The first known case of Zika virus transmission in the United States was reported in Dallas, Texas on Tuesday by local health officials, who said it likely was contracted through sex and not a mosquito bite.

"This needs to be further investigated to understand the conditions and how often or likely sexual transmission is...This is the only the second mooted case of sexual transmission," WHO spokesman Gregory Hartl told Reuters. For now the key to control the virus was eliminating mosquitos and wearing proper clothing.