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Even a Mild Covid-19 Infection, Damage the Brain, UK study finds.

Oxford Study
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March 8, 2022.

Where a US study with veterans data found that covid-19 may bring 20 heart-related diseases last week, a new UK study published online yesterday(March 7, 2022) by University of Oxford experts, finds even a mild covid-19 (Sars-coV-2) infection causes brain damage.

Researchers from the University of Oxford, University College London, Imperial College London, and the National Institutes of Health discovered that the virus reduces grey matter thickness in areas of the brain associated with smell and memory.

Lead author Professor Gwenaelle Douaud, from the Wellcome Centre for Integrative Neuroimaging, at the University of Oxford, said: “We were looking at essentially mild infection, so to see that we could see some differences in their brain and how much their brain had changed compared with those who had not been infected was quite a surprise.”

How does this covid-19 affect the brain study conducted?


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The UK Biobank project has been tracking the health of 500,000 people for about 15 years and has a database of scans from before the pandemic, providing a unique opportunity to study the virus’s long-term health effects.

Oxford University’s associate professor of neurosciences, Gwenalle Douaud, and colleagues examined the brain changes of 785 UK Biobank participants (aged 51–81) who had two brain scans, on average 38 months apart, as well as cognitive tests.

Between their two scans, 401 people tested positive for SARS-CoV-2 infection, with 15 of them being hospitalized; the remaining 384 people were age- and gender-matched controls.

The researchers discovered several long-term effects of infection (with an average of 141 days between participants who received a COVID diagnosis and the second imaging scan), including a greater reduction in grey matter thickness in the orbitofrontal cortex and parahippocampal gyrus (regions associated with smell and memory of events).

Furthermore, participants with COVID-19 showed evidence of tissue damage in areas associated with the olfactory cortex, an area associated with smell, as well as an average reduction in whole-brain sizes.

Participants infected with SARS-CoV-2 showed a greater cognitive decline between scans, which was associated with atrophy of a brain region known as the cerebellum, which is linked to cognition.

The authors also conducted a control analysis on people who developed pneumonia that was unrelated to COVID-19 to demonstrate that the changes were specific to COVID-19 and not due to the general effects of contracting respiratory diseases.

What did the study expert Say?

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“We were quite surprised to see clear differences in the brain even with a mild infection,”

Study lead Douaud explained that it is normal for people to lose 0.2 percent to 0.3 percent of grey matter in memory-related areas of the brain every year as they age, but in the study evaluation, people who had been infected with the coronavirus lost an additional 0.2 percent to 2% of tissue compared to those who had not been infected.

Stuy author Douaud added, “Since the abnormal changes we see in the infected participants’ brains might be partly related to their loss of smell, it is possible that recovering it might lead to these brain abnormalities becoming less marked over time.

Similarly, likely, the harmful effects of the virus (whether direct or indirect via inflammatory or immune reactions) decrease over time after infection. The best way to find out would be to scan these participants again in one or two years,”.

“The brain is plastic, which means that it can re-organize and heal itself to some extent, even in older people,” said Prof Gwenaëlle Douaud at the University of Oxford. 

What Did Experts say about this UK Study?

Avindra Nath, clinical director of the U.S. National Institute of Neurological Disorders and Stroke, who was not involved in the research said, “It is a very novel study with conclusive data,” and “The findings are very intriguing, with important implications for the population at large.”

Dr. Serena Spudich, chief of neurological infections and global neurology at the Yale School of Medicine, who was not involved in the study said, “To me, this is pretty convincing evidence that something changes in brains of this overall group of people with Covid,”

“It opens up all sorts of questions that other researchers can follow up about the effect of coronavirus infection on cognitive function, on brain fog, and other areas of the brain – and to focus research on how best to mitigate that.” UK Biobank chief scientist Prof Naomi Allen said.

Experts in Australia and New Zealand have appreciated the study,

Professor Paul Parizel holds the David Hartley Chair in Radiology at the Royal Perth Hospital and the University of Western Australia, said, “This is a landmark study. Not only does it document the impact of the SARS-CoV-19 virus on brain tissue, but it also demonstrates the tremendous scientific potential of big data analytics applied to brain MRI scans.

“The findings of the study are remarkable,” said Dr. Sarah Hellewell is a Research Fellow in the Curtin University Faculty of Health Sciences and the Perron Institute for Neurological and Translational Science.

Professor Trichur Vidyasagar is Head of the Visual & Cognitive Neuroscience Laboratory in the Department of Optometry & Vision Sciences at the University of Melbourne, and an Honorary Professorial Fellow at the Florey Department of Neuroscience & Mental Health said, “This is as good a study as is possible to evaluate the effects over time of SARS-CoV-2 infection on the brain after supposedly ‘recovering’ from COVID-19.” and he added, “The study suggests that long-term effects of COVID-19 on the brain are not to be taken lightly even in those with the milder disease who did not need hospitalization during the acute illness.”

What are the limitations of the study?


While the study discovers a link between infection and brain function, it is unclear why.

 Previous research has found that people who experience significant and repeated loss of smell also experience a loss of grey matter. However, this study did not assess whether or not people lost their sense of smell.

Dr. Joanna Hellmuth, a neurologist at the University of California, San Francisco, is researching post-COVID symptoms. She stated that it is unclear what caused the brain changes observed in this study.

The authors cautioned that the findings were only for a brief period, but they “raise the possibility that longer-term consequences of SARS-CoV-2 infection may contribute to Alzheimer’s disease or other forms of dementia in the future.”

Professor Gwenaëlle Douaud, the lead author on the study, said, “A key question for future brain imaging studies is to see if this brain tissue damage resolves over the longer term.”

More studies will bring more truths about the causes, that will lead us to find the cure. 

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