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Harvard study explains how COVID-19 causes loss of smell

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How Covid-19 causes loss of smell in some patients

It's important to consider that the patients included in this study had one of the most severe presentations of this disease, ARDS, which is associated with the cytokine storm which occurs in rare, but often fatal, cases of COVID -19. A new research has now revealed the reason behind this loss of smell and taste. Covid-19 patients, for example, typically recover their sense of smell within a couple of weeks, whereas the condition brought about by other viral infections are known to damage olfactory sensory neurons to the extent that it can take months for people to recover their sense of smell.

The researchers set out to better understand how smell is altered in coronavirus patients by pinpointing the cell types most vulnerable to SARS-CoV-2, the virus that causes COVID-19.

Viruses from the coronavirus lineage responsible for COVID-19 have been circulating in bats for decades, long before the virus started infecting people past year, a new study suggests. COVID-19 patients are 27 times more likely to have smell loss but are only around 2.2 to 2.6 times more likely to have fever, cough or respiratory difficulty, compared to patients without COVID-19. ACE2 are the receptors (or doors) that allow the virus to enter the body's cells.

However, a new study by the Harvard University has revealed that the enzyme ACE2 is instead found in cells providing "metabolic and structural support" to those olfactory sensory neurons and to some stem and blood vessel cells.

Experts from Harvard Medical School in the United States have identified the cell types used for smelling which are most vulnerable to infection by SARS-CoV-2, the virus that causes COVID-19.

"We found evidence of ongoing inflammation within the heart muscle, as well as of the heart's lining in a considerable majority of patients", said Puntmann, a consultant physician, cardiologist and clinical pharmacologist at University Hospital Frankfurt in Germany.

This implies that in most cases, the virus is unlikely to permanently damage olfactory neural circuits and lead to persistent anosmia, Datta said.

"And so we think, on the whole, this is good news, and suggests that people who lose their sense of smell, for the most part, are going to go on to get their sense of smell back", Datta said.

"Anosmia seems like a curious phenomenon, but it can be devastating for the small fraction of people in whom it's persistent", Datta said. "We need more data and a better understanding of the underlying mechanisms to confirm this conclusion", he said.

"It can have serious psychological effects and may be a significant public health issue if we have an increasing population with permanent loss of smell". To show their new model's utility for testing vaccine candidates, the researchers immunized female mice with two doses of a recombinant subunit vaccine candidate and then infected them with the adapted virus.

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