Harvard Medical School researchers reveal they have discovered why some coronavirus patients lost their sense of smell. Doctors call the symptom "anosmia," and it is one of the earliest signs of coronavirus infection.
In most cases, COVID-19 symptoms appear five to six days on average after infection and several patients report losing their sense of smell usually after two to three days. Other early symptoms of the infection are cough that does not go away, and high fever.
Some studies say the loss of the sense of smell is a better way of confirming a coronavirus infection as compared to other well-known symptoms, such as cough and fever. During the early days of the pandemic, scientists were puzzled by exactly how certain COVID-19 patients lost some of their senses.
Scientists know that viral infection, such as sinus, common cold, or other upper respiratory tract infections, can cause smell loss. In many of these cases, the sense of smell returns as soon as the symptoms go away. For COVID-19, however, the smell loss pattern is different. Many patients report a sudden loss of smell and then a sudden full return to normal within several days to two weeks.
Researchers embarked on a mission to better understand how the infection affects the sense of smell in some patients. They did this by identifying the cell types they believe are very susceptible to SARS-CoV-2.
After analysing different datasets, scientists found that the virus attack cells supporting the olfactory sensory neurons. Situated in the nasal cavity, the neurons detect and transmit smell information to the central nervous system.
According to Sandeep Robert Datta, co-author of the study, their findings show that the novel coronavirus alters the sense of smell in some patients by upsetting the function of supporting cells. Datta is a Harvard Medical School neurobiology professor.
This means the virus does not cause lasting damage to the olfactory neural circuits, but only causes someone infected with the virus to temporarily lose their sense of smell. "I think it's good news, because once the infection clears, olfactory neurons don't appear to need to be replaced or rebuilt from scratch," Datta stated.
The co-author added that more research needs to be conducted to gather additional data and have a better understanding of the fundamental processes that cause the phenomenon in order to confirm their conclusions. Their research and findings were published on Friday, in Science Advances journal and has been peer-reviewed.