The study provides more evidence of a link between infection with Zika virus during early pregnancy and brain abnormalities in the fetus.
The research, by a Finnish-American team and published in the New England Journal of Medicine, is also the first to report isolation of infectious Zika virus in cells cultured from fetal brain tissue.
Plus, it shows that genetic traces of Zika virus can be detected in maternal blood samples during the period when potential fetal brain damage is developing, even weeks after symptoms have subsided.
Zika virus is spread by the same Aedes mosquito that carries dengue and chikungunya. Infection with Zika typically presents as mild illness and a rash.
A suspected link between Zika infection and microcephaly has spurred the World Health Organization (WHO) to declare the virus a "public health emergency of international concern."
The new study surrounds a single case of a woman who became infected with Zika during the first trimester of pregnancy - during the 11th week of gestation - while she was visiting Central America.
The researchers found genetic traces of Zika virus in samples of the woman's blood. Her spouse tested negative for the virus.
Evidence may suggest Zika virus adapts to fetal brain
Scans of the brain of the fetus taken part way through the second trimester (at 20th week of gestation) showed severe brain abnormalities in the fetus.
With MRI neuroimaging techniques, it is possible to detect brain abnormalities before the development of the intracranial calcifications and microcephaly previously associated with Zika virus infections.
The authors note that, "Given the grave prognosis, the patient elected to terminate the pregnancy at 21 weeks of gestation."
For their study, the researchers mapped the entire genome of the Zika virus they isolated and found it differed from strains previously reported in Central America by eight mutations.
Speculating on these genetic differences, senior author Prof. Vapalahti, professor of zoonotic virology at the University of Helsinki, suggests:
"Some of these mutations may be associated with the adaptations of the virus to the fetal brain."
The researchers found the highest postmortem levels of Zika virus traces in the fetal brain, with substantial presence in the placenta and umbilical cord, and lower levels in fetal muscle, liver and other organs.
The main contribution of the study is that it may help to develop ways to detect fetal damage due to Zika infection during pregnancy, say the authors, while Prof. Vapalahti adds:
"Our research also helps confirm the causal relation between the Zika virus and severe damage to the fetal central nervous system."
The researchers note that the virus samples they isolated from the fetal brain cells will also be a great help to future Zika virus research.
The finding follows another study Medical News Today recently learned about that found the risk of their fetus or newborn having microcephaly is around 1 in 100 for women infected with Zika in their first trimester.