Discovery Links Virus to Schizophrenia and Bipolar Disorder
A groundbreaking study by Johns Hopkins Medicine has uncovered a possible connection between hepatitis C virus (HCV) infections and serious psychiatric conditions like schizophrenia and bipolar disorder. Published in Translational Psychiatry, the research revealed that HCV is present in the brain’s choroid plexus—a structure that produces cerebrospinal fluid and helps regulate immune activity in the brain—but not in the brain tissue itself.
This finding supports the long-standing theory that infections may play a hidden role in psychiatric illnesses. “Some people with symptoms of bipolar disorder or schizophrenia may actually have a hepatitis C infection instead,” said lead researcher Dr. Sarven Sabunciyan, a neuroscientist at Johns Hopkins. “Potentially, treating the viral infection will improve the psychiatric symptoms in these people.”
What the Research Team Found
Using viral RNA sequencing technology, researchers analyzed brain samples from 256 deceased individuals—some with schizophrenia, bipolar disorder, or major depression, and others without psychiatric diagnoses. They focused specifically on the choroid plexus, a structure known to be vulnerable to infection. Out of more than 3,000 viruses tested, HCV was the only one significantly associated with schizophrenia and bipolar disorder.
The results were striking: HCV was found exclusively in the choroid plexus of people with these disorders, never in healthy individuals or those with depression. The team then analyzed health records of 285 million patients. They discovered HCV prevalence was 3.6% in people with schizophrenia and 3.9% in those with bipolar disorder. This compared to 1.8% for major depression and just 0.5% for those without psychiatric conditions.
These numbers, the researchers argue, suggest that the relationship between HCV and mental illness isn’t just due to behaviors like intravenous drug use, which are common across all three psychiatric groups. Instead, the virus itself may be contributing to disease pathology.
How a Liver Virus Reaches the Brain
The choroid plexus forms the blood-cerebrospinal fluid barrier—a critical checkpoint that keeps harmful substances out of the brain. But it’s also a target for viruses. When HCV infects this area, it doesn’t need to enter the brain directly to cause problems. According to Sabunciyan’s team, the virus appears to trigger changes in gene expression in nearby brain regions, particularly the hippocampus, which controls memory and emotion.
Though HCV wasn’t detected in the hippocampus itself, samples from infected individuals showed dramatic changes in brain gene activity. Specifically, the presence of HCV in the choroid plexus was linked to the suppression of certain repetitive genetic elements—especially Alu and L1 sequences—that are involved in regulating immune response and brain function. This suggests a possible immune-triggered mechanism where the body’s reaction to the virus may alter brain chemistry.
Are the Effects Reversible?
While the study does not prove that clearing the virus will reverse psychiatric symptoms, the researchers are optimistic. Past studies have shown that antiviral treatment for HCV can improve cognitive symptoms and reduce brain inflammation. One Taiwanese study even reported a reduced risk of developing schizophrenia in patients treated with antiviral drugs.
“Our findings show that it’s possible some people may be having psychiatric symptoms because they have an infection,” Sabunciyan said. “And since hepatitis C is treatable, it might be possible for this patient subset to be treated with antivirals and not have to deal with psychiatric symptoms.”
Implications for Diagnosis and Treatment
The researchers suggest that screening for HCV should become routine in psychiatric care, especially for patients with schizophrenia or bipolar disorder. “Given that the worldwide rate of schizophrenia and bipolar disorder is around 1 and 3 percent respectively, identifying and treating HCV in even a small subset of these patients could help hundreds of thousands of people,” Sabunciyan said.
Further investigations are already underway to determine whether the presence of HCV or other viruses in cerebrospinal fluid could serve as a biomarker for psychiatric disease. The team also plans to explore if other viruses that hide in the brain’s lining may have similar effects.
The findings have reignited interest in the “viral hypothesis” of mental illness—a theory that infections may cause or contribute to psychiatric disorders by altering immune function or damaging the brain. While the idea has long been debated, this study provides some of the most direct evidence yet.
“This is a very elegant study,” commented Dr. Jessica Faccioli, a neurologist who has written extensively on HCV-related brain disorders. “It not only reinforces the role of neuroinflammation in psychiatric disease, but also shows us a potential path forward: treat the infection, and you might relieve the symptoms.”
A Call for Broader Screening
Up to 50% of people with chronic HCV infection experience neurological or psychiatric symptoms such as fatigue, depression, or cognitive decline, even when liver damage is mild or absent. Many of these patients may never realize that their brain fog or mood swings are connected to a viral infection.
The authors emphasize the importance of universal HCV screening, especially in psychiatric patients. “Our work highlights a blind spot in mental health care,” Sabunciyan said. “We need to start considering that infections like HCV might not just be side effects of risky behavior, but actual drivers of disease.”
The team’s next steps include analyzing cerebrospinal fluid for viral signatures, studying more brain regions, and testing whether antiviral treatment can reverse psychiatric symptoms in infected patients. If confirmed, this research could reshape the way doctors understand—and treat—serious mental illnesses.
For now, the message is clear: for a subset of patients battling disorders like schizophrenia and bipolar disorder, the road to recovery might begin not with a new psychiatric drug, but with an old antiviral one.
