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.