Scientists at Colorado State University (CSU) have detected a notably high number of Culex mosquitoes in northern Colorado this season, which could translate into high infection rates of West Nile virus (WNV). But so far there is no indication that the virus is spreading quickly from mosquito populations to birds, horses, or people.

A wet spring and summer and the resulting large mosquito population create high potential for the spread of the virus, but to date it has turned up in only a small number of mosquito samples, CSU experts say.

Still, public health agencies advise precautions. Key steps include draining standing water around your yard, garden, and farm; wearing long sleeves and pants, especially from dusk through dawn, when mosquitoes are most active; and using insect repellent with DEET.

The year’s first human case of the disease in Colorado was detected in a Mesa County man on July 8. On July 24, the CSU Veterinary Diagnostic Laboratories confirmed the state’s first two equine cases of West Nile virus, in horses from Boulder County and Alamosa County.

Greg Ebel, BA, SM, ScD, director of CSU’s Arthropod-Borne and Infectious Diseases Laboratory, said the number of Culex mosquitoes trapped in Larimer County during the first few weeks of testing this summer was higher than it has been seen since 2007, a severe year for the virus. Culex is a family of mosquitoes that spreads the virus through bites. Two Culex mosquito species, which are prevalent in Colorado, have been found to be particularly effective vectors.

Ebel’s lab, which performs testing for the city of Fort Collins