Zika infection kills brain cells in the adult mouse brain — pandemic might be worse than thought

New research on mice suggests the Zika virus can infect and destroy certain brain cells in the adult brain, as well. Up until now, it was believed the most vulnerable group were pregnant women because the virus http://www.zmescience.com/medicine/zika-virus-placenta-crossing/" rel="nofollow - crosses over to the placenta where it kills developing brain cells, shrinking the baby brain’s volume and ultimately leading to the http://www.zmescience.com/medicine/diseases-medicine/zika-virus-abnormality-02022016/" rel="nofollow - dreaded abnormally underdeveloped infant heads we’ve all seen.

The study performed by researchers at  http://www.rockefeller.edu/" rel="nofollow - The Rockefeller University and http://www.lji.org/" rel="nofollow - La Jolla Institute for Allergy and Immunology  suggests Zika could be a lot more sly than we’ve let on so far. The fact that it might affect adult brain cells, not just those of fetuses, warrants serious scrutiny in the following months. There are tens of thousands of reported cases in Latin America while more than 60 countries have reported travel-related transmissions. http://abcnews.go.com/Health/florida-zika-outbreak-cases-outbreak-growing/story?id=41426272" rel="nofollow - In Florida , US, 440 people have been diagnosed with travel-related Zika and another 30 contracted the virus locally during this outbreak.

“This is the first study looking at the effect of Zika infection on the adult brain,” says  http://www.rockefeller.edu/research/faculty/labheads/josephgleeson/#content" rel="nofollow - Joseph Gleeson , adjunct professor at Rockefeller, head of the http://lab.rockefeller.edu/gleeson/" rel="nofollow - Laboratory of Pediatric Brain Disease , and Howard Hughes Medical Institute investigator. “Based on our findings, getting infected with Zika as an adult may not be as innocuous as people think.”

The brain’s stem cells

Before the brain fully develops in specialized regions, a fetus’ brain is entirely made of neural progenitor cells, a sort of brain stem cells. In time, these cells develop into what they’re coded to do: neurons, glial cells etc. Once a baby is born and up until adulthood, the brain will contain progenitor cells and their role is critical. Neurons constantly die throughout our lives and when this happens, some of them are replaced by new ones developed from the progenitor cells that are always on standby.

Now, researchers at Rockefeller claim neural progenitor cells are targeted by Zika infections which would serve to explain microcephaly, a developmental condition which leads to smaller-than-normal heads, as well as other disabilities.

The team identified two primary regions in the brain whose neural progenitor cells are targeted by Zika: the subventricular zone of the anterior forebrain and the subgranular zone of the hippocampus — both vital for memory and learning. In a mouse model engineered by Gleeson’s team to mimic the Zika response in humans, researchers found adult neural progenitor cells could indeed become infected.

“Our results are pretty dramatic–in the parts of the brain that lit up, it was like a Christmas tree,” says Gleeson. “It was very clear that the virus wasn’t affecting the whole brain evenly, like people are seeing in the fetus. In the adult, it’s only these two populations that are very specific to the stem cells that are affected by virus. These cells are special, and somehow very susceptible to the infection.”

“Zika can clearly enter the brain of adults and can wreak havoc,” says http://www.lji.org/faculty-research/labs/shresta/#overview" rel="nofollow - Sujan Shresta , a professor at the La Jolla Institute of Allergy and Immunology. “But it’s a complex disease–it’s catastrophic for early brain development, yet the majority of adults who are infected with Zika rarely show detectable symptoms. Its effect on the adult brain may be more subtle, and now we know what to look for.”

In the infected brain regions, the researchers found evidence of cell death and reduced regeneration of new ones. It may be possible that some infected Zika adults could experience cognitive decline and, in extreme cases, neuropathological conditions like depression or Alzheimer’s. In healthy humans, the immune system ought to keep Zika from attacking brain cells, researchers report in http://dx.doi.org/10.1016/j.stem.2016.08.005" rel="nofollow - Cell Stem Cell . Those with a weakened immune response stand at risk, though.

http://www.zmescience.com/science/news-science/zika-infection-adult-brain/

Zika can infect adult brain cells, not just fetal cells, study suggests

The more researchers learn about the Zika virus, the worse it seems.

A growing body of research has established that the virus can cause severe birth defects — most notably microcephaly, a condition characterized by an abnormally small head and often incomplete brain development. The virus also has been linked to cases of Guillain-Barré syndrome in adults, a rare autoimmune disorder that can result in paralysis and even death.

