Juan Carlos Finlay

Juan Carlos Finlay (December 3, 1833 to August 19, 1915). Juan Carlos Finlay was a doctor who was born in Port-au-Prince (now Camagüey, Cuba) and died in Havana. He was, therefore, born Spanish and died Cuban. He investigated yellow fever, of viral origin.

Finlay managed to explain the mode of transmission of yellow fever by postulating the existence of an intermediate transmitting agent. In 1881 he published a work in the Annals of the Royal Academy of Havana in which he identified that agent as the Aedes aegypti mosquito: the mosquito, by biting a sick person, would acquire the microorganism responsible for the disease, which would then be transmitted by biting a healthy person. Finlay, a fervent Catholic, while praying the Rosary one night, observed a mosquito hovering over his head trying to bite him; and that’s when he started considering his theory.

After presenting this theory internationally, it was initially received with skepticism, as it was unprecedented, despite which he continued researching the subject. Together with the doctor Claudio Delgado Amestoy, between 1881 and 1900, he performed up to 104 inoculations on volunteers, causing at least 16 cases of yellow fever, one of them very typical. He also observed that infected individuals became resistant. He deduced that the greater resistance of the local population to yellow fever could be explained on the basis of natural inoculations during childhood or in utero of benign forms of the disease that would provoke immunity in the infected child. He designed and disseminated the measures that should be taken to avoid yellow fever, which involved eliminating mosquito larvae breeding sites.

In 1901, in a campaign led by the American doctor William Gorgas (Cuba was then a colony of the United States, after independence from Spain), yellow fever was eliminated in Cuba after eradicating the main breeding sites of Aedes aegypti, following the recommendations of Finlay. This proved to be the definitive confirmation of his theory, after which he was appointed Senior Chief of Health. Later he was officially nominated for the Nobel Prize on several occasions, although he never received this award.

There is currently a UNESCO microbiology prize in his honor.

[Author: Gonzalo Colmenarejo. IMDEA Alimentación. SCS-España]