U.S. Zika case sparks questions about sex and mosquito germs

NEW YORK - A sexually transmitted case of Zika in Texas has scientists scrambling to understand how much of a risk infection through sex is for the usually mosquito-spread illness.

Experts still stress that mosquitoes are the main culprit in the Zika epidemic menacing Latin America and looming over the United States.

"Mosquitoes would be the great river of transmission, while sexual transmission is going to be akin to a mountain stream," said William Schaffner, an infectious disease expert at Vanderbilt University.

But the Texas case has spurred more discussion about additional ways in which Zika and other illnesses, commonly thought to be carried only by mosquitoes, might be spread.

Other types of transmission can be hard to spot in the midst of outbreaks in which many mosquito-borne infections are occurring, noted Ali Khan, a former disease investigator for the U.S. Centers for Disease Control and Prevention.

"It's very hard to parse this out in the middle of an epidemic," said Khan, now dean of the University of Nebraska's college of public health.

Discerning something like sexual transmission would have to occur in a place where an outbreak was not raging, he said. That's what happened in Dallas.

The current Zika epidemic is on track to cause millions of infections in Latin America and the Caribbean, but no transmission was reported in the United States until the Dallas case this week.

Health officials said a person there - who had not traveled to an outbreak area - was infected. An investigation concluded the person caught the virus through sex with a person who had recently returned from Venezuela, where Zika infections have been growing.

Officials released few details about the case, except to say both patients have recovered. But it wasn't the first to raise the possibility of sexual transmission of the virus.

A Colorado State University researcher, Brian Foy, picked up the virus in Africa and apparently spread it to his wife back home in 2008. More recently, it was found in one man's semen in Tahiti.

Now, after the Dallas case, "we're all kind of scrambling in the scientific community how best to tackle this and how best to research it," said Foy.

Most people infected with Zika experience, at the most, only mild symptoms. But mounting evidence in Brazil has suggested a connection between the virus and babies born with brain defects and abnormally small heads.

The Zika epidemic and possible link to microcephaly cases in Brazil prompted the World Health Organization to declare a global emergency on Monday, calling the virus' rapid spread and its apparent link to the birth defect an "extraordinary event" that poses a threat to the rest of the world.

Perhaps a bigger worry than sex is what dangers may lurk in blood donations from people who have been in Zika outbreak areas, said W. Ian Lipkin, a Columbia University infectious diseases researcher.