Evidence for recombination in natural populations of dengue virus type 1 based on the analysis of complete genome sequences

Unité de Virologie Tropicale, Institut de Médecine Tropicale du Service de Santé des Armées, Unité des Virus Emergents, Université de la Méditerranée, BP 46, Parc du Pharo, 13998 Marseille Armées, France 1 Laboratoire de Virologie Moléculaire, Tropicale et Transfusionnelle, Faculté de Médecine, Unité des Virus Emergents, Université de la Méditerranée, Marseille, France 2 Laboratoire de Biologie Médicale, Hôpital Laveran, Marseille, France 3 Author for correspondence: Hugues Tolou. Fax +33 4 91 59 44 77. e-mail imtssa.viro{at}worldnet.fr Recombination events are known to occur in non-segmented RNA viruses like polioviruses or alphaviruses. Analysis of the subgenomic sequences of dengue virus type 1 (DENV-1) structural genes has recently allowed the identification of possible recombination breakpoints. Because DENV is a major human pathogen, this discovery might have important implications for virus pathogenicity, vaccine safety and efficiency, or diagnosis and, therefore, requires clear confirmation. We report the complete sequence determination of one Asian and two African strains of DENV-1 isolated from human patients. Rigorous sequence analysis provided strong evidence for the occurrence of intragenomic recombination events between DENV-1 strains belonging to different lineages. Singapore S275/90 strain appears to be the evolutionary product of a recombination event between viruses belonging to two distinct lineages: one lineage includes an African strain isolated in Abidjan (Ivory Coast) and the other includes isolates from Djibouti and Cambodia. The ‘Recombination Detection Program’, bootscanning and analysis of diversity plots provided congruent results concerning the existence of a two-switch recombination event and the localization of recombination breakpoints. Thus, the 5' and 3' genomic ends of the Singapore S275/90 strain were inherited from a Djibouti/Cambodia lineage ancestor and an internal fragment located in the envelope/NS1 region originated from an Abidjan lineage ancestor.