By Lena H. Sun November
22
These 2016 photos show Brazilian infants born with microcephaly caused by the Zika virus. (Felipe Dana/AP)
One of the biggest unknowns
about the Zika virus is the extent of damage it causes during pregnancy. Much
of the early alarm focused on babies born with abnormally small heads and often
underdeveloped brains.
A study releasedTuesday by the Centers for Disease Control and Prevention provides
disturbing new data about a small group of Zika-infected babies in Brazil, who
were born with normal-size heads but developed microcephaly five
months to a year after birth.
The report is the first to
document infants with laboratory evidence of Zika infection in utero who
experienced “poor head growth with microcephaly developing after
birth.” Although other researchers have described cases of babies
developing microcephaly after birth, they could only presume that those infants
had been infected congenitally.
The new study documents that
even without microcephaly, Zika-infected babies can have severe neurological
damage and other problems. All the infants examined had brain abnormalities,
such as decreased brain volume, structures in the brain that were too large and
filled with fluid, and decreased brain tissue with a specific pattern of
calcium deposits indicating damage.
In a few cases, the mothers
had ultrasounds during pregnancy that showed the infants' brain abnormalities.
But in other babies, these problems only showed up during CT scans or MRIs
conducted after birth.
Clinical photographs of an infant with congenital Zika syndrome, who was born in Brazil with a normal-size head. At 12 months, the infant had clear microcephaly. (CDC)
Along with the lagging rate of
head growth, these infants suffered other significant neurological damage. As a
result, some have too much muscle tone, which restricts how their bodies can
move. Some have muscle weakness on one side or the other. Some have involuntary
muscle contractions that cause tremors. Others have difficulty swallowing, as
well as seizures and vision problems.
“This is clear evidence that
children can be severely affected even if they didn’t have microcephaly at
birth,” CDC Director Tom Frieden said. “To me, the major key question we don’t
have the answer for is this: How affected will infants be who don’t have
microcephaly?”
Because of research into the
outbreak in Brazil, a distinct pattern of birth defects from Zika infection
during pregnancy is now officially known as congenitalZika syndrome. CDC officials say the latest findings further
underscore the importance of screening pregnant women for Zika, conducting
comprehensive medical and developmental follow-ups of babies whose mothers were
exposed to the virus during pregnancy and following their children after birth.
In addition, early
neuroimaging, even among infants with a normal head size, might identify brain
abnormalities related to Zika infection during pregnancy, officials said.
“It’s the brain problems, not
the size of the head,” said Cynthia Moore, a clinical geneticist and birth-defects
expert for the CDC and an author of the study.
Doctors confirmed the link
between the Zika virus and microcephaly in April. While the most visible sign
of microcephaly is the small size of the head, its actually inside the brain
where the most damage occurs. (Whitney Leaming, Julio Negron/The
Washington Post)
Denise Jamieson, a clinical
obstetrician-gynecologist who is one of the leaders of CDC’s Zika response,
said the findings are prompting the agency to review guidanceabout screening infants born to Zika-infected women.
Some obstetricians such as
Jeanne Sheffield, director of maternal-fetal medicine at Johns Hopkins
Medicine, said that they already counsel Zika-infected women that normal head
circumference at delivery does not mean a child is unaffected. Similar findings
about Zika were discussed at a September conference on Zika sponsored by the
National Institute of Child Health and Human Development.
The latest report follows the
World Health Organization’s decision last week that Zika is nolonger a global health emergency but a significant and enduring public
health challenge that must be managed with more dedicated resources and
expertise.
The CDC study, conducted in
collaboration with researchers in Brazil, looked at 13 infants from the states
of Pernambuco and Ceara in the country’s northeast, the region hardest hit by
Zika. All were born between October 2015 and this past August with a normal
head size. Virtually all showed brain abnormalities on CT scans or MRIs,
several of them as early as a few days after birth.
The babies underwent extensive
imaging and brain, eye, hearing and orthopedic examinations. All 13 showed a
slowdown in head growth, and in 11 babies, that decline had slowed to the point
where it met the definition of microcephaly, Moore said.
Researchers said they don’t
know how Zika infection during pregnancy can lead to an infant’s developing
microcephaly after birth. They said the decrease in head size might be the
consequence of earlier destruction of critical neural stem cells or other
neural cells, a persistent inflammatory response or continued infection of
neural cells.
Officials say pregnancy
registries in Puerto Rico, where Zika continues to spread rapidly, and on the
U.S. mainland are tracking pregnant women with any evidence of Zika. Those
surveillance systems will be a critical way to understand the full spectrum of
the disease and proportion of infected babies, they say.
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