|
 In February, the World Health Organization declared Zika a global
health emergency based on its association with thousands of cases in
Brazil of microcephaly, a birth defect marked by small head size
that can cause severe developmental problems.
Scientists have been scrambling to understand how a mosquito-borne
virus that generally causes mild symptoms in adults could do so much
such damage to a developing fetus.
The studies in pregnant mice, published in the journals Nature, Cell
and Cell Stem Cell, showed Zika invading brain cells in fetal mice,
demonstrating convincingly that Zika can attack fetal brain tissue
and cause injury.
There are no vaccines or medicines for Zika infections. Experts say
the new findings will pave the way toward testing vaccines and
treatments in mice before trying them on humans.
Normally, mice do not develop Zika infections, so each of the
research teams developed different ways to cause pregnant mice to
pass the virus to their offspring.
In the Nature paper, researchers infected two commonly available
strains of laboratory mice with extremely high doses of Zika
cultivated from a Brazilian patient from Paraiba, a state at the
center of Brazil's Zika outbreak.
Their study showed that the Brazilian strain can get through the
placenta and inhibit the growth of fetal mice, even causing signs of
microcephaly.
The research, led by Alysson Muotri of the University of California,
San Diego School of Medicine and Patricia Beltrao Braga of the
University of Sao Paulo in Brazil, also showed the virus could
infect clusters of brain cells in lab dishes, disrupting growth or
causing cells to die.
Dr. Derek Gatherer, a biomedical and life sciences expert at
Lancaster University in Britain, said the study "adds to the weight
of evidence that Zika virus is the cause of the apparent spike in
microcephaly and other birth defects observed in Brazil," and
suggests that other countries with Zika transmission may see similar
spikes.
SIGNIFICANT ABNORMALITIES
Separate experiments by Dr. Michael Diamond of Washington University
in St. Louis and a team of Chinese researchers also showed Zika was
capable of damaging fetal brain cells.
Diamond's experiments, published in Cell, involved mice with
compromised immune systems. In one, the team bred mice with
genetically weakened immune systems. When exposed to Zika, the virus
killed most fetuses within a week, and those that survived had
significant abnormalities, including severely stunted growth.
[to top of second column] |
In these mice, the researchers saw genetic material from the Zika
virus in the mouse placentas that was 1,000 times greater than in
the blood of the mothers, suggesting the virus had been growing in
the placenta.
In the second model, normal pregnant mice were given an antibody
that blocked their immune response. When exposed to Zika, the fetal
mice survived, but their growth was stunted, and viral genetic
material was present in their heads and bodies.
In the third study, in Cell Stem Cell, Chinese researchers directly
injected Zika into the brains of fetal mice in utero.
When these mice were born, they showed characteristic features of
microcephaly, according to collaborators Zhiheng Xu of the Chinese
Academy of Sciences and Cheng-Feng Qin of the Beijing Institute of
Microbiology and Epidemiology.
After the mice were injected during the equivalent of the second
trimester in humans, the fetal brains shrank as the amount of virus
increased.
Diamond said the mouse experiments will be useful for testing new
vaccines and drugs.
"Now, we can begin to see whether vaccines can prevent transmission
of the Zika virus to the fetus," Diamond said.
U.S. health officials have concluded that Zika infections in
pregnant women can cause microcephaly. The WHO has said there is
strong scientific consensus that Zika can also cause Guillain-Barre,
a rare neurological syndrome that causes temporary paralysis in
adults.
(Reporting by Julie Steenhuysen; Editing by Will Dunham)
[© 2016 Thomson Reuters. All rights
reserved.] Copyright 2016 Reuters. All rights reserved. This material may not be published,
broadcast, rewritten or redistributed.
 |
