Sexual transmission of the Zika virus is more common than previously thought, according to the World Health Organization (WHO).
After an emergency committee meeting on Tuesday, the UN health agency also said there was increasing evidence of links between Zika and various birth defects.
Zika is most commonly spread by mosquitoes but several countries have reported cases of sexual transmission.
The WHO last month said the outbreak constitutes a global emergency.
WHO Director General Dr Margaret Chan said “reports and investigations in several countries strongly suggest that sexual transmission of the virus is more common than previously assumed”.
She called the development “alarming”.
Dr Chan also said that microcephaly – a birth defect strongly linked to the Zika outbreak in Brazil – was just one of several conditions that the WHO had linked to the virus.
Another is Guillain-Barre Syndrome (GBS). Nine countries have now reported an increase in cases of GBS, a rare condition that can cause temporary paralysis and death.
Dr Chan said problems linked to Zika were now being seen not just in women of child-bearing age, but children, teenagers and older adults.
She said public health officials should not wait for definitive scientific proof of links between the virus and various health conditions before issuing guidance.
The WHO has advised pregnant women to avoid travelling to areas with ongoing Zika outbreaks, and to practice safe sex with anyone who has or abstain from sex for the duration of their pregnancy.
“Women who are pregnant in affected countries or travel to these countries are understandably deeply worried,” Dr Chan said.
The US is investigating more than a dozen possible cases of Zika in people who may have been infected through sex.
A vaccine for the Zika virus could be ready for human trials later this year, Dr Anthony Fauci, who is leading the US government’s research programme, said last week.
Dr Fauci, director of the National Institute of Allergy and Infectious Diseases, said he hopes to start testing a DNA vaccine by September.