The spread of Zika through sex is happening more frequently than anticipated

Ricardo Moraes/Reuters

Cases of sexually transmitted Zika virus are more frequent than the World Health Organization had anticipated, and that suggests that sexual transmission of the virus may be more common that we thought as well.

"Reports and investigations from several countries strongly suggest that sexual transmission of the virus is more common than previously assumed," the WHO's Director-General Dr. Margaret Chan said in a briefing on the latest Zika emergency committee meeting on Tuesday.

The Zika virus is predominantly transmitted via mosquitoes, though cases of sexual transmission are increasingly being reported. In February, the CDC reported it was investigating 14 possible cases of sexually transmitted Zika, of which two were confirmed, four more were probable, six are still under investigation, and two have been ruled out.

Only about one in five people ever experience symptoms once infected with Zika. However, the virus's links to a birth defect called microcephaly, in which babies are born with abnormally small heads, make these reports of sexual transmission troubling for pregnant women.

Beyond microcephaly, other birth defects have also been associated with Zika, including fetal death, placental insufficiency (in which the placenta can't deliver enough oxygen and nutrients to a developing baby), fetal growth restriction, and injuries to the central nervous system.

Chan concluded that yes, Zika is a neurotropic virus, or one that affects the nervous system. Evidence is also growing around the connection between Zika and Guillain-Barré Syndrome, a typically temporary neurological condition that can cause paralysis.

It still remains to be seen whether Zika causes these conditions or whether they are linked in some other way. In the meantime, Chan said, "Strong public health actions should not wait for definitive scientific proof."

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