Denver health officials announed Monday that they had confirmed the city’s first human case of West Nile virus this year, hitting the milestone a bit later than usual.
Typically, the city has its first known West Nile case in August. The majority of people infected with West Nile have no symptoms, and most who do feel sick don’t seek testing, because the virus resembles the flu.
Other counties identified cases earlier in the summer, indicating the virus was circulating in mosquitoes. Jefferson County had Colorado’s first case of the year in early June.
Colorado has had a relatively low , with 40 counted so far. Two people have died and 20 have needed hospital care.
Over the last decade, the annual number of cases statewide ranged from a low of 35 in 2020 to a high of 634 in 2023.
The weather was favorable for mosquitoes this year, with a relatively warm winter allowing more to survive and a hot summer allowing the bugs to mature faster. The number of mosquitoes doesn’t always correlate with confirmed West Nile infections, however. Mosquitoes typically get infected after biting birds, and the amount of virus in the avian population varies from year to year.
Mosquito activity generally slows down as temperatures start to drop in the evenings, but doesn’t stop completely until the first hard freeze, according to the Denver Department of Public Health and Environment.
