Covid-19, primarily a respiratory disease, could also strike the brain. Suspected since the start of the pandemic, the neurological effects of the disease now seem to have been proven by recent work, including in the case of mild forms.
A deleterious impact
We observe “a deleterious impact linked to SARS-Cov-2”, the virus at the origin of Covid-19, in the brains of people infected months earlier, according to a study published this Monday in the journal Nature. This work is important because it provides the strongest evidence to date that Covid can have long-term consequences on the brain, in particular the “gray matter” which includes neurons.
A not so recent observation
The idea is not new. It has been almost mentioned since the start of the pandemic in early 2020, many doctors having then observed neurological disorders in patients with Covid. Since then, many studies have gone in this direction. Some have shown that the proportion of cognitive disorders was higher in former Covid patients. Others have directly observed the brains of patients and found abnormalities there.
A more specific study
However, the first category of studies cannot demonstrate a direct causal mechanism. As for the second work, they were carried out on a small number of patients, generally suffering from severe forms. In some cases, these were even autopsies of deceased patients. The study published on Monday is much more conclusive. She studies a relatively large number of people – several hundred – and is interested in the state of their brains, depending on whether or not they have been affected by Covid-19.
What are the results ? Former Covid-19 patients have generally seen their brains shrink. On average, an infection with the virus results, several months later, in a loss or lesion of 0.2% to 2% of brain tissue in addition to what is observed in healthy people. Should we therefore panic and imagine a virus that systematically rises within the brain and irreparably attacks the neurons? Far from it, and the study does not make it possible to conclude either on the mechanisms of these cerebral attacks or on their irreversibility.
The sense of smell at the center
The researchers make a crucial observation, but which can be interpreted in several ways: after a Covid-19 infection, the areas of the brain most affected are those related to the perception of odors. However, the loss of smell is one of the most common symptoms of Covid-19. This is likely because the olfactory nerve is being attacked by the virus or, as a recent study suggests, by the immune response to infection.
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