West Nile - Cases of this virus have been reported in all of the continental United States. Most people experience mild or no symptoms. However, about 1 out of 150 infected people develop serious, sometimes fatal, illness.
Eastern equine encephalitis (EEE) - This is one of the most severe mosquito-transmitted diseases in the U.S., with approximately 33 percent mortality and significant brain damage to those who get encephalitis, a brain inflammation, from it. Fortunately, it’s rare in humans, and only a few cases are reported in the U.S, each year, mostly in the Atlantic and Gulf Coast states. Most people who get it experience no symptoms.
Zika - Symptoms of this virus are mild in most people, but if a pregnant woman gets infected, the virus can cause serious birth defects, including microcephaly. In 2018, no local mosquito-borne Zika virus transmission has been reported in the continental United States. Previously, it has been reported in the Miami-Dade County area of Florida and in Brownsville, Texas.
Malaria - Rare in the U.S., between 1957 and 2015, just 63 outbreaks of locally transmitted mosquito-borne malaria have occurred and usually were the result of local mosquitoes biting people who had returned after visiting countries where it’s endemic.
Source: Centers for Disease Control