The World Health Organization is declaring the Zika virus a global emergency. The organization’s director general said during a teleconference that a coordinated international response is needed to fight the mosquito-borne virus. Based on cases of microcephaly in which infants are born with smaller-than-usual brains, Dr. Margaret Chan called the Zika virus an “extraordinary event.” The disease has been linked to thousands of birth defects in Brazil. The declaration is aimed at fast-tracking financial aid and research.