The Aedes mosquito, carrier of the Zika virus

A person in Texas has contracted the Zika virus through sexual contact, according to health official of the Dallas County Health and Human Services. In a first reported case for the US, it was reported a man infected with the mosquito-borne disease in Venezuela returned to the US and subsequently infected his sexual partner. It was previously thought the virus was spread only by mosquito bites.

In the wake of the case, the U.S. Centers for Disease Control and Prevention (CDC) have advised men returning from infected areas to use condoms with their sexual partners. People in affected countries should protect carefully against mosquito bites.

Pregnant women in particular, they said, should be protected from the semen of someone potentially infected. Microcephaly – which leads to head and brain deformation in babies – has been linked to the virus, which has now been reported in some 24 countries worldwide.

For Dr. William Schaffer of Vanderbilt University Medical School, this development brings new problems to the table, “This opens up a whole new range of prevention issues,” he said. “Mosquito transmission is the highway, whereas sexual transmission is the byway.”

Countries most heavily affected in the recent outbreak include those in the Caribbean and Latin America, where infection by mosquito is still considered the most common form of transmission. The virus is spread from the bite of the female Aedes aegypti mosquito, the same insect to carry dengue fever.

County authorities in Texas sought to assuage fears, saying there had been no reports of the virus spread by mosquito bites in the US. The CDC referred to the infected person as a “nontraveler in the continental United States,” adding there was no threat to an unborn foetus in this case.

The World Health Organisation declared an international health emergency earlier this week, warning up to 4 million people could become infected in the next year alone.