Molecular epidemiology of dengue in the Pacific: introduction of two distinct strains of the dengue 2 type-1 virus into Hawaii

In 2000, a major dengue epidemic, caused by the type-1 virus (DENV-1), began in the Pacific and Asia, with cases still being reported in 2006. The phylogenetic analysis of full-length sequences of the envelope-protein gene of DENV-1 isolates recovered during outbreaks in Hawaii and Tahiti in 2001-2002 indicated that most Hawaiian isolates were Tahitian in origin. All the Hawaiian and Tahitian isolates were identified as the Pacific subtype (i.e. subtype IV) of DENV-1. A Hawaiian isolate, collected from a resident who had travelled to Samoa, differed significantly at the nucleotide level, however, from all the other Hawaiian strains, clustering, in the phylogenetic analysis, with a virus previously isolated from another visitor to Samoa. These results not only indicate that two distinct strains of DENV-1 were introduced into Hawaii in 2001 but also illustrate the ease with which dengue can be carried across distances of many thousands of miles.