✅ Limit outdoor activity at dusk and dawn when mosquitoes are most active.
• ✅ Wear protective clothing — long sleeves, pants, and socks. Apply insect repellent to clothing for added protection.
• ✅ Eliminate standing water around your home at least weekly: empty water from tires, cans, flowerpots, gutters, rain barrels, birdbaths, toys, and puddles.
• ✅ Install or repair screens on windows and doors to keep mosquitoes out.

When to Seek Medical Care

If you or a loved one develops severe symptoms — such as a high fever, intense headache, confusion, or neurological changes — contact a health care provider immediately.

Learn More

For more detailed information, visit the CDC West Nile Virus page.