ERVW-1 and microcephaly: Thus, all ZIKV strains associated with epidemic urban, mosquito-borne transmission; sexual transmission via semen; GBS; and congenital Zika syndrome include this M protein substitution along with D683E in the envelope glycoprotein and V763M and T777M in the transmembrane domain of E. Another substitution, M/T2634V, likely occurred after ZIKV spread from French Polynesia or another island in the South Pacific to the Americas (estimated from August 2013 to April 2014) and thus could be associated with the higher incidence of microcephaly in Brazil than in the South Pacific outbreaks (8, 11).