Chikungunya, a mosquito-borne virus first identified in Tanzania in the 1950s, has now reached the United States. The Centers for Disease Control and Prevention confirmed the first two cases of domestic transmission in Florida last week, following ongoing outbreaks in the Caribbean. While rarely fatal, the virus can cause agonizing joint pain. Meanwhile, in the northeastern U.S., researchers have identified the potentially deadly Eastern equine encephalitis, another pathogen transmitted by mosquitoes, though the virus hasn’t resulted in any infections this year. Roxanne Rutledge Connelly, a mosquito specialist at the University of Florida, identifies which species are virus-carrying culprits, and talks about the potential for these diseases to spread.