This week in Stem Cell Reports, McMahon et al. investigated the in vitro infection of brain tissue by SARS-CoV-2. Human embryonic stem cell-derived cortical organoids were exposed to SARS-CoV-2 at three viral loads, from 102-105 plaque-forming units/mL, for 14 days. Infection was confirmed using immunohistochemistry and quantitative real-time PCR. Cortical organoids were infected even from the lowest viral load and, consistent with previous studies, neurons showed little to no infection while choroid plexus cells showed moderate infection. Further experimentation found that organoids were infected within 6 hours of exposure, but replication of SARS-CoV-2 did not occur within 4 days post infection. The authors then used glial and astrocytic markers to show that SARS-CoV-2 preferentially infects astrocytes and radial glial progenitor cells, presenting the first demonstration of glial tropism of SARS-CoV-2. Glial cells are vital to neuron function; therefore, infection could play a key role in explaining the neurological manifestations of COVID-19. Furthermore, infection of glial cells may implicate the blood-brain barrier as a mechanism for SARS-CoV-2 to enter the brain.

This paper investigated the effect of persistent olfactory and gustatory dysfunction following COVID-19 infection on quality of life. An online survey was administered to 431 individuals who reported both SARS-CoV-2 infection within the last 6 months and persistent COVID-19 symptoms. Participants reported the presence or absence of persistent symptoms, rated the severity of olfactory and gustatory dysfunction during infection and at present on a 1-10 visual analogue scale, and responded to a questionnaire scoring the mental and physical components of quality of life.

Persistent olfactory and gustatory symptoms were the second and third most common persisting symptoms (reported by 24.6% and 19.5% of participants, respectively), after fatigue (42.9%), and their presence strongly correlated with lower scores on the mental component of quality of life. Multiple regressions significantly predicted mental quality of life scores from the severity of olfactory and gustatory symptoms.

The authors conclude that this outcome supports the establishment of infrastructure and effective therapies for individuals with persistent chemosensory dysfunction. They use previous studies to highlight the contribution of chemosensory dysfunction to depression, eating disorders and social isolation, supporting their appeal to avoid psychological morbidities by treating these patients early.