Persistent fatigue, lack of concentration, short-term memory holes, are often not just symptoms of stress, but can be persistent aftermath of Covid-19 disease. The so-called Long Covid (see the special) probably affects more than 10% of patients healed, a high percentage that has given the turbo to research in this sector. The latest studies, presented in an article on Nature, indicate that the physiological mechanisms and processes underlying enduring neurological symptoms may be multiple and in part new. Two recent and still to be published researches, in fact, indicate that particular cells, astrocytes and pericytes, important for the correct functioning of neurons, could be directly affected by the coronavirus. These are initial clues, obtained mainly in vitro, or in a test tube, therefore to be confirmed, which however provide first indications on how the coronavirus could move in the brain.
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Various evidence collected so far indicates that even if Sars-Cov-2 fails to penetrate the brain and hit it directly, it is still able to cause negative effects indirectly. The problem, in fact, is that the excessive response of the immune system activated against the pathogen – the same that is responsible for the lesions to many organs in patients with severe Covid – can also cause inflammation in the brain. “This is one of the possible mechanisms, but probably not the only one – he underlines Luca Battistini, scientific deputy director of the Santa Lucia Irccs Foundation in Rome and researcher in Neuroimmunology – with which Covid-19 affects some neuronal circuits, causing persistent and chronic disorders “, from tiredness to pains and muscle fatigue to mental fog, all of which vary in magnitude. “The widespread and shared idea – adds the expert, who is widely involved with his group in the study of neurological symptoms due to Covid – is that the mechanisms of action underlying these symptoms are multiple and still largely to be understood” .
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In some cases, for example, the hyperactivation of the immune system can lead even after some time (for this reason we always speak of Long Covid) to the sudden appearance of pathologies with a rapid course and with acute manifestations even very serious. “This is the case of the Guillain-Barré syndrome”, comments Battistini, an inflammatory disease of the peripheral nerves that in the worst situations can even lead to death. “This in some patients can occur weeks or even months after the Covid-19 infection. The risk is that, due to the pandemic, more and more episodes will occur, with the need to rethink the health management of these new emergencies”. With this in mind, the Santa Lucia group is studying these syndromes associated with Covid in a dedicated project.
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But today there is more. Recent evidence, still being published, indicates that the coronavirus could also directly attack nerve cells, damaging some structures. The possibility of the virus entering the brain is not that remote, according to experts. “This eventuality – remarked the neuroimmunologist, not involved in the research mentioned – cannot be excluded and the entry routes could be more than one. They range from the olfactory mucosa (which we know well is affected by the virus) up to an infiltration through the lymphatic vessels, whose access has been recently demonstrated by a work of an American colleague, Jonathan Kipnis “.
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The novelty of today’s studies lies in the identification of specific cells, astrocytes and pericytes, as possible direct targets of the coronavirus. Astrocytes are star-shaped cells – as the name implies – very abundant in the brain and which have various functions, including supplying nutrients to neurons. Pericytes are particular cells that line some blood vessels, important and widely studied to understand the behavior and regulation of the blood-brain barrier, the natural defense of the brain from external attacks.
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