The first known case of Zika virus transmission in the United States was reported in Texas on Tuesday by local health officials, who said it likely was contracted through sex and not a mosquito bite, a day after the World Health Organization declared an international public health emergency.
The virus, linked to severe birth defects in thousands of babies in Brazil, is spreading rapidly in the Americas, and WHO officials on Tuesday expressed concern that it could hit Africa and Asia as well.
Zika had been thought to be spread by the bite of mosquitoes of the Aedes genus, so sexual contact as a mode of transmission would be a potentially alarming development.
The U.S. Centers for Disease Control and Prevention confirmed it was the first U.S. Zika case in someone who had not traveled abroad in the current outbreak, said CDC Director Dr. Tom Frieden on Twitter.