MIAMI • The Zika virus has been transmitted sexually, top United States health authorities confirmed on Tuesday, fuelling fears of the rapid spread of the disease blamed for a surge in the number of brain-damaged babies.
With concern growing that an outbreak sweeping Latin America could spread much farther, the health authorities in Texas said they had confirmation of the virus being transmitted by sexual contact and not just by tropical mosquitoes.
That is a troubling prospect for the US, Canada and Europe, where Zika had so far appeared only in travellers returning from affected areas.
"The patient was infected with the virus after having sexual contact with an ill individual who returned from a country where Zika virus is present" this year, a Dallas County statement read.
The county subsequently tweeted that the virus was contracted from someone who had travelled to Venezuela, and that a second case of Zika imported from Venezuela has also been documented.
Dr Tom Frieden, director of the US Centres for Disease Control and Prevention (CDC), later on Tuesday confirmed in an e-mail the case of sexually transmitted infection reported earlier in Texas. Last month, the CDC said it was aware of one reported case of sexual transmission of Zika and one case of the virus being present in a man's semen after it disappeared from his blood.
Zika, which was first identified in Uganda in 1947, causes relatively mild flu-like symptoms and a rash. But there is growing alarm over an apparent link between the current outbreak and a rise in birth defects and cases of a potentially crippling neurological disorder called Guillain-Barre syndrome.
Latin American nations, particularly Brazil, have reported a surge in cases of microcephaly, which causes babies to be born with abnormally small heads, since the Zika outbreak was declared in the region last year.
The virus is spread primarily by the Aedes aegypti mosquito, whose habitat is concentrated in the tropics, giving temperate countries an apparent reprieve. But sexual transmission would complicate matters.
"The majority of Zika infections are asymptomatic," said Dr Peter Horby, professor of emerging infectious diseases and global health at Oxford University. "Is there a risk of sexual transmission from people who had asymptomatic infection? For how long can sperm be infectious? This highlights our ignorance of this virus."
A day after declaring the spike in serious birth defects in South America an international emergency, the World Health Organisation said it had created a global Zika response unit to contain the virus.
WHO expert Anthony Costello emphasised the urgency of rapid action, stressing that there was no reason to believe the crisis would remain limited to Latin America. "We know that the mosquitoes that carry Zika virus... are present through most of Africa, parts of southern Europe and many parts of Asia, particularly South Asia," he said.
Underlining Mr Costello's point, Thai officials announced that a man had contracted the virus in the country. Cape Verde off the coast of West Africa has reported domestic cases, while Indonesia yesterday confirmed one case dating back to last year, in Jambi, Central Sumatra.