SARS-CoV-2, the virus behind the Covid-19 pandemic, can persist in the skull and its surroundings i.e. meninges for years after infection, leading to a long-lasting effect on the brain, according to a major German study.
Researchers from Helmholtz Munich and Ludwig-Maximilians-Universitat (LMU) found that SARS-CoV-2 spike protein remains in the brain's protective layers -- the meninges, and the skull's bone marrow for up to four years after infection.
These spike proteins are responsible for triggering chronic inflammation in affected individuals and increase the risk of neurodegenerative diseases, the team found.
The study ‘Persistence of spike protein at the skull-meninges-brain axis may contribute to the neurological sequelae of COVID-19,’ by Prof. Ali Ertürk, Director at the Institute for Intelligent Biotechnologies at Helmholtz Munich among others said that the long-term neurological effects include “accelerated brain ageing, potentially leading to a loss of five to 10 years of healthy brain function in affected individuals."
The study, published in the journal Cell Host & Microbe, said that the patients may also have neurological symptoms of long Covid such as headaches, sleep disturbances, and “brain fog,” or cognitive impairment.
About five to 10 per cent of people infected with Covid are likely to experience long Covid -- approximately 400 million individuals may carry a significant amount of the spike protein.
Notably, vaccines against the deadly virus significantly reduce the accumulation of the spike protein in the brain, said the researchers.
“Vaccination reduced but did not eliminate spike protein accumulation after infection in mice. Our findings suggest persistent spike protein at the brain borders may contribute to lasting neurological sequelae of COVID-19,” said the researchers.
The reduction was “only around 50 per cent in mice, leaving residual spike protein that continues to pose a toxic risk to the brain”.
For the study, the team developed a novel AI-powered imaging technique to understand how the SARS-CoV-2 spike protein affects the brain.
The method, which offers a three-dimensional visualisation of viral proteins, was deployed to find previously undetectable distributions of spike protein in tissue samples from Covid-19 patients and mice.
The findings revealed significantly elevated concentrations of spike protein in the skull's bone marrow and meninges, even years after infection.
The spike protein binds to so-called ACE2 receptors, particularly abundant in these regions.
The study also suggested a mechanism for the virus’s entry into the central nervous system. “In both mouse and COVID-19 human tissues, we found spike protein in the skull meninges connections (SMCs), which the virus or virus components could use to travel from the skull marrow to the meninges and the brain parenchyma,” said the authors.
