Since the first case was diagnosed in April 2015 in Brazil, the Zika virus has spread throughout the Americas. While mosquito-borne virus has fairly mild, flu-like symptoms, it's also thought to cause microcephaly, a birth defect in which babies are born with heads that are smaller than normal. Because mosquito bites are so hard to prevent and there's currently no vaccine or treatment for Zika, the World Health Organization has declared Zika a global public health emergency. Yesterday the governor of Florida declared a state of emergency in the state's nine counties in which cases of Zika have been diagnosed.

When you see the number and span of Zika's incidence, it's easy to see why public health officials are worried. This interactive map depicts the number of diagnosed cases of Zika virus by country, denoted by purple circles. It is missing three new cases announced yesterday—two in Australia and one in Ireland, the first to be diagnosed outside the Americas. Officials expect more cases to follow in these places and others.