Apart from affecting the respiratory system, the SARS-CoV-2 virus causes several neurological disorders as it damages the brain.
SARS stands for Severe Acute Respiratory Syndrome as the SARS-CoV-2 virus primarily infects the respiratory system. The Spike (S) protein of the SARS-CoV-2 virus interacts with the ACE-2 (angiotensin-converting enzyme) receptors that are abundantly found in the respiratory region. After entering the cell, the virus can cause severe inflammation and damage to the respiratory tissues. The ACE-2 receptors are also found on the surface of many gastrointestinal tissues, which is why diarrhoea is a common symptom of a SARS-CoV-2 infection.
The SARS-CoV-2 virus has the added danger of affecting the Central Nervous System, specifically the brain. Despite the incidence of neurological dysfunction being higher in the hospitalised COVID-19 patients, it was also seen in cases of mild and asymptomatic infection. Anosmia (loss of smell) and ageusia (loss of taste) which are some of the primary symptoms of a SARS-CoV-2 infection indicates that the virus attacks the nervous systems. Patients who have contracted a COVID-19 infection have neurological discrepancies in the form of brain fog, inattention, agitation, confusion, disorientation, depression, dementia, stroke, and in very extreme cases, encephalitis.
The brain is protected from pathogenic infections by the powerful blood-brain barrier. The nervous system also has a very low concentration of ACE-2 receptors making it difficult for the virus to directly impact the brain. So it baffled the scientists as to how this tiny virus was able to infect the brain as it was already so protected. Many researchers speculate that the virus affects the brain through the olfactory mucosa present in the nasal cavity (bordering the brain) since there is a loss of smell and taste.
The bright side is that scientists are able to uncover the mechanisms through which the virus affects the brain. One of the studies (not yet peer-reviewed) showed that after a COVID-19 infection there was the loss of grey matter in many areas of the cerebral cortex. This is the part of the brain associated with memory and perception, which could explain why people experience brain fog and trouble recollecting things after a COVID-19 infection. Another study states that the virus could somehow affect the star-shaped cells called astrocytes which are responsible for providing nutrition to the neurons. The virus could damage the gene expression rate of the astrocyte and this dysfunctioning of the neurons.
A possible explanation for the occurrence of strokes in people who have suffered from a COVID-19 infection is that the virus can reduce blood flow to the brain thus impairing the functions of neurons. Cells called pericytes surround the capillaries that supply blood to the brain. The virus affects the shape and functioning of the pericytes which constricts the capillaries thus reducing the blood flow to the brain. The same study even proposes considering drugs that treat high blood pressure for such kinds of strokes.
It is well known that any kind of virus infection can trigger an autoimmune response in the body and cause long term damage even after the viral infection has cleared out. The SARS-CoV-2 virus is capable of over activating the immune system to the extent that it attacks several of the body’s own tissues. If this overactivity is not controlled it can lead to long COVID. A study, conducted by scientists at the University of Freiburg found the presence of autoantibodies against the brain proteins in the cerebrospinal fluid of COVID-19 patients. These autoantibodies were triggered by the SARS-CoV-2 virus and caused severe damage and inflammation in the brain leading to encephalitis.
Patients who previously had suffered from MERS or SARS-CoV-1 infection also experienced memory impairment. These viruses are capable of damaging the protective myelin sheath and cause symptoms similar to that of multiple sclerosis. People who suffer from Alzheimer’s Disease or dementia are also more susceptible to contracting a severe COVID-19 infection.
The SARS-CoV-2 is certainly a peculiar and dangerous virus as it has wreaked havoc in extremely unpredictable ways. The only way to completely overcome the pandemic is by understanding the ways of the virus, formulating appropriate treatments and taking precautions such as vaccinations and maintaining social distance.