Seemingly harmless, symptomless virus may actually cause Parkinson’s disease: study

While some cases of Parkinson’s disease are genetic, the vast majority have no known cause.

Now, scientists have discovered that a virus that has flown under the radar for years might be a potential contributor to the neurodegenerative disorder.

“We wanted to investigate potential environmental factors – such as viruses – that might contribute to Parkinson’s disease,” Igor Koralnik, the lead author of the study and chief of neuroinfectious diseases and global neurology at Northwestern Medicine, said in a press release.

“Using a tool called ‘ViroFind’, we analyzed post-mortem brain samples from individuals with Parkinson’s and from those who died of other causes. We searched for all known human-infecting viruses to identify any differences between the two groups.”

What they found was that the Human Pegivirus (HPgV) — a blood-borne, symptomless virus from the same family as hepatitis C — was present in the brains and spinal fluid of 50% of people with Parkinson’s but not in those without it.

The findings — published Tuesday in the journal JCI Insight — could be a major breakthrough in unlocking some of the factors that lead to this tricky disease and provide new insight into a virus that was previously considered benign.

“HPgV is a common, symptomless infection previously not known to frequently infect the brain,” Dr. Koralnik said.

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

“This suggests it could be an environmental factor that interacts with the body in ways we didn’t realize before.

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

Blood samples from more than 1,000 people enrolled in the Parkinson’s Progression Markers Initiative, a project launched by The Michael J. Fox Foundation, showed that people with HPgV had unique immune system “signals” — patterns that appeared both in the bloodstream and the brain.

“With the blood samples, we observed 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. But as we followed each person over time, we saw a more complicated picture.”

In people with a Parkinson’s-linked mutation in the LRRK2 gene, the immune system reacted to the virus differently than in those without the mutation — suggesting the virus may interact with certain genes to help set the disease in motion.

“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,” added Dr. Koralnik.

Now, the team wants to go bigger, examining more brains to determine how often HPgV sneaks past the blood-brain barrier.

“One big question we still need to answer is how often the virus gets into the brains of people with or without Parkinson’s,” said Dr. Koralnik.

“We also aim to understand how viruses and genes interact; insights that could reveal how Parkinson’s begins and could help guide future therapies.”