West Nile virus cases in Colorado are up this year, likely due to the hot, moist summer

Hart Van Denburg/CPR News
A downpour blows in over the La Garita Mountains in Saguache County on the west side of the San Luis Valley, Thursday, June 30, 2022.

Public health officials are warning Coloradans to cover up and spray insect repellent as West Nile virus cases continue to climb above normal levels. 

State data shows there have been 63 confirmed cases of the West Nile virus this year. That’s on pace to shatter the rolling five-year average of 99 cases per year. About two-thirds of this year’s cases have resulted in hospitalization. 

West Nile virus is most commonly spread through mosquito bites. The virus is not spread through respiratory droplets or fluids. 

Deputy state epidemiologist Jennifer House said recent weather conditions have increased the number of mosquitoes in Colorado, as well as the amount of virus active in each insect. 

“The hot summer that we've been seeing could be contributing to a higher viral load in the mosquitoes,” House said. “We're unfortunately not done with that yet. The risk will remain high until we have a good hard freeze in the area.”

Most people infected do not develop any symptoms. Those who do mostly face a “febrile illness,” which consists of symptoms such as fever, joint pains, diarrhea or a rash. Those infected usually make a full recovery, but fatigue and weakness could last for months afterwards. Still, about one in 150 people infected could develop a severe illness that impacts the central nervous system. 

“The neuroinvasive cases are the individuals that often end up hospitalized and can have long term effects from the infection. And unfortunately some people can die from it,” House said. 

There have been five confirmed deaths since the beginning of 2022. 

So far, a majority of the cases are concentrated in Montrose County.

The southwest Colorado county is giving out a limited number of free “dunks,” or insect larvicide, which prevent mosquitoes from laying eggs in water for over a month. Lisa Gallegos, the communicable disease specialist for Montrose, said the tool is also available at many major retailers. 

Until summer ends, Gallegos said there are easy ways to protect yourself against mosquito bites and the potential for contracting the virus.

“[Coloradans] should make sure that they're using repellent, which contains ‘DEET’ in it,” Gallegos said. “If you're out at dusk or dawn, wear long pants, socks, and long sleeve shirts to protect yourself. And if possible, try not to go out during those times.” 

If you develop symptoms similar to West Nile virus, a test can be administered by personal healthcare providers. There are no vaccines or medications available to treat the virus.