Brain-eating fungus causes the immune system to attack neurons

Infections often conjure images of bacteria or viruses, but certain fungi can also take their toll on us. They can hide in unsuspecting corners of the environment and interact with living organisms in ways that raise many questions.

One particular fungus, Beauveria bassiana, has captured attention because of its interactions with insects.

Its spores settle on an insect and then germinate and penetrate through the cuticle. The insect dies within days and forms the substrate for a white fungal mold that grows and flourishes.

Prof. Alicia Hidalgo, from the University of Birmingham, directed a recent investigation into infections in insects by this devastating fungus.

Immune responses to brain fungus

Fruit flies became the chosen subjects for this study because their immune system shares some features with that of more complex creatures.

Researchers often turn to these small insects when exploring disease processes in a simple model.

The researchers analyzed the effect of the fungus on the brains of flies and found that flies infected with B. bassiana suffered a reduction in the number of brain cells.

They identified that the fly’s own immune system was “tricked” by the invading fungus to start destroying brain cells.

In flies, Toll receptors are agents of the immune system. When infected with the fungus, the Toll-1 receptors in the flies triggered the release of antimicrobial peptides that attack and kill pathogens.

However, the fungus also provoked the Toll-1 receptors to produce another molecule, called Sarm, that suppresses the immune response and destroys brain cells instead.

“We have shown a process for how fungi have evolved to trick the immune system to get into the brain,” said Prof. Hidalgo. Her findings suggest that a normal line of defense can accidentally turn against the very organ it’s meant to protect.

Sarm’s link to neurodegeneration

When the immune system tries to confront this fungus, the Sarm molecules step up their activity; they have the potential to sabotage defenses by encouraging cell damage in the brain.

“The key antagonist in the immune process is Sarm, a so-called master of destruction, that is causing cell death in the brain. The ability of B. bassiana to trick the fruit fly immune system into activating the master of destruction Sarm and kill cells enables spores to beat the blood-brain barrier and start feeding on brain cells,” commented Hidalgo.

The process, known as neurodegeneration, describes the gradual breakdown of nerve cells. If immune signals become confused, the result might be nerve destruction in the brain.

Experts note that this fungus, though hazardous to insects, is widely used for insect management in agriculture. It is developed into a type of pesticide and used to kills certain insects.

The findings offer a curious look at how a single microbe might manipulate host biology for its own benefit.

What does this fungus mean for humans?

“It is important to stress that B. bassiana cannot affect humans,” explained Dr. Deepanshu Singh, now a post-doc at the University of Manchester. The fungus targets insects, but it stays clear of mammals.

Still, other fungi are known to reach the human brain under certain conditions. These discoveries hint that parallel strategies might pop up in different species, especially when fungal organisms are trying to survive inside a host.

A broader perspective on fungal threats

Some scientists believe that future work could explore whether similar immune system misdirection happens in other animals.

Understanding how these pathogens find loopholes in the immune system may help researchers develop new interventions.

Fungal infections often get less attention than bacterial or viral illnesses, yet they can still pose serious threats.

The possibility that a fungus might slip into the human central nervous system and confuse its defenses encourages further research.

Implications for neurodegenerative diseases

The discovery that a fungal infection can manipulate immune responses to attack brain cells raises questions about similar mechanisms in humans.

Some neurodegenerative diseases, such as Alzheimer’s disease and Parkinson’s disease, involve immune system dysfunction and excessive inflammation in the brain.

If certain pathogens can trigger destructive immune pathways, this could offer new insights into how inflammation contributes to neurodegeneration.

Researchers may investigate whether similar immune evasion tactics occur in human infections, potentially linking fungal exposure to long-term neurological effects.

Possible next steps in fungal research

Scientists hope to identify molecules that can protect nerve cells when the immune system is tricked. Pinpointing the exact signals could spark novel medical approaches for people at risk of certain fungal infections.

Research also continues on ways to control fungal spread in agricultural settings without harming beneficial insects.

B. bassiana remains a useful tool for pest management, though its tactics highlight the complexity of the microbe-host relationship.

The study is published in PLOS Biology.

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