Scientist Profile #2: Carlos Juan Finlay and the Theory of Biological Vectors

Recently I went through my childhood stamp collection while visiting my parents house. I had forgotten the vibrancy and life that was present in the stamps. As a child my favourites had been the ones with horses on them (don’t try to pretend this wasn’t you at some age), but the next most exciting category was the insects.

Carlos Juan Finlay was a Cuban physician and scientist who lived between 1833 and 1915.  Last year was the centenary of Finlay’s death. Finlay was the first person to propose that Yellow Fever was spread by the bite of one species of mosquito. The stamps in my collection were from 1981, printed to mark the Centenary of the Theory of Biological Vectors.  The stamp depicts a portrait of Carlos Finlay in front of a silhouette of an Aedes eegypti mosquito. The mosquito and disease originated in Africa, but were moved to the Carribbean through international trade.  Finlay writes that in Cuba “I have found no direct allusion to this insect before the year 1538”.

As a young man,  Finlay was very unlucky in his own health. When in Europe for his education Finlay contracted both Cholera and Typhoid Fever. This personal connection to Typhoid may have given him extra motivation to study contagious diseases. In 1881 Finlay published a paper linking the bite of the mosquito with contraction of the disease. The translation of his paper states that “it seems natural that this agent could be found in that class of insects which, by penetrating into the interior of the blood vessels, could suck up the blood together with any infecting particles contained therein, and carry the same from the diseased to the healthy.”

The theory was not immediately popular with doctors of the time. They preferred the idea that the disease was spread by ‘filth’. Finlay had spent more than 19 years researching the disease before the U.S Medical Commission took up the idea.  Previously the disease was thought to be spread by atmospheric, miasmic or meteorological influences, weak character or unclean living conditions. Miasmas were believed to be  the presence of poisonous air full of decaying particles, characterised by a bad odour. The miasma theory itself was not very far off the money for water borne diseases like Cholera,  where there was a correlation between contaminated water sources and foul odours. The miasma theory was replaced by the germ theory, this was what Finlay was basing his research on.

The presence of Yellow Fever and Malaria was one of the reasons why the first attempt at building the Panama Canal by the French in 1871 was unsuccessful. It is reported that during the building of the railroad alone 6000 workers died from now-preventable diseases including Yellow Fever. The new knowledge added by mosquito research led the new American builders to greatly reduce deaths and successfully complete the project.

It was not until 1897 when a physician called Ronald Ross identified a parasitic protozoa in blood from a malaria mosquito that they theory was finally fully accepted by the scientific community. Ross received a Nobel Prize. Finlay did not (although he was nominated seven times, destined to be always the bridesmaid, never the bride).

The 180’th anniversary of Finlays birth was celebrated by a Google Doodle in 2013. While not shown to Australian google users, you can see the doodle in their archive. A larger version of the Finlay stamp can be found here.


References: Finlay C J (1881). The Mosquito Hypothetically Considered as the Agent of Transmission of Yellow Fever. Translated by R Matas. Annals of the Royal Society of Havana.

The Science Museum, Miasma Theory.



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