Yolo County reports first death of West Nile virus in 2026
Hot summer weather and long days increase chances of exposure
By HANNAH OSBORN — city@theaggie.org
On Sept. 8, Yolo County Public Health issued a press release, confirming the first human death from West Nile Virus in Yolo County this year. The individual had the neuroinvasive form of the virus, which is the most severe in impact. The announcement followed the county’s first confirmed human case in 2026, one of 18 this year in the state.
“The death comes as West Nile virus activity has increased in both Yolo County and statewide, with more mosquito samples testing positive for the virus,” the press release reads. “Public Health has confirmed two additional cases of neuroinvasive West Nile virus in county residents this year, after only recording a single case in 2025.”
Davis Arbovirus Research and Training (DART) is a UC Davis Veterinary Medicine program composed of two laboratories studying mosquito-borne viruses. Professor Chris Barker, principal investigator of the Barker Lab, shared how university research is addressing the spread of West Nile virus.
“My lab’s research seeks better ways to detect and control risk of mosquito-transmitted viruses like West Nile and dengue viruses,” Barker said via email. “As examples of our work, we are studying the effects of wide-area vector control on West Nile virus infection in mosquitoes and we are experimenting with a more targeted way to control West Nile virus using ivermectin-coated bird feed that is eaten by wild birds and kills the mosquitoes that bite the birds within a short time after feeding, which is similar to treating pets to control fleas and ticks.”
Barker also discussed the presence of West Nile virus and its risk to humans in Yolo County, especially regarding seasonal changes.
“Overall, West Nile virus infection risk has been close to average in Yolo County this year, with elevated risk of infection during summer but lower levels than other recent years,” Barker said. “Risk is dropping rapidly now as days get shorter and temperatures cool, which reduces mosquito activity and virus transmission. In southern California, the risk of West Nile virus infection in LA and Orange counties has been unusually high this year and remains concerning even now.”
Practices like wearing insect repellent and considering wardrobe and time of day are methods recommended by Barker to decrease the risk of infection while temperatures remain high and more ideal for mosquito activity.
“There is still some risk of West Nile virus infection during the late summer, so the best way to protect ourselves from infection is to wear repellent when we are outdoors, especially when spending time outdoors in late afternoons or evenings when the [mosquitoes] that transmit West Nile virus tend to bite,” Barker said. “Wearing loose-fitting clothing that covers arms and legs is also helpful for blocking the access of blood-feeding mosquitoes to our skin.”
Barker also shared pest management methods to reduce mosquito presence, which impacts not only West Nile vector species, but other mosquito species in Davis that are present further in the fall season.
“Eliminating standing water around homes or apartments helps to reduce mosquito populations, especially from spring to late summer when mosquitoes are most active,” Barker said. “The invasive mosquito, Aedes aegypti, doesn’t transmit West Nile virus but is a major nuisance biter that is still active well into fall. This species has been spreading across the Central Valley since 2013 and is now found in nearly every town in Yolo and Sacramento counties, including Davis.”
The Yolo County Health and Human Services Agency offers residents free insect repellent through the Wellness Vending Machine Program, which has a location in Davis at 600 A St. Residents seeking more information on the West Nile virus and reducing the risk of infection can consult Sacramento-Yolo Mosquito & Vector Control District’s website.
Written by: Hannah Osborn— city@theaggie.org