2023-11-08 03:04:43
Symptoms associated with COVID-19 have evolved since the start of the pandemic, particularly with the appearance of variants of the virus. Initially, anosmia, loss of sense of smell, was considered one of the characteristic symptoms of SARS-CoV-2 infection. With the emergence of the Omicron/BA.1 variant, anosmia has become less common. This variation in symptoms led researchers to wonder whether the virus’s ability to affect the nervous system was at play.
To answer this complex question, researchers from the Pasteur Institute and Paris Cité University used an animal model, golden hamsters, to study the ability of different variants of SARS-CoV-2 to infect the central nervous system. . They selected several strains of the virus, including the original Wuhan strain, as well as the Gamma, Delta, and Omicron/BA.1 variants, to conduct their experiments.
Anosmia and neuronal infection: two distinct phenomena
The study results revealed that all of these SARS-CoV-2 variants have the ability to invade the central nervous system and infect the olfactory bulbs, brain structures essential for processing olfactory information. Olfactory bulb infection is not specific to a particular variant nor linked to a specific clinical symptom, such as anosmia.
Researchers identified an ORF7ab genetic sequence in the Wuhan strain, linked to anosmia. When this genetic sequence is absent, as is the case for some variants, the loss of smell in infected animals is reduced. However, the infection of neurons persists.
These results suggest that anosmia and neuronal infection are two distinct phenomena and may occur independently. Thus, even an asymptomatic infection can be characterized by the spread of the virus in the nervous system.
The mechanism of neuronal infection
To understand how SARS-CoV-2 manages to infect the brain, researchers used human neurons in culture in vitro. Their observation revealed that the SARS-CoV-2 variants studied, including the ancestral Wuhan variant, are able to move back and forth along the axons of neurons, effectively exploiting the physiological mechanisms of the latter to spread .
Long-term health implications
It remains to be determined whether the virus can persist in the brain beyond the acute phase of infection. This could have implications for persistent symptoms of “long Covid”, such as anxiety, depression and brain fog, described in some patients.
Sources :
Neuroinvasion and anosmia are independent phenomena upon infection with SARS-CoV-2 and its variants, Nature Communications, 26 juillet 2023
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