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Janine Santos holds her three-month-old son Shayde Henrique, who was born with microcephaly, in Joao Pessoa, Brazil. Photo: AP
LifestyleHealth & Wellness

Study may have found link between Zika virus and microcephaly in babies

Doctors at three US universities infect lab-grown human stem cells with virus and discover 90 per cent of one type of brain cell are quickly hijacked to make copies of it. Their findings could be used to identify potential therapies

Zika virus
Jeanette Wang
Jeanette Wang
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A team of researchers suspect they have discovered how the Zika virus probably causes microcephaly in fetuses. The virus selectively infects cells that form the brain’s cortex, or outer layer, making them more likely to die and less likely to divide normally and make new brain cells.

They say their experiments also suggest the highly susceptible lab-grown human stem cells they used could be employed to screen for drugs that protect the cells or ease existing infections.

READ MORE: Hong Kong faces greater threat from Zika virus with arrival of summer

It’s very telling that the cells that form the cortex are potentially susceptible to the virus, and their growth could be disrupted by the virus
Dr Guo-li Ming, lead researcher

“Studies of fetuses and babies with the telltale small brains and heads of microcephaly in Zika-affected areas have found abnormalities in the cortex, and Zika virus has been found in the fetal tissue,” said Dr Guo-li Ming, a professor of neurology, neuroscience, and psychiatry and behavioural science at the Institute for Cell Engineering at Johns Hopkins University in the United States. “While this study doesn’t definitely prove that Zika virus causes microcephaly, it’s very telling that the cells that form the cortex are potentially susceptible to the virus, and their growth could be disrupted by the virus.”

READ MORE: The Zika virus explained: why the world is not taking chances with birth defect-linked disease spread by mosquitoes

In 2015, the Zika virus began spreading throughout the Americas and a potential link was seen between the virus and a significant increase in cases of fetal microcephaly, as well as other neurological abnormalities. This connection and the proliferation in cases led to the World Health Organisation declaring Zika virus an international public health emergency.

A biologist at a Brazilian university works with Aedes mosquito cells. Scientists are developing a test for presence of genes associated with the Zika virus and related health conditions. Photo: Reuters
Ming led the research team along with Dr Hongjun Song, a professor of neurology and neuroscience at the institute, and Dr Hengli Tang, a virologist at Florida State University in the US.

Results of the experiments, conducted by researchers at Johns Hopkins, Florida State University, and Emory University, also in the US, are described online in the journal Cell Stem Cell.

READ MORE: Wiping out the mosquito species carrying the Zika virus is a good case for gene modification

In a quickly executed study that reflects the global public health threat posed by Zika, the researchers compared its effect on cells known as cortical neural progenitor cells to two other cell types: induced pluripotent stem cells and immature neurons. Induced pluripotent stem cells are made by reprogramming mature cells, and can give rise to any cell type in the body, including cortical neural progenitor cells. Cortical neural progenitor cells in turn give rise to immature neurons.

The Aedes aegypti mosquito that spreads the Zika virus. The mosquitoes breed in stagnant water. Photo: AP
The experiments, conducted in less than a month, began when Tang reached out to Ming and Song, who use stem cells to study early brain development. The Johns Hopkins labs sent team members and cells to Tang’s lab, where the cells were exposed to Zika virus. Then the cells’ genetic expression – evidence of which genes were being used by the cells and which weren’t – were analysed in Peng Jin’s laboratory at Emory University.

According to Tang, three days after exposure to the virus, 90 per cent of the cortical neural progenitor cells were infected, and had been hijacked to churn out new copies of the virus. Furthermore, the genes needed to fight viruses had still not been switched on, which is highly unusual. Many of the infected cells died, and others showed disrupted expression of genes that control cell division, indicating that new cells could not be made effectively.

Aedes mosquito cells inoculated with Zika virus are seen through a microscope in a university laboratory. Photo: Reuters
Using specific, known types of cells allowed the researchers to see where the developing brain is most vulnerable, Song says. He and Ming are now using the cells to find out more about the effects of Zika infection on the developing cortex. “Now that we know cortical neural progenitor cells are the vulnerable cells, they can likely also be used to quickly screen potential new therapies for effectiveness,” Song adds.

Zika virus has recently emerged as a public health concern, but it was first discovered in Uganda in the 1940s. Since then, small outbreaks have appeared in Asia and Africa, but symptoms were generally mild and did not appear to have any long-term effects. Carried by infected Aedes aegypti mosquitoes, Zika is largely transmitted through bites, but can also occur through intrauterine infection or sexual transmission.

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