Intimate contact as a mode of transmission will be a potentially alarming development

The first known case of Zika virus transmission in the United States has been reported in Texas by local health officials, who said it likely was contracted through sex and not a mosquito bite, after the World Health Organization declared an international public health emergency.

The unidentified person had not traveled but had sex with a person who had returned from Venezuela and fallen ill with Zika, health officials said. The US Centers for Disease Control issued a statement saying lab tests confirmed the non-traveler was infected with Zika.