At least one strain of the H5N1 avian influenza virus leaves survivors at significantly increased risk for Parkinson’s disease and possibly other neurological problems later in life, according to new research from St. Jude Children’s Research Hospital.
In the Proceedings of the National Academy of Sciences, researchers reported that mice that had survived infection with an H5N1 flu strain were more likely than uninfected mice to develop brain changes associated with neurological disorders like Parkinson’s and Alzheimer’s diseases. The study revealed the H5N1 flu strain caused a 17% loss of the same neurons lost in Parkinson’s as well as accumulation in certain brain cells of a protein implicated in both diseases.
“This avian flu strain does not directly cause Parkinson’s disease, but it does make you more susceptible,” said Richard Smeyne, Ph.D., associate member in St. Jude Developmental Neurobiology, and the paper’s senior author.
“Around age 40, people start to get a decline in brain cells. Most people die before they lose enough neurons to get Parkinson’s. But we believe this H5N1 infection changes the curve. It makes the brain more sensitive to another hit, possibly involving other environmental toxins,” Smeyne explained.
Smeyne noted the work involved a single strain of the H5N1 flu virus, the A/Vietnam/1203/04 strain. The threat posed by other viruses, including the current H1N1 pandemic flu virus, is still being studied.
Early indications are that the H1N1 pandemic strain carries a low neurologic risk, said Richard Webby, Ph.D., director of the World Health Organization Collaborating Center for Studies on the Ecology of Influenza in Animals and Birds, which is based at St. Jude. Webby, who is also an associate member of the St. Jude Department of Infectious Diseases, was not involved in the H5N1 study led by Smeyne.
This study also supports the theory that a hit-and-run mechanism is at work in Parkinson’s disease. The investigators believe the H5N1 infection sparks an immune response that persists long after the initial threat is gone, setting patients up for further devastating losses from a second hit, possibly from another infection, drug or environmental toxin. In this case, researchers believe the flu virus is the first hit that sets up development of Parkinson’s at a later time.