Some kinds of influenza viruses may set up people infected with them to be at higher risk of developing chronic neurodegenerative diseases like Parkinson's and Alzheimer's later in life, according to a new study.
Researchers from St. Jude Children's Research Hospital in Memphis examined the impact of the H5N1 avian flu virus in the brains of mice.
During the study, Richard Smeyne and colleagues sprayed a solution containing a highly pathogenic subtype of H5N1 avian flu into the noses of 225 mice.
They found that the virus infected nerves in the gut, then entered the brain stem and finally reached the brain.
In the brain, it led to chronic activation of the immune system, even long after the viral infection had been cleared.
This immune system activity later led to protein aggregation and neuron loss in the brain, and to symptoms like tremor and loss of coordination - the hallmarks of Parkinson's and Alzheimer's.
"Infection with influenza virus might leave the brain vulnerable to damage from future infections with new influenza strains," New Scientist quoted Smeyne as saying.
He said that this is more likely to happen in young children or during an flu pandemic.
Smeyne suspects that all flu viruses, including the current H1N1 swine flu pandemic, could cause symptoms of encephalitis, or inflammation of the brain.
However, he insists that there is currently no proof that flu viruses other than the H5N1 he worked with can enter the central nervous system.
The study has been described in the Journal Proceedings of the National Academy of Sciences.