The theory that exposure to such viruses could make people more susceptible to neurodegenerative diseases is controversial, but not new. An increase in people exhibitin neurological symptoms associated with Parkinson's disease occurred after the 1918 influenza pandemic. There are no reports yet of survivors of the more recent H5N1 flu exhibiting Parkinson's disease. But according to Richard Smeyne, a developmental neurobiologist and the senior author of the new study, it's too early to draw any conclusions about whether those who were infected with H5N1 are at a greater risk of developing neurodegenerative diseases.

Researchers in the new study found that all 225 mice developed tremors and other movement difficulties when a virus solution was sprayed in their noses. Smeyne and his colleagues were able to track the virus over a period of ten days as it moved from the gut through the nervous system to the brain stem, mid-brain and ultimately throughout most of the rest of the brain. At 21 days into the study, the virus had cleared the system of the infected mice, but the research team found the areas affected by the virus still showed signs of inflammation and elevated levels of phosphorylated alpha-synuclein at the end of the 90-day study.

Mice that were infected with the H5N1 virus did indeed experience a loss in dopamine-releasing neurons—the same neurons destroyed by Parkinson's disease. While this 17% neuron die-off is much less significant than the 70% reduction typically experienced by those with Parkinson's Disease, Smeyne believes bird viruses may leave those exposed with greater susceptibility to Parkinson's.

Malú Tansey, a neuroscientist focused on inflammation and neurodegenerative disease at Emory University in Atlanta said the study produced strong evidence that the virus can kill dopamine neurons. But she added, "I don't think people should be overly concerned if they're exposed to avian flu virus that they're going to get Parkinson's disease. But it should prompt investigators to reexamine inflammation as a potential contributing factor to neurodegenerative disease."

News Release: Bird Flu Virus a Possible Trigger for Parkinson's: Science Now