Genetic characterization of chikungunya virus isolates from Aedes aegypti mosquitoes collected during a recent outbreak in Bangkok, Thailand.

Chikungunya virus (CHIKV) is a mosquito-borne emerging pathogen that is transmitted to humans through the bite of female Aedes mosquitoes. CHIKV infection has become a major public health concern worldwide, as it has a significant impact on the healthcare system. Since 2004, the virus has emerged in Africa and subsequently spread to countries located near the Indian Ocean, including India, and to Europe, the Americas, and Asia. In Thailand, a large CHIKV outbreak occurred during 2008-2009 and was caused by a virus originating from the east/central/south African (ECSA) CHIKV genotype. Since then, the ECSA genotype of CHIKV has continued to circulate and has caused sporadic cases in different areas in Thailand. Approximately 20,000 reported cases have been confirmed by the Bureau of Epidemiology, Ministry of Public Health, Thailand, from January 1, 2018 to July 31, 2020. However, the causes of this CHIKV re-emergence remain unclear. To obtain a better understanding of CHIKV circulation during the recent outbreak in Bangkok, Thailand, complete genome analysis of CHIKV isolates from field-caught mosquitoes collected in outbreak areas was performed. A total of 28 Ae. aegypti samples (21 females and 7 males) were collected, and individual mosquitoes were used for CHIKV detection and isolation. Eleven of 28 (39.29%) female and three of 28 (10.71%) male mosquitoes were positive for CHIKV by E1 nested RT-PCR. Four CHIKV isolates were successfully isolated from four female Ae. aegypti mosquitoes. Based on complete genome analysis, several amino acid substitutions were identified in the protein coding region. The E1:K211E and E2:V264A mutations in the background of the E1:226A mutation were observed in all four CHIKV isolates. An important observation was the presence of one amino acid substitution, leading to an E1:K245R change. This mutation was found in all four CHIKV isolates from mosquitoes in this study and in Thai patients described previously. Additionally, phylogenetic analysis indicated that the four CHIKV isolates belonged to the Indian Ocean clade of the ECSA genotype. The results obtained in this study provide detailed information on the molecular characteristics and evolution of currently circulating CHIKV strains in Thailand, which are useful for developing prevention and control strategies.