30 million Americans are infected with a brain parasite without knowing it

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In a recent study from the University of Virginia, researchers found why more than 30 million Americans are infected with a brain parasite spread by cats and contaminated meat but most will never show symptoms.

The finding could have important implications for brain infections, neurodegenerative diseases, and autoimmune disorders.

The study is published in Nature Communications. One author is Tajie Harris, Ph.D. from the Department of Neuroscience.

In the study, the researchers found that the parasite, Toxoplasma gondii, is kept in check by brain defenders called microglia.

These microglia releases a unique immune molecule, IL-1α, that recruits immune cells from the blood to control the parasite in the brain.

This process works so well that very few people develop symptomatic toxoplasmosis, the disease the parasite causes.

Understanding the role of microglia is essential because they are normally the only immune cells inside the brain.

The new finding shows how they recruit help when needed, and that discovery could apply to any brain condition with an immunological component—including brain injury, neurodegenerative disease, stroke, multiple sclerosis, and more.

The researchers have in recent years completely rewritten our understanding of the brain’s relationship with the body’s immune system.

For decades, textbooks taught that the brain was disconnected from the immune system. The research, however, showed that was not the case, to the shock of the scientific community.

Scientists are now exploring the implications of that major discovery.

One area of focus is microglia and their role in defending the brain. This has been a difficult question to answer because microglia are closely related to other immune cells elsewhere in the body.

In the study, the team that infection caused microglia to die in an inflammatory fashion—a way that the closely related immune cells do not.

Microglia could recognize the parasite’s presence directly, or they could recognize damage to brain tissue, a phenomenon that occurs in many diseases.

This finding helps explain why most people have no trouble controlling the brain parasite, while some—especially people who are immunocompromised—can become very sick.

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