A case of Zika virus infection transmitted by sex, rather than mosquito bite, was discovered in Texas on Tuesday, a development sure to complicate plans to contain a global epidemic.

The Dallas County Health and Human Services Department reported that a patient with the Zika virus was infected after having sex with someone who had returned from Venezuela, where Zika is circulating.

After the report, the Centers for Disease Control and Prevention changed its advice to Americans visiting regions in which the Zika virus is spreading.

Men having sex after traveling to these areas should consider wearing condoms, officials said, although they did not indicate for how long this would be necessary. Pregnant women should avoid contact with semen from men recently exposed to the virus, federal officials also said. The agency plans to issue further guidelines soon.