The Centers for Disease Control and Prevention Wednesday cautioned pregnant women to avoid Brownsville, Texas, where mosquitoes are believed to have infected five people with the Zika virus.

Brownsville is now a “cautionary area,” federal health officials said, after the south Texas city last week became home to the second Zika outbreak in the continental U.S. The CDC says a cautionary area is one where Zika has been transmitted locally, but health officials don’t see evidence of “widespread, sustained local spread” of the...