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A virus that causes a fatal brain disease in horses and sheep could be linked to mental disorders in humans, a scientist is set to tell a UK conference on Wednesday.
Borna Disease Virus (BDV) causes severe, often fatal encephalitis - inflammation of the brain - in animals.
But there are suggestions that it could also lead to subtle changes in the human brain, causing psychiatric disorders such as schizophrenia.
Professor Norbert Nowotny, of the University of Veterinary Science, Vienna, says more work is needed to confirm the link with humans - and to find out how the virus could be transmitted.
He will present his work to the meeting of the European Societies of Clinical and Veterinary Virology and the Society for General Microbiology at the Royal College of Physicians, London.
History
The disease caused by BDV, Borna Disease, was first described in the late 1800s after a large number of horses died in an epidemic, near Borna in Saxony, Germany.
BDV is still mainly found in animals in central Europe.
Epidemics such as that which gave the disease its name are rare, and usually only sporadic cases of BDV are recorded.
In addition to being found in horses and sheep, cattle, dogs and rabbits can also be affected by BDV.
Infections in cats and ostriches have also been reported.
By learning more about how the virus is transmitted we can take actions to prevent it from causing disease in humans and in animals
Professor Norbert Nowotny, University of Veterinary Sciences
The link with human mental health disorders is controversial, and has been questioned in some recent studies.
Scientists also disagree on how to test for the link.
It has been made because behavioural abnormalities, including some resembling human psychiatric disorders, have been seen in rats and non-human primates.
Controversy
BDV antibodies and genetic markers of the disease have also been found in the blood cells of psychiatric patients.
Professor Nowotny admitted linking BDV to human mental health disorders is controversial.
He added that it was suspected that in humans the disease affects the activity of neurotransmitters, chemicals that transmit information across the junction between one nerve cell and another nerve cell or a muscle.
This could then lead to psychiatric disorders.
Professor Nowotny said BDV had been detected in a person suffering from chronic fatigue syndrome.
He added: "The link between BDV and psychiatric disorders such as some subgroups of schizophrenia and depression may be very difficult to prove for certain.
"However by learning more about how the virus is transmitted we can take actions to prevent it from causing disease in humans and in animals," he said.
Exposure
Dr Daniel Thomas, principal scientist at the Centre for Disease Surveillance, Wales, worked on a study looking at BDV in farmers.
He told BBC News Online: "We found there was some evidence that our group of farmers might be exposed to this virus, but we didn't find any evidence that it made them ill."
The research was part of an ongoing study into whether farmers are affected by zoonoses - infections such as Weils Disease, which can be passed from animals to humans.
But Dr Thomas said the teams findings may not be conclusive because mental health problems may not have shown up yet, and people with severe mental illnesses may not have been working, and therefore not recruited to the study.
Dr John Fazakerley, a leading UK expert on Borna disease, based at the Centre for Infectious Diseases at the University of Edinburgh, said there was not yet enough evidence to confirm or deny a link between BDV and human mental disorders.
Even if one is made, the virus would only be implicated in a small proportion of cases.
"It may be some subsections of schizophrenia and various forms of manic depression where the cause may eventually come down to be this virus."
A large ongoing US study could provide the definitive answer, he said.
Borna Disease Virus (BDV) causes severe, often fatal encephalitis - inflammation of the brain - in animals.
But there are suggestions that it could also lead to subtle changes in the human brain, causing psychiatric disorders such as schizophrenia.
Professor Norbert Nowotny, of the University of Veterinary Science, Vienna, says more work is needed to confirm the link with humans - and to find out how the virus could be transmitted.
He will present his work to the meeting of the European Societies of Clinical and Veterinary Virology and the Society for General Microbiology at the Royal College of Physicians, London.
History
The disease caused by BDV, Borna Disease, was first described in the late 1800s after a large number of horses died in an epidemic, near Borna in Saxony, Germany.
BDV is still mainly found in animals in central Europe.
Epidemics such as that which gave the disease its name are rare, and usually only sporadic cases of BDV are recorded.
In addition to being found in horses and sheep, cattle, dogs and rabbits can also be affected by BDV.
Infections in cats and ostriches have also been reported.
By learning more about how the virus is transmitted we can take actions to prevent it from causing disease in humans and in animals
Professor Norbert Nowotny, University of Veterinary Sciences
The link with human mental health disorders is controversial, and has been questioned in some recent studies.
Scientists also disagree on how to test for the link.
It has been made because behavioural abnormalities, including some resembling human psychiatric disorders, have been seen in rats and non-human primates.
Controversy
BDV antibodies and genetic markers of the disease have also been found in the blood cells of psychiatric patients.
Professor Nowotny admitted linking BDV to human mental health disorders is controversial.
He added that it was suspected that in humans the disease affects the activity of neurotransmitters, chemicals that transmit information across the junction between one nerve cell and another nerve cell or a muscle.
This could then lead to psychiatric disorders.
Professor Nowotny said BDV had been detected in a person suffering from chronic fatigue syndrome.
He added: "The link between BDV and psychiatric disorders such as some subgroups of schizophrenia and depression may be very difficult to prove for certain.
"However by learning more about how the virus is transmitted we can take actions to prevent it from causing disease in humans and in animals," he said.
Exposure
Dr Daniel Thomas, principal scientist at the Centre for Disease Surveillance, Wales, worked on a study looking at BDV in farmers.
He told BBC News Online: "We found there was some evidence that our group of farmers might be exposed to this virus, but we didn't find any evidence that it made them ill."
The research was part of an ongoing study into whether farmers are affected by zoonoses - infections such as Weils Disease, which can be passed from animals to humans.
But Dr Thomas said the teams findings may not be conclusive because mental health problems may not have shown up yet, and people with severe mental illnesses may not have been working, and therefore not recruited to the study.
Dr John Fazakerley, a leading UK expert on Borna disease, based at the Centre for Infectious Diseases at the University of Edinburgh, said there was not yet enough evidence to confirm or deny a link between BDV and human mental disorders.
Even if one is made, the virus would only be implicated in a small proportion of cases.
"It may be some subsections of schizophrenia and various forms of manic depression where the cause may eventually come down to be this virus."
A large ongoing US study could provide the definitive answer, he said.