WHO: Sexual transmission of Zika more common than thought
Sexual transmission of Zika is more common than previously thought, the World Health Organization said Tuesday. But scientists still have unanswered questions about the first mosquito-borne disease known to spread through sex, including how long it lasts in semen.
Investigations in several countries "strongly suggest" the virus spreads through sex more often than scientists assumed, said WHO director-general Margaret Chan, who spoke after convening a meeting of the group's emergency committee. The U.S. is investigating more than a dozen possible cases of sexually transmitted Zika.
Mosquitoes spread the vast majority of infections, but the reports could spell difficulty ahead for monitoring the growing epidemic that is linked to major birth defects and a condition that causes paralysis.
Determining how often sexual transmission occurs is difficult in nations such as Brazil, where an estimated 1 million people have been infected with Zika, the CDC's Lyle Petersen said at a meeting last week of the Pan American Health Organization, part of the WHO. It's easier to track occasional cases of sexual transmission in the USA or Europe, where the disease is not yet spreading through local mosquitoes.
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The virus is now active in more than 30 countries and territories, mainly in Latin America and the Caribbean. The Centers for Disease Control and Prevention reports more than 150 travel-associated cases in the U.S.
Nine countries with Zika outbreaks report increases in Guillain-Barre syndrome, in which the body's immune system attacks the nerves and causes paralysis, the WHO said Tuesday.
New studies have shed light on how the virus causes major birth defects, such as microcephaly, in which babies are born with abnormally small heads and incomplete brain develop. Researchers recently found Zika appears to target fetuses' brains, Chan said.
"Clearly, Zika virus infection in pregnancy can produce very bad outcomes," Chan said. "All of this news is alarming."
Scientists know of few other mosquito-borne illnesses that cause birth defects, said Amesh Adalja, a senior associate at the Center for Health Security at the University of Pittsburgh Medical Center.
Although researchers found one case of congenital West Nile virus infection that led to eye and brain abnormalities, "this appears to be a rare occurrence," Adalja said. Japanese encephalitis, also spread by mosquitoes, can pass from a mother to a developing fetus and is linked to miscarriages.
Petersen has studied mosquito-borne illnesses for two decades, but said he has "never seen anything" like the abnormalities linked to Zika.
WHO strengthened travel recommendations Tuesday, advising pregnant women not to travel to locations experiencing an outbreak of the virus. Previously, WHO recommended pregnant women "consider delaying travel" to such areas, in line with CDC recommendations.
So far, health officials have reported a spike in cases of microcephaly linked to Zika only in Brazil. That could change.
"What we see in Brazil now is what could occur in Colombia and other countries in coming months," said David Heymann, chair of the WHO's emergency committee and a professor of infectious disease epidemiology at the London School of Hygiene and Tropical Medicine.
Although pesticides are effective against the virus-carrying mosquitos, the WHO said a growing number of the bugs are resistant to the chemicals. The agency recommends countries use strategies that don't include insecticides, such as cleaning up trash to eliminate mosquito breeding sites, emptying and covering home water storage containers and using screens on doors and windows.