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 The woman was not identified but she was infected while traveling on
vacation in Mexico, Guatemala and Belize in November 2015. The exact
location of transmission was not known.
It was not until the 19th week of her pregnancy that signs of the
birth defect first showed up on an ultrasound. A follow up study
using magnetic resonance imaging or MRI showed extensive brain
abnormalities. Studies showed that the fetal brain had shrunken from
a normal head circumference in the 47th percentile during week 16 to
the 24th percentile in week 20. Even so, the head circumference was
still not small enough to be classified as microcephaly, the
researchers reported.
But given the extent of the damages seen on the MRI, the woman
elected to terminate the pregnancy in the 21st week.
“What our paper suggests is that physicians should use caution in
reassuring patients who have normal fetal ultrasound examinations
early in their pregnancies," said Adre du Plessis, Director of the
Fetal Medicine Institute at Children’s National Health System in
Washington, D.C., a coauthor of the study published on Wednesday in
the New England Journal of Medicine.
Du Plessis said single ultrasounds may not capture
infection-associated fetal brain abnormalities that may worsen over
the course of the pregnancy.
"There is an enormous amount we don't know about this current strain
and outbreak of Zika virus. It seems to be behaving differently than
in the past," du Plessis said in a conference call with reporters.
"What we do know for sure is if the fetal brain is affected this
appears to be a very bad situation," he said.
Zika to date has not been proven to cause microcephaly in babies,
but there is growing evidence that suggests a link. The condition is
defined by unusually small heads that can result in developmental
problems. Brazil - hardest hit by the virus - said it has confirmed
more than 900 cases of microcephaly, and considers most of them to
be related to Zika infections in the mothers. Brazil is
investigating nearly 4,300 additional suspected cases of
microcephaly.
In the paper, scientists examined the case of the woman who is from
Washington, D.C. She became infected with Zika during her 11th week
of pregnancy.
Although Zika infections typically remain present in the blood for 5
to 7 days, the virus in this patient remained present in this
woman's blood until 10 days after the fetus was aborted.
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Dr. Cheng-Ying Ho, a neuropathologist at Children’s National, said
the finding raises questions about whether there is a correlation
between the duration of virus infection in the mother and the
severity of the brain injuries in the fetus.
An autopsy of the fetus showed high concentrations of the virus in
the brain, placenta and umbilical cord. Virus isolated from the
brain showed it was still infectious, growing easily in lab dishes
of human nerve cells, the study reported.
Study co-author Dr. Roberta DeBiasi, an infectious disease expert at
Children’s National, called the high levels of virus in the fetal
brain and placenta "concerning and suggests that the virus may be
able to hide from the immune system there."
The study authors believe the findings call into question current
recommendations for Zika testing in pregnant women, which only
recommend testing for presence of the virus within two weeks of an
infection. Subsequent tests look for antibodies of the virus but not
the virus itself.
Current recommendations do not include the use of MRI imaging tests,
which are much more costly than ultrasounds and may not be
accessible to pregnant women in countries with Zika transmission.
"What really matters is whether there is evidence of changes in the
brain to suggest injury in the context of a proven viral infection
in the mother," du Plessis said.
"That is where MRI is the gold standard for picking up changes in
the brain, even though it has limitations in terms of availability
and cost," du Plessis said.
(Reporting by Julie Steenhuysen; Editing by Bernard Orr)
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