Common parasite may be affecting your brain without symptoms

Scientists have found that a common parasite might have a bigger impact on brain function than we previously realized – even when it infects only a few cells.

Most people who carry the parasite Toxoplasma gondii never even realize. It can hide in the brain for years without causing any symptoms.

A new study from researchers at the University of California, Riverside sheds light on how this microscopic intruder messes with the brain’s communication system.

What the parasite does in brain cells

Toxoplasma gondii is able to infect almost any warm-blooded animal, including humans. It tends to settle in the brain, where it forms long-lasting cysts inside neurons. Once there, it can stay dormant for decades.

Using both mouse models and human cells, the researchers found that infected neurons release fewer extracellular vesicles – small packets used by cells to pass information. This breakdown in communication can have ripple effects throughout the brain.

Emma H. Wilson, a professor of biomedical sciences in the UC Riverside School of Medicine, led the research team.

“We found this disruption in EV signaling can interfere with how neurons and glial cells, especially astrocytes, maintain a healthy brain environment,” said Professor Wilson. “Even a handful of infected neurons can shift the brain’s neurochemical balance.”

“This suggests that communication between neurons and supporting glial cells is not only critical, but also vulnerable to hijacking by parasites.”

A common infection with hidden risks

About 10–30% of people in the U.S. are estimated to be infected with Toxoplasma gondii. The parasite is usually picked up from eating undercooked meat or contact with cat feces.

While a healthy immune system keeps it in check, it can become dangerous in people with weakened immunity, such as those undergoing chemotherapy or living with HIV.

Current tests can only show if someone has been exposed by detecting antibodies. They can’t tell if the parasite is still in the brain or whether it’s affecting brain health.

According to Professor Wilson, the research opens the door to using EVs as biomarkers, which can be isolated from blood.

When brain chemistry breaks down

Professor Wilson explained that in healthy mouse brains, astrocytes help keep neurotransmitters like glutamate in balance, preventing neurons from becoming overexcited.

But when Toxoplasma gondii infects neurons and disrupts their EV signaling, that balance is lost. Glutamate levels rise, which can lead to seizures, neural damage, or changes in brain connectivity.

“The parasite may play a larger role in neurological and behavioral conditions than we previously thought,” said Professor Wilson.

Blood clues and future treatments

The research team is now analyzing human blood samples to search for EVs that could signal a Toxoplasma gondii brain infection.

They are also working to understand how glial cells sense and respond to parasite proteins. This knowledge could one day lead to new treatments – or even a vaccine.

“Our brains have built-in defenses that may recognize and respond to neurons infected by Toxoplasma gondii,” noted Professor Wilson. “If we can learn how to support or enhance that process, we may be able to better protect people, especially the most vulnerable.”

What this means for the public

Despite its potential effects, the parasite is often misunderstood. “There’s no need to avoid someone who is infected; most people live their entire lives without symptoms,” said Professor Wilson.

“Pregnant individuals should be cautious as the parasite can cause serious birth defects if contracted for the first time during pregnancy.”

The most effective prevention is proper food handling and hygiene. “Cook meat thoroughly, wash vegetables, and always wash your hands after handling cat litter, especially from young cats, which are more likely to shed the parasite.”

This research doesn’t mean everyone needs to panic. But it does mean we should take this tiny parasite seriously – not just because of what it does when active, but because of how it quietly changes the way brain cells talk to each other.

Understanding those changes may eventually help protect millions of people living with chronic infections they never knew they had.

The full study was published in the journal PLOS Pathogens.

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