Yellow fever: rapid field entomological assessment during yellow fever outbreaks in Africa: handbook: methodological field approaches for scientists with a basic background in entomology

Overview

Yellow fever (YF) is one of the most important mosquito-borne viral haemorrhagic diseases transmitted to humans. It is mostly vectored by the genus Aedes in Africa, and it is a serious public health problem in Africa, as well as in the South and Central Americas. In the past few decades, despite a highly effective vaccine, YF is re-emerging in Africa (Reiter et al., 1993; Thonnon et al. 1998; Onyango et al., 2004a, 2004b; Ellis & Barett, 2008; Gould et al., 2008), with an increase in reported urban outbreaks in Africa. The increase in virus circulation among the non-immune human population – along with its geographical spread – was highly disconcerting, as multiple outbreaks occurred simultaneously in several places.

Surveillance remains the best approach for early detection of outbreaks. The current surveillance system implemented in almost all African countries includes only a human component, which is based on clinical detection of jaundice, blood sample collection, and immunoglobulin M (IgM) detection in national laboratories and their confirmation in a regional laboratory. This approach, while strongly recommended, is limited, because disease transmission is often only alerted when it is already established in the community. This may be too late for a disease like YF, which is characterized by a large proportion of asymptomatic cases.