Influenza Infection Found to Increase Risk of Parkinson's Disease

A majority of incidences of Parkinson’s disease have unknown causes, despite significant ongoing research to identify driving factors.

Findings from a study published by npj Parkinson’s Disease suggest that a strain of influenza may increase the risk of developing Parkinson’s disease in mice models. If confirmed in humans, these results could provide further incentives to vaccinate against the flu.

"This study has provided more evidence to support the idea that environmental factors, including influenza may be involved in Parkinson's disease," said researcher Richard J. Smeyne, PhD. "Here we demonstrate that even mice who fully recover from the H1N1 influenza virus responsible for the previous pandemic (also called 'swine flu') are later more susceptible to chemical toxins known to trigger Parkinson's in the lab."

The investigators previously found that a deadly H5N1 strain of influenza infects nerve cells, travels to the brain, and causes influenza, which can result in the development of Parkinson’s-like symptoms in mice. This strain, commonly referred to as the Bird Flu, kills more than 60% of those infected with the virus.

Other studies also show that when inflammation in the brain does not resolve properly, such as in the case of a head injury, it can lead to Parkinson’s disease.

To build on previous findings, the authors of the current study investigated the H1N1 virus, which is less lethal and does not infect neurons; however, the strain still results in inflammation due to inflammatory molecules released by the immune system, according to the study.

The authors used mice models that developed Parkinson’s-like symptoms after exposure to the toxin MPTP. This toxin is known to cause Parkinson's disease by destroying dopaminergic neurons in the brain.

The investigators discovered that even after the initial infection had subsided, mice that were infected with H1N1 developed more severe symptoms of Parkinson’s disease compared with mice that had not been infected, according to the study.

Interestingly, when mice received an influenza vaccine or received antiviral drugs at the onset of the infection, the sensitivity to MPTP was eliminated, the authors reported.

These findings suggest that exposure to particular strains of influenza could result in an increased risk of developing Parkinson’s disease. Since the investigators discovered that vaccination against influenza reduced the risk of Parkinson’s disease, it highlights the importance of receiving the yearly vaccine, according to the study.

"The H1N1 virus that we studied belongs to the family of Type A influenzas, which we are exposed to on a yearly basis," Dr Smeyne said. "Although the work presented here has yet to be replicated in humans, we believe it provides good reason to investigate this relationship further in light of the simple and potentially powerful impact that seasonal flu vaccination could have on long-term brain health."