It seems that unborn children aren't the only ones vulnerable to the devastating effects of Zika as a new study suggests that the infection can also cause severe damage to the brain of full-grown adults.
Previous studies have associated the Zika virus to a development of serious brain defects in infants, including microcephaly, which causes the child to be born with an abnormally sized head.
Subsequent research also showed a potential link between the mosquito-borne disease and a rare paralysis-inducing disorder known as Guillain-Barré syndrome.
In a new study featured in the journal Cell Stem Cell, researchers at the Rockefeller University in New York and the La Jolla Institute for Allergy and Immunology (LIAI) in California have discovered that the virus may also attack a particular type of brain cell responsible for memory and learning abilities of a person.
Rockefeller University professor Joseph Gleeson and his colleagues engineered laboratory mice to display the same characteristics of a human infected with the Zika virus. They then used fluorescent biomarkers in order to tag specific infection sites in the animals.
The researchers were surprised to find that the Zika virus hijacked a group of brain cells in the mice known as neural progenitor cells, leaving the animals with a relatively smaller brain and suffering from mental impairment.
"Our results are pretty dramatic — in the parts of the brain that lit up, it was like a Christmas tree," Gleeson said. "It was very clear that the virus wasn't affecting the whole brain evenly, like people are seeing in the fetus."
Neural Progenitor Cells
According to the researchers, neural progenitor cells can mostly be found in the brain of developing fetuses, serving as a form of stem cell. When people grow into adulthood, some of the neural progenitor cells remain in their bodies to replenish the neurons in their brains.
While this helps maintain the good function of the brain, it also leaves the organ susceptible to Zika as the virus tends to attack neural progenitor cells. When this happens, the brain experiences a retarded growth.
Gleeson and his colleagues believe that the reason why adults are more resistant to Zika compared to infants is they have more development neurons. However, the presence of neural progenitor cells means that they are still vulnerable to brain damage by the virus.
"We asked whether [these cells] were vulnerable to Zika in the same way the fetal brain is," Gleeson pointed out. "The answer is definitely yes."
The researchers, however, noted that their study provides only an initial finding to how the Zika virus can affect the brain cells of adult humans. They were only able to focus on its impact on engineered mice and only at a single point in time during the infection.
Gleeson and his team said more studies are needed to determine whether the results they were able to arrive at will be the same as those for infected humans. They also want to find out if the damage they witnessed on the adult brain cells will result in long-term damage to the neurons.
Increased Brain Cell Deaths And Reduced Neuron Generation
One key finding of the study is that the mice that were infected with the Zika virus had more dead brain cells while also suffering from a reduced neuron generation, which is crucial to an individual's ability to learn and remember.
A person who suffers damage in his neural progenitor cells would show poor cognitive performance and have a higher likelihood of developing serious mental conditions such as Alzheimer's disease and depression.
LAIA professor and study co-author Sujan Shresta explained that the Zika virus has been shown to be devastating to the early development of the brain. However, many of the adults infected with the virus rarely show any detectable symptom of the disease.
Through the help of the recent findings, Shresta said they now know what specific signs to look for in these individuals.