A new study led by researchers at Dartmouth, in collaboration with Harvard Medical School, has found that even a tiny dose of the herpes simplex virus (HSV) in newborn mice can lead to memory and learning problems later in life.
This research, published in PLOS Pathogens, raises concerns about how early exposure to HSV might affect brain development and could provide insights into human neurological diseases like Alzheimer’s.
HSV is a common virus that usually infects the skin and nervous system. Most people carry the virus without any serious symptoms because it remains dormant in their bodies. However, for newborns, whose immune systems are still developing, HSV infections can be much more dangerous.
Severe neonatal HSV infections affect about 14,000 newborns worldwide each year and can cause life-threatening illness.
Doctors already know a lot about the effects of HSV infections that show clear symptoms in newborns. However, much less is known about cases where babies are infected but don’t show any symptoms at the time. Researchers wanted to find out whether these unnoticed infections could still cause long-term harm to the brain.
To test this, the research team created a special model using newborn mice. When the mice were just one day old, they were exposed to a very small amount of HSV through their noses. The virus didn’t cause any obvious signs of illness in the baby mice.
After waiting six months for the mice to grow up, the scientists tested their learning and memory using methods similar to those used to track Alzheimer’s disease in humans.
The results were striking. Mice that had been exposed to HSV as newborns performed worse on memory and learning tests than mice that had not been infected. This suggests that even a mild, unnoticed HSV infection early in life can cause long-lasting effects on brain function.
“This is a slightly scary concept,” said Dr. David Leib, a professor at Dartmouth’s Geisel School of Medicine and one of the study’s lead authors. “It shows that low-level infections in newborns, even when they don’t cause obvious illness, can have serious consequences much later in life.”
A Possible Solution: Maternal Vaccination
The researchers also found an encouraging way to prevent this damage. They discovered that if mother mice were vaccinated against HSV before giving birth, their babies were protected from the virus. The antibodies passed from the mother to her pups—either before birth or through breast milk—prevented memory problems later in life.
“This is really exciting because maternal vaccination is already used for other infections in humans,” Leib explained. “New maternal vaccines are currently being tested, and our study suggests that vaccinating mothers against HSV could be a way to protect babies from brain damage.”
What’s Next?
The research team is now exploring ways to prevent or reverse the memory problems caused by early HSV exposure. They plan to test antiviral drugs that could stop the virus from reactivating in the brain. They are also looking at anti-inflammatory drugs to see if they can reduce immune-related damage caused by the infection.
“Our next big question is: Can we actually fix the cognitive decline?” said Leib. “If we can find a way to stop the virus from causing brain damage, it could have important implications for preventing neurological diseases like Alzheimer’s in humans.”
What This Means for Human Health
This study adds to growing evidence that HSV might play a role in neurological diseases, including Alzheimer’s. Researchers have noticed that people with Alzheimer’s tend to have higher levels of HSV in their brains. The new findings in mice suggest that early exposure to HSV might be one factor that increases the risk of memory problems later in life.
Of course, mice and humans are different, and more research is needed to see if the same effect happens in people. However, if similar results are found in humans, this study could lead to new ways to protect babies from long-term brain damage. It could also open the door to new treatments for memory loss related to viral infections.
In the meantime, the discovery that maternal vaccination can prevent brain damage in mice is a hopeful sign. If future research confirms this effect in humans, it could be a simple and effective way to reduce the risk of neurological disorders in children.
The research findings can be found in PLOS Pathogens.
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