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.
Dallas County Health and Human Services said it received confirmation of the case in Dallas from the US 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.
The Texas Department of State Health Services was slightly more cautious in its assessment, saying in a statement, Case details are being evaluated, but the possibility of sexual transmission from an infected person to a non-infected person is likely in this case.
County authorities said there were no reports of the virus being locally transmitted by mosquitoes in the Texas county.
A CDC spokesman confirmed the results of a test for Zika infection but said local officials investigated the mode of transmission.
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.