First Zika Virus sexual transmission reported in Texas

The first known case of sexual transmission of the Zika virus in the U.S. was reported in Texas on Tuesday by local health officials. Those officials said it likely was contracted through sex and not a mosquito bite. Two days ago the World Health Organization declared an international public health emergency.

The virus which is thought to cause severe birth defects in thousands of babies in Brazil, is spreading into the Americas.

Dallas County Health and Human Services said it received confirmation of the case in Dallas from the U.S. Centers for Disease Control and Prevention.

The county department said on Twitter that the person was infected through sexual contact with someone who had traveled to Venezuela. The person infected did not travel to the South American country, county health officials said.

County authorities said there were no reports of the virus being locally transmitted by mosquitoes in the Texas county.

Previously, international health officials had noted one case of possible person-to-person sexual transmission. But the Pan American Health Organization said more evidence was needed to confirm sexual contact as a means of Zika transmission. The medical literature also has one case in which the virus was detected in semen.

The virus has been linked to microcephaly, in which babies have abnormally small heads and improperly developed brains.

The WHO has said the virus could infect 4 million people in the Americas. It said on Tuesday it launched a global response unit to fight the mosquito-borne virus.