In the light of modern researches yellow fever must now be considered as a disease produced, in individuals belonging to certain human races, by a two-host, microscopic, perhaps ultra-microscopic germ, endoparasite of the female of a particular species of mosquito—the Stegomyia fasciata (Theobald).
This germ pursues its parasitic existence in the body of the infected stegomyia during a period of 59 days, as experiments have proved, and probably, under ordinary circumstances, till the death of its mosquito-host. In order, however, that it may complete its life cycle, secure the perpetuation of its species and find its way into the body of other healthy stegomyias, it is necessary that it should penetrate, through the bite of the infected insect, into the body of a person who is liable to undergo an attack of yellow fever.
After parting from its mosquito-host, the germ apparently goes through certain evolutions in the body of
FINLAY CJ. NEW ASPECTS OF YELLOW FEVER ETIOLOGYARISING FROM THE EXPERIMENTAL FINDINGS OF THE LAST THREE YEARS.. JAMA. 1904;XLII(7):430-431. doi:10.1001/jama.1904.92490520020001e