DENGUE mon ancestor. This finding was consistent with a Sri Lankan origin for DENV-3 subtype III circulating in the Latin American and Caribbean regions (5) and with exten- sion of the virus from a single importation event. A phylogenetic tree was constructed based on partial sequences of the prM/M-E gene region (position 437–1144) of the genomes, including the strains from Saint Martin and several other previously characterized strains from different origins (16–19). DENV isolated from Saint Martin was grouped in subtype III, as defined by Lanciotti (17) (data not shown). Another phylogenetic tree was constructed with the strains analyzed by Messer (5) (Figure 3). Despite the high overall similarity of the subtype III sequences, distinct groups could be distin- guished. The 6 isolates from Saint Martin clustered together. The small lineage difference of D3StMart2 is supported by a 95-bootstrap value, but no evidence sug- gests that such difference implies multiple introductions or a longer transmission period. However, Saint Martin DENV-3 fell in the Latin American cluster defined by Messer (5), which also includes isolates from Guatemala, Nicaragua, and Mexico. Isolates from Saint Martin were particularly close to Martinique isolates (6) and the 00PuertoR1 isolate, which were the geographically and temporally closest isolates of the cluster. The analysis of the deduced amino acid sequences generated a similar phylogram. Altogether, these results indicate that the Saint Martin viral isolate belongs to the genotype Puerto Rico 2000 previously reported (5). These results also confirm a common origin for all DENV-3 circulating in the Caribbean and Latin American region; their ancestor probably originated from Sri Lanka. Additional American DENV-3 strain sequences, encompassing the insertion site, should help to confirm this hypothesis. The question arose whether the introduction from Sri Lanka was a single event in the Latin American region, first appearing in Panama (5), then spreading through the Caribbean subregion and South America. In fact, viruses belonging to subtype III were first reported in Nicaragua and Panama in 1994 (20). They were then identified in Guatemala from 1996 to 1998; in Puerto Rico, Barbados, and Jamaica in 1998 (18); and in Martinique in 1999 (6). The introduction of DENV-3 in Saint Martin was reported in 2000 (http://www.carec.org/annrep00/index.html), but the subtype was not determined. No virus isolation was reported for 3 years, until the viruses we characterized were isolated. The rapid extension of DENV-3 belonging to subtype III, which have almost completely replaced preexisting DENV of serotype 1 and 2, is indicative that these particular viruses have adapted to Caribbean and Latin American conditions. Together with previous studies (5,6), identification of viruses belonging to sub- type III in another area of the Caribbean region confirms RESEARCH Figure. 3. Phylogenetic tree of dengue type 3 subtype III viruses, based on prM/M and partial E nucleotide sequences (nucleotide numbers 437 to 1144) available in GenBank database. Phylograms were constructed with the MEGA 2 program (15), using the Jukes-Cantor algorithm and the neighbor joining method. The percentage of successful bootstrap replicates (1,000 bootstrap replications, confidence probability 90%) is indicated at nodes. The length of branches is proportional to the number of nucleotide changes (percentage of divergence). The strains sequenced in this work are underlined. Dark triangles correspond to viruses of the same group clustering together; dots indicate a change in scale. the remarkable epidemiologic success of this particular lineage of dengue viruses. Comparable substitution of local DENV by a new genotype was previously described in the Caribbean region (12). New viruses, often originating from Southeast Asia, arise as successive waves, replacing previous ones. In this regard, sampling of DENV-3 subtype III virus nucleotide sequences from all countries in the Caribbean and the peri-Caribbean area need to be expanded so that we can understand DENV circulation in the region. Acknowledgments We are indebted to H. Puggelli for primer synthesis. This work was partially funded by the French Armed Forces Medical Service and the French “Délégation Générale pour l’Armement.” The opinions and assertions contained herein are the private ones of the writers and are not to be construed as official or 760 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 11, No. 5, May 2005