A person in Texas has become infected with the Zika virus through sex, the first case of the illness being transmitted inside the United States, health officials confirmed Tuesday.

Dallas County health officials said the unidentified patient had sexual contact with an infected individual who had returned from Venezuela and fallen ill with Zika.  The U.S. Centers for Disease Control and Prevention (CDC) issued a statement saying lab tests confirmed the non-traveling patient was infected with the virus.

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“Now that we know Zika virus can be transmitted through sex, this increases our awareness campaign in educating the public about protecting themselves and others,” Zachary Thomson, director of DCHHS, said in a statement. “Next to abstinence, condoms are the best prevention method against any sexually transmitted infections.”

The virus, which has been linked to birth defects in the Americas, is primarily spread through mosquito bites, but investigators had been exploring the possibility it could be sexually transmitted. There was a report of a Colorado researcher who picked up the virus in Africa and apparently spread it to his wife back home in 2008, and it was found in one man's semen in Tahiti.

There are no reports of the virus being locally transmitted by mosquitoes in Dallas County, Fox 4 reported. However, health officials said it could happen eventually.

The CDC says it will issue guidance in the coming days on prevention of sexual transmission of Zika virus, focusing on the male sexual partners of women who are or may be pregnant. The CDC has already recommended pregnant women postpone trips to more than two dozen countries with Zika outbreaks, mostly in Latin America and the Caribbean, including Venezuela. It also said other visitors should use insect repellent and take other precautions to prevent mosquito bites.

In the epidemic in Latin America and the Caribbean, the main villain identified so far is called Aedes aegypti — a species of mosquito that spreads other tropical diseases, including chikungunya and dengue fever. It is found in the southern United States, though no mosquito-borne transmission has been reported in the continental United States to date. There have been about 30 cases in the U.S. in the last year, all travelers who brought it into the country.

The World Health Organization on Monday declared a global emergency over the rapidly spreading Zika virus, saying it is an "extraordinary event" that poses a threat to the rest of the world. The declaration was made after an emergency meeting of independent experts called in response to a spike in babies born with brain defects and abnormally small heads in Brazil since the virus was first found there last year.

WHO officials say it could be six to nine months before science proves or disproves any connection between the virus and babies born with abnormally small heads.

The CDC said that in the recent Texas case, there's no risk to a developing fetus.

Zika was first identified in 1947 in Uganda. It wasn't believed to cause any serious effects until last year; about 80 percent of infected people never experience symptoms.

The most common symptoms are fever, rash, joint pain and red eyes. The illness is usually mild with symptoms lasting several days to a week. Symptoms usually start two days to a week after being bitten by an infected mosquito.

The Associated Press contributed to this report.