Introduction: Western Australia (WA) travelers with acute febrile illness may act as sentinels to monitor incidence and prevalence of dengue in the Asia-Pacific region, including Indonesia. The WA Traveller Study has monitored the transmission of dengue virus (DENV) in Bali, the most popular tourist destination of WA residents, for almost seven years. This surveillance provides valuable and timely information, especially for the regions where detailed viral molecular analysis may not be routinely undertaken.
Methods: During 2016, DENV was isolated from WA travelers with well-defined DENV infection. cDNA was synthesized from viral RNA and DENV envelope gene was PCR-amplified and sequenced. The phylogenetic trees were performed using Randomized Axelerated Maximum Likelihood with General Time Reversible (GTR+Γ4) model.
Results: Fifty-two out of 60 viruses that were successfully isolated and sequenced, originated in Bali. All four DENV serotypes, with one genotype for each serotype, were identified circulating in Bali. There were multiple lineage introductions of DENV-1 and -2 into Bali from other countries in the region and these lineages co-circulated with local lineages which had circulated for several years. In addition, our data revealed that Genotype IV of DENV-1 that circulated previously in 2010 in Bali has been completely replaced by Genotype I and the shift likely occurred prior to 2016. Interestingly, DENV-3 and -4 isolates were less divergent and no introduction of the virus within these serotypes into Bali.
Conclusions: Dengue infection is still hyperendemic in Bali. Given the fact that multiple introductions of DENV strains into Bali occur annually suggests that Bali is a melting pot of DENV diversity, and in turn, it could serve as a hub for dengue transmission and mixing. Therefore, continuous surveillance using WA travelers as sentinels is needed to monitor dengue dynamic circulation in this region as well as in other Southeast Asia countries.