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COVID-19 still kills millions today despite the availability of vaccines. After the initial infection has cleared, many patients have persistent symptoms, sometimes lasting up to months or years. Different studies have revealed that SARS-CoV-2 infection causes lesions in certain organs, such as the lungs or the heart. A more recent study also suggests that the virus can lead to brain damage and significant loss of gray matter, even in mild cases. Although the study involved a large number of subjects, many questions remain unanswered. Further investigation will therefore be necessary.
Led by a group of researchers from the University of Oxford, the study is believed to be the first to involve subjects who underwent brain scans before and months after infection. These include a cerebral scanner to measure the density of dopamine transporters, the molecule essential for the interneuron transmission of information. Logically, the decrease in density of these transporters therefore indicates neuronal structural failures.
The English researchers thus brought together 785 test subjects from the UK Biobank medical database. Each of these people had two brain scans about three years apart. Between each scan, 401 of the participants tested positive for Covid between March and April 2021, while the other 384 uninfected formed a control group. Cognitive tests were also submitted to all participants, whose age groups (51 to 81 years) and medical records were more or less similar.
Infected participants, scanned an average of 141 days after infection, showed 0.2-2% greater loss of gray matter than healthy subjects. However, in normal times and taking into account the age group of the participants, the annual loss of gray matter due to aging would be between 0.2 and 0.3%. Additionally, Covid patients also lost more overall brain volume and showed more tissue damage in multiple areas of the brain.
” Although the infection was mild for 96% of our participants, we found greater loss of gray matter volume and greater tissue damage in infected participants, on average 4.5 months after infection. “Says Gwenaëlle Douaud in a press release, lead author of the study and professor in the department of clinical neurosciences at the University of Oxford.
It is therefore important to note that these losses and lesions were observed even in subjects who presented only mild forms of the disease. And although only 15 test participants developed a severe form, the study suggests that this slice of patients had more severe brain sequelae. All infected patients also showed a greater decrease in cognitive abilities for complex tasks, which would be partly due to brain abnormalities. And even if these negative impacts were more marked in older patients, the availability of pre-infection imaging data reduces the risks that pre-existing factors will be misinterpreted as effects of the disease.
Even if the results are more or less revealing, the study, published in Naturemust be investigated in order to draw conclusions. ” A key question for future brain imaging studies is to see if this brain tissue damage resolves in the longer term. raises Douaud. The study is indeed likely to arouse some fear in patients, because it is not yet known how far these sequelae will go and how they will affect their daily lives. Also, post-infection scans were only done once. It is therefore not known how the lesions evolve. Nevertheless, ” the brain is plastic, which means it can reorganize and heal to some degree, even in older people “, assures the expert in her statement to The Guardian.
And although the recovered patients showed a greater deficit than normal on cognitive tests, Douad and his team point out that these tests were rudimentary. These included exercises related to attention and the ability to perform complex tasks. In addition, the tests specifically soliciting the most atrophied areas were apparently not sufficiently advanced, according to other experts interviewed by the New York Times.
Some of the greatest loss of gray matter is in areas related to smell, which are also involved in memory and other functions. However, Covid patients obtained similar results in related tests as healthy people, which suggests that the virus seems to affect concentration and the speed of information processing above all.
Although almost all areas of the brain are versatile, gray matter losses have also been detected in areas of the brain that are not involved in smell. The study authors speculate that this could be due to inflammation or sensory deprivation related to anosmia. Moreover, the study was only carried out on people of a certain age (51 to 81 years). The results therefore cannot fully explain “brain fog”, an often reported symptom, in younger patients. Further research is therefore needed for the study to be truly conclusive.