‘Harmless’ Virus Found in Parkinson’s Patients’ Brains, New Study Shows

A new study from researchers at Northwestern Medicine suggests that a common and typically harmless virus may play a role in the development of Parkinson’s disease.

The Northwestern Medicine research team did not expect to find the Human Pegivirus (HPgV) in the brains and spinal fluid of people with Parkinson’s disease. The virus, however, was not found in people without Parkinson’s, who were the study’s control group. The study was published in the journal JCI Insight.

HPgV is in the same family as hepatitis C and is not known to cause any disease. The virus is transmitted through the blood and can be detected through blood tests. It also does not cause any symptoms nor is it known to frequently infect the brain, according to Dr. Igor Koralnik, chief of neuroinfectious diseases and global neurology at Northwestern Medicine.

“We were surprised to find it in the brains of people with Parkinson’s at such high frequency and not in the controls,” Dr. Koralnik said in a press release. “Even more unexpected was how the immune system responded differently, depending on a person’s genetics.”

The immune system response might suggest that there could be an environmental factor that interacts with the body in ways that weren’t recognized before, Dr. Koralnik said.

“For a virus that was thought to be harmless, these findings suggest it may have important effects, in the context of Parkinson’s disease,” Dr. Koralnik said. “It may influence how Parkinson’s develops, especially in people with certain genetic backgrounds.”

Dr. Koralnik explained that the research team wanted to investigate potential environmental factors, such as viruses, that might contribute to Parkinson’s disease. Parkinson’s can be hereditary in some cases, but most of the time it isn’t, and the cause of the disease remains unknown.

An estimated 1.1 million people in the United States are living with Parkinson’s disease, and the number is expected to rise to 1.2 million by 2030, according to statistics from the Parkinson’s Foundation.
An estimated 90,000 people in the United States are diagnosed with Parkinson’s each year, the foundation reports. What’s more, Parkinson’s is the second most common neurodegenerative disease after Alzheimer’s disease.

As Parkinson’s progresses, people with the disease develop tremor, rigidity, and other movement problems that make it difficult to walk. Loss of balance and falls become more prominent in the later stages. The disease ultimately prevents people from performing their daily living activities.

About the Study

The Northwestern Medicine research team used a tool called “ViroFind” to analyze brain samples of deceased individuals. The investigators examined the brains of 10 individuals with Parkinson’s disease and 14 individuals who died from other causes—those who did not have Parkinson’s served as the control group.

HPgV was found in the brains of five of the 10 people with Parkinson’s, but it did not appear in the brains of people in the control group. The team also observed that HPgV was in the spinal fluid of those with Parkinson’s, which suggests the virus could be active in the nervous system. The virus was not found in the spinal fluid of the people who did not have Parkinson’s.

The researchers also discovered that people who had HPgV in their brains also had higher levels of tau, a protein that can build up and damage brain cells, and complexin-2, a protein involved in brain signaling. These changes are often seen in diseases that impact memory and movement, which researchers believe indicates that HPgV might contribute to brain changes associated with Parkinson’s.

In addition to examining the brain samples of deceased individuals, the Northwestern Medicine investigators also looked at blood samples from more than 1,000 participants in an initiative launched by The Michael J. Fox Foundation. The team noticed similar immune-related changes, mirroring those found in the brain, Dr. Koralnik said.
“People who had the virus showed different signals from the immune system than those who didn’t, and this pattern was the same, no matter the genetics,” Dr. Koralnik said. “But as we followed each person over time, we saw a more complicated picture.”

What the investigators saw was the involvement of a mutated gene. The team discovered that patients with a particular Parkinson’s-related gene mutation, called LRRK2, responded differently to HPgV compared to those who had Parkinson’s but not the mutation.

“We plan to look more closely at how genes like LRRK2 affect the body’s response to other viral infections to figure out if this is a special effect of HPgV or a broader response to viruses,” Dr. Koralnik said.

More Research Is Necessary

Detecting traces of HPgV more often in the brains of people with Parkinson’s disease raises the possibility of a link between viral exposure and Parkinson’s disease, “but it’s far too early to say the virus causes the disease,” Dr. Joel Salinas, a behavioral neurologist and associate professor at NYU Grossman School of Medicine and chief medical officer of Isaac Health, told Fox News Digital.

Dr. Salinas, who was not involved in the study, also said that much more extensive and long-term research will be necessary to determine if this link has “real clinical significance.”

“For now, people should know this is early research and not a reason to worry—there’s no overwhelming evidence yet that this virus causes Parkinson’s, similar to how work on herpesviruses in Alzheimer’s has suggested a possible link but remains to be fully established,” Dr. Salinas said.

The Northwestern Medicine researchers plan to expand their study to determine how often HPgV is found in people with Parkinson’s, whether it plays a role in the disease, whether other viruses may be involved, and hopefully answer other questions.

“One big question we still need to answer is how often the virus gets into the brains of people with or without Parkinson’s,” Dr. Koralnik said in the press release. “We also aim to understand how viruses and genes interact; insights that could reveal how Parkinson’s begins and could help guide future therapies.”

Source Links:
https://www.foxnews.com/health/harmless-virus-found-lurking-parkinsons-patients-brains-new-study-shows
https://news.feinberg.northwestern.edu/2025/07/17/scientists-discover-a-possible-environmental-trigger-for-parkinsons-disease/
https://www.nm.org/healthbeat/medical-advances/Could-a-Common-Virus-Be-Linked-to-Parkinsons-Disease
https://www.parkinson.org/understanding-parkinsons/what-is-parkinsons/stages