The Un health body said that a surge in cases of microcephaly – a devastating condition in which a baby is born with an abnormally small head and brain – was likely caused by the mosquito – borne Zika virus and declared the situation a public health emergency of international concern. For decades after Zika was first discovered in 1947, in Ugunda, the mosquito – borne virus was of little concern, sporadically causing “mild’ illness in human populations.