ERVW-1 and infection: Several theories have been proposed for the phenomenon including infection of neuronal progenitor stem cells during pregnancy [19], enhancement of infection due to pre-existing antibodies to Dengue virus (DENV) and/or West Nile virus (WNV) [20], presence of mutations in the envelope glycoprotein of the Asian lineage [21], environmental factors, etc. The incidence of microcephaly during the 2015 ZIKV outbreak was ~100 fold higher than the baseline microcephaly cases in the US, providing the first evidence of a link between Zika infection and birth defects.