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Parkinson's Virus Link

17 July 2025

A new study by Northwestern Medicine in Chicago, published in JCI Insight, suggests that a typically harmless virus might be a contributing environmental factor in the development of Parkinson’s disease. Although some cases of Parkinson’s have genetic origins, the majority have no clear cause.


“We wanted to explore whether environmental elements, like viruses, might play a role in Parkinson’s,” said Dr Igor Koralnik, chief of Neuroinfectious Diseases and Global Neurology in the Department of Neurology. “We used a specialized tool called ‘ViroFind’ to examine brain tissue from deceased individuals who had Parkinson’s and compared them to those who died from unrelated causes. Our goal was to detect any human-infecting viruses and see if there were differences between the groups.”


Their investigation revealed the presence of Human Pegivirus (HPgV) in the brain tissue of Parkinson’s patients, while none was found in the control group. HPgV, a virus in the same family as hepatitis C and transmitted through blood, has not previously been associated with any illness.


“HPgV is usually considered a benign infection that doesn’t cause symptoms or frequently reach the brain,” said Dr Koralnik. “We were surprised by how often we found it in the brains of Parkinson’s patients, and not in others. Even more striking was the varied immune response depending on the genetic makeup of the individuals. These findings suggest that HPgV might influence Parkinson’s development in ways we hadn’t previously considered, especially in people with certain genetic traits.”


The research team studied brain samples from 10 Parkinson’s patients and 14 individuals without the disease. They found HPgV in five of the 10 Parkinson’s brains and in none of the control samples. The virus was also detected in the spinal fluid of Parkinson’s patients, but not in the control group. The brains of those with HPgV showed more severe neurological changes, such as increased tau pathology and alterations in certain proteins.


To broaden their analysis, the scientists also studied blood samples from over 1,000 individuals enrolled in the Parkinson’s Progression Markers Initiative, a programme supported by The Michael J Fox Foundation to accelerate research and treatment.


“In the blood, we saw immune responses similar to those in the brain,” said Dr Koralnik. “Those infected with HPgV had immune system markers that differed from those without the virus. This was consistent regardless of genetic differences. However, when we tracked individuals over time, the picture became more complex.”


One key finding involved people with a mutation in the LRRK2 gene, which is linked to Parkinson’s. Their immune response to HPgV differed from those without the mutation. The research team is now looking to explore whether LRRK2 specifically alters the body’s reaction to HPgV, or if it changes the immune response to viruses more broadly.


The researchers plan to expand the study to determine how common HPgV is among Parkinson’s patients and what role it might play in the disease process.


“One major question is how frequently this virus enters the brain in people with and without Parkinson’s,” Koralnik said. “We’re also eager to uncover how genetic and viral interactions may influence the disease. These insights could eventually lead to new prevention or treatment strategies.”


Parkinson's is a progressive neurological condition caused by a loss of nerve cells in the part of the brain that produces dopamine, a neurotransmitter that controls movement. Parkinson's is the fastest growing neurodegenerative condition in the world. More than 10 million people worldwide are living with Parkinson’s, and the figure is expected to rise to 25 million by 2050. According to Parkinson's UK, around 166,000 people in the UK live with Parkinson’s, with a new diagnosis every 20 minutes.

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