Zika virus is a mosquito-transmitted virus that generally causes no symptoms or a mild illness, but is associated with microcephaly in infants whose mothers contract it during pregnancy. In January, 2016 the US Centers for Disease Control and Prevention (CDC) issued a health advisory and travel alert urging pregnant women to avoid traveling to countries where Zika virus transmission is ongoing. The cases that have been reported in the United States are those of women who had recently traveled outside of the country. There are currently no cases of transmission occurring within the United States.