In the early 1900s, Walter Reed led the United States Army Yellow Fever Commission, which performed extensive testing to confirm that yellow fever spread through mosquito bites, the Army Historical Foundation states. The team had to disprove competing theories, including the belief that yellow fever transmission was related to poor sanitation and direct exposure to bacteria. The commission’s work is responsible for the eventual eradication of yellow fever.
Epidemics of yellow fever caused high mortality rates in the United States between 1596 and 1900, and during the Spanish-American War of the late 1800s, disease caused more deaths than combat, the National Museum of Health and Medicine notes. Reed, an army surgeon and major, was a pioneer in the fields of pathology and bacteriology. In 1899, he convincingly refuted Giuseppe Sanarelli’s theory that bacterial agents caused yellow fever, leading to Reed’s appointment as the board president of a Cuban expedition to study yellow fever.
Reed supported the mosquito hypothesis presented by the Cuban doctor, Carlos Juan Finlay, according to the Army Historical Foundation. Reed’s team tested the theory by allowing mosquito hatchlings to feed on people infected with yellow fever and bite uninfected volunteers. The scientists discovered that the mosquitos only contracted the virus after feeding on humans within their first three days of infection.