Aedes aegypti mosquitoes sit in a petri dish at the Fiocruz institute in Recife, Pernambuco state, Brazil, Wednesday, Jan. 27, 2016. The mosquito is a vector for the proliferation of the Zika virus currently spreading throughout Latin America.

Image Credit: AP Photo/Felipe Dana

DALLAS - Health officials in Texas on Tuesday reported the first case of the Zika virus being transmitted within the United States amid the current outbreak in Latin America — a person who was infected through sex.

Dallas County health officials said the unidentified person had not travelled but had sex with a person who had returned from Venezuela and fallen ill with Zika, which has been linked to birth defects in the Americas. The virus 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.

"It's very rare, but this is not new," Zachary Thompson, director of the Dallas County Health and Human Services, told WFAA-TV in Dallas. "We always looked at the point that this could be transmitted sexually."

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 travellers 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 per cent 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.

While Thompson told the television station that the case of sexual transmission is "a game-changer," he added that he didn't want people in Dallas County to overreact. Health officials and Thompson noted that sexual partners can protect themselves by using condoms to prevent spreading sexually transmitted infections.

News from © The Associated Press , 2016