Federal health officials warned pregnant women on Wednesday to avoid visiting Brownsville, Tex., because of the threat of infection with the Zika virus.

At least five cases of Zika transmitted by local mosquitoes have been reported in the last few weeks, and temperatures are still high enough for mosquitoes to thrive, the Centers for Disease Control and Prevention said.

Federal officials issued similar warnings for Miami-Dade County last August. Cases were ultimately discovered in four areas, all of which have since been declared free of local transmission.

Brownsville is on the border with Mexico, which has seen local transmission of the virus for months, and on the shores of the Gulf of Mexico.