United States health officials are investigating whether 14 new Zika virus infections may been transmitted through sexual contact, raising questions about the role of sex in spreading a disease that has been linked to birth defects in Brazil.
Several of the cases involved pregnant women, the US Centers for Disease Control and Prevention (CDC) warned on Tuesday.
In two of the suspected cases, the infection has been confirmed in women whose only known risk factor was sexual contact with an ill male partner who had recently travelled to an area where the virus was present, the CDC said.
Most experts had believed that sexual transmission of the illness was rare, but the new alert suggests sexual transmission of Zika may be more of a factor than previously thought.
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Dr Peter Hotez, endowed chairman of Tropical Pediatrics at Texas Children's Hospital, told Al Jazeera that it was a significant development for a virus mostly transmitted by mosquitos.
"These are all men in the early stages of infection, meaning that they have the ability to transmit the virus in the first two weeks of it to their wives or partners," Hotez said.
"This is a rare event, but transmission through sex is possible in certain circumstances … However, we should still focus on Zika spreading through mosquitos."
No spread through women
All of the newly reported cases of sexual transmission have been in the US. There have been no reports of women transmitting Zika to male sex partners.
In a recent study, British researchers reported evidence of Zika in the semen of a 68-year-old as long as 62 days after he was infected.
Zika infection generally causes mild symptoms, but it may be linked to thousands of cases of birth defects in Brazil known as microcephaly, which is marked by undersized heads and underdeveloped brains.
There is no cure or treatment for Zika infection.
For pregnant women, the CDC recommended that if a male partner has travelled to an area of active Zika transmission that couples use a condom correctly and consistently for the duration of the pregnancy, or that they abstain from sex entirely.
Source: Al Jazeera and agencies