Chemosensory dysfunctions including anosmia, hyposmia, ageusia, and hypogeusia constitute one of the chief symptoms of SARS-CoV2 infection. Meta-analyses suggest that the prevalence of olfactory dysfunction ranged between 41.0-61.0% and that of gustatory dysfunction between 38.2-49.0% in COVID-19. Indeed, self-reported loss of smell and taste has been observed to be more prognostic than other symptoms including fatigue, fever, or cough in predicting symptomatic infection (Agyeman et al., 2020;Mastrangelo et al., 2021). Significantly, loss of taste is consistently reported as a common symptom of long COVID-19, defined as persistence of symptoms four weeks after infection (Biadsee et al., 2021). Following over four-hundred SARS-CoV-2 infected individuals for severity, improvement, and recovery of subjective chemosensory dysfunction for four months, Schwab et al. have reported that the recovery from loss of taste became stagnant after about two months with little improvement subsequently (Schwab et al., 2021). An overview of emerging research on the pathogenesis of long COVID-19 and an opinion about potential mechanisms for gustatory dysfunction is included below.
GUSTATION-THE PROCESS OF TASTE PERCEPTIONGustation is an integrated event of multiple physiological processes occurring concurrently through activation of specialized taste, orosensory, and gastrointestinal fibers (Simon et al., 2006). The taste buds, that constitute the peripheral chemosensory units, are distributed in the papillae of the tongue, palate, larynx, and esophagus. Each taste bud consists of 50-100 tightly packed specialized epithelial cells called taste receptor cells that are of three types. Type-I are glial-like cells, type-II cells express