Animal experiment shows Zika causing birth defects

An international team of researchers revealed in a Nature report Wednesday that Brazilian Zika virus strain could cause birth defects in mice.

The Zika virus can cross the placenta and cause growth restriction, including signs of microcephaly, in mice, according to the report. It can also infect human brain organoids in culture, inducing cell death and disrupting layers of neural tissue known as cortical layers.

The rising number of infants born with malformations, including microcephaly and other neurological diseases, has been linked to the outbreak of a Zika virus strain. But scientists still need more direct evidence to confirm this connection.

Researchers from the United States, Brazil and Senegal used Zika virus isolated from a clinical case in northeast Brazil to infect two different strains ((SJL and C57BL/6)) of pregnant mice.

They found that those born from SJL Zika-infected females displayed clear evidence of whole-body growth delay and showed signs of microcephaly, such as cortical malformations, compared to controls.

In contrast, no significant changes were observed in pups born from C57BL/6 Zika-infected females, which may be due to the robust anti-viral immune response of this mouse strain.

They also showed that the virus was capable of inducing cell death in mouse neural tissue and that it could infect human brain organoids, inducing cell death and disrupting cortical layers.

The virus crosses the placenta and causes microcephaly by targeting cortical progenitor cells, inducing cell death and impairing neurodevelopment, said the researchers.

Despite making progress in investigating the link between Zika virus and birth defects, some scientists say there still are many questions that need to be answered.

"Meanwhile, the mouse studies leave many unknowns...What are the features of the viral sequences present in Brazil that account for differences in pathogenesis from the African sequences? And what lessons of variability in host susceptibility can be learnt from the fact that, in this study, one mouse strain was susceptible, the other absolutely resistant,"said Prof Daniel Altmann at the Imperial College London. Endit