Infection with some influenza viruses may lead to a higher risk of developing Parkinson's disease later in life, according to a new U.S. study.
The work, inspired by the story behind the 1990 movie Awakenings, suggests that aggressive flu strains can pass into the brain and deplete dopamine-creating neurons, leaving a person more vulnerable to developing the neurodegenerative disease.
Awakenings is the story of how American neurologist Oliver Sacks figured out he could revive people suffering from a strange sleeping sickness called encephalitis lethargica, or von Economo's encephalopathy, using the newly discovered Parkinson's drug L-dopa.
An epidemic of von Economo's encephalopathy in parts of Europe and North America coincided with the 1918 Spanish flu, and some people believe infection with that virus was the trigger for the illness.
A team of scientists from St. Jude Children's Research Hospital in Memphis, Tenn., which is studying whether there is a viral component to the development of Parkinson's disease, decided to look at the question using another highly virulent flu strain - that of the H5N1 avian flu.
"In some ways, that movie was the initiating factor for our work with the H5N1 avian influenza virus," said senior author Richard Smeyne, a neurologist who drew on the expertise of St. Jude's world-renowned influenza research team to do the work. A co-author is Robert Webster, a leading figure in the world of influenza.
"We were interested in the fact that many of the people infected after the Spanish flu developed post-encephalic Parkinsonism," Dr. Smeyne said.
The ensuing article, published in the Proceedings of the National Academy of Sciences, looked at the impact of the H5N1 virus in the brains of mice. The scientists found the virus passed into the brain, killing some dopamine-creating neurons.
Dr. Smeyne said a corresponding loss in humans - if it occurs - wouldn't be enough to trigger Parkinson's on its own. But it could make a person more vulnerable to developing it, or speed up the point in life at which someone might develop the disease, he said.
An expert on the virus that caused the Spanish flu, Jeffery Taubenberger, said the study raises an interesting hypothesis, but does not answer the question of whether flu viruses play a role in the development of Parkinson's.
Dr. Taubenberger, who led a team that excavated remnants of the virus that caused the Spanish flu and then sequenced the virus, said a sort of mythology has encompassed the 1918 outbreak, ascribing to it powers it probably did not have.
Work he has done looking at whether the virus was responsible for the epidemic of von Economo's encephalopathy does not support a link, he said.
Dr. Taubenberger suggested a study of survivors of H5N1 infection could shed light on whether they suffer any neurological or neurodegenerative conditions that might be linked to that virus.
Dr. Smeyne said the neurodegenerative aspect his team sees with H5N1 probably does not exist for all flu viruses and may not be true for the milder swine flu or H1N1 virus causing the current flu pandemic.
"It's a fairly mild form of influenza. There doesn't seem to be encephalitis associated with it," he said.
"That would suggest we would not see it (crossing into the brain). But I think without the direct experimental evidence which we need to look at, I think that we can't say one way or the other at this point."
