Texas has likely joined Florida as a state with local, mosquito-borne transmission of the Zika virus.

On Nov. 28, public health officials there reported a case of Zika virus in a Brownsville woman who hadn’t traveled to Mexico or any other area with active Zika transmission. Brownsville sits on the border of Mexico at the state’s southern tip, and is home to Aedes species mosquitoes known to carry the virus. The area had recently been sprayed for mosquitoes.

Zika’s telltale genetic thumbprint was found in the woman’s urine, but her blood was negative, so the virus could no longer be spread from her by mosquito. She was not pregnant. There are no other suspected cases of local transmission, according to Texas officials.

“We knew it was only a matter of time before we saw a Zika case spread by a mosquito in Texas,” John Hellerstedt, MD, commissioner of the Texas Department of State Health Services, said in a statement . “We still don’t believe the virus will become widespread in Texas, but there could be more cases, so people need to protect themselves from mosquito bites, especially in parts of the state that stay relatively warm in the fall and winter.”

The state public health officials recommend testing all pregnant women who have traveled – or who have sexual partners who have traveled – to areas with active Zika transmission. In addition to Mexico, the list includes Southeast Asia, Central and South America, the Caribbean, Cape Verde, and Pacific islands including Tonga, Samoa, and Papua New Guinea.

Texas officials also recommend antibody testing of pregnant women in southern Texas if they have two or more symptoms – fever, itchy rash, joint pain, and eye redness – and anyone statewide with at least three symptoms.

As of Nov. 23, a total of 4,444 Zika cases have been reported to the Centers for Disease Control and Prevention in U.S. states and the District of Columbia. Just 182 of those cases were the result of local spread by mosquitoes in Florida. Puerto Rico has reported nearly 32,000 locally-transmitted cases.

The 257 previously confirmed cases in Texas were all associated with travel. Most were in the Houston and Dallas–Fort Worth areas.

Local and state health officials are working with the CDC to pinpoint how and where the Brownsville infection occurred. Mosquitoes are being trapped, and workers are going door to door to educate people about Zika and request urine samples to screen for infection.