[ http://www.washingtonpost.com/news/to-your-health/wp/2016/08/19/florida-gov-rick-scott-confirms-new-zika-transmissions-in-miami-beach/" rel="nofollow - Florida Gov. Rick Scott confirms new Zika transmissions in Miami Beach ]

Now, in a study in mice, researchers have found evidence that suggests adult brain cells critical to learning and memory also might be susceptible to the Zika virus.

“This was kind of a surprise,” Joseph Gleeson, a professor at http://newswire.rockefeller.edu/2016/08/18/zika-infection-may-affect-adult-brain-cells-suggesting-risk-may-not-be-limited-to-pregnant-women/" rel="nofollow - Rockefeller University and one of the authors of http://www.cell.com/cell-stem-cell/fulltext/S1934-5909%2816%2930252-1" rel="nofollow - the study published Thursday in the journal Cell Stem Cell, said in an interview. “We think of Zika health concerns being limited mostly to pregnant women.”

[ https://www.washingtonpost.com/news/to-your-health/wp/2016/05/25/for-zika-infected-pregnancies-microcephaly-risk-may-be-as-high-as-13-percent/" rel="nofollow - For Zika-infected pregnancies, microcephaly risk may be as high as 13 percent ]

In a developing fetus, the brain is made primarily of “neural progenitor” cells, a type of stem cell. Researchers believe these cells are especially susceptible to infection by the Zika virus, which can hinder their development and disrupt brain growth. 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.

But some neural progenitor cells remain in adults, where they replenish the brain’s neurons over a lifetime. These pockets of stem cells are vital for learning and memory. Gleeson and his colleagues suspected that if Zika can infect fetal neural progenitor cells, the virus might have the same ability to infect adult neural progenitor cells. That’s precisely what they found.

“We asked whether [these cells] were vulnerable to Zika in the same way the fetal brain is,” Glesson said. “The answer is definitely yes.”

Gleeson is the first to admit that the findings represent only an initial step in discovering whether Zika can endanger adult human brain cells. For starters, the study was conducted only in mice, and only at a single point in time. More research will be necessary to see whether the results of the mouse model translates to humans, and whether the damage to adult brain cells can cause long-term neurological damage or affect behavior.

But the initial findings suggest that the Zika virus, which has spread to the United States and more than 60 other countries over the past year, may not be as innocuous as it seems for adults, most of whom never realize they have been infected. Researchers found that infected mice had more cell death in their brains and reduced generation of new neurons, which is key to learning and memory. The possible consequences of damaged neural progenitor cells in humans would include cognitive problems and a higher likelihood for conditions such as depression and Alzheimer’s disease.

[ https://www.washingtonpost.com/news/powerpost/wp/2016/08/11/obama-administration-to-shift-81-million-to-fight-zika/" rel="nofollow - Obama administration to shift $81 million to fight Zika ]

“Zika can clearly enter the brain of adults and can wreak havoc,” Sujan Shresta, another study co-author and a professor at the La Jolla Institute of Allergy and Immunology, said in a statement. “But it’s a complex disease — it’s catastrophic for early brain development, yet the majority of adults who are infected with Zika rarely show detectable symptoms. Its effect on the adult brain may be more subtle, and now we know what to look for.”

William Schaffner, an infectious-disease expert at Vanderbilt University Medical Center, agreed Thursday that the findings are preliminary. But he also called it troubling.

“Here’s the deal: The more we’ve learned about the Zika virus, the nastier it is,” said Schaffner, who was not involved in the study. He said scientists have had concerns all along about Zika’s ability to damage the brain, but until now the worries have focused mostly on the developing brain. “This mouse study will increase our anxiety. ... It’s an additional potential way that this virus can cause human illness.”

That’s a possibility that demands further examination, he said, given the hundreds of thousands of people already infected by Zika — a number that continues to grow daily.

“Our attention, quite understandably, has been devoted to pregnant women and newborns, and preventing those infections,” Schaffner said. “This mouse study will tell investigators that, in addition to pregnant women, you have to establish some studies in older children and adults as well.”

Gleeson agreed. “We don’t want to have this be a panic. Zika, for the most part, is a benign condition in healthy humans," he said. “But we also need to look at the potential consequences in a careful way.”

https://www.washingtonpost.com/news/to-your-health/wp/2016/08/18/zika-can-infect-adult-brain-cells-not-just-fetal-cells/

Study Suggests Zika May Damage Adult Brains