Here's What We Know Now About Zika and Birth Defects

Zika virus is spreading, and scientists are growing more concerned about its link to an epidemic of brain defects known as microcephaly.

As the Zika virus spreads, hitting 52 countries to date according to the World Health Organization’s Friday update, health authorities are increasingly worried about microcephaly. At the same time, new research is tightening the connection between the virus and this potentially devastating birth defect.

So far, only Brazil and French Polynesia have experienced sustained outbreaks of microcephaly, but that could potentially change quickly. Zika has reached the Americas, the Caribbean, Europe and and the Pacific, according to the WHO. (On Friday, researchers in Colombia reported they had found infants with microcephaly there too.) The WHO says that just two pregnancies exhibiting the defect have been confirmed in women who were infected while pregnant and traveling in the Zika zone: one in Slovenia, and one in Hawaii.

As the epidemic advances, investigations are moving in two directions: attempting to pin down just what is causing microcephaly, and whether countries have the detection and financial resources they will need to prevent or assist affected pregnancies.

In Brazil, 641 cases of microcephaly have been confirmed since the virus arrived in the country last year, according to the Ministry of Health; there have been 139 miscarriages and infant deaths from complications of microcephaly. Another 4,222 are being investigated, and 1,046 suspected cases have been rejected for not meeting the case definition of microcephaly.

At the AACD Rehabilitation Hospital in Recife, Brazil, a physiotherapist examines children with Zika-related microcephaly and counsels their mothers.

At the AACD Rehabilitation Hospital in Recife, Brazil, a physiotherapist examines children with Zika-related microcephaly and counsels their mothers.
Such a large outbreak “is extraordinarily unusual,” Dr. Thomas Frieden, director of the U.S. Centers for Disease Control and Prevention, said last week during the private Milken Institute Public Health Summit in Washington, DC. He pointed out that until now only two infections, rubella and cytomegalovirus, were known to cause microcephaly, adding: “In more than 50 years, no other pathogenic cause of severe fetal malformation has been identified—and as far as I know, never before has there been the possibility that you could be bitten by a mosquito, and end up with an infant with a devastating birth defect.”

The CDC, which is anticipating more U.S. cases beyond the single known affected birth (plus two miscarriages and two elective abortions), is struggling to better understand how the virus affects infants’ brains.

“Microcephaly is just a very crude estimate of the size of the head, but really what we are seeing is a pattern of severe brain abnormalities—destruction of brain tissue, and then basically the skull collapses,” said Dr. Denise Jamieson, an obstetrician who is co-leader of the pregnancy and birth defects group in the CDC’s Zika Virus Response Team. As a result, she says, researchers are starting to think of microcephaly as a suite of defects.

As for pinning down Zika as the cause, a recent study found Zika virus in brain tissue of microcephalic infants. “We’re not saying currently that Zika causes adverse pregnancy outcomes such as microcephaly, but we are gathering more evidence every day suggesting there is a link,” Jamieson said.

Living with Microcephaly Hilda Venancio da Silva, 38, takes her three-month-old son, Matheus Jober Junior Silva, to the beach in Olinda, Brazil. She was so uncomfortable with the way people stared at the child that she later left the beach.

The lack of brain development in microcephaly has been seen in rare cases before, she said. In the medical literature, it is called “fetal brain disruption sequence,” and while not common, it is associated with the pregnant women being traumatically injured or contracting other viral illnesses. Overall, Jamieson said, the current rate of microcephaly in the United States is six cases per 10,000 births.

To detect an increase—which could happen if women residing in the U.S. were infected while pregnant and traveling, or were made pregnant by infected sexual partners, or if Zika began to spread on the U.S. mainland—the CDC has made Zika a “nationally notifiable” disease, which requires physicians to report diagnoses to state health departments, who forward the information to the CDC. The agency has also set up a birth registry, expected to go live this week on its website, that will collect the information gathered by health departments and sift it for clues.

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Two scientific papers published Friday help illuminate the puzzle of how Zika affects pregnancy and how it causes brain damage. An examination of the pregnancies of 88 women in Rio de Janeiro, published in the New England Journal of Medicine, revealed “serious and frequent problems in fetal and central nervous system development” in 29 percent of the pregnancies in which women who had experienced Zika symptoms and were pregnant allowed prenatal imaging. (Some declined or could not obtain it.)

Arthur Ferreira Da Conceicao, who is 4 months old, was born with microcephaly after his mother contracted Zika while pregnant. He and his family live in Ibura, Recife, Brazil.

The women were infected not just in their first trimester but across the durations of their pregnancies. Not all of the pregnancies have come to term yet, but so far, the researchers said, there have been two miscarriages and six live births. Both the live infants and those yet to be born show a range of birth defects: not just microcephaly but calcifications in brain tissue, abnormalities of brain structure, eye disorders, clubfoot, and several children small for their gestational age.

Also Friday, researchers from Florida State University, Johns Hopkins University, and Emory University published in the journal Cell Stem Cell a description of an experiment in which they infected a range of human cells with Zika virus in the lab. The virus showed a preference for developing in and destroying cells similar to those that form the cortex, the grey matter, of the brain during fetal development: infecting up to 90 percent of them, destroying a third, and retarding the development of the rest. The cells did not appear to mount an immune response to the virus. The researchers cautioned that their work was very preliminary, but said it might provide the first steps in understanding why Zika appears to destroy infants’ brain tissue.

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