Yellow fever: A brief history of a tropical Virosis

Yellow fever is a zoonotic arbovirosis, the agent of which is transmitted by mosquitoes. In humans, this virus can cause hemorrhagic hepato-nephritis, while mild or inapparent infections are common.

The catastrophic epidemics that occurred, mainly in the 18^th and the 19^th centuries, in Latin America and the United States as well as in the port cities of West Africa and Europe, had considerable demographic, socio-economic and political repercussions.

The viral nature of the infectious agent and its transmission by the Aedes aegypti mosquito, previously suspected by Beauperthuy, were demonstrated by Carlos Finlay in 1881 and confirmed by the American Commission led by Walter Reed in Havana in 1900 and by the French Commission led by Emile Marchoux in Rio de Janeiro in 1901-1905. The control of Ae. aegypti could then be implemented effectively.

It was only in 1927 that the yellow fever virus was isolated in Africa, its continent of origin, by French researchers from the Pasteur Institute in Dakar and by the American and English teams of the Rockefeller Foundation. Soon after, epidemiologists realized that there were forest cycles of the virus, involving monkeys and vectors other than Ae. aegypti, and consequently recognized the existence of a wild reservoir of the virus.

Once the virus was isolated, work on vaccine development could begin. This research was carried out by the Institut Pasteur in Dakar and by the Rockefeller Foundation. The two teams succeeded in obtaining two live vaccines conferring excellent and long-lasting protection: the neurotropic "Dakar" vaccine (1934) and the "Rockefeller" 17D vaccine (1937), which was better tolerated.

From then on, the fight against of yellow fever involved entomological control and vaccine protection, and it was a huge success until the 1960s. Unfortunately, the control programs were gradually reduced, and in some countries terminated. This resulted in the return of Ae. aegypti in urban areas and in insufficient vaccination coverage. Risks of epidemics reappeared, in Latin America as well as Africa.

In the early 21^st century, epidemiologists are worried about these resurgences, especially since we still have no indisputable explanation for the absence of the disease on the Asian continent. Obviously, yellow fever is not a disease of the past.