Via Emerging Infectious Diseases: Ahead of Print -Importation of Zika Virus from Vietnam to Japan, November 2016. The conclusion:
Our phylogenetic analysis suggested that the Asian lineage can be divided into 3 clades (Southeast Asian, Pacific, and American), and the strain we isolated belonged to the Southeast Asian clade. A previous study indicated that a strain isolated in Singapore in 2016 (ZKA-16-291; GenBank accession no. KX827309) also belonged to the Southeast Asian branch, and it was distinct from the isolates obtained in the Americas.
Therefore, it is possible that the isolate from the current case was the strain that is already circulating in Vietnam and was not imported from South America. Our isolate formed smaller plaques in Vero cells than those observed with the other Asian lineage ZIKV/Hu/S36/Chiba/2016 strain (Pacific clade).
We also confirmed that the plaque sizes of the PRVABC59 (American clade) and MR766-NIID (African lineage) strains resemble that of ZIKV/Hu/Chiba/S36/2016 (data not shown), suggesting that the Southeast Asian clade Zika virus strains might have a lower cytotoxicity and replicative ability than the American clade and African lineage.
In conclusion, the replicative ability of Zika virus might differ by region and thus influences endemic potential. Further studies are necessary to validate these findings.