There are outbreaks of Zika in more than 50 countries and territories, particularly in the Americas. Although the illness caused by the Zika virus is usually mild, the infection during pregnancy can cause the serious birth defect microcephaly, as well as other severe fetal brain defects and Guillain-Barré syndrome. For this reason the World Health Organization (WHO) declared the Zika virus a Public Health Emergency of International Concern (PHEIC).