Chapter 1: The Impact of COVID-19 on Olfactory Function

Recent research involving more than 2,500 patients across Europe indicates that approximately 85.9% of individuals experiencing mild COVID-19 symptoms suffered from a diminished sense of smell. On average, this condition persisted for about three weeks, although for a quarter of the participants, the loss of olfaction lasted for over two months. The study, which appeared in the Journal of Internal Medicine, was led by Jerome R. Lechien from Paris Saclay University. It aimed to explore the correlation between the extent of olfactory dysfunction and the severity of COVID-19 symptoms. Notably, only about five percent of those with moderate cases and seven percent of critical cases reported a loss of smell.

“Olfactory dysfunction is more common in mild cases of COVID-19 compared to moderate or severe cases, with 95% of patients regaining their sense of smell within six months post-infection,” remarked Lechien.

The temporary loss of smell, referred to as anosmia, has been recognized by experts as a more reliable early symptom of infection than typical indicators like fever or cough.

Section 1.1: Mechanisms Behind Olfactory Dysfunction

So, what leads to the disruption of smell in COVID-19 patients? Initially, researchers theorized that the virus might be affecting the olfactory sensory neurons responsible for detecting and sending chemical signals from the nose to the brain. However, subsequent studies have shown that these neurons do not possess the ACE2 receptor protein, which the coronavirus uses to enter human cells.

Instead, it appears that SARS-CoV-2 affects the support structures of olfactory neurons—specifically, the stem cells and the cells lining the blood vessels in the nasal cavity.

“Our research suggests that the novel coronavirus alters the sense of smell not by directly infecting the neurons but by impacting the function of the supportive cells,” explained Sandeep Robert Datta, a scientist at Harvard Medical School.

Subsection 1.1.1: Positive Outlook on Recovery

On a hopeful note, anosmia related to COVID-19 is generally a temporary issue. “This is encouraging news, as it appears that once the infection subsides, olfactory neurons do not need to be entirely replaced or rebuilt,” Datta added. “However, further research and a deeper understanding of the mechanisms involved are essential to fully validate this finding.”

Sources: Harvard Medical School, Journal of Internal Medicine, EurekAlert.