[Molecular epidemiology of yellow fever]

Although the causative agent has long been identified and a safe, effective vaccine is available, yellow fever still poses a threat in South America and tropical areas of Africa where it mainly affects young people. The presentation of yellow fever has changed relatively little since description of the first outbreaks, but study has entered a new age thanks to development of more accurate techniques for characterization of viral strains. Comparison of the RNA sequences of virus from different geographical regions has demonstrated the existence of several stable genotypes which have been designated as topotypes. These topotypes have yet to be correlated with different viral activity but their recognition has allowed better epidemiologic surveillance of the disease. Study of the viral genome has also allowed improvement of diagnostic techniques, identification of factors influencing virulence, and enhancement of understanding of viral mutations. Ultimately knowledge of the processes underlying viral evolution could assist development of effective preventive strategies.