Imagine waking up and discovering your morning coffee smells like unwashed socks, your eggs reek of feces and your favorite comfort food tastes metallic. That’s parosmia, a common symptom following COVID-19 infection that can leave the sense of smell permanently altered. It may improve with time but it can also take a long time, as we hear from people who have been living with it for years.
When the Covid-19 smell disorders pandemic began, olfactory symptoms quickly emerged as one of the most alarming signs of infection. For many, the things they used to enjoy, or even rely on, for health and well-being such as chocolate, coffee and minty toothpaste became unrecognizable. They would smell like rancid garbage or rotting meat and, to the person affected by this phenomenon, could trigger full-throttle reactions of disgust and revulsion.
It’s thought that the virus enters the olfactory epithelium and kills the sustentacular cells that wrap around the olfactory receptor neurones and provide them with structural and metabolic support. This can cause a malfunction in the neurons, leading to anosmia. But the good news is that these sustentacular cells can regenerate more rapidly than the neurons themselves, so anosmia is usually temporary.
In fact, a number of studies indicate that most COVID-19 patients experience some form of smell disorder but only about 20 percent are completely anosmic. Others experience less severe forms of the condition, referred to as phantosmia. In some cases, the disorder persists for up to a year after the end of the pandemic.
But what is the reason that some people suffer longer than others, and how can they overcome this harrowing new reality? In this week’s episode, we speak to olfactory researcher Zara Patel who has been investigating how scent therapy can help those suffering from this debilitating symptom. We also hear from COVID-19 long haulers who have experienced this troubling complication of their viral infection.
A new study by researchers at Monell Chemical Senses Center and AbScent has shed light on why some COVID-19 patients experience persistent distortions in their sense of smell. The work is published in the peer-reviewed journal Chemical Senses.
The team conducted a series of experiments on both human and rat nasal olfactory epithelium. They isolated the stem cells in the olfactory epithelium, known as basal cells and found that these cells express two proteins: ACE2 and TMPRSS2. Both genes encode proteins needed for the SARS-CoV-2 virus to infect the olfactory neurons, but only if those neurones are already compromised by a malfunctioning sustentacular cell. The research shows that olfactory stem cells from a healthy individual will express neither of these proteins and therefore are less susceptible to SARS-CoV-2 infection, which is what happened during the COVID-19 pandemic.
Then, they analyzed 30 participants with either a phantosmic or complete loss of their sense of smell (anosmia) and 30 healthy controls. They performed gas chromatography on each participant’s smelly compounds and separated them into their component parts so they could be identified. The data showed that olfactory stem cells in the olfactory nose can regenerate if they are exposed to the odor compounds ACE2 and TMPRSS2.