Carlos Finlay presents his mosquito-transmission theory of yellow fever at the Fifth International Sanitary Conference

Background. The International Sanitary Conferences were a series of meetings held to address disease epidemics. The Fifth Conference, held in Washington, D.C., was the first to include United States participation. The first conference, organized by the French Government in 1851, had aimed to standardize international quarantine regulations against cholera, plague, and yellow fever.

The Theory. Carlos Finlay, a Cuban epidemiologist, theorized in 1881 that the Aedes aegypti mosquito acted as a disease vector for yellow fever. He proposed that a mosquito biting an infected victim could subsequently bite and infect a healthy person, contradicting the long-held belief in direct person-to-person transmission.

Reception. Finlay's presentation at the 1881 International Sanitary Conference was not well-received. His theory faced significant skepticism, resulting in ridicule and mockery from the scientific community at the time, despite its eventual recognition as a pioneering contribution to epidemiology.