How does COVID affect the brain?
Scientists are increasingly concerned about the emergence of a syndrome called "long-term COVID", in which a large proportion of COVID-19 patients will experience long-term symptoms.
Studies have shown that about 5-24% of confirmed COVID cases still have symptoms for at least 3 to 4 months after infection.
People no longer believe that the long-term risk of COVID is directly related to age or the initial severity of COVID disease. Therefore, young people and people who initially have mild COVID may still experience long-term COVID symptoms.
Some long-term COVID symptoms start quickly and persist, while others appear after the initial infection has passed.
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Symptoms include extreme fatigue and persistent respiratory complications.
As neuroscientists, we are particularly concerned that many long-term COVID patients report difficulty concentrating and planning-known as "brain fog."
So how does COVID affect the brain? This is what we currently know.
How does the virus enter our brain?
There is evidence that respiratory viruses (including influenza) are related to brain dysfunction. In the record of the Spanish flu pandemic in 1918, there were numerous reports of dementia, cognitive decline, and difficulty with exercise and sleep.
Evidence from the SARS outbreak in 2002 and the MERS outbreak in 2012 shows that these infections cause depression, anxiety, memory difficulties, and fatigue in approximately 15-20% of survivors.
There is no conclusive evidence that the SARS-CoV-2 virus that causes COVID can penetrate the blood-brain barrier, which usually protects the brain from large and dangerous blood-borne molecules that enter the blood.
But some data suggests that it may “hitchhiking” into the brain through the nerve that connects our nose to the brain.
Researchers suspect that this is because in many infected adults, viral genetic material was found in the nose that initiates the smell process-which coincides with the loss of smell experienced by COVID patients.
How does COVID damage the brain?
These nasal sensory cells are connected to an area of the brain called the "limbic system", which is involved in emotions, learning, and memory.
In a British study published online as a preprint in June, researchers compared brain images taken by people before and after exposure to COVID. They showed that some parts of the limbic system were reduced in size compared to uninfected people. This may indicate a susceptibility to brain diseases in the future and may play a role in the appearance of long-term COVID symptoms.
COVID may also indirectly affect the brain. The virus can damage blood vessels and cause bleeding or blockage, which can lead to interruption of the blood, oxygen, or nutrient supply to the brain, especially in the areas responsible for solving the problem.
The virus also activates the immune system, and in some people, this triggers the production of toxic molecules, which reduces brain function.
Although research in this area is still emerging, the impact of COVID on the nerves that control intestinal function should also be considered. This may affect digestion and the health and composition of intestinal bacteria, which are known to affect brain function.
The virus may also impair the function of the pituitary gland. The pituitary gland, commonly referred to as the "master gland", regulates the production of hormones. This includes cortisol, which controls our response to stress. When cortisol is deficient, this may cause long-term fatigue.
This is a recognized phenomenon for patients who have been diagnosed with SARS. What is disturbing with COVID is that people’s symptoms persist for up to a year after infection.
Given the significant contribution of brain diseases to the global burden of disability, the potential long-term impact of COVID on public health is huge.
Regarding the long-term COVID, there are some major unresolved issues that need to be investigated, including how the disease occurred, what the possible risk factors are, the scope of the results, and the best way to treat it.
It is important that we begin to understand what causes the widespread changes in symptoms. This can be due to many factors, including the strain of the virus, the severity of the infection, the impact of pre-existing diseases, age and vaccination status, and even physical and psychological support provided from the beginning of the disease.
Although there are many questions about long-term COVID, one thing is certain: we need to continue to make every effort to prevent the escalation of COVID cases, including getting vaccinated as soon as you qualify.
