You may know someone who, after covid-19, tends to forget certain things, suffers from headaches or has not yet fully recovered their sense of smell. These symptoms are included within the phenomenon of brain fog in which a part of the population has been plunged as a result of the pandemic. If it lasts over time, its effects can end up being harmful.
The nervous system suffers: smell, insomnia…
Despite the fact that the SARS-CoV-2 coronavirus infection mainly affects the respiratory system, most patients suffering from covid-19 show neurological symptoms such as loss of smell, headache, sleep disturbance and memory deficit.
On the other hand, several studies indicate that patients with neurodegenerative disorders such as Alzheimer disease are more likely to suffer from the disease more severely.
Taken together, these signs are a clear indicator that the virus is also affecting the nervous system. That is why it is increasingly important to study what the long-term effects and sequelae of this disease in the brain may be.
Trojan horse and neural highways
But how does SARS-CoV-2 get to the brain? Reaching this organ directly is not easy because it is surrounded by a true wall of blood vessels known as the blood-brain barrier. Despite this, SARS-CoV-2 is capable of circumventing this protection by different mechanisms.
For starters, it can send signals that cause the blood-brain barrier to change. In addition, it is capable of entering our own cells and using them as a vehicle to sneak into the brain. The strategy is a true Trojan horse, since the pathogen masquerades as something recognizable by our body to be able to cross barriers that, otherwise, would be insurmountable.
Finally, SARS-CoV-2 can also travel through neurons, which are distributed throughout our body forming a network of nerves. The virus is capable of reaching one of the neuronal extensions and moving through them as if they were a highway that ends in the brain. Precisely in the nose, the place of entry and infection of the virus, is the olfactory nerve, which could be a direct entry route to the brain.
Indirect affection to the brain that can be very dangerous
The covid-19 virus can also affect the brain indirectly. It is what happens when our immune system reacts to the presence of foreign microorganisms releasing molecules called cytokines. These molecules act as a call signal and induce an inflammatory reaction in the tissue where they are located.
This response, in principle, is beneficial, because it manages to attract the different cells of the army that will fight against the infection. However, if it lasts over time, a state of chronic inflammation that can be very dangerous and compromise the functions of different organs, including the brain.
Precisely in individuals with diseases associated with aging, this state of chronic inflammation is prevalent. Specifically, Alzheimer’s patients are known to suffer from neuroinflammation. This means that the immune system of your brain is active continuously and over time, causing damage to structures and greater neuronal death and neurodegeneration.
Can covid-19 cause Alzheimer’s?
Now, then, what is the link between neurodegenerative processes and covid-19? The relationship between viral infections and neurodegeneration It has been known for a long time, and as can be deduced, the point at which both pathologies converge is inflammation.
In the case of SARS-CoV-2, its ability to induce a generalized inflammatory state in our body may facilitate the progression of neurodegenerative diseases. Also, the cytokine storm generated as an exacerbated defense mechanism is capable of deregulating physiological parameters. For example, the number of oxidizing molecules increases in neurons due to an imbalance in iron levels that makes the damage worse. This leads to more neuronal death and greater neurodegeneration.
In favor of this theory, some studies show that patients with covid-19 present neuronal losses in the same regions of the brain where damage occurs in Alzheimer’s disease. In addition, biomarkers of neurodegeneration are increased in many patients hospitalized for covid-19.
It is clear that SARS-CoV-2 has a more profound impact on the brain of patients than initially thought. A better understanding of the interaction of this virus with the central nervous system could prevent the development of neurodegenerative diseases such as Alzheimer’s, also worldwide and, for the time being, without a cure.
Juana Andreo Lopez, FPI researcher. Researcher at the Center for Network Biomedical Research in Neurodegenerative Diseases (CIBERNED) and at the Malaga Biomedical Research Institute (IBIMA), University of Malaga; David Baglietto Vargas, Senior Distinguished Researcher Beatriz Galindo. Researcher at the Center for Network Biomedical Research in Neurodegenerative Diseases (CIBERNED) and at the Malaga Biomedical Research Institute (IBIMA), University of Malaga and Miriam Bettinetti LuquePredoctoral researcher at the Center for Network Biomedical Research in Neurodegenerative Diseases (CIBERNED) and the Malaga Biomedical Research Institute (IBIMA), University of Malaga.
This article was originally published on The Conversation.
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