Immunologists have ruled out the role of Borna disease virus (BDV) in bipolar depression, schizophrenia, anxiety disorder and dementia.

They based their findings on the first blinded, case-control study, which negates the results of a number of past studies linking the virus to mental disorders.

Blinded experiment is the one in the volunteers are prevented from knowing certain information that might lead to conscious or subconscious bias on their part, invalidating the results.

Researchers at the Centre for Infection and Immunity (CII) of Columbia University's Mailman School of Public Health conducted the study with collaborators from the US, Germany and Australia, the journal Molecular Psychiatry reports.

"Our study provides compelling evidence that bornaviruses do not play a role in schizophrenia or mood disorders," says Mady Hornig, director of translational research at the CII, according to a Columbia statement.

CII director and senior study author W. Ian Lipkin notes that "it was concern over the potential role of BDV in mental illness and the inability to identify it using classical techniques led us to develop molecular methods for pathogen discovery".

Researchers evaluated 198 patients with schizophrenia, bipolar disorder and major depressive disorder, carefully matching each one of them with a similar group of healthy volunteers of the same sex, age, region and socio-economic status.

They also tested blood of patients and controls for the presence of BDV genetic material and antibodies to BDV.

Not only did the researchers find no relationship between mental illness and bornavirus, they found no evidence of active or historical infection with BDV in any of the subjects.