Covid-19 affects central nervous system

A recent study suggests that the coronavirus that causes Covid-19 could infect the central nervous system like other coronaviruses. Is this related to the cases of anosmia reported by doctors among those infected?

Coronavirus versus Flu: their differences, their similarities At the very beginning of the epidemic, Covid-19 was compared to the flu, with some calling it "the flu." However, it is not. Since then, scientists around the world have shared their observations, drawing in particular on those of the Chinese.

The more than 340,000 people suffering from Covid-19 complain abouta triad of symptoms typical infection: fever, cough and difficulty breathing. But some also complain of rarer ailments like headaches, nausea and vomiting. These symptoms are usually associated with a neurological condition. Do they witness the invasion by le coronavirus responsible for Covid-19 of central nervous system ?

Yan-Chao Li, researcher at the University of Jilin in China, discusses this hypothesis in an article in The Journal of Medical Virology February 27, 2020 (and corrected on February 17, 2020 March 2020).

The neurotropism of coronaviruses

even though coronavirus be virus essentially respiratory, several researches state their capacity to also infect the central nervous system and to cause neurological disorders.

The neurotropism of coronaviruses is known, in particular for the beta-coronavirus family to which the SARS-CoV, MERS-CoV and the SARS-CoV-2 which is currently spreading. The neurons of the central nervous system are often the cell targeted by the virus which causes their degeneration. The HEV 67N, a porcine coronavirus, is the first to be identified in the brain pigs. 91% ofhomology between this strain and a human beta-coronavirus, HCoV-OC43, responsible for the common cold.

The path taken by coronaviruses is not known with precision, but it would seem that viruses use synaptic pathways to pass from the cardiorespiratory center to the spinal cord. Mechanoreceptors and chemoreceptors of peripheral nerve endings in the lower respiratory tract are thought to be the door entry point through which the virus reaches the central nervous system.

The neurological symptoms of Covid-19 affect only a minority of people: 8% suffer from headaches and 1% from nausea and vomiting. On the other hand, a study of 240 patients with Covid-19 describes neurological manifestations such as loss of consciousness and acute cerebrovascular disorders in 88% of the severe cases studied.

An explanation for anosmia?

In recent days, doctors report that a minority of patients complain ofanosmia. It is a loss ofsmell often associated with loss of taste (ageusia). Anosmia can be caused by impaired nerve olfactory, the first cranial nerve that connects the nasal cavity to the olfactory bulb located at the base of the brain. When the damage is neurological, the anosmia can be constant.

In the case of the Covid-19, does anosmia witness the invasion of the central nervous system virus?

Not necessarily. Anosmia is a very common symptom in respiratory diseases such as rhinitis or colds. In this case, it is not the olfactory nerve that is involved but a lack of permeability of the nasal cavities, the nose clogged up, which prevents odors from reaching the olfactory receptors. The anosmia is then generally transient.

The virus has not yet been observed in the brainstem patients, as was the case during a Review carried out in mice with MERS-CoV and SARS-CoV. The neurotropism of SARS-CoV-2, responsible for Covid-19, is for the moment only an assumption and scientific data are lacking to attest it with certainty. But being aware of this possibility could have an impact on care and treatment, which are always symptomatic of the disease.

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