A researcher at Boston Medical Center (BMC) and the Boston University School of Public Health (BUSPH) warns that Zika virus could spread quickly to and potentially within the US. The mosquito-borne virus, which is believed to cause microcephaly in infants who are exposed in utero, causes rash and flu-like symptoms in adults and children who have been infected. Zika virus dates back to 1947; however, the first well-documented outbreak in humans was not reported until 2007. An outbreak in French Polynesia in 2013 was responsible for 19,000 suspected cases, and since October 2015, nearly 4,000 cases of Zika virus-related microcephaly have been reported in Brazil. Microcephaly is abnormal smallness of the head, a congenital condition associated with incomplete brain development and a range of neurological complications. The findings are published online in advance of print in the Annals of Internal Medicine.