Integrated approach to yellow fever surveillance: pilot study in Senegal in 2003-2004]

The aim was to undertake a pilot study of integrated surveillance of yellow fever (YF) in Senegal, based on i) a human surveillance involving healthcare centers in the 11 administrative regions of the country ii) an entomological surveillance including domestic and sylvatic environment and iii) screening mosquitoes for YF virus using RT-PCR method. The integrated approach of human and entomological surveillance was conducted for 2 years (2003-2004). Surveillance in human population was based on screening samples of YF suspected cases (i.e. patients with acute (< or = 15 days) febrile illness with jaundice) for YF specific IgM antibodies. The entomological surveillance was carried out by collecting mosquitoes using human landing catch method and attempt to detect YF virus on them by RT-PCR. Forty five percent of the healthcare centres notified at least one suspected YF case during 2003-2004 periods. Among the 342 sera collected over 2 years, 2 revealed anti-YF IgM antibodies leading to investigations which allowed identification of the source and place of infection and implementation of a reactive focused YF immunization campaign. In addition, YFV was detected by RT-PCR from 49 out of 1762 mosquitoes tested and distributed as follows: in the sylvatic environment, 29 from Aedes furcifer and 1 from Aedes aegypti while in the domestic area, 15 Aedes aegypti and 4 Aedes furcifer. RT-PCR was found more sensitive and rapid than viral isolation for YF virus detection in mosquitoes. The pilot study in Senegal for YF surveillance integrating human and entomological parameters in domestic and sylvatic areas showed that this approach is very efficient in detecting yellow fever virus circulation due to the complementarity of the two systems. Therefore, in the light of the encouraging results presented herein, similar studies in different context and areas are needed to further validate and allow the extension of its application to other endemic regions of Africa.