Coronavirus | Researchers find cells that may explain loss of smell in COVID-19 patients

Virus may be inflicting an indirect attack on the olfactory sensory cells, says study

Updated - August 30, 2020 06:22 pm IST

Published - April 07, 2020 08:37 pm IST - NEW DELHI

A man wearing a face mask sits beside pigeons during a lockdown aimed at preventing the spread of new coronavirus in Hyderabad, Telangana on April 7, 2020.

A man wearing a face mask sits beside pigeons during a lockdown aimed at preventing the spread of new coronavirus in Hyderabad, Telangana on April 7, 2020.

Can a loss of smell be an early warning for a COVID-19 infection? Multiple reports have surfaced, primarily from Europe and the United States, from physicians and ear, nose and throat specialists, of COVID-19 patients complaining of an inability to smell — or anosmia. However, it is not clear whether neurons in the brain that are responsible for recognising various odours are damaged, or whether other cells may be involved.

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Not directly

Researchers at Delhi’s Indrapastha Institute of Information Technology report in the study that is still being peer-reviewed but available as a public preprint, that it is not neurons but a class of cells in the upper regions of the nasal cavity that may be involved: these are called sustentacular cells and horizontal basal cells. Crucially, both are not directly involved in helping us smell, but nourish and support the cells that help us do, and so the virus may be inflicting an indirect attack on the olfactory sensory cells.

While research on this aspect of the disease is emerging, studies say the loss of smell is different from diminished smell or a lack of perceiving flavour in food when one is afflicted with a cold or stuffy nose.

Researchers Krishan Gupta, Sanjay Kumar Mohanty, Siddhant Kalra, Aayushi Mittal, Tripti Mishra, Jatin Ahuja, Debarka Sengupta and Gaurav Ahuja inferred this by bio-informatics tools and estimating the presence of a key enzyme — called ACE 2 (Angiotensin Converting Enzyme) — in these olfactory cells. The coronavirus has spike proteins that bind to ACE 2 receptors on human cells and the enzyme’s presence is a proxy to revealing the signature of the virus in the body’s cells.

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Clinical symptoms

Research so far suggests that it take between 5-14 days for clinical symptoms of the virus — dry cough, laboured breathing and fever — to show and unless this manifested, those infected are likely to continue socialising and spreading the virus.

The authors did not offer comment on their work because it has not yet been published in a scientific journal. Samir Brahmachari, a molecular biologist and former Director-General of the Council for Scientific and Industrial Research (CSIR), who was familiar with the study, said that the findings pointed to a potential diagnostic.

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“Because the loss of smell surfaces much earlier, anyone who does not feel sick but registers a significant inability to smell could self-isolate and cease infecting others. A questionnaire could be used via an app, for users to check or report these systems to a doctor,” he told The Hindu .

An analysis by a team at King's College London showed that 59% of COVID-19 positive patients reported a loss of smell and taste, compared with only 18% of those who tested negative for the disease. These results were much stronger in predicting a positive COVID-19 diagnosis than self-reported fever, he added.

‘Potential application’

“Multiple clinicians have highlighted the abrupt loss of smell in a large number of SARS-CoV-2 [coronavirus] infected individuals, particularly from Britain, the U.S., France, South Korea, China, Germany and Iran, therefore, collectively reinforce its potential application as the first line of diagnostics in the patients possessing SARS-CoV-2 hallmark symptoms,” the report adds.

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