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West Nile virus detected in four Colorado counties, as experts brace for active mosquito season

Posted at 7:50 PM, Jul 06, 2023
and last updated 2023-07-07 08:06:04-04

DENVER — State health officials are warning residents to protect themselves against West Nile virus after finding mosquitoes carrying the virus in at least four Colorado counties so far.

Tests of mosquitoes in Boulder, Delta, Weld, and Larimer counties all returned positive results. No human cases have been reported yet this year, but 206 human cases were reported in 2022, with 20 of those resulting in death.

Dr. Robert Hancock, a professor of biology at Metropolitan State University in Denver, also warned that the wet and cool spring and early summer we are experiencing is leading to a boom in mosquito populations. More standing water throughout the state, in addition to more moist soil, has created a perfect breeding ground for the flying insects.

“We are making lots of mosquitoes [through] tremendous increases in breeding areas,” Dr. Hancock explained. “And, we are keeping the mosquitoes that we make alive, because it is so humid and relatively cool. Those are the things that kill mosquitoes: Temperature and lack of humidity.”

West Nile virus detected in four Colorado counties, as experts brace for active mosquito season

More mosquitoes doesn’t necessarily mean more West Nile virus, because the “relationship between West Nile and mosquito abundance is multifaceted,” Dr. Hancock said. Still, the risk could be elevated due to the fact that the species most likely to transmit the disease in Colorado lays its eggs on water.

Most people infected with West Nile Virus don’t experience symptoms, but some can become seriously ill and even die. Dr. Hancock experienced this grave threat through his own family, when his brother developed a serious neuroinvasive case of West Nile virus in 2017.

“It took months of rehab. He had to live in a rehab facility. And he’s still alive and with us today, but he still can’t swallow,” Dr. Hancock said. “West Nile is no joke. If you want to be a Coloradan that enjoys the outdoors in a year like this year, or any year, there are precautions that you take.” 

The Colorado Department of Public Health and Environment (CDPHE) says most human cases of West Nile virus are reported in August and September. To protect yourself, the agency recommends:

  • Limiting activities outdoors at dusk and dawn, when mosquitoes are most active
  • Wearing long pants, long-sleeved shirts, and socks in areas where mosquitoes are active
  • Using an insect repellent containing DEET, picaridin, oil of lemon eucalyptus, or para-menthane-diol

Dr. Hancock also stressed the importance of eliminating sources of standing water near your home, which can become a breeding ground for the mosquitose that carry West Nile.

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