Zika May Damage Adult Brains Too, Study Finds

(CN) — The Zika virus could cause more severe side effects in adults than previously known, as the virus may cause long-term memory damage that resembles Alzheimer's disease, according to a study published Thursday.

Health experts believed that Zika only impacts the brains of developing fetuses and did not pose serious problems for healthy adults.

However, a new study suggests that certain adult brain cells may be vulnerable to the virus as well — specifically cells that serve to replace lost or damaged neurons throughout adulthood, which are thought to be to critical to learning and memory.

While it is unclear whether the damage could have long-term biological implications or possibly affect behavior, Zika may be more harmful than previously thought.

"This is the first study looking at the effect of Zika infection on the adult brain," said study co-author Joseph Gleeson. "Based on our findings, getting infected with Zika as an adult may not be as innocuous as people think."

Their findings were published in the journal Cell Stem Cell.

Zika, which spread rapidly through Central and South America over the past eight months, has been linked to a series of birth defects and issues that affect the brains of developing fetuses, making the virus especially dangerous for women who are pregnant or wish to become pregnant.

Microcephaly — a congenital disorder that leads to abnormally small heads and potential brain damage — has the strongest body of scientific research connecting it to Zika, but several others may be linked to the virus as well.

Sujan Shresta, a professor at the La Jolla Institute for Allergy and Immunology and a study co-author, explained that while additional research is needed, their study highlights what researchers should measure and observe in future studies of Zika's impact on adult brains.

"Zika can clearly enter the brain of adults and can wreak havoc," Shresta said. "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."

Early in gestation, before our brains develop into a complex organ with specialized zones, the brain comprised entirely of neural progenitor cells. Progenitor cells are the stem cells of the brain, with the capability to replenish the brain's neurons throughout its lifetime.

In healthy individuals, neural progenitor cells eventually become fully formed neurons. They become resistant to Zika at some point during this progression, researchers believe.

But current research suggests that the virus targets neural progenitor cells, leading to the loss of these cells and to reduced brain volume, resembling what happens with microcephaly.

The mouse model engineered by Shresta and her team to mimic Zika infection in humans used fluorescent biomarkers to reveal that adult neural progenitor cells can be hijacked by the virus.

In addition to a host of congenital disorders, Zika has been linked to Guillain-Barre syndrome, a rare condition in which the immune system attacks parts of the nervous system causing muscle weakness or even paralysis.

"The connection has been hard to trace since Guillain-Barre usually develops after the infection has cleared. We propose that infection of adult neural progenitor cells could be the mechanism behind this," Shresta said.

It's unclear whether findings in the mouse model can be applied to humans, and the long-term consequences of Zika infections in adults remains murky.

"Given this study, I think the public health enterprise should consider monitoring for Zika infections in all groups, not just pregnant women," Gleeson said.

In a separate study published Thursday in the journal JCI Insight, researchers from Yale University released findings that appear to demonstrate how Zika crosses the maternal-fetal barrier known as the placenta.

While scientists knew Zika could be transmitted from mother to fetus, it was unclear how the virus does so.

Led by Erol Fikrig, the researchers examined Zika infection of three different cell types in the placenta, including cytotrophoblasts, fibroblasts, and placental macrophages.

The team isolated cells from placental tissue of term pregnancies and infected them with Zika virus in culture. The majority of fibroblasts and 10 to 15 percent of placental macrophages were infected and thereafter shed the virus.

Fikrig's team also found that placental macrophages in intact placental tissue could also be infected with Zika in culture, though they did not observe infection of fibroblast tissue.

The study suggests that placental macrophages could be vulnerable to Zika infection, though additional research is needed to determine the contribution of placental macrophages in maternal-fetal Zika transmission, according to the team.

"This finding helps toward understanding a critical mechanism of the virus. If researchers continue down the path, it could shift how we counsel and protect those women who are at risk for Zika," study co-author Michael Simoni told Yahoo Beauty.

Women who are infected with Zika or are at risk of exposure receive increased screening. There is currently no treatment for pregnant women with the virus, however.

Follow @SeanDuffyCNS

Subscribe to Closing Arguments

Sign up for new weekly newsletter Closing Arguments to get the latest about ongoing trials, major litigation and hot cases and rulings in courthouses around the U.S. and the world.

Email *

Submit