Fig 1.
Map of Thailand showing the sample collection site in the 13 provinces.
Map of Thailand showing sampling areas in Bangkok (1,137 cases), Samut Prakan (173 cases), Samut Sakhon (344 cases), Nonthaburi (1 case), Ratchaburi (1 case), Kanchanaburi (1 case), Tak (1 case), Maha Sarakham (1 case), Chon Buri (34 cases), Ranong (1 case), Phuket (108 cases), Songkhla (1 case), and Surat Thani (3 cases).
Fig 2.
Suspected and confirmed chikungunya cases between October 2018 and February 2020.
The number of suspected and confirmed cases whose samples were sent to the Center of Excellence in Clinical Virology, Faculty of Medicine, Chulalongkorn University. The numbers on bar graphs indicated the numbers of positive cases detected in each month between October 2018 and February 2020.
Table 1.
CHIKV-infected patients classified according to the presence of joint pain and age groups.
Fig 3.
Detection of CHIKV RNA by real-time RT-PCR and IgM antibody specific to CHIKV antigen by rapid test.
Results of 1,295 CHIKV infected patients were shown. Samples were tested by both real-time RT-PCR and rapid test for IgM antibody as described in the Materials and Methods. The Ct value and cut-off index (COI) represent the results of real-time RT-PCR and rapid IgM tests, respectively. COI is based on the ratio of assay signal to cut-off value of which COI≥1 = positive for anti-CHIKV IgM antibody and COI <1 = negative for anti-CHIKV IgM antibody. Curve equations and determination coefficients (R2) are indicated.
Table 2.
Comparison between real-time PCR, rapid IgM/IgG, and ELISA IgM/IgG as detection methods for diagnosis of chikungunya.
Fig 4.
Phylogenetic tree analysis of CHIKV whole genome.
Phylogenetic reconstruction of CHIKV whole-genome generated using the Maximum-Likelihood method with 1,000 ultrafast bootstrap replicates. Bootstrap values are represented at the branch nodes. The three major genotypes of CHIKV are highlighted in different colors. CHIKV strains isolated from this study are shown in red text (GenBank accession numbers MT495605-MT495608, MT640255, and MT640256). Bold lines in different colors show the specific amino acid substitutions in E2 and E1.
Fig 5.
Phylogenetic tree analysis of the partial CHIKV E1 gene.
A phylogenetic tree was constructed from partial E1 sequences of the 251 CHIKV isolates from this study and the selections from the GenBank database. The tree was constructed with MEGA X using the maximum-likelihood method with 1000 bootstraps. Bootstrap values are represented at branch nodes. The three major genotypes of CHIKV are highlighted in different colors. CHIKV isolated from this study is shown in red text. The specific amino acid substitutions in E1 are shown by bold lines in different colors.