Dengue is a mosquito-borne disease that has spread to over 100 countries. Dengue fever is caused by dengue virus (DENV), which belongs to the Flavivirus genus of the family Flaviviridae. DENV comprises 4 serotypes (DENV-1 to DENV-4), and each serotype is divided into distinct genotypes. Thailand is an endemic area where all 4 serotypes of DENV co-circulate. To understand the current genotype distribution of DENVs in Thailand, we enrolled 100 cases of fever with dengue-like symptoms at the Bamrasnaradura Infectious Diseases Institute during 2016–2017. Among them, 37 cases were shown to be dengue-positive by real-time PCR. We were able to isolate DENVs from 21 cases, including 1 DENV-1, 8 DENV-2, 4 DENV-3, and 8 DENV-4. To investigate the divergence of the viruses, RNA was extracted from isolated DENVs and viral near-whole genome sequences were determined. Phylogenetic analysis of the obtained viral sequences revealed that DENV-2 genotype Cosmopolitan was co-circulating with DENV-2 genotype Asian-I, the previously predominating genotype in Thailand. Furthermore, DENV-3 genotype III was found instead of DENV-3 genotype II. The DENV-2 Cosmopolitan and DENV-3 genotype III found in Thailand were closely related to the respective strains found in nearby countries. These results indicated that DENVs in Thailand have increased in genotypic diversity, and suggested that the DENV genotypic shift observed in other Asian countries also might be taking place in Thailand.

Dengue virus (DENV), one of the most rapidly spreading mosquito-borne pathogens, causes acute febrile illness with various clinical symptoms. Four DENV serotypes are known, designated DENV-1 to-4. We previously determined whole-genome sequences of 21 DENV isolates obtained during 2016-2017 and reported the emergence of the Cosmopolitan genotype of DENV-2 and genotype III of DENV-3 in Thailand. The objective of the present study, conducted in 2018 at the Bamrasnaradura Infectious Diseases Institute, was to characterize the DENV genotype distribution among severe dengue patients. A total of 100 hospitalized severe dengue patients were enrolled with written informed consent. Serum specimens were tested by multiplex real-time reverse transcription-polymerase chain reaction. A total of 94 cases were DENV detected, with 46 DENV-1, 38 DENV-2, 10 DENV-4, and no DENV-3 cases. Sequence determination of the DENV envelope-protein gene was successful in 73 cases. Genotyping of the resultant sequences revealed 40 DENV-1 genotype I, 26 DENV-2 including 18 genotype Cosmopolitan and 8 genotype Asian I, and 7 DENV-4 genotype I cases. DENV-1 was the most prevalent in the current study, and the ratio of DENV-2 genotype Cosmopolitan apparently increased since our previous study. These results suggest that genotypic diversity might be increasing in Thailand.

Acute Zika virus (ZIKV) infection may mimic dengue virus (DENV) infection. We aimed to study the clinical difference of ZIKV disease among suspected non-severe DENV patients comparing children and adults. Patients with acute illness suspected of DENV disease plus no evidence of plasma leakage at the Bamrasnaradura Infectious Diseases Institute, Nonthaburi, Thailand, were enrolled from December 2016 to September 2018. Clinical data including DENV rapid diagnostic test (RDT) results were collected. Zika virus diagnosis was confirmed by real-time reverse transcription PCR on urine. Of 291 (180 pediatric and 111 adult) cases enrolled, 27 (10 pediatric and 17 adult) confirmed ZIKV cases were found. Rash was more frequent among pediatric ZIKV than pediatric non-ZIKV cases (100% versus 60%, P = 0.01). Rash, arthralgia, and conjunctivitis were more frequent among adult ZIKV than adult non-ZIKV cases (100% versus 29.8%, 64.7% versus 26.6%, 52.9% versus 9.7%, all P < 0.01, respectively). The median (interquartile range [IQR]) duration of rash was 4.5 (3.0, 7.25) days and 6.0 (4.5, 7.0) days in pediatric and adults ZIKV cases, respectively. Pediatric ZIKV cases had more fever (100% versus 58.5%, P = 0.03) but less arthralgia (20% versus 64.7%, P = 0.04) and less conjunctivitis (10% versus 52.9%, P = 0.04) than adult ZIKV cases. No ZIKV cases with DENV RDTs performed around day 3 of illness were positive for dengue nonstructural protein 1 (NS1) antigen. In dengue-endemic settings, rash and fever in children, and rash, arthralgia, and conjunctivitis in adults, particularly if rash persists for ≥ 3 days, plus negative dengue NS1 Ag during early febrile phase should prompt ZIKV diagnostic testing.