Date Published: June 29, 2017
Publisher: Public Library of Science
Author(s): Sompong Vongpunsawad, Duangnapa Intharasongkroh, Thanunrat Thongmee, Yong Poovorawan, Kevin K Ariën.
The abundance of Aedes mosquito species enabled widespread transmission of mosquito-borne chikungunya virus (CHIKV) and dengue virus (DENV) in Southeast Asia. Periodic seroprevalence surveys are therefore necessary to assess the viral burden in the population and the effectiveness of public health interventions. Since the current seroprevalence for CHIKV and DENV in Thailand are unknown, we evaluated evidence of past infection among Thais. Eight-hundred and thirty-five serum samples obtained from individuals living in central and southern Thailand were assessed for anti-CHIKV and anti-DENV IgG antibodies using commercial enzyme-linked immunosorbent assays. Overall, 26.8% (224/835) of individuals were seropositive for CHIKV, the majority of whom were also DENV-seropositive (91.1%, 204/224). Approximately half of all adults in their fifth decade of life had attained CHIKV seropositivity. Children under 15 years of age in southern Thailand were significantly more likely to be CHIKV-seropositive compared to those residing in central Thailand. In contrast, 79.2% (661/835) of Thais were DENV-seropositive, 30.9% (204/661) of whom also had antibodies to CHIKV. CHIKV/DENV dual seropositivity among Thais was 24.4% (204/835). The age-standardized seroprevalence for DENV was three times that of CHIKV (80.5% vs. 27.2%). Relatively high CHIKV seroprevalence among adults living in central Thailand revealed an under-recognized CHIKV burden in the region, while the low-to-moderate transmission intensity of DENV (seroprevalence <50% at 9 years) is expected to reduce the impact of DENV vaccination in Thailand. This most recent seroprevalence data provide serological baselines for two of the most common mosquito-borne viruses in this region.
Dengue burden on the world’s population is estimated at approximately 60 million symptomatic infections resulting in 10,000 deaths each year . Although mosquito-borne viruses have long been endemic in Southeast Asia, the dengue virus (DENV) outbreak described in 1958 concomitant with the first identification of chikungunya virus (CHIKV) in Thailand increased the awareness of arboviruses responsible for acute febrile illness in the region [2,3]. Infection caused by DENV and CHIKV presents similar clinical symptoms and are sometimes difficult to differentiate . Typical symptoms of DENV infection are fever, rash, headache, myalgia, while CHIKV infection produces an additionally more pronounced musculoskeletal and neuropathic pain [5,6]. Complications from DENV infection can lead to life-threatening dengue hemorrhagic fever and dengue shock syndrome, both of which necessitate careful management of care. Meanwhile, CHIKV infection may result in debilitating arthralgia and acute and chronic arthritis long after an individual has recovered from primary infection. Consequently, accurate diagnosis can be difficult without molecular diagnostics especially in many resource-limited settings where arboviruses are endemic .
Awareness of the scope of CHIKV and DENV endemicity in Southeast Asia is important in assisting the diagnosis and control of these mosquito-borne viruses. Although they account for significant morbidity in the region, the extent of the viral burden is often obscured by inadequate surveillance and clinical misdiagnosis. Past seroprevalence studies over several decades have demonstrated that the presence of anti-CHIKV and anti-DENV antibodies increased with age [19–20]. For CHIKV, which is the only circulating alphavirus in Thailand, seroprevalence reached approximately 50% by 45 years of age in Thais residing in central Thailand . Almost 40 years later, our study showed that the current CHIKV seropositive rate in this region has noticeably decreased. Meanwhile, the observation that individuals younger than 15 years of age in southern Thailand were more likely to be CHIKV seropositive compared to their counterparts in central Thailand may in part be due to the sharp increase in the antibody conversion rate attributed to the well-documented CHIKV outbreaks in southern Thailand in 1995  and again in 2008 [22–23]. Surprisingly, higher seroprevalence in central rather than southern Thailand among 50–59 year-olds suggests that CHIKV circulation may have been under-recognized in the past, despite its reported absence in central Thailand between 1979 and 1982 . Although outbreaks of CHIKV of Asian lineage occurred prior to 1990, ECSA lineage appears to predominate in recent years [12–13]. Limited antigenic diversity of CHIKV likely affords heterologous protection to infection by different CHIKV lineages in previously infected population .