Zika virus proven to cause birth defects in mice pups

Scientists have delivered the first proof that the mosquito-borne Brazilian Zika virus can cause birth defects in mice.

Experiments carried out by a team from Brazil and the US also confirmed that the virus, suspected of causing brain damage in babies, can readily damage and kill human brain tissues.

Health officials in Brazil believe as many as 5,000 cases of microcephaly in newborn babies have arisen over the past few months as a direct result of a Zika outbreak.

Little had been known about the virus, which can be transferred by biting mosquitoes.

However, many of the babies affected showed signs of the virus, leading medics to believe there was a link between pregnant women being bitten by mosquitoes and microcephaly in the resulting infants.

Crossing placenta

Now, experimental evidence has been delivered showing Zika readily crosses the placenta of pregnant mice to cause brain damage in their foetuses.

The virus triggered a range of neurological defects, including general growth restriction and signs of microcephaly, a condition that damages the developing brain.

The virus tended to accumulate in neural tissues, said the researchers from the University of Sao Paulo, Brazil and the University of California, San Diego, writing in the journal Nature.

They infected the mice using the ZIKV viral strain, recovered from an infant from Brazil who had developed microcephaly.

The resultant pups showed a range of damage including growth delay, malformation of the brain and microcephaly.

“We didn’t only see microcephaly - we saw birth defects,” said Dr Patricia Beltrao Braga of the University of Sao Paulo.

They challenged mouse nerve tissue with the virus and found it triggered cell death in the tissue.

Succumbed to virus

They repeated these experiments using human neural cells, and the human tissue also succumbed to the virus.

“The cells died quite fast,” said Dr Alysson Muotri of USC San Diego.

“The health effect of the Zika virus is likely to be more widespread than we currently documented. To me this is the tip of the iceberg,” he said.

The study reinforces growing evidence linking the Zika outbreak “to the alarming number of cases of congenital brain malformations”, the authors write.

The research provides a useful model which can be used to test therapeutic approaches and vaccines, they add.

“This paper 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,” said Dr Derek Gatherer, of Lancaster University.

Differences between humans and mice mean similar tests are needed involving larger mammals such as monkeys.