Neuroscientists are proposing that a ‘third wave’ of neurological consequences of COVID-19 may include an increased risk of Parkinson’s disease.
In an article published in the Journal of Parkinson’s Disease, researchers at the Florey Institute of Neuroscience and Mental Health in Melbourne say the ever-increasing number of reports of neurological symptoms in patients, from mild (hyposmia) to severe (encephalitis) suggest the potential for neurotropism of SARS-CoV-2.
They are therefore calling for long term monitoring of people who have recovered from COVID-19 infection to look for potential long term neurological effects.
Professor Kevin Barnham and colleagues say there are lessons to be learned from previous viral pandemics and long term neurological outcomes.
“We can take insight from the neurological consequences that followed the Spanish Flu pandemic in 1918 where the risk of developing Parkinson’s disease increased two to three-fold. Given that the world’s population has been hit again by a viral pandemic, it is very worrying indeed to consider the potential global increase of neurological diseases that could unfold down track,” he said.
And while there is no evidence that viruses are causally linked to parkinsonism, the researchers note there is a hypothesis that “an unknown pathogen” results in a neuronal insult and is the first ‘hit’ in a dual ‘hit’ hypothesis of Parkinson’s disease.
“This hypothesis proposes that there is an initial insult from a neurotropic pathogen that enters the brain through the nasal or gastric pathways and induces long-lived activation of the glial cells that predisposes the brain to oxidative insult in later life,” they write.
“Or alternatively may become primed to react abnormally to stimuli in the aging brain and to become neurotoxic and destructive during neurodegeneration. “
“As such, the second ‘hit’ is pathogenic and deleterious due to an already primed neural system. It is for this reason that the current COVID-19 pandemic could provide valuable insights into the effect of viral infections/inflammation in neurodegenerative conditions to neurologists and neuroscientists, as there are many case reports of severe neurological complications in hospitalized patients, as well as sensory loss in many patients.
The researchers note that a common feature of COVID-19 – anosmia – also presents in around 90% of people in the early stages of Parkinson’s disease and a decade ahead of motor symptoms.
And diagnosis of Parkinson’s disease currently relies on presentation of motor dysfunction, but research shows that by this time 50-70% of dopamine cell loss in the brain has already occurred.
“By waiting until this stage of Parkinson’s disease to diagnose and treat, you’ve already missed the window for neuroprotective therapies to have their intended effect,” says Professor Barnham.
The researchers hope to establish a simple, cost-effective screening protocol aiming to identify people in the community at risk of developing Parkinson’s, or who are in early stages of the disease, at a time when therapies have the greatest potential to prevent onset of motor dysfunction.
They plan to put the proposal forward for funding from the Australian Government’s Medical Research Future Funding scheme. Additionally, the team have developed two neuroprotective therapies currently under investigation and have identified a cohort of subjects who are ideally suited to study the treatments.