Covid symptoms: Study links long-term loss of smell to brain damage


A loss of smell or an impaired perception of odours was identified as one of the key symptoms of the coronavirus in the initial stages of the pandemic. There is evidence, however, that the symptom has faded as the virus has evolved. In a bid to understand the mechanisms behind the olfactory changes, researchers have studied the lining of the nasal cavity in depth. For a new body of research, however, scientists chose to dig deeper and study the tissue inside the brain.

The research, published in the journal JAMA Neurology, has warned that an infection from the virus is tied to damage in the part of the brain that controls smell.

The scientists drew their conclusion from the study of 23 deceased COVID-19 patients, who were compared to a control group of 14 deceased people without COVID-19.

Lead author of the study, Cheng-Ying Ho, NMD, PhD, associate professor from Johns Hopkins University School of Medicine, wrote: “The striking anoxic pathology in some cases indicates that olfactory dysfunction in COVID-19 may be severe and permanent.”

He told Medscape: “The results show the damage caused by Covid can extend beyond the nasal cavity and involve the brain.

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“We wanted to go a step beyond to see how the olfactory build was affected by Covid infection.”Tissues were extracted from the post-mortem tissue in the brain, lung, and other organs for analysis.

The findings revealed a higher prevalence of damaged blood cells and axons – a cable that transmits impulses between neurons – in the brains of Covid patients.

The team also found axon deterioration was about 60 percent more pronounced in patients with Covid, while the damage to microscopic blood vessels was 36 percent more severe in these patients.

The researchers noted that axon damage in some patients suggests that Covid-induced smell loss could be severe and irreversible.


However, researchers found no evidence of a correlation between the severity of symptoms and the damage to the nerve cells of microscopical blood vessels.

The findings shed valuable light on some of the mechanisms at play in the long-term loss of smell that afflicts a large portion of the population.

Data released by the Covid Symptoms Study initiative last year found the symptom affected around 60 percent of people aged 16 to 65 who catch Covid.

But Professor Ho pointed out that these figures were released before the advent of the Omicron variant, which is less likely to cause smell loss in patients with Covid.

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