However, new research in mice from scientists at The Rockefeller University and La Jolla Institute for Allergy and Immunology suggests that certain adult brain cells may be vulnerable to infection as well.
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USA researchers have found that Zika can attack special populations of brain cells in adult mice in the part of the brain involved in learning and memory, raising new questions about how the virus may be impacting millions of adults who have been infected with the virus.
Based on a mouse study, they believe the virus could get into nearly anyone’s brain-not just those of developing fetuses.
Prof Gleeson added: “In more subtle cases, the virus could theoretically impact long-term memory or risk of depression, but tools do not exist to test the long-term effects of Zika on adult stem cell populations”.
Shresta and colleagues published their findings today in Cell Stem Cell.
Study authors, led by senior author Dr. Erol Fikrig, an epidemiology, infectious diseases and microbial pathogenesis professor at Yale, wrote in the study that the Hofbauer cells, which are thought to reside around the placenta, could aid in delivery of the Zika virus to the fetal brain.
Virus carrier: Spread by mosquitoes, Zika is widespread in Central and South America, and is becoming more prevalent across the globe. Adults have fewer of the cells than a developing embryo. These pockets of stem cells are vital for learning and memory.
The neural stem cells that are the focus of the new study are precursors – cells with the potential to generate specialized cells called neurons and glia that make up the nervous system. Yet little is understood about how the virus crosses the maternal-fetal barrier, a layer of cells that serves as a filter to protect the fetus from harmful substances.
The mature brain retains niches of these neural progenitor cells that appear to be especially impacted by Zika. Most adult neurons are believed to be resistant to Zika, which could explain why adults seem less at risk from the virus’s most devastating effects.
The study looked at the small number of neural progenitor cells which remain in adults and found that in mice, the adult cells “could indeed be hijacked by the virus”.
“This was kind of a surprise”, Joseph Gleeson, a professor at Rockefeller University and one of the co-authors of the study published Thursday in the journal Cell Stem Cell, said in an interview. “It was very clear that the virus wasn’t affecting the whole brain evenly, like people are seeing in the fetus”.
It’s known that the virus is attracted to neural stem cells, according to the study published August 18 in the journal Cell Stem Cell. “These cells are special, and somehow very susceptible to the infection”.
Two parts of the brain, including the hippocampus, which is associated with memory, saw evidence of cell death and reduced generation of new neurons, said the study. Integration of new neurons into learning and memory circuits is crucial for neuroplasticity, which allows the brain to change over time.
Without this process, the brain slides into cognitive decline and other conditions, such as depression and Alzheimer’s disease, can arise. However, they suggest that some people, such as those with weakened immune systems, may be vulnerable to the virus in a way that has not yet been recognized. To find out, his team injected the virus into lab mice and examined their brains for Zika infection.
Ms Shresta said the emergence of Guillain-Barre, which usually develops after the Zika infection has cleared, could be linked to the infection of adult neural progenitor cells. “We propose that infection of adult neural progenitor cells could be the mechanism behind this”. The mice model of Zika infection may not reflect how the virus acts on humans. “Our next step is to answer those questions-do the cells recover?”
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Illumination of the fluorescent biomarker in green revealed that the adult mouse brain could be infected by Zika. “We think of Zika health concerns being limited mostly to pregnant women”.
