February 18, 1881

Carlos Finlay

Finlay proposes an unidentified intermediary in yellow-fever transmission

Finlay's supposedly famous mosquito announcement did not mention a mosquito.

Washington, 18 February 1881

At the seventh session of the Fifth International Sanitary Conference in Washington on 18 February 1881, Carlos Finlay — a special Spanish delegate representing Cuba and Puerto Rico — addressed the dispute between contagionists and non-contagionists over yellow fever.

He believed neither camp could explain every observed outbreak, so he added a third character to the chain: an independent agent that carried the disease from a patient to a healthy person.

Three conditions, no name

Finlay said transmission required three things — a prior yellow-fever case, a susceptible person, and that independent carrying agent. He called it a plausible hypothesis.

He did not identify the agent as a mosquito at this session. That came six months later, on 14 August 1881, before the Royal Academy of Medical, Physical and Natural Sciences of Havana.

Nobody argued

No discussion followed his statement. The conference was principally concerned with international quarantine and sanitary cooperation, and its proceedings run to 449 pages.

Delegates did approve a separate proposal for a temporary yellow-fever scientific commission, 14 in favour with four abstentions and none against. That commission never materialized, and experimental confirmation of mosquito transmission waited until the U.S. Army Yellow Fever Commission's work in 1900.

Sources

Researched 23 Aug 2026 6 sources 2 audit passes

How this was checked

Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →

What the sources leave uncertain

The February 18 date and seventh-session setting are well supported by the official proceedings and WHO historical scholarship.
The uncertainty concerns what Finlay disclosed, not the date: he proposed an independent intermediary but did not identify it as a mosquito in Washington.
The name Aedes aegypti is modern terminology. In his later work Finlay referred to the mosquito using the classification Culex.