GENEVA – Sexual transmission of the Zika virus is more common than previously thought, the World Health Organization said Tuesday, citing reports from several countries.
After a meeting of its emergency committee on Tuesday, the U.N. health agency also said there is increasing evidence that a spike in disturbing birth defects and neurological problems are caused by Zika, which is mostly spread by mosquito bites. When WHO declared the explosive outbreak in the Americas to be a global emergency last month, it said that the evidence that Zika was responsible was only circumstantial.
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.” The U.S. is investigating more than a dozen possible cases of Zika in people who may have been infected through sex.
Chan also said nine countries have now reported increasing cases of Guillain-Barre syndrome, a rare condition that can cause temporary paralysis and death. She said that problems linked to Zika, including Guillain-Barre syndrome, are now being seen not just in women of child-bearing age, but children, teenagers and older adults.
Zika is also now spreading to new countries, WHO said. It noted local transmission has now been reported in 31 countries across Latin America and the Caribbean.
“All of this news is alarming,” Chan said.
Despite the lack of definitive evidence proving that Zika causes birth defects and neurological problems, Chan said officials shouldn’t wait for definitive scientific proof before making recommendations.
“Microcephaly is now only one of several documented birth abnormalities associated with Zika infection during pregnancy,” she said, adding that it can cause growth problems, injuries to the central nervous system and fetal death.
WHO’s emergency committee called for “intensified” research into the relationship between new clusters of babies born with abnormally small heads and other neurological disorders. It said particular attention should be given to studying the genetics of the different Zika virus strains and establishing studies to determine if there is a causal relationship.
So far, cases of babies born with small, deformed heads linked to Zika have only been confirmed in Brazil and French Polynesia, though officials say they expect reports from other countries once the virus has been circulating there long enough to affect pregnant women. Colombia has reported several suspected cases of microcephaly.
“Women who are pregnant in affected countries or travel to these countries are understandably deeply worried,” Chan said.
WHO recommends pregnant women avoid travel to areas with ongoing Zika outbreaks and that if their partners travel to affected countries, they should practice safe sex or abstain from sex for the duration of their pregnancy.
The WHO said sexual transmission was “relatively common” and that health services in Zika-affected areas should be ready for potential increases in cases of neurological syndromes such as microcephaly and congenital malformations.
“Pregnant women whose sexual partners live in or travel to areas with Zika virus outbreaks should ensure safe sexual practices or abstain from sex for the duration of their pregnancy,” the WHO said in a statement, based on advice from its Emergency Committee of independent experts.
Previously the U.N. health agency had advised women to consider deferring nonessential travel to areas with ongoing transmission of the mosquito-borne virus, which is spreading through Latin America, including Olympics host Brazil.
The link between Zika and babies born with small heads and developmental problems, as well as Guillain-Barre syndrome which can cause paralysis, has not been proven scientifically but studies point in that direction, it said.
“Clearly Zika infection during pregnancy will produce very bad outcomes,” WHO director-general Chan told a news conference. “It is important we recommend strong public health measures and not wait until we have definitive proof.”
David Heymann, who chairs the WHO Emergency Committee set up on Feb. 1, said of the recommendation: “The onus is on countries to identify and report where they have outbreaks and where they don’t.”
The WHO did not recommend any general trade or travel restrictions. But it said that existing mechanisms under the WHO’s International Health Regulations should be explored, including recommendations that airports be sprayed to eliminate mosquitoes and their breeding grounds.
“We can expect more cases and further geographical spread,” Chan said. “Sexual transmission is more common than previously assumed.”
Bruce Aylward, WHO Executive Director for Outbreaks and Emergencies, told reporters that sexual transmission had only been documented as spreading from men to women.
“There’s no evidence of women-to-men (transmission), so this dead-ends,” he said.