Infection of Syrian hamsters with SARS-CoV-2 led to significant immunostaining of SARS-CoV-2 in the olfactory epithelium and underlying lamina propria (specifically the sustenacular cells, not the olfactory neurons). Cilia damage was noted, which may explain the loss of olfaction in COVID-19 patients. Significant Iba1 immunostaining was also noted in these areas (see image), suggesting an activated immune response.

Boston University

A study from Japan assessed the onset of SARS-CoV-2 virology upon infection in Syrian hamsters. Severe respiratory pathology was noted, in both the upper and lower respiratory tracts, along with a significant immune response that was protective against reinfection in previously-affected mice as well as other non-infected hamsters upon serum administration