The Zika outbreak in Brazil and other parts of Latin American and the Caribbean has coincided with a sharp increase in the number of babies born with microcephaly, which results in abnormally small heads and brains.
There has also been a rise in other brain and eye birth defects in countries affected by the Zika outbreak. But firm evidence of a link between the virus and these birth defects has been lacking.
In a new study, researchers at the University of California, San Francisco (UCSF), found that a protein the Zika virus uses to infect skin cells and cause a rash is also present in stem cells of the developing brain and retina of a fetus.
The so-called AXL protein sits on the surface of cells and can provide an entry point for Zika. Learning more about the link between Zika and AXL could lead to drugs to block Zika infection, according to the researchers.
The brain and eye birth defects occurring in areas with Zika outbreaks are "precisely the kind of damage we would expect to see from something that was destroying neural and retinal stem cells during development," said study senior author Dr. Arnold Kriegstein. He is director of UCSF's Center of Regeneration Medicine and Stem Cell Research.
"If we can understand how Zika may be causing birth defects, we can start looking for compounds to protect pregnant women who become infected," Kriegstein said in a university news release.
The study was published online March 30 in the journal Cell Stem Cell.
A mosquito-borne virus, Zika has been suspected of causing thousands of cases of microcephaly in Brazil.
While the bulk of Zika cases leading to microcephaly may occur via maternal infection during pregnancy, cases of sexual transmission from a man to his female partner have come to light, according to the U.S. Centers for Disease Control and Prevention.
Zika infection is usually a mild illness in adults, and many cases may occur without symptoms, experts say. However, because of the risk to babies, the CDC is advising that men with known or suspected infection with Zika refrain from sex -- or only have sex with a condom -- for six months after a diagnosis.
The agency also advises that, for couples involving a man who has traveled to or resides in an area endemic for Zika:
- The couple refrain from sex, or use condoms during sex, throughout the duration of a pregnancy.
- They refrain from sex, or use condoms during sex, for eight weeks if the man has returned from travel to a Zika-endemic area but has not shown signs of infection.
- For couples living in a Zika-endemic area, they refrain from sex or engage in sex only with a condom for as long as active Zika transmission persists in that area.
The latest guidelines also recommend that women who know they've been infected, or who have no symptoms but have recently been to a Zika-endemic area, or think they might have been exposed via sex, should wait at least eight weeks before trying to get pregnant.
The CDC has also advised that all pregnant women consider postponing travel to any area where Zika virus transmission is ongoing. If a pregnant woman must travel to or live in one of these areas, she should talk to her health-care provider first and strictly follow steps to prevent mosquito bites.
In the majority of Zika infections, symptoms included rash (97 percent of cases), fever and joint pain.
"Zika virus disease should be considered in patients with acute onset of fever, rash, arthralgia [joint pain], or conjunctivitis [pink eye] who traveled to areas with ongoing Zika virus transmission or who had unprotected sex with someone who traveled to one of those areas and developed compatible symptoms within two weeks of returning," according to the CDC.
First discovered in Uganda in 1947, the Zika virus wasn't thought to pose major health risks until last year, when it became clear that it posed potentially devastating threats to pregnant women.
The Zika virus has now spread to over 38 countries and territories, most in Latin America and the Caribbean. The World Health Organization estimates there could be up to 4 million cases of Zika in the Americas in the next year.
For more on Zika virus, visit the U.S. Centers for Disease Control and Prevention.
To see the CDC list of sites where Zika virus is active and may pose a threat to pregnant women, click here.
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