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Health officials in Texas said Monday a woman had been infected with Zika after being bitten by a mosquito there, making Texas the second state to have documented local transmission of the virus.

The woman lives in Cameron County, which sits along the Mexican border and on the Gulf Coast. The mosquitoes that are the main drivers of the virus thrive in hot, humid climates, and experts had identified South Texas as one of the most likely locations to see the virus spread by local mosquitoes.


The infection was confirmed by lab tests, Texas officials said. The woman, who is not pregnant, had not traveled recently to any place where the virus is spreading and officials say they ruled out other possible modes of transmission, which include sex.

This summer, officials identified local Zika transmission in Miami, and new cases are still being reported almost daily in Miami-Dade County. While the Miami area and Cameron County are now the only two places in the continental United States to confirm local cases, many experts think it’s likely that transmission has occurred outside the so-called “Zika zones” because the virus is hard to track.

The woman in Texas no longer has live virus in her blood, officials said. That means if she is bitten by a mosquito now, that mosquito cannot become infectious itself and spread the virus to other people.


“We knew it was only a matter of time before we saw a Zika case spread by a mosquito in Texas,” Dr. John Hellerstedt, the state health commissioner, 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.”

Starting Monday night, state and county officials will be going door to door around where the woman lives to try to see if anyone else might have been infected. City officials in Brownsville have conducted spraying around her home.

The Zika virus causes no symptoms in up to 80 percent of people who are infected. People who do show symptoms have a few days of a mild illness, with fevers and rashes. But if the virus infects pregnant women, it can cause an array of devastating defects in fetuses.

There have been more than 4,400 Zika cases in the continental United States, according to the Centers for Disease Control and Prevention, but the large majority of them have been acquired while the person was traveling elsewhere. Texas has had 253 travel-related cases. There have been fewer than 200 local cases reported in Florida.

In past years, Cameron County has had local transmission of dengue and chikungunya, other viruses spread by the Aedes aegypti mosquitoes that transmit Zika.

Experts say Zika is not likely to spread explosively in the continental United States like it has in Latin America and the Caribbean in part because window screens and air conditioning are more common here, meaning residents are less exposed to mosquitoes.