Most people had never heard of the Zika virus before the current epidemic in Latin America and the Caribbean brought it into the limelight. First discovered in 1947 and named after the Zika Forest in Uganda, the virus spreads from person to person through the bite of an infected Aedes mosquito. The symptoms include fever, rash, conjunctivitis, and joint pain, and are often mild enough that a person will not seek medical attention or even realize that they’re infected. However, in pregnant women, the Zika virus can have serious consequences, leading to a birth defect called microcephaly and other brain abnormalities in the developing fetus.
Now researchers at Johns Hopkins University School of Medicine, Emory University, and Florida State University have studied the virus and identified that it targets brain stem cells and causes microcephaly and other brain defects by stunting the growth of cortical neural precursors that go on to develop into the cerebral cortex (gray matter), which is responsible for higher brain functions in human beings.
The journal Cell Stem Cell reports that scientists observed the behavior of the Zika virus in the laboratory and found that it flourished and spread rapidly in Petri dishes containing neural stem cells, leading to disruption of growth and death of these precursor cells. Within a few days of exposure to the virus in the laboratory, 90 percent of the neural precursor cells in the Petri dish were infected and showed disruption in their ability to divide and grow. In addition, the Zika virus was also noted to hijack these cells and use them to generate more copies of itself.
Infants born with microcephaly have an abnormally small head and incomplete brain development. The condition is linked to a host of associated problems such as seizures, developmental delay, intellectual disability, movement and balance impairment, hearing and vision problems, and difficulty swallowing. These problems are lifelong and can range from mild to severe or even life-threatening.
Co-author of the study and postdoctoral fellow at Johns Hopkins in Baltimore, Maryland, Zhexing Wen, states that although a direct link between the Zika virus and microcephaly remains to be established, the discovery that the virus certainly targets these cells and affects their growth is an important one.
Since the current Zika epidemic began in Brazil, more than 5,000 cases of microcephaly have been confirmed, reports the World Health Organization, and the virus continues to spread in the region. Dr. Sallie Permar of the Laboratory of Neonatal Viral Pathogen Immunity at Duke University in Durham, North Carolina, says these findings have identified the potential mechanism by which the Zika virus leads to stunted brain growth, thus paving the way to combat the virus and prevent microcephaly by developing antiviral therapies that block this mechanism of the virus.
Understanding how the Zika virus affects brain stem cells is an entrance point for scientists hoping to combat its effects on the fetus. The understanding that neural stem cells (multi-potent self-renewing cells that develop into the nervous system in humans) are particularly vulnerable to the virus will help screen new therapies for effectiveness, states Hongjun Song, Professor of Neurology and Neurosciences at the Institute for Cell Engineering at Johns Hopkins.
Image courtesy of NPR.org