Not To Be Sniffed At?

Loss of the sense of smell (anosmia) is a key symptom of a Covid-19 infection in humans (https://www.theguardian.com/science/2020/dec/05/anosmia-how-covid-brought-loss-of-smell-centre-stage). This seems to occur because the Sars-CoV-2 virus uses ACE2 receptors to invade the cells of its host. Although the olfactory neurones don't have this receptor, ACE2 receptors are located higher up in the olfactory system. So, the inflammation produced here, can cause a 'splash-back' loss of the sense of smell, by preventing transmission of impulses to the brain. The general public often confuse the senses of taste and smell (both are essentially the responses to the shapes of food and other molecules). The receptors on the tongue only detect the 5 basic tastes of salty, bitter, sweet, sour and umami. Much of our ability to 'taste' food, is actually the work of our olfactory neurones. Anosmia often leads to a loss of appetite (not a good thing, if you want to recover from an infection). Between 44 and 77% of Covid-19 patients lose their sense of smell. Individuals with a higher viral load appear to be most likely to experience this symptom. Although around 67% recover from anosmia in 6-8 weeks, it can be much longer (or never?) in other cases. Recovery doesn't appear to be related to damage of the olfactory neurones as these, unusually, regenerate every 6 weeks. Persistent anosmia seems to depend on the degree of inflammation produced in the higher regions of the olfactory tract.