While definitive proof is still lacking, the operating assumption is these profound birth defects are likely due to maternal infection with the Zika Virus during the first or second trimester (see ECDC: Complications Potentially Linked To The Zika Virus Outbreaks In Brazil & French Polynesia).Over the past month more than 2000 excess microcephalic births have been registered in Brazil, and those numbers are expected to rise significantly over the months ahead.  Meanwhile, countries just now seeing the arrival of the virus are girding themselves to deal with similar public health challenges. Much of Central & South America, along with the Caribbean are at risk. Included also are parts of North America where the two primary Aedes mosquito vectors can be found.

Source: Avian Flu Diary: Viral Creep: Zika Spreading In Central & South America