The World Health Organization today declared Zika virus an international public health emergency. WHO also recommended enhanced surveillance, the development of new diagnostic tools and “aggressive measures” to reduce Zika infections, particularly among pregnant women and women of child-bearing age, in addition to intensifying research efforts aimed at vaccines and treatments. A marked increase in infants born with microcephaly, a birth defect resulting in smaller than normal head size, has been reported during the Zika outbreak in Brazil. It is not known how many of the cases are actually associated with the virus. Until more is known, the Centers for Disease Control and Prevention strongly advises pregnant women to consider postponing travel to Zika-affected areas, or talk to their health care provider before they do and strictly follow steps to avoid mosquito bites during the trip. Only about one in five people infected with the mosquito-borne virus will get sick, and their illness is usually mild. There are currently no vaccines or medications to prevent or treat Zika infection.