Low seroprevalence of Zika virus infection among adults in Southern Taiwan

Abstract

BackgroundWe recently conducted a serosurvey of newly arrived workers in Taiwan from four Southeast Asian countries which revealed that 1% of the migrant workers had laboratory-confirmed recent Zika virus (ZIKV) infection. Taiwan, where Aedes mosquitoes are prevalent, has a close relationship with Southeast Asian countries. Up to now, 21 imported cases of ZIKV infection have been reported in Taiwan, but there has been no confirmed indigenous case. The aim of this serosurvey was to assess whether there was unrecognized ZIKV infections in Taiwan.MethodsA total of 212 serum samples collected in a cross-sectional seroepidemiologic study conducted during the end of the 2015 dengue epidemic in Tainan, Taiwan, were analyzed. Anti-ZIKV IgM and IgG were tested using commercial enzyme-linked immunosorbent assays (ELISAs). Plaque reduction neutralization tests (PRNTs) for ZIKV and four dengue virus (DENV) serotypes were performed for samples with positive anti-ZIKV antibodies. A confirmed case of ZIKV infection was defined by ZIKV PRNT90 titer ratio ≥ 4 compared to four DENV serotypes.ResultsThe mean age of the 212 participants was 54.0 years (standard deviation 13.7 years), and female was predominant (67.0%). Anti-ZIKV IgM and IgG were detected in 0 (0%) and 9 (4.2%) of the 212 participants, respectively. For the 9 samples with anti-ZIKV IgG, only 1 sample had 4 times higher ZIKV PRNT90 titers compared to PRNT90 titers against four dengue virus serotypes; this individual denied having traveled abroad.ConclusionsThe results suggest that undetected indigenous ZIKV transmission might have occurred in Taiwan. The findings also suggest that the threat of epidemic transmission of ZIKV in Taiwan does exist due to extremely low-level of herd immunity. Our study also indicates that serological tests for ZIKV-specific IgG remain a big challenge due to cross-reactivity, even in dengue non-endemic countries.

Mapping the cryptic spread of the 2015–2016 global Zika virus epidemic

“…Thus, it was possible that ZIKV had already circulated silently in Tamil Nadu by the end of 2016, which later gave rise to the first reported case in 2017. Moreover, in a recent study published in October 2019, low ZIKV seroprevalence was observed in serum samples collected from Southern Taiwan at the end of 2015, providing evidence of possible undetected autochthonous transmission [61]. Overall, the abovementioned epidemiological evidence adds to the credibility of our results, and underscores the necessity of local investigation in the rest of the susceptible spatial units that were found to have a high potential of cryptic ZIKV spread during 2015-2016.…”

“…Both spatial units have reported dengue outbreaks within the past few years [71,72], as well as imported ZIKV infections as recently as the early 2020 [73,74]. These, combined with the latest discovery of low ZIKV seroprevalence in southern Taiwan and a neighbouring province of Guangdong [61,75], suggest that the potential risk of future ZIKV outbreaks should not be overlooked.…”

Zika Virus Antibody Titers Three Years after Confirmed Infection

“…The low ZIKV seroprevalence three years after infection is in line with previous studies, in which it was shown that nAbs and NS1 antibodies against ZIKV decline rapidly, and indicate that ZIKV serology in flavivirus endemic populations is very challenging several years after the initial infection [ 11 , 12 ]. This could possibly in part explain why the reported ZIKV seroprevalence in regions in Africa and Asia, where ZIKV has already been circulating for many years, is low [ 21 , 22 , 23 ]. One possible solution to increase the sensitivity of ZIKV serological assays in populations that did not recently suffer from a ZIKV outbreak is to set a lower cut-off for a positive test result.…”

Use of seroprevalence to guide dengue vaccination plans for older adults in a dengue non-endemic country

“…Third, the serotype-specificity of DENV NS1 IgG ELISA ranged from 75%-80% in primary DENV infection, which is lower than that of PRNT and requires further verification [ 33 ]. Fourth, the cross-reactivity of antibodies between DENV and Zika virus was not determined in this study because there were only three imported Zika cases, with no indigenous cases during the study period [ 76 ] and only a very low seroprevalence of Zika virus infection [ranging from 0.47% (1/212) to 4.2% (9/212)] was documented in Tainan [ 77 ]. Finally, the lack of individual data on comorbidities and past history of dengue illness, as well as other environmental factors of the living areas limit our understanding of the risk factors for acquiring DENV infection and/or severe dengue illness among older adults and the elderly.…”