West Nile’s geographic reach in California has shrunk, according to data compiled by the California Health and Human Services Agency. West Nile cases have surfaced in 37 counties this year, represented by the circles in the graphic, down from the 40 through the same period last year. The total is on par with the 38 county five-year average year-to-date, according to the California West Nile website — a collaboration between the State Department of Public Health, UC Davis Arbovirus Research and Training and the Mosquito and Vector Control Association of California. Human cases have likewise dipped to 276 from 300 in 2015, year-to-date.

The number of mosquitoes found to be infected with West Nile, however, jumped from 2,890 in 2015 to 3,360 year-to-date.

Climate change could be expanding the scope of some flaviviruses, including West Nile, by creating a more hospitable environment for mosquitoes. About 68 percent of the state could see a heightened risk of West Nile due to climate change by 2050, according to a 2014 model out of the Center for Tropical Research at UCLA’s Institute of the Environment and Sustainability.