A newly published study in the Journal of Internal Medicine found that 86 percent of patients who experienced mild forms of Covid-19 developed loss of their senses of taste and smell, compared with 4 percent to 7 percent of those with moderate to severe cases.
According to NBC News, the research study included more than 2,500 patients across France, Belgium, and Italy. The majority of those studied regained their senses within about two months of infection.
Researchers are still baffled as to why the loss of smell and taste is more common among people with milder forms of the virus. The study’s authors have theorized that these patients may have higher levels of certain antibodies that might limit the coronavirus’s spread to the nose.
Any nasty cold, flu, or bad allergies can cause nasal congestion so severe that it renders those senses useless. In those cases, using a decongestant can help treat it, but experts say this is not the case with Covid-19. Instead, the coronavirus dulls those senses through a completely different line of attack.
In a person’s sense of smell, odor molecules enter the nose and land on a type of tissue called the olfactory epithelium, which is filled with neurons, that pick up the odor molecule and transport it through the olfactory bulb and into the brain. From there, the brain then interprets and identifies what the scent is that you are smelling.
The neurons on this journey from the nose to the brain are guided by support cells covered in a receptor called ACE-2. The coronavirus’s primary target in human cells means the virus attacks these support cells.
Experts theorize that the virus zones in on those cells, disrupting the pathway for the neurons to get to their destination in the brain. The effects mean people lose their sense of smell, affecting how people experience their sense of taste.
While there is no guarantee that those nerve connections will ever return to their normal pathways, the fact that at least some reaction is occurring — even if it is drastically changing — may be a good sign.
“We actually think that those nerve endings are trying to grow and repair themselves,” Dr. Bradley Goldstein, an associate professor at Duke University School of Medicine in North Carolina, told NBC. “They’re not sending the right signals yet, but things need to heal,” he said.