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West Nile virus alert: High levels of infected mosquitos in Boulder County

West Nile virus alert: High levels of infected mosquitos in Boulder County

4-to-24 times higher than normal

Protect yourself and your family

Pools of mosquitoes from multiple traps in Boulder County have tested positive for West Nile virus (WNV) at a high level — 4-to-24 times higher than normal. Unfortunately, the wet weather followed by high temperatures creates an ideal environment for mosquitos to breed. Take time to protect yourself and your family.

What are WNV symptoms?

West Nile Virus (WNV) is a potentially deadly or crippling disease spread through common mosquito bites.

Most people infected with the virus won’t even feel sick, but 1 in 5 will suffer a flu-like illness that can last longer than one week and, in some cases, more than three months. Symptoms can include:

  • fever
  • extreme fatigue
  • head and body aches
  • a skin rash

Many infected people will lose time from work and have difficulty performing normal daily activities. A severe WNV infection can lead to meningitis, encephalitis, paralysis or even death, so it’s important to protect yourself and your family.

Fight the Bite: Pay attention to the 5 Ds

There is no vaccine to prevent WNV. Also, there are no antiviral therapies for WNV, so prevention is the mainstay of protection. 

The best way to prevent an infection is to protect yourself from mosquito bites. You can do that by remembering the “5 Ds”:

  • DAWN and DUSK are the peak mosquito-biting periods. Take extra care to use insect repellent and protective clothing during these periods.
  • DRESS in long sleeves, long pants, socks, and closed shoes during peak mosquito hours or when in areas of high mosquito activity, including near weeds and tall grass or around water.
  • DEET 30-35% is an effective insect repellent, but there are alternatives:
    • Picaridin (known as KBR 3023 and icaridin outside the US)
    • IR3535
    • Oil of lemon eucalyptus (OLE)
    • Para-menthane-diol (PMD)
    • 2-undecanone
  • DOORS and windows should have well-fitting screens. Check screens for holes that may allow mosquitoes inside.
  • DRAIN standing water around your home. Mosquitoes will breed and multiply in the stagnant water found in clogged gutters, empty wheelbarrows, and unused flowerpots. 

More information about West Nile virus, mosquito activity in Boulder County and precautionary steps is available at

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