The unidentified person had not travelled but had had sex with a person who had returned from Venezuela and fallen ill with Zika, Dallas County health officials said.
The US Centres for Disease Control (CDC) issued a statement saying lab tests confirmed the non-traveller was infected with Zika. The virus, which has been linked to birth defects in the Americas, 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,” said Zachary Thompson, director of Dallas County Health and Human Services. “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 that pregnant women postpone trips to countries with Zika outbreaks, mostly in Latin America and the Caribbean, including Venezuela.
Health chiefs said yesterday that two adults have been confirmed with the Zika virus in Ireland. The cases – the first of their kind in the country – are unrelated and both patients are said to be currently well and fully recovered. Both individuals have a history of travel to a Zika affected country, Ireland’s Health Service Executive (HSE) confirmed.
The HSE said the newly discovered Zika cases in Ireland are “not an unexpected event” as many other European countries have reported cases as a result of people travelling to affected areas.
In the epidemic in Latin America and the Caribbean, a species of mosquito called Aedes aegypti – that spreads other tropical diseases, including chikungunya and dengue fever – has been identified.
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 US in the last year, all travellers who brought it into the country.
The World Health Organisation (WHO) has 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 is no risk to a developing foetus.
Zika was first identified in 1947 in Uganda. It was not believed to cause any serious effects until last year; about 80 per cent of infected people never experience any symptoms.