WHO: Zika 'guilty until proven innocent' of causing birth defects
The Zika virus should be considered "guilty until proven innocent" of causing birth defects, the World Health Organization said Friday.
"Research has got to be done, and done urgently, because there is a very real possibility that this virus could be responsible for some of the horrific consequences," said Bruce Aylward, the WHO's executive director ad interim for outbreaks and health emergencies.
The virus hasn't been definitively proven to cause the defects, but the WHO is operating on the assumption Zika causes microcephaly, in which infants are born with abnormally small heads and incomplete brain development, Aylward said.
Even without definitive proof Zika causes microcephaly, researchers have found "accumulating evidence" of a strong connection, Aylward said.
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Researchers found genetic material from the virus in the brains, placenta and amniotic fluid of several infants with microcephaly, including ones miscarried or aborted by women infected with Zika while pregnant.
So far, Brazil is the only country in the Americas to report an increase in microcephaly. Colombia has reported 25,000 Zika cases, but has not yet seen an increase in microcephaly, possibly because the virus arrived in that country more recently, Aylward said.
It's possible Zika only causes microcephaly if women are infected early in pregnancy. If that is the case, Colombia could see an increase in the birth defects this summer.
The strongest answer to the question of whether the virus causes microcephaly would come from a case-control trial, in which doctors study pregnant women to see if those with Zika infections are more likely than others to give birth to babies with microcephaly, according to an earlier interview with Anthony Fauci, director of the National Institute of Allergy and Infectious Disease. Brazilian doctors are already working on this type of trial.
Brazilian doctors plan to study 200 babies born with microcephaly and 400 babies without the condition, said Ernesto Marques, an associate professor of infectious diseases and microbiology at the University of Pittsburgh and a public health researcher at the Fundação Oswaldo Cruz, a medical research institute in Rio de Janeiro.
Doctors will analyze blood samples from the babies' umbilical cords, as well as blood from the mother, Marques said. Doctors also will perform ultrasounds on the babies' skulls.
Scientists are trying to determine how Zika could cause microcephaly, Marques said. Although Zika is spread by the same mosquitoes that transmit the dengue and chikunguyna viruses, neither of these diseases is linked to birth defects.
Doctors would like to know if something causes the placenta, which provides nourishment through the umbilical cord, to allow the Zika virus to reach the developing fetus, he said.
"Normally, the placenta protects the fetus very well," Marques said from Recife, Brazil, where he is working. "It protects against dengue. It protects against chikungunya. Why doesn't it protect against Zika?"
Scientists wonder if it's possible the Zika virus needs help from a second source, such as another virus, to harm a fetus, Marques said. The second source could relate to nutrition or environmental exposures, he said.