Which mosquito-borne disease has been found in the most states in the U.S.?

The choice of St. Louis encephalitis as the mosquito-borne disease found in the most states in the U.S. reflects its historical prevalence and widespread distribution. St. Louis encephalitis is endemic across many parts of the United States, particularly in the Midwest and southern regions. Its ability to be transmitted by a variety of mosquito species contributes to its presence in multiple states.

West Nile virus is also widespread and has been reported in numerous states since its introduction in the U.S. However, St. Louis encephalitis has a longer history and traditionally has been documented across an extensive range of states, often reported in more rural areas where certain species of mosquitoes thrive.

Malaria and dengue fever have seen less consistent reporting across the U.S., primarily due to the limited habitats for their primary vectors and the lower incidence of these diseases compared to West Nile and St. Louis encephalitis. Malaria has been largely controlled in the U.S. since the mid-20th century, and dengue fever is mainly found in warmer states with specific conditions.

Overall, St. Louis encephalitis stands out due to its established presence historically and epidemiologically across a wide range of states in the country.