Zika virus infection in humans is usually mild or asymptomatic. However, some babies born to women infected with Zika virus have severe neurological sequelae. An unusual cluster of cases of congenital microcephaly and other neurological disorders in the WHO Region of the Americas, led to the declaration of a public health emergency of international concern by the World Health Organization (WHO) on 1 February 2016. By 5 May 2016, reports of newborns or fetuses with microcephaly or other malformations – presumably associated with Zika virus infection – have been described in the following countries and territories: Brazil (1271 cases); Cabo Verde (3 cases); Colombia (7 cases); French Polynesia (8 cases); Martinique (2 cases) and Panama (4 cases). Additional cases were also reported in Slovenia and the United States of America, in which the mothers had histories of travel to Brazil during their pregnancies. ¹