Some of the coronavirus patients are losing the sense of smell, is it a new symptom?

Covid-19 is caused by the SARS-CoV-2 virus that hijacks two human proteins to invade cells

We are learning new things every day about coronavirus. Scientists have found one new symptom of COVID-19. World Health Organization has recognized ‘the loss of smell and taste’ as the new symptom in novel coronavirus patients. Health authorities of various countries including the US also agree on the new symptom. A recent study on mice suggests why the loss of smell is being witnessed in many coronavirus patients. The findings have been reported in the American Chemical Society’s journal ACS Chemical Neuroscience.

Covid-19 is caused by the SARS-CoV-2 virus that hijacks two human proteins to invade cells. One is TMPRSS2 which virus uses to replicate its genetic material and the other is ACE2 receptor on the cell surface which opens the door for the virus.

The research that was done on mice found out that these two proteins are produced by certain cells of the nasal cavity that contribute to the mice’s sense of smell (which means ours too). The ‘sustentacular cells’ had the highest level of SARS-CoV 2 receptors which are found in the olfactory epithelium. These sustentacular cells help transfer odours from the air to neurons.

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Researchers found out that mature olfactory neurons do not express ACE2, while the sustentacular cells express ACE2.

After the research, researchers said that the sense of smell in COVID-19 patients is vanishing because the sustentacular cells assist neurons in sending odours after processing binding proteins.

Key Finding: Sense of smell depends on age

The study found out that larger amounts of the proteins are made in older mice than the younger mice. More entry proteins a host cell has easier it would be for the virus to bind, enter and then infect the cell. Older people are more likely to lose their sense of smell than the younger ones because of the presence of high level of entry proteins in the nasal epithelium in the elderly.

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Is mice experiment valid for humans?

It is believed that the entry proteins have similar expression patterns in all the mammal species. This makes mice a suitable model for the human condition.

What do Indian Health officials believe?

We tried to reach Health official from our side to know how they are seeing the sense of smell as the new COVID-19 symptom. Dr Vivek Kumar, Medical Officer at Government Doon Medical College and Hospital Dehradun, Uttarakhand said that he hasn’t received any guidelines from the Health Ministry of India or from WHO regarding the new symptom.

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