By CBS Baltimore Staff

BALTIMORE (WJZ) — Inflammation causing nerve damage, not COVID-19 itself, could be the reason for the loss of smell associated with COVID-19 infections, according to a newly released Johns Hopkins Medicine-led study.

Anosmia–loss of smell–is a frequent and sometimes long-term symptom associated with COVID-19 infections.

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The study’s lead author, Cheng-Ying Ho M.D., Ph.D., is an associate professor of pathology at the Johns Hopkins University School of Medicine. She wanted to find out why anosmia is common with COVID-19 but not other respiratory diseases.

“We decided to dig deeply into the mechanics of smell to see what actually occurs at the cellular level when SARS-CoV-2 invades the body,” Ho said.

The researchers collected and studied tissues from the olfactory bulb at the base of the brain — a region that transmits nerve impulses carrying information about odors — of 23 people who died from COVID-19 and a control group of 14 who died from other causes and who had no detectable COVID-19 virus at the time of their deaths.

The tissue was evaluated for any detectable SARS-CoV-2 particles, characteristics of the cells, blood vessels and neurons within them, and the number of axons present. Axons are the portions of neurons that transmit electrical impulses.

Of those 23 people who died from COVID-19, three were determined to have lost their sense of smell, four had diminished ability to smell and two had loss of both smell and taste. None of the 14 patients in the control group had lost either smell or taste.

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“When we compared the tissues from patients without COVID-19 with those from persons who had been infected with SARS-CoV-2 — especially the ones with diminished or complete loss of smell — we found that the group with COVID showed more severe vascular injury and far fewer axons in the olfactory bulb,” Ho said.

That result didn’t change when researchers controlled for age, suggesting that the damage was linked to COVID-19 infection, Ho said.

But there’s more. While the virus could be linked to the damage, the study said SARS-CoV-2 particles were not found in the olfactory bulb in most of the patients with COVID-19.

Dr. Ho said this finding suggests that inflammation from the COVID-19 infection damages the neurons, reduces the numbers of axons available to send signals to the brain and results in the olfactory bulb “becoming dysfunctional.”

The research was done on patients who had the original strain of COVID-19. Next, Ho and her team want to repeat the study on tissues taken from patients who died from the delta and omicron variants to “better predict if delta and omicron are more or less likely to cause loss of smell.”

Researchers from the University of Maryland School of Medicine, the University of Maryland Brain and Tissue Bank, the Office of the Chief Medical Examiner and Orlando Health contributed to the study.

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Read the full study published Monday in JAMA Neurology.

CBS Baltimore Staff