[Paul-Louis Simond and yellow fever].

P.L. Simond participated in the Pasteur Institute mission sent to Rio de Janeiro from 1901 to 1905 to investigate yellow fever and was to make an important contribution to the knowledge of the disease. At that time, the aetiologic agent of yellow fever was still unknown, and its transmission by mosquitoes was controversial. Several authors had observed apparent differences in the susceptibility to the illness between African and European populations. Otherwise, the soundness of epidemic control measures then being administered was often called into question. As such, many points needed to be definitely clarified. During the four years they spent in Brazil, the Pasteur Institute scientists--and particularly Simond--achieved important results. They confirmed the viral aetiology of yellow fever, were able to define several pathological aspects of the disease and conduct various serotherapeutic tests. The role of Aedes aegypti (known at the time as Stegomyia fasciata) was also confirmed and the bionomics of the mosquito began to be studied. This research laid the ground for classical measures of controlling the vector and preventing outbreaks of the disease. Furthermore, Marchoux and Simond observed the vertical transmission of yellow fever virus in Ae. aegypti; this phenomenon of major epidemiological importance remained controversial until it was confirmed in the field as recently as 1997. The French scientists were also able to specify many aspects of the epidemiology of yellow fever, particularly its apparent low pathogenicity in young children--a possible explanation for the fact that local residents of endemic zones often had a certain level of immunity as a result of benign infection contracted in childhood. P.L. Simond later spent several months in Martinique where he set up a successful yellow fever vector control programme. Clearly Simond, who had already acquired much expertise in the epidemiology of vector-borne diseases, played a key role in the success of the mission sent by Institute Pasteur to Brazil, and, more generally, in the scientific advances of yellow fever prevention.