Serologic and Virologic Studies of an Imported Dengue Case Occurring in 2014 in Okinawa, Japan

After returning from Bali, Indonesia, in February 2014, a 72-year-old man was hospitalized in Okinawa owing to a high fever and rash. Dengue was clinically suspected, and the patient tested positive for IgM against dengue using a commercial kit. Serologically, the patient showed secondary seroreactivity. Significant increases in neutralization titers (N-titers) against all 4 serotypes of dengue virus (DENV) and Japanese encephalitis virus (JEV) strains were recognized in convalescent-phase sera comparing to acute phase sera. The N-titer against DENV serotype 1 (DENV-1) was the highest among all DENV serotypes. Interestingly, the N-titers against JEV strains were significantly higher than those against all types of DENV comparing to acute phase sera. The virus was isolated from the acute-phase serum and identified as DENV-1 and designated RD14/Okinawa. The patient's symptoms were due to DENV-1 infection. Phylogenetic sequencing analysis indicated that the isolate RD14/Okinawa belonged to genotype I of DENV-1, which is closely related to the Southeast Asian strains and isolates found during the dengue outbreak in Japan in 2014. We should undertake control measures against dengue in Okinawa, which is a subtropical area with Aedes albopictus activity throughout year.