Researchers are finally making progress in understanding how the SARS-CoV-2 coronavirus causes odor loss. And a number of potential therapies are still being tested, including steroids and blood plasma.When it comes to COVID-19 signaling, odor disturbances gradually decrease as the virus grows. “Our inboxes are not as flooded as they once were,” said Valentina Parma, a psychiatrist at Monell Chemical Senses Center in Philadelphia, Pennsylvania, who helped with difficult questions from patients during the first two years of the epidemic.
A study published last month1 surveyed 616,318 people in the United States who had COVID-19. It found that, compared with those who were infected with the original virus, people who had experienced Alpha variability – the first variant of the emerging anxiety – were 50% more likely to have chemosensory disorders. These good opportunities are up to 44% in the latest version of Delta, and up to 17% in the latest version, Omicron.But not all the news is good: the vast majority of people who became infected at the beginning of the epidemic are still experiencing chemosensory effects.
The 2021 study followed 100 people with mild cases of COVID-19 and 100 people who were found not to have it. More than a year after their infection, 46% of those with COVID-19 still had bad breath; in contrast, only 10% of the control group had developed odor loss, but for some reason. In addition, 7% of those infected may lose their sense of smell, or ‘anesmia’, by the end of the year. Given that more than 500 million cases of COVID-19 have been confirmed worldwide, tens of millions of people are likely to have chronic odor problems.For these people, help may not be forthcoming. Simple tasks such as tasting food or smelling flowers are now “extremely stressful”, says Parma.
At the beginning of the epidemic, studies showed3 that the virus attacks cells in the nose, called sustentacular cells, that provide nutrition and support to sensory neurons.Since then, clues have emerged about what happens to odorless neurons after infection. Researchers including biochemist Stavros Lomvardas at Columbia University in New York City examined those who died as a result of COVID-19 and found that, although their neurons were perfect, they had fewer receptors embedded in the membrane to detect odor molecules than usual4.
This was because the nuclei of neurons had previously been disrupted. Typically, the chromosomes of these nuclei are organized into two parts – a structure that enables neurons to produce specific odor receptors at higher levels. But when the team looked at the automatic neurons, “the nuclear structure was invisible,” Lomvardassaid.Some studies suggest why some people lose their long-term odor. In January, a team of researchers reported that5 found genetic mutations in humans that were associated with greater odor or loss of taste. Mutations – mutations in a single ‘letter’, or base, of DNA – are derived from two hardened genes, called UGT2A1 and UGT2A2. Both contain proteins that remove odor molecules from the nose after they have been detected. However, it is not yet clear how SARS-CoV-2 interacts with these genes.
There is also evidence of permanent brain changes in people who lose their sense of smell. In a study published in March6, 785 people in the United Kingdom had two brain tests. About 400 people were infected with COVID-19 between the screens, so scientists were able to detect structural changes. COVID-19 survivors have shown a number of changes, including signs of tissue damage in areas connected to the brain’s olfactory center. It is not yet clear why this was so, but another possibility is the lack of ideas. Says Danielle Reed, a geneticist at Monell: “When we cut out the nasal passages, the brain becomes more powerful. “It’s one of the clearest things we know about taste and aroma.”
Experimental treatment
At present, many therapies are being tested, usually in small clinical trials. But it is still early days, so the only thing that many researchers are currently recommending scent training7. To find universal treatment, many researchers are experimenting with steroids, which reduce inflammation. COVID-19 is known to cause severe inflammation, which may be involved in odor disturbances. So, in theory, steroids can help – but, in fact, the results have been disappointing. For example, a 20218 study provided odor training for 100 people with post-COVID anosmia. Fifty of them also received nasal spray with the steroid mometasonefuroate, while another 50 did not. There was no significant difference in outcome between the two groups.Another treatment for plasma with platelet-rich; this is done with the patients’ own blood and is rich in organic chemicals that can cause healing. A screening study published in 20209 followed seven patients who had plasma plasma-rich plasma in their nostrils: five showed improvement after three months.
Similarly, a preprint published in February of this year 10 followed 56 people and found that plasma rich in platelets made them more sensitive to odors. Unlike the COVID-19 vaccine, which was tested at an unprecedented rate due to extensive government support, treatment for post-COVID chemosensory malfunction is ongoing. Philpott is in the early stages of a small study of vitamin A, a previous study that suggested that it might help with other types of odor loss. “The fact is that this study will take a whole year to continue, and it will take us about mid-next year before we analyze the data and report it,” Philpott said. “If we get a good profit, our next task will be to apply for additional funding so that we can do a thorough examination.”
Source Journal Reference: Michael Marshall, COVID and smell loss: answers begin to emerge, Nature News (2022), doi: https://doi.org/10.1038/d41586-022-01589-z
