An overview of Zika virus in Thailand Duncan R. Smith1*, Wannapa Sornjai1, Anusara Jitsada1, Suwipa Ramphan1, Nitwara Wikan1, Chayawat Phatihattakorn1, Mongkol Uiprasertkul1, Prasert Auewarakul1, Sarawut Khongwichit1, Ploenphit Promma1, James C. McAvin2 1Mahidol University, Thailand; 2Biosciences Research Management, USA *Corresponding Author
Although early immunological studies proposed the circulation of Zika virus (ZIKV) in Thailand in the 1950s, the first confirmed evidence of ZIKV dates to 2006. However, the circulation of ZIKV in Thailand for more than a decade has been associated with less than 2000 confirmed cases of Zika fever. To try to understand the dynamics of ZIKV transmission in Thailand, we have investigated the presence of ZIKV neutralizing antibodies (nAbs) in healthy Thais, as well as surveyed mosquito collected in Thailand over 2 years. In addition the growth characteristics of two ZIKV isolates, one isolated from a case of Zika fever, and one isolated from the brain of a case of microcephaly resulting from infection of a pregnant woman during her first trimester have been investigated. Markedly, ZIKV neutralizing antibodies (PRNT50>10) were detected in 70% of sera from a cohort of 135 healthy Thais. No association was found between the presence of ZIKV nAbs and other flaviviral exposure. Screening of Aedes mosquitoes collected from Rayong province, Thailand over two successive years (2017 and 2018) failed to detect ZIKV in the local mosquito population. Full sequence characterization of a ZIKV isolate from a case of microcephaly showed the virus was the local endemic ZIKV, and did not carry the supposed microcephaly associated prM Ser139→Asn139 (S139N) mutation. However, growth characteristics analysis showed that the propagation of this virus was slower than the isolate from a case of Zika fever. Our results are consistent low levels of ZIKV transmission being maintained by the high levels of ZIKV nAbs, but that the local, endemic ZIKV is able to cause microcephaly.
Funding This work is supported by Mahidol University, the Thailand Research Fund and Mahidol University (BRG6080006) and the National Science and Technology Development Agency (P-16-50685 and FDA-CO-2559-1569-TH). WS is supported by a Mahidol University Post- Doctoral Fellowship.