Jason Farned and his team at the San Gabriel Valley Mosquito and Vector Control District had spent years preparing for the likely arrival of dengue, a dangerous virus typically found in tropical climates outside the mainland United States. They’d watched nervously as invasive Aedes mosquito species that can carry the virus appeared in Los Angeles about a decade ago and began to spread, likely introduced by international trade and enticed to stay by a warming climate that makes it easier for mosquitoes to thrive. Then, in October 2023, an email came from the Pasadena Public Health Department: A…