Impact of Toxoplasmosis on Brain Function

Recent research has uncovered that a common parasite can significantly affect the brain function of its intermediate hosts, which may include humans.

Toxoplasmosis, caused by the parasite Toxoplasma gondii, disrupts neuronal communication, even with a relatively small number of affected neurons. This was shown through a study examining mouse brain cells, both cultured in labs and taken from living specimens.

Infected neurons produced fewer extracellular vesicles (EVs)—tiny packets crucial for intercellular communication. This finding adds weight to the ongoing discussion about the behavioral effects of toxoplasmosis.

“We discovered that the disruption in EV signaling can affect how neurons and glial cells, particularly astrocytes, keep a healthy brain environment,” explains parasite immunologist Emma Wilson from the University of California Riverside School of Medicine.

“Even a few infected neurons can alter the neurochemical balance in the brain. This indicates that neuron-glial cell communication is not only essential but also susceptible to manipulation by parasites.”

T. gondii is notorious for inducing behavioral changes—whether for better or worse—in its hosts. It prefers to invade and reside inside particular cells, mainly neurons, and can cross the blood-brain barrier. Inside, it can remain dormant for many years.

This parasite is remarkably successful, affecting nearly all warm-blooded species. However, it can only reproduce in cats; some research indicates that infected creatures display behaviors that increase their chances of encountering cats, such as rodents being drawn to the scent of cat urine instead of avoiding it.

Though some studies have suggested behavioral manipulation by the parasite, the evidence is largely circumstantial, especially regarding humans, where attributing behavioral changes to a single cause is quite complex.

The recent study shifts focus from behavioral changes to concrete physical evidence. Researchers infected mouse neurons with T. gondii and meticulously analyzed the production and content of EVs, comparing infected neurons to healthy ones.

They found that both EV production and the contents of these vesicles were altered in infected neurons. Given that EVs relay information between neurons and astrocytes, this had ripple effects on astrocytic gene expression, which led to increased production of specific immune markers and a reduction in a transporter that clears excess glutamate from the brain.

Too much glutamate is associated with serious issues, including seizures and neural damage, which are complications commonly arising from severe toxoplasmosis cases. This might indicate that the influence of T. gondii is underestimated.

“The role of the parasite in neurological and behavioral conditions could be larger than we previously assumed,” Wilson comments.

Interestingly, a significant number of people carry T. gondii. It often enters the body through poorly prepared foods, like undercooked meat, or contact with cat feces. In some regions, prevalence rates can reach as high as 80 percent, while estimates in the U.S. suggest that 10 to 30 percent of the population may be infected.

Most individuals remain unaware of their neuro hitchhikers and live without noticeable impacts. However, for some—especially infants, the elderly, pregnant women, and those with compromised immune systems—infection can pose serious risks.

Effective prevention includes thoroughly cooking meat, washing vegetables, and maintaining hygiene after handling cat litter. Ongoing research from scientists like Wilson may enhance our understanding of these parasites and improve protective measures.

“Our brains may have built-in defenses that can recognize and respond to neurons infected by T. gondii,” Wilson states. “If we can learn to bolster that response, it could enhance protections for vulnerable populations.”

The findings have been published in PLOS Pathogens.