The World Health Organization has declared the Zika virus an international public health emergency. While the virus itself is usually not life-threatening, it appears to be linked to microcephaly, which causes babies to be born with abnormally small heads. Microcephaly also causes a host of other health problems, including seizures, developmental delays, hearing loss and vision problems. The WHO says the Zika virus is “spreading explosively” and that up to 4 million people in the Americas could be infected by the end of this year. World Health Organization Director-General Dr. Margaret Chan spoke out at a news conference in Geneva.

Dr. Margaret Chan: “I am now declaring that the recent cluster of microcephaly and other neurological abnormalities reported in Latin America, following a similar cluster of French Polynesia in 2014, constitutes a public health emergency of international concern.”

Scientists have linked rising temperatures from global warming to the increased incidence of mosquito-borne infections such as Zika.