A Seattle expert in microcephaly, the devastating birth defect that appears linked to Zika virus infections in Brazil, said he’s seeing a pattern of cases that are unusually severe, raising worrisome questions about the outbreak.

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The devastating birth defects linked to an outbreak of mosquito-borne Zika virus in Brazil may be even more severe than suspected, according to a Seattle Children’s hospital expert who’s spent decades studying and treating the condition known as microcephaly.

Babies are being born not just with unusually small heads, but with additional severe defects of the brain, said Dr. William Dobyns, a medical geneticist and pediatric neurologist at the hospital’s Center for Integrative Brain Research.

Problems include large amounts of fluid between the brain and skull, malformations in the crucial cerebral cortex and scattered calcifications that indicate severe infection.

“They have clear evidence of destruction of the brain,” said Dobyns. “It has been called ‘microcephaly’ in quotes, but it’s clear that it’s far more than that.”

Dobyns said he has reviewed a half-dozen brain scans from children in Brazil after receiving them from colleagues there. Though it’s a small sample, he said there are dismaying similarities in the images.

“I’m seeing an extremely rare, recognizable pattern,” he said.

Babies affected by the condition are showing signs that go beyond a general definition of microcephaly, which is a clinical finding of a smaller-than-normal head size. It is sometimes measured as a head circumference more than two standard deviations below the mean age for age, sex and gestation. Severe cases are often defined as a head circumference more than three standard deviations below the mean.

The brain scans Dobyns examined showed the heads of these babies are “way small, way small,” he said. The affected infants have severe cerebral palsy and epilepsy evident from birth and significant feeding problems.

Officials with the Centers for Disease Control and Prevention (CDC) confirmed reports of serious brain defects with calcium deposits in infants in Brazil who were not tested but presumed to be infected with Zika virus.

And there may be many more of them.

Suspected cases of microcephaly have spiked in Brazil, climbing perhaps 20 times higher than normal since last spring, when the first Zika virus infections were reported.

More than 4,700 cases have been reported since October, according to Brazil health officials. But only about 400 have been confirmed, and the link between the virus and the birth defects has not been proven. More than 3,000 cases are still being investigated.

“I personally do believe something is going on here,” said Dobyns, “based on a stunning increase in the incidence of microcephaly.”

Officials in Brazil have reported evidence of Zika virus in amniotic fluid from pregnant women carrying fetuses diagnosed with microcephaly, and in spinal fluid of babies with the disorder born to Zika-affected mothers. CDC scientists have found evidence of Zika in brains of newborns who died.

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“With each passing day, the link between Zika and microcephaly becomes stronger,” Dr. Tom Frieden, director of the CDC, told reporters Friday.

Of course, at the start of any public-health emergency, the worst cases are detected first, said Dr. William Schaffner, an infectious disease expert at Vanderbilt University in Nashville, Tenn.

Zika infections were reported in Brazil starting last spring and were followed by growing reports of the birth defect. The virus is spreading rapidly and has now been detected in more than 25 countries. U.S. territories, including Puerto Rico, the Virgin Islands and American Samoa, have reported local spread, the CDC said.

Microcephaly can produce a spectrum of milder to severe disabilities. Babies can have problems ranging from intellectual limits and learning disabilities to constant seizures.

But the expertise of Dobyns, who estimates he has reviewed or treated 700 to 800 cases of microcephaly during the past 20 to 30 years, is valuable, Schaffner added.

Dobyns said he has asked Brazilian colleagues to pull together and share more case reports and brain scans from affected children.

About 25,000 microcephaly cases are reported in the U.S. each year. The Zika virus has not yet spread in the United States, but local transmission is expected, particularly in the South, where the Aedes aegypti and Aedes albopictus mosquitoes that transmit the virus are found.

Those types don’t live in Washington state, which means there’s virtually no risk of local Zika virus transmission here, said Liz Dykstra, an entomologist with the Department of Health.

“Those are the two species that everyone has their eyes on,” she said. “We do not have and we’ve never detected either of those species in Washington.”

But when widespread local Zika transmission does start in U.S. states — and it will, Dobyns said — it brings with it the risk of the microcephaly cases now seen in Brazil.

“This is a severe and complex form of microcephaly with significant brain damage,” he said. “What we don’t know is what percentage of affected children have this condition.”