Zika virus disease in the US

"Dallas County Health and Human Services has received confirmation from the Centers for Disease Control and Prevention of the first Zika virus case acquired through sexual transmission in Dallas County in 2016," the department said a statement.

Zachary Thompson, the health department's director, said the case proved that Zika could be transmitted sexually.

“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,” he said. “Next to abstinence, condoms are the best prevention method against any sexually-transmitted infections.”

A total of 31 people in the US are believed to have been diagnosed with Zika in the US in the past 12 months, but all of those cases originated in Central and South America, where the virus is more prevalent.

Symptoms are typically mild in adults, but babies whose mothers have contacted the disease can be born with smaller heads and brains.

Brazil has been the country worst-affected by Zika, though the virus has been reported in more than 20 countries.