Zika virus can cause an infectious disease called Zika fever. Zika fever often causes no symptoms, or only mild symptoms. Scientists know that people in Africa and Asia have been getting Zika fever since the 1950s. In 2014, the virus spread eastward across the Pacific Ocean - first to French Polynesia, then to Easter Island. Finally, in 2015, it spread to Mexico, Central America, the Caribbean, and South America. In these places, Zika virus has become a pandemic.