Sedaghat says researchers have long thought that the olfactory tract may be the primary way that coronaviruses enter the central nervous system. There was evidence of this with SARS, or severe acute respiratory syndrome, a viral illness that first emerged in China in November 2002 and spread through international travel to 29 countries. Studies using mouse models of that virus have shown that the olfactory tract, or the pathway for communication of odors from the nose to the brain, was a gateway into the central nervous system and infection of the brain.
“These symptoms of psychological distress, such as depressed mood and anxiety are central nervous system symptoms if they are associated only with how diminished is your sense of smell,” says Sedaghat. “This may indicate that the virus is infecting olfactory neurons, decreasing the sense of smell, and then using the olfactory tract to enter the central nervous symptom.”
Infrequent but severe central nervous system symptoms of COVID-19 such as seizures or altered mental status have been described, but depressed mood and anxiety may be the considerably more common but milder central nervous symptom of COVID-19, explains Sedaghat.
“There may be more central nervous system penetration of the virus than we think based on the prevalence of olfaction-associated depressed mood and anxiety and this really opens up doors for future investigations to look at how the virus may interact with the central nervous system,” says Sedaghat.
For the cross-sectional telephone questionnaire study: The two-item Patient Health Question (PHQ-2) and the two-item Generalized Anxiety Disorder questionnaire (GAD-2) were used to measure depressed mood and anxiety level, respectively during COVID-19 and for participants’ baseline pre-COVID-19 state.
Funding for the study came from Kantonsspital Aarau, Aarau, Switzerland.
Featured image of man placing a disposal mask on his face is courtesy of Unsplash.