Dengue virus type 3 infection in a traveler returning from Costa Rica to Japan in 2023.

The number of dengue cases has increased dramatically in recent years. In Latin America, the number of cases and deaths in 2023 was the highest ever recorded. We report on a patient who had been infected with dengue virus during his stay in Costa Rica in September 2023, and developed the disease after returning to Japan. Plasma obtained from the patient was used for diagnosis and dengue virus serotyping by real-time PCR. The nucleotide sequence of the envelope region of dengue virus was then determined by the direct sequencing method, and this sequence was used for phylogenetic analyses. The patient was found to be infected with dengue virus type 3 genotype III. The sequence from the present case was more homologous with sequences registered in Florida, USA, associated with travel to Cuba in 2022 than with sequences registered in Costa Rica 10 years ago. The Pan American Health Organization reported that only dengue virus type 1 and 2 cases were reported in Costa Rica in 2019-2021, whereas dengue virus type 3 and 4 cases started being reported in 2022. In 2023, the reported numbers of cases with dengue virus types 3 and 4 exceeded those of dengue virus types 1 and 2. In addition, regional differences in endemic strains have been observed in Costa Rica. Our findings suggest that the dengue virus type 3 that infected the patient was more likely an influx of a strain that had been circulating in Caribbean countries such as Cuba in recent years, rather than a re-emergence of an indigenous virus in Costa Rica. The serotypes of dengue virus prevalent in Costa Rica have been changing since 2022. All four serotypes were prevalent in 2023, with a particularly sharp increase in the number of cases of dengue virus types 3 and 4. Future monitoring and surveillance are essential because changes in endemic serotypes can cause antibody-dependent enhancement, which can lead to severe dengue disease presentations.