The unlikely spread among cattle and one dairy worker has scientists looking through the data to better understand this spillover. They say the risk to humans hinges on whether the virus can evolve in key ways to better infect mammals.
The Culex mosquitoes carry the virus and are found across California, according to the state's public health department. In June, officials confirmed three dead birds were infected with West Nile in Simi Valley, Thousand Oaks, and Ventura.
