Giving anti-inflammatory drugs, such as corticosteroids, early on could help people regain their sense of smell after being infected with Covid-19, according to a new study.
Over 27 million people worldwide have experienced Covid-related loss of smell or taste. Olfactory dysfunction caused by the disease typically resolves within 2-4 weeks. Yet, in some cases, symptoms persist for longer. Now, scientists are looking at drugs that could help patients regain their sense of smell in the early stages of infection.
Several theories exist about how SARS-CoV-2 infection affects smell. One hypothesis is that the virus directly affects the olfactory nerve cells responsible for signaling odor information to the brain.
However, the leading theory is that the infection affects cells in the nasal cavity. One way this can happen is through innate immune cells - cells produced and released by the immune system to fight off infection. When infected with COVID-19, the human body produces immune cells that destroy the infected nasal cells to fight off the virus. However, even when no signs of SarsCov-2 are left, the prolonged presence of innate immune cells in the tissue persists. This may explain why a person can recover from COVID-19 but still lack the ability to smell.
"This is something that has been demonstrated for lots of cases with SarsCov-2," Nicolas Meunier, an author of the study and a neurobiologist specializing in smell, told Tech Times in an interview. "After the infection, inflammation remains really high in the tissue. Even when the viruses had been cleared."
Anti-inflammatories like corticosteroids are important drugs to fight inflammation. Now, Meunier and his colleagues studied how these drugs would affect olfactory recovery.
In the study, researchers infected hamsters with SARS-CoV-2 and treated them with dexamethasone, a corticosteroid, starting two days after infection. The team evaluated viral load, weight loss, food intake, and olfactory abilities.
To study the hamsters' smell abilities, the team used a "buried food test." This is a test where scientists see if animals can find hidden food in their bedding. The food, often a small piece of cheese, is hidden below the surface of the substrate at different depths. The hamster is then placed in the test environment, where it has limited time to locate the hidden food. Researchers change how deep they hide the food to see how well animals can use their sense of smell to find it.
"We decided to make the test a bit harder for them [hamsters] by putting the food very deep into the bedding. It was surprising to see an animal not be able to detect food digged just five centimeters below. They lose this [olfactory] ability a few days after infection," added Meunier.
Hamsters given anti-inflammatory medicine did better at finding hidden food than those who didn't. The team also checked the nerve cells in the noses of hamsters. They found that hamsters treated with corticosteroids had more of these cells than those who didn't get the treatment. This might mean that the drugs helped the hamsters' sense of smell improve.
"Olfactory neurons [nerve cells] detect the odors and associability to smell, and [...] they were at a higher level after the treatment with corticoids," adds Meunier.
Meunier and his team also noticed that hamsters treated with dexamethasone ate more food than the ones who didn't get the treatment. This might be because they were better at smelling and finding the food. But caution is needed when looking at these patterns. "It is difficult to say that this [extra food intake] is only related to the improvement in olfactory skills because corticoids are known to increase feeding behavior. You usually eat more when you are treated with corticoids," Meunier explains.
The findings suggest that corticosteroid treatments could work well if given early when someone first notices they can't smell properly. Junki Maruyama, a professor at UTMB who was not involved in the study, said in an interview that the results could be applied to human patients, "especially to prevent long-term olfactory dysfunction."
But Meunier is a bit more cautious. "There are a lot of secondary effects that make these drugs not so easy to give to humans." He finishes by saying that his study is just the beginning of figuring out how anti-inflammatory drugs might help lessen the impact of viral infections on the sense of smell.
About the author: Bárbara Pinho is a freelance science journalist. Her work work has appeared in New Scientist, Chemistry World, Discover, Chemistry & Industry News, and National Geographic. Her website is https://www.barbarapinho.com/
