Sexually Transmitted Zika Case Confirmed in Texas
This image of the Zika virus was taken using a transmission electron microscope. The virus particles are 40 nanometers in diameter, with an outer envelope, and an inner dense core.
Credit: Cynthia Goldsmith/CDC

A person in Dallas appears to have spread the Zika virus to another person through sex, Texas health officials said today.

Officials at Dallas County Health and Human Services (DCHHS) said that a person in the area was infected with the Zika virus after having sexual contact with another person who had returned from Venezuela, where the virus is spreading, and was ill. The case was confirmed by the Centers for Disease Control and Prevention (CDC), the DCHHS said today (Feb. 2).

"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 Thompson, the DCHHS director, said in a statement. Thompson noted that abstinence or condoms are the best prevention methods against sexually transmitted diseases. [Zika Virus FAQs: Top Questions Answered]

The Zika virus, which is currently spreading in more than 20 countries in Central and South America and the Caribbean, is usually transmitted by mosquitoes. But in rare cases, the virus has been reported to spread through sex, according to the CDC.

For example, in 2008, an American scientist contracted the virus while working in Senegal, and apparently transmitted the virus to his wife when he returned home to Colorado. Sexual transmission was the most likely way that the wife became infected, according to a 2008 report of the case written by the scientist and his colleagues.

And in a study published last year, researchers reported finding the Zika virus in the semen of a man who was infected with the virus during the 2013 outbreak in French Polynesia.

The Dallas case is the first report of the Zika virus spreading in the United States this year. Health officials predict that there could be small outbreaks of the Zika virus in the country from the spread of the virus by mosquitoes, but this hasn't happened yet.

Infection with the Zika virus usually causes no symptoms, but can lead to mild illness in some people, including fever, rash, joint pain or red eyes. However, health officials are concerned about a link between the Zika virus in pregnant women and microcephaly, a birth defect in which the baby's head is abnormally small. In Brazil, the number of suspected cases of microcephaly rose dramatically in 2015, at the same time the country was experiencing a Zika virus outbreak. Researchers have also found the Zika virus in the brain tissue of infants born with microcephaly.

On Monday (Feb. 1), the World Health Organization called the link between the Zika virus and microcephaly "a public health emergency of international concern."

The CDC recommends that all U.S. pregnant women consider postponing travel to the areas where the Zika virus is spreading, including 24 countries in Central and South America.

Follow Rachael Rettner @RachaelRettner. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.