How can Covid-19 affect the human brain?

How can Covid-19 affect the human brain?
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Cognitive impairment caused by severe Covid-19 is comparable to the decline that takes place between the ages of 50 and 70, according to a recent study by the University of Cambridge and Imperial College London.

The researchers said the degeneration was equivalent to lose 10 IQ points. The findings, published earlier this month, were the latest in a series of studies that suggest Covid-19 has an impact on the brain.

The lasting impact of Covid-19 on the millions of people who contracted it is still being assessed more than two years into the pandemic, with few areas of uncertainty as urgent and troubling as the effects potentially long-lasting on the brain.

Scientists are examining the precise mechanisms behind the neurological effects and whether the symptoms will prove to be temporary, or whether the greatest health burdens may yet be found in the future.

What are the most striking findings about the impact of Covid-19 on the brain?

Amid a growing body of anecdotal evidence, Alzheimer’s Disease International, a federation of dementia associations, suggested in September that the degenerative effect of the coronavirus could be fueling the “dementia pandemic”. The World Health Organization estimates that the number of people with dementia, currently around 55 million, will rise to around 80mn by 2030 as the elderly population grows.

A study Oxford University researchers published in March found tissue damage and shrinkage in parts of the brain linked to smell in people who had only mild bouts of Covid-19. The researchers, who analyzed almost 800 brain scans from the UK Biobank – one of the largest biomedical databases in the world – found a reduction in whole brain size compared to uninfected people and, on average, greater cognitive decline.

The loss of smell, which people began to notice at the start of the pandemic, may have been caused by damage to the olfactory nerve that runs through the brain and transmits this function, a study has found. Posted in JAMA Neurology last month.

Diagram showing the olfactory mechanisms of the body and how Covid-19 could affect them as shown by the results of recent scientific studies

To what extent are the experts concerned?

Dr. S. Andrew Josephsonholder of the chair of neurology at the University of California at San Francisco and editor of JAMA Neurology, said people with even mild Covid have described symptoms, such as mental fatigue, that may be related to the brain. “We’re seeing more and more studies that show changes in the brain that may be associated with it,” he said.

Difficulties with memory, language and concentration are among a wide range of symptoms that fall under the umbrella term ‘long Covid’. Defined as suffering from symptoms for 12 weeks or more after a diagnosis of Covid-19, medical experts have estimated that it affects more than 100 million people.

But other experts suggest that superficially worrying findings may not be as concerning as they first appeared.

“The majority of patients we see clinically have . . . impaired concentration and ability to direct thought,” said Alan Carson, consultant neuropsychiatrist at the University of Edinburgh. “It’s very unpleasant, but it’s not a permanent neurodegenerative condition – it’s treatable.”

Serena Spudich, professor of neurology at the Yale School of Medicine, said it was unclear how many changes in the brain are specific to Covid, or what they mean. “People can lose gray matter and it may mean little in real life,” she said.

What research is being done to find out more?

Research into the link between Covid-19 and dementia is in its early stages. The scientists said it was theoretically possible that the disease could affect the brain in the same way as some other viruses.

A US study in 2020 found that people living with HIV had a 50% higher risk of developing dementia. If Sars-Cov-2 has traveled “along brain pathways in a similar way to HIV, it is possible that Covid infection increases the risk of Alzheimer’s disease”, reflected Dennis Chan, who leads a study on cognitive impairment in the long Covid funded by the UK’s National Institute for Health and Care Research.

Other scientists said the belief that the virus could spread through the wider central nervous system via the olfactory nerve now appeared to be mistaken. “It’s proven to be incredibly difficult to infect the brain with coronavirus,” Carson said.

Josephson said researchers were analyzing cerebrospinal fluid samples from living patients for “any unusual antibodies or inflammatory cells” that could shed new light on the long Covid.

Discouraging precedents in history have so far not been repeated, experts have suggested.

Clinicians were concerned that the pandemic “might be associated with encephalitic Parkinson’s disease that was described after the Spanish flu,” said Anna Cervantes-Arslanian, a neurologist at Boston University School of Medicine.

But a study she led found that only 0.5% of people with severe Covid-19 had meningitis or encephalitis. About 10% had impaired brain function or structure, research finds published in April in the journal Investigations in intensive care.

Are new treatments being developed?

Researchers led by Chan are using MRI scans to understand the causes of Covid’s effects on memory, thinking speed and decision-making. He said his team would also test cognitive rehabilitation techniques used to treat memory problems after stroke, such as setting tasks to increase mental focus.

Other scientists are investigating the possibility of new pharmaceutical treatments. Studies are underway to examine the changes in tissues and organs that cause or are caused by Covid-19 in order to test treatments.

Josephson said it was unclear whether the brain impacts were caused by an overactive immune system or the other way around. However, he said that if this could not be established quickly, it might be better to test drugs that modify the immune system, either by lowering it or by strengthening it, to help those whose symptoms suggest a deficiency. cognitive.

But disentangling the impact of Covid from other elements that are only indirectly associated with the virus remains an ongoing puzzle for researchers.

“The effects of Covid on the brain are real – some people have very discrete, defined conditions and some have things that we don’t understand as well,” Spudich said. “The problem is that there are so many other social factors, pressures, stresses associated with these pandemic times that it definitely clouds the waters.”

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