Abstract
Between 2018 and 2019, the incidence of chikungunya was approximately 15,000 cases across 60 provinces in Thailand. Here, the clinical presentations in chikungunya, emergent pattern, and genomic diversity of the chikungunya virus (CHIKV) causing this massive outbreak were demonstrated. A total of 1,806 sera samples from suspected cases of chikungunya were collected from 13 provinces in Thailand, and samples were tested for the presence of CHIKV RNA, IgG, and IgM using real-time PCR, enzyme-linked immunoassay (ELISA), commercial immunoassay (rapid test). The phylogenetic tree of CHIKV whole-genome and CHIKV E1 were constructed using the maximum-likelihood method. CHIKV infection was confirmed in 547 (42.2%) male and 748 (57.8%) female patients by positive real-time PCR results and/or CHIKV IgM antibody titers. Unsurprisingly, CHIKV RNA was detected in >80% of confirmed cases between 1 and 5 days after symptom onset, whereas anti-CHIKV IgM was detectable in >90% of cases after day 6. Older age was clearly one of the risk factors for the development of arthralgia in infected patients. Although phylogenetic analysis revealed that the present CHIKV Thailand strain of 2018-2020 belongs to the East, Central, and Southern African (ECSA) genotype similar to the CHIKV strains that caused outbreaks during 2008-2009 and 2013, all present CHIKV Thailand strains were clustered within the recent CHIKV strain that caused an outbreak in South Asia. Interestingly, all present CHIKV Thailand strains possess two mutations, E1-K211E, and E2-V264A, in the background of E1-226A. These mutations are reported to be associated with virus-adapted Aedes aegypti. Taken together, it was likely that the present CHIKV outbreak in Thailand occurred as a result of the importation of the CHIKV strain from South Asia. Understanding with viral genetic diversity is essential for epidemiological study and may contribute to better disease management and preventive measures.
Highlights
Chikungunya is a vector-borne infectious disease caused by the Chikungunya virus (CHIKV), an Alphavirus in the family Togaviridae
We investigated samples from 1,806 patients with suspected CHIKV infections that were sent to our center from October 2018 to February 2020
Among 1,806 suspected cases, 1,295 (547 male and 748 female) patients were confirmed to have CHIKV infection based on positive results of real-time reverse transcription-polymerase chain reaction (RT-PCR) and/or IgM antibody testing
Summary
Chikungunya is a vector-borne infectious disease caused by the Chikungunya virus (CHIKV), an Alphavirus in the family Togaviridae. CHIKV infection was initially identified in 1952 in a febrile patient in Tanzania, Africa [1]. CHIKV can be transmitted to humans by Aedes aegypti and Aedes albopictus mosquitoes. The common consequences of CHIKV infection are severe arthritis and polyarthralgia, which can persist for weeks or months. There is currently no effective antiviral drug or vaccine to treat or prevent CHIKV infection, respectively. Real-time reverse transcription-polymerase chain reaction (RT-PCR) for the detection of CHIKV RNA and testing of IgM antibody specific to CHIKV antigen are widely used for laboratory diagnosis of CHIKV infection [4,5,6]. CHIKV infection has been detected in over 100 countries and millions of people worldwide have been infected
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