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Evidence Grows Linking Zika, Microcephaly and Other Nerve Syndromes

Chatham House

Scientists are still scrambling to get a full scientific picture of the Zika virus, but experts already know enough to be scared of it.

“Strong public health actions should not wait for definitive scientific proof,” Margaret Chan, director general of the World Health Organization (WHO), said Tuesday, after meeting in Geneva, Switzerland with the agency's Review Committee on Zika.

New findings offer the first hint of answers about how Zika might be damaging the developing brain and fetus, and how devastating this outbreak might become.


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Over the last week, the outbreak has topped 30 countries and travelers “in every region of the world” have reported infections, Chan told journalists after the meeting.

There have been more reports of babies delivered with birth defects and adults diagnosed with neurological problems after infections with Zika. A recent study in Cell Stem Cell showed that the virus targets early brain cells in lab dishes and interferes with their development. And a report in the New England Journal of Medicine (NEJM) found that 29 percent of 88 Brazilian women studied had problems with their pregnancies after infection with Zika, including the deaths of two previously healthy fetuses.

“All of this news is alarming,” Chan said.

The investigators who conducted the NEJM study were surprised to find that Zika, at least at first glance, appears to be more dangerous than rubella (also known as German measles)—an infection whose pregnancy terrors were ended in the West decades ago with a vaccine.

“This clustering of negative things in women who are otherwise healthy and young—it was a big surprise to us,” says Karin Nielsen, an expert in pediatric infectious diseases at Mattel Childrens' Hospital at UCLA, who helped lead the NEJM study.

Rubella can cause a range of birth defects including microcephaly and other types of brain malformations and central nervous system problems that are now appearing with Zika.

But rubella has a devastating effect only when contracted during the first half of pregnancy. With Zika, Nielsen and her colleagues found problems later in pregnancy, too.

Nielsen says she’s particularly haunted by the two previously-healthy fetuses who died after their mothers—residents of Rio de Janiero, which has been hit hard by Zika—contracted the infection at 25 and 32 weeks respectively into their pregnancies. The virus somehow prevented nutrients from reaching the fetus through the placenta, Nielsen says. And that means there is no safe time in pregnancy to catch Zika.

The range of conditions Nielsen saw in these Zika patients—from problems of brain development to problems with blood flow—convinced her that the link is real and the virus a grave danger to pregnancies.

“I don’t have any doubt. I’m pretty much convinced we’re seeing a congenital syndrome related to this virus,” Nielsen says.

Though terrifying, the New England Journal report provides the first piece of concrete evidence to talk about with patients, says Carey Eppes, a maternal and fetal medicine doctor at Baylor College of Medicine in Houston, who was not involved in the study.

Her high-risk pregnancy practice now includes a lot of women who recently visited Zika-infested countries—many of whom traveled over Christmas to see spouses and family in Mexico or Central America.

Among the questions Eppes still can’t answer for them: are fetuses at risk if their mothers catch Zika but don’t show any symptoms? What about the fetuses of women who contract Zika from having sex with an infected partner, which appears to be rare, but has nonetheless happened at least 14 times in the U.S.?

And as her patients begin to worry more about stillbirth, Eppes says she doesn’t even know what to look for as warning signs of a troubled fetus.

“Normally, we’d look at baby’s heartbeat and see if there’s any sign of intrauterine distress, and I don’t know if that’s what babies with Zika would show,” she says.

Viral epidemiologist Amelia Pinto still stops short of blaming Zika for all the health problems that have been noted since Zika arrived in Brazil in late 2014. “There are so many other confounding issues,” Pinto says, an assistant professor in the Department of Molecular Microbiology & Immunology at Saint Louis University.

An expert in flaviviruses, the category which includes Zika and also dengue, she would like to know more about other infections these pregnant women might have had, in addition to Zika.

Clinicians already know, for example, that a second infection with dengue is worse than the first. In the lab, dengue and Zika cross-react, Pinto says, suggesting that a Zika infection following a dengue infection could be worse than either alone—though no one knows how they interact in the real world. (One recent study from French Polynesia found that people who had recent dengue infections as well as Zika were no more likely to develop a neurological disorder known as Guillain-Barré Syndrome than people infected only with Zika.)

All of these questions could have been answered years, if not decades ago, if anyone had taken a closer look at Zika, says Madhukar Pai, director of Global Health Programs for the McGill University Faculty of Medicine.

Although it’s possible that the virus, first identified in 1947, has become more dangerous recently, it’s far more probable that there were outbreaks that authorities failed to notice.

“These sorts of things have been happening in most poor countries for decades,” he says. “It’s only when it touches the West that anyone is even thinking of them.”

This lack of proper public health surveillance dooms the world to repeat scenarios like we saw with Ebola and are now seeing with Zika, he says.

“You can’t do much once it starts appearing here,” he says. “You’ve got to do something in countries where there are problems.”

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