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Chinese scientists on Wednesday announced the first direct evidence linking the Zika virus to microcephaly in mice experiments.

Xu Zhiheng with the Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences introduce the collaborative research to the press in Beijing, capital of China, May 11, 2016. Chinese researchers said Wednesday they have found direct evidence that Zika infection causes microcephaly, a birth defect marked by an abnormally small head, in mouse experiments. [Photo: Xinhua]

Microcephaly is a medical condition in which abnormal brain development of a fetus or infant results in a head that is smaller than normal.

A dramatic rise in microcephaly cases among newborns was discovered in Brazil and elsewhere as the Zika virus spread wildly in those regions. In most cases, mothers of babies with microcephaly had been infected with the Zika virus.

Scientists had suspected a close link between Zika infection and microcephaly, but didn't have any direct proof to confirm.

The new discovery was made in a collaborative research project conducted by teams led by Xu Zhiheng at the Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences and Qin Chengfeng with the Institute of Microbiology and Epidemiology under the Academy of Military Medical Sciences.

Scientists injected the Zika virus strain, which was isolated from a Chinese patient, into fetal mouse brains.

According to Xu, the Zika virus replicated quickly in the brains of the fetal mice and infected neural stem cells, causing abnormal proliferation and differentiation of neural stem cells and neuron death.

The mice carried to term displayed the characteristic features of microcephaly and were found to have genetic abnormalities.

The Chinese scientists' research provided the first animal model for studying the Zika virus. Its findings were published online in the journal "Cell Stem Cell" on Thursday.

"We hope the model can be used in drug and vaccine tests, helping with the prevention and treatment of Zika infection," said Qin.