Genetic reassortment of Rift Valley fever virus in nature

Rift Valley fever virus (RVFV), a phlebovirus of the Bungaviridae family, i s an arthropod-borne virus which emerges periodically throughout Africa, em phasizing that it poses a major threat fur animal and human populations. To assess the genetic variability of RVFV, several isolates from diverse loca lities of Africa were investigated, by means of reverse transcription-PCR f ollowed by direct sequencing of a region of the small (S), medium (M), and large (L) genomic segments. Phylogenetic analysis showed the existence of t hree major lineages corresponding to geographic variants from West Africa, Egypt, and Central-East Africa. However, incongruences detected between the L, M, and S phylogenies suggested that genetic exchange via reassortment o ccurred between strains from different lineages. This hypothesis, depicted by parallel phylogenies, was further confirmed by statistical tests. Our fi ndings, which strongly suggest exchanges between strains from areas of ende micity in West and East Africa, strengthen the potential existence of a syl vatic cycle in the tropical rain forest. This also emphasizes the risk of g enerating uncontrolled chimeric viruses by using live attenuated vaccines i n areas of endemicity.