Brazil saw a dramatic increase in numbers of babies born with microcephaly, a condition linked to the Zika virus. Babies with the condition are born with an abnormally small head, or the head stops growing at birth. The Zika virus, transmitted by mosquitoes, generally causes mild, flu-like symptoms, and the exact causal link to microcephaly—an otherwise rare condition—is not fully understood. The World Health Organization recorded 2,289 Zika-linked microcephaly cases in Brazil from the beginning of the outbreak in 2015 to the end of 2016, and declared the Zika virus an international public health emergency. A large number of the Brazilian cases occurred in the northeastern interior, one of the poorest regions of the country, where many people had to travel long distances to reach a hospital for treatment.