Is covid-19 a brain disease?
Recent findings show that up to more than two-thirds of patients with covid-19 had neurological complications, and many develop a mental health problem within 90 days of contracting the virus. This has led the European Brain Council to consider covid-19 a brain disease.
Quite early after the recognition of the severe acute respiratory syndrome (SARS), the coronavirus SARS-CoV-2 was found responsible for a pandemic with many signs of the brain being affected (Mao L et al. 2020). In addition to the classical signs of respiratory disease, covid-19 may also affect the nervous system in several ways:
a) central nervous system; dizziness, headache, impaired consciousness, acute cerebrovascular disease, ataxia, and seizure
b) peripheral nervous system; taste impairment, smell impairment, vision impairment, and nerve pain
c) skeletal muscular interaction with the nervous system; paralyses, weakness
There are convincing data showing that the central nervous system is strongly and markedly affected during covid-19 infections. For example, several reports suggest that fatigue and other general psychiatric conditions like depressions and anxiety are quite common; approximately 20 to 70 % of infected patients have symptoms/signs of the brain being affected during covid-19 infections (The European Brain Council 2021). The most commonly reported long-term health consequences include fatigue, headaches, difficulty breathing, anxiety and depression, chest pains, joint pains and dizziness (Norwegian Institute of Public Health 2020).
Moreover, there are indications that viral infections in general, and covid-19 in particular, may be important for development of neurodegenerative diseases like dementia, Parkinson’s disease, amyotrophic lateral sclerosis, and multiple sclerosis (Karim S et al. 2014).
What is the link between the covid-19 infection and the brain?
We know that the SARS-CoV-2 virus infects host cells by using a specific type of receptor named the angiotensin converting enzyme (ACE2) receptor, observed in several organs including the lung, heart, kidney, and intestine. A receptor is a protein that can bind another protein with very high specificity. Thus, a receptor allows very specific signals or transport to take place.
ACE2 receptors are also found on endothelial cells (covering the inside of small vessels supplying the brain) and on vascular smooth muscle cells (regulating the tension in the small vessels) in the brain (Ferrario CM et al. 2005; Hamming I et al. 2004).
The ACE2 receptors are also present on the surface of some cell types such as in the olfactory epithelium (cells covering the “smell” nerve) in the nose. The path from the olfactory nerve to the inside of the brain is very short, and this is a likely pathway for infecting the brain with SARS-CoV-2 virus (Jakhmola S et al. 2020).
It has been shown that patients dying from covid-19 infections have damaged small vessels in several parts of the brain, most likely due to infections via cells covering the inside of small vesicles in the brain (Lee M-H et al. 2021).
These findings may explain why many patients have so many symptoms of covid-19 infections affecting the central nervous system, and that we in Lifebrain also believe it is correct to classify the pandemic as a brain disease.
Mao L et al. Neurologic manifestations of hospitalized patients with coronavirus disease 2019 in Wuhan, China. JAMA Neurol 2020, 77, 683-90
European Brain Council (2021) “EBC statement: The impact of covid-19 on brain health. January 2021”: retrieved February 15, 2021
Karim S et al. The role of viruses in neurodegenerative and neurobehavioral diseases. CNS Neurol Disord Drug Targets. 2014, 13, 1213–23.
Ferrario CM et al. Effect of angiotensin-converting enzyme inhibition and angiotensin II receptor blockers on cardiac angiotensin-converting enzyme 2. Circulation 2005, 111, 2605–10
Hamming I et al. Tissue distribution of ACE2 protein, the functional receptor for SARS coronavirus. A first step in understanding SARS pathogenesis. J Pathol. 2004, 203, 631–7.
Jakhmola S et al. SARS-CoV-2, an underestimated pathogen of the nervous system. SN Compr Clin Med 2020,2, 2137–46
Lee M-H et al. Microvascular injury in the brains of patients with Covid-19. N Engl J Med 2021, 384, 481-3
Norwegian Institute of Public Health (2020) Facts about the SARS-CoV-2 virus and COVID-19 disease, retrieved February 16th, 2021.