ABSTRACT
Over the past two decades; dengue virus serotype 3 (DENV-3) has caused unexpected epidemics of Dengue hemorrhagic fever (DHF) in Sri Lanka; East Africa; and Latin America. We used a phylogenetic approach to evaluate the roles of virus evolution and transport in the emergence of these outbreaks. Isolates from these geographically distant epidemics are closely related and belong to DENV-3; subtype III; which originated in the Indian subcontinent. The emergence of DHF in Sri Lanka in 1989 correlated with the appearance there of a new DENV-3; subtype III variant. This variant likely spread from the Indian subcontinent into Africa in the 1980s and from Africa into Latin America in the mid-1990s. DENV-3; subtype III isolates from mild and severe disease outbreaks formed genetically distinct groups; which suggests a role for viral genetics in DHF