Case of West Nile virus confirmed in another county on Colorado's rain

By Alan Gionet

Updated on: August 3, 2023 / 12:26 PM / CBS Colorado

Another human case of the West Nile virus has shown up as Colorado's rain soaked Front Range plays host to a banner year for mosquitoes. This time the West Nile case is in Boulder County.

"The resident, in their 40s, was believed to be infected while in Lafayette and has not been hospitalized," said Boulder County Health in a statement.

West Nile virus has been found in mosquitoes in seven of the 13 counties that have tested mosquitoes this season. That includes Arapahoe, Boulder, Delta, Denver, Larimer, Pueblo, and Weld counties. The Colorado Department of Public Health and Environment says all three of Denver's sentinel surveillance zones for West Nile virus are positive and that, "may mean bad news for human cases of West Nile virus in Denver," said the CDPHE in its own statement on the issue.

RELATED: First 2023 Northern Colorado West Nile virus death confirmed after rapid spike of culex mosquitoes

Eight out of 10 cases of the West Nile virus in humans are asymptomatic.

"Of those that do experience symptoms it's described as febrile. So it'll be a headache, feel very tired and achy a very small portion of those that do experience symptoms develop neurologic symptoms. And those are the cases that can be dangerous and can lead to death," said CDPHE medical entomologist Dr. Chris Roundy.

Precipitation has created a surging population of mosquitoes along the Front Range this year. But as summer started, they were mosquitoes that do not carry West Nile.

"Earlier this year we saw a spike in aedes mosquitoes which don't transmit human diseases, but are really nasty biters. But late June we saw a sharp change. And we saw a very rapid increase in those culex mosquitoes that do transmit West Nile. The small brown culex mosquitoes tend to bulk up their populations later in the summer. August is the worst month of the year for West Nile.

Spraying is effective at keeping mosquito populations down, but not all communities spray.

"I do wish that we could spray for mosquitoes everywhere, that is up to the local counties and cities to make their own decision and call on that," said Roundy.

Signs were up by Waneka Lake, the reservoir in Lafayette Wednesday indicating spraying this week.

"Some of our highest concentrations do tend to be in more rural areas. This is harder for mosquito control efforts to be effective," Roundy added.

Culex mosquitoes are known to travel up to two miles from their hatching place. They have no home, but wander in search of a blood meal. The West Nile virus is found in birds and the mosquitoes move it from birds to humans.

Repellants with DEET are the most effective in keeping mosquitoes at bay. Experts also suggest long sleeves and pants. Drain standing water weekly. If you cannot Dr. Roundy suggests Bti pellets. Bti is a naturally occurring bacterium found in soils. When used properly it does not harm people, animals or other insects including honeybees. Mosquitoes are also most active between dusk and dawn.

Alan Gionet is a reporter for CBS News Colorado. Read his latest reports or check out his bio and send him an email.

First published on August 3, 2023 / 7:47 AM

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