Compiled by Zakiyah Ebrahim
The |
Health24
July 30, 2020, 11:45
- Anosmia is a common symptom among people with mild Covid-19.
- New research has discovered why the virus can cause a temporary loss of smell.
- However, more observation is needed to confirm the team’s findings.
Evidence of loss of smell (anosmia) as a symptom of Covid-19 first emerged in late February 2020. In April, the symptom was officially added to the Center for Control and Prevention’s list of Covid-19 symptoms. of Diseases. At that stage, however, very little was known about how and why the virus affects an infected person’s sense of smell.
Previous studies suggested that sensory neurons (which detect and transmit smell to the brain) were vulnerable cell types, but new research indicates otherwise. An international team of researchers led by neuroscientists at Harvard Medical School (HMS) recently identified the types of olfactory cells that are most vulnerable to infection with SARS-CoV-2 (the virus that causes Covid-19).
The results were published in Scientific advances.
Mainly temporary anosmia in cases of Covid-19
Loss of smell has been shown to be one of the most reliable neurological indicators of early infection with the new coronavirus. A previous study published in the journal. Clinical infectious diseases They found that between 25% and 50% of patients report anosmia and ageusia (loss of taste) as the first symptoms of Covid-19.
A closer look at global patient records found that this symptom is just as likely to predict a positive PCR for SARS-CoV-2 (polymerase chain reaction) as fever, cough, or nasal congestion. According to the study press release, emerging data indicates that most Covid-19 patients experience a certain level of anosmia, but that it is often only temporary.
Some studies have also hinted that anosmia in patients with Covid-19 differs from anosmia caused by other viral infections, including other coronaviruses. Covid-19 patients, for example, generally regain their sense of smell within a couple of weeks, while the condition caused by other viral infections damages olfactory sensory neurons to the extent that it can take months for people to regain consciousness. . Of smell
Why are olfactory sensory neurons vulnerable?
According to the researchers’ results, olfactory sensory neurons do not express the gene encoding the ACE2 receptor protein. ACE2s are the receptors (or gates) that allow the virus to enter cells in the body.
Instead, it is olfactory support cells, not neurons, that are vulnerable to SARS-CoV-2 infection. The discovery that infection of non-neuronal cell types is potentially responsible for anosmia in Covid-19 patients, therefore, is helping scientists better understand the progression of the disease.
Their data suggests that a temporary loss of support cell function in the olfactory epithelium (tissue in the nasal cavity involved in smell), which indirectly causes changes in olfactory sensory neurons, is what can cause anosmia related to Covid-19.
“Our findings indicate that the new coronavirus changes the sense of smell in patients not by directly infecting neurons but by affecting the function of supporting cells,” said study lead author Sandeep Robert Datta, associate professor of neurobiology at the Blavatnik Institute from HMS, adding:
“However, we still don’t fully understand what those changes are. Sustain cells have been largely ignored, and we seem to need to pay attention to them, similar to how we have a growing appreciation of the critical role glial cells play in the brain. . “
Anosmia and mental health conditions
Datta explained that the results imply that in most cases the virus is unlikely to permanently damage a patient’s olfactory neural circuits and cause persistent anosmia, adding that the condition is often associated with mental and social health problems, like depression and anxiety. . This 2016 study, for example, found that in people with anosmia, symptoms of depression worsened with the severity of olfactory dysfunction.
“I think that is good news, because once the infection clears up, olfactory neurons don’t seem to need to be replaced or rebuilt from scratch. But we need more data and a better understanding of the underlying mechanisms to confirm this conclusion.”
The team now hopes their results can lead to treatments for the condition, as well as the development of improved odor-based diagnoses for Covid-19.
“Anosmia seems like a curious phenomenon, but it can be devastating for the small fraction of people in whom it is persistent. It can have serious psychological consequences and could be a major public health problem if we have a growing population with permanent loss of smell, Datta said.
Other observations would be more convincing.
While the study results are making progress in understanding the link between SARS-CoV-2 and anosmia, former HMS professor William A. Haseltine wrote in Forbes that the results are based on indirect observations:
“Biopsies of infected tissue showing that the virus does indeed infect and replicate in the supporting cells would be more helpful. An observation of both damage and tissue recovery would be even more compelling,” he wrote.
