The Culex is loose.
Public health officials are advising anyone planning on celebrating Fourth of July outdoors that millions of the genus of mosquito, known as Culex, which carries West Nile virus are stealth and hungry.
The first person hospitalized with neurological symptoms for the 2024 season was infected in Arapahoe County, according to the Colorado Department of Public Health.
Scientists have been identifying the Culex mosquito in their traps for weeks.
“These mosquitoes have been here since the beginning of June. We need to protect ourselves,” said Jefferson County Public Health Environmental Health Specialist Rachel Reichardt. “We are an epicenter of this disease.”
Still, this year is "not as crazy as last year" when abnormal amounts of rain presented a perfect breeding ground for the bugs, according to Anna Wanek of Vector Disease Control International Lab in Broomfield.
"That doesn't mean people shouldn't be careful," she said.
There is no cure for the West Nile virus in humans, but there is a vaccine for horses — which are hit particularly hard by the disease.
Last year more Coloradans died from West Nile than any other state. Fifty-one people succumbed to the virus in Colorado in the 2023 season, which stretches from June until around the end of September. That’s when cold temperatures usually kill off the mosquitoes for the winter.
Last year in Colorado, a total 634 people reported the West Nile virus. The state with the second-most reported cases, California, had 473 total — but it also has a much larger population.
The four D's
West Nile can be avoided, Reichardt said, if partiers, fireworks-watchers and parade-goers follow the "four D’s:"
- Dawn and dusk: Use caution at these times that the Culex feed.
- Defense: Use mosquito repellant you are comfortable with. Reichardt said that if DEET is not for you, “lemon eucalyptus oil has been found to be protective.”
- Drain: Mosquitoes can breed in the smallest puddle. Said Reichardt: “They love stagnant water to breed in. When rain comes, dump out the planters and buckets around your home.”
- Dress: To prevent bites, wear long sleeves and pants, which can be loose-fitting for relief on these hot days.
Eighty percent of people who are bitten by a Culex mosquito that is infected with the West Nile virus will not suffer symptoms. Those who do could experience a fever, headache and skin rash. More serious complications include swollen lymph nodes, disorientation, muscle weakness and coma.
“People do die,” said Reichardt, who added that scientists cannot predict who will get sick.
Some cities don't spray so it's up to you
Though Colorado has 54 different breeds of mosquito, Culex is the primary WNV carrier that then transfers to humans by the bite of a breeding female.
Dozens of Colorado cities do not spray for mosquitoes, including: Denver, Boulder, Castle Rock, Lakewood, Monument and Centennial.
The chemical used to spray comes from a chrysanthemum plant. Permethrin is lethal to ants, flies, moths, fleas as well as mosquitoes, but is also toxic to pollinators.
In Weld County, mosquito spraying is performed in almost every city, including: Greeley, Firestone, Hudson, LaSalle, Frederick, Windsor and Dacono.
Five West Nile virus tidbits
- There’s a WNV vaccine for horses, but not for humans.
- Only female mosquitos bite for their needed “blood meal.” The protein supplies the nutrition they need to get them through the egg-laying process.
- Mosquitos are attracted to smell, so heavy breathers who emit CO2 are more likely to be bitten by them. Also attractive to mosquitos are flowery perfumes (they smell like the nectar they crave) and sweat.
- WNV was first isolated in a woman in the West Nile district of Uganda in 1937. Sixty-five years later, WNV first appeared in Colorado (2002).
- Mosquitos do not have the ability to distinguish between human blood types and thus are NOT attracted to particular blood types.
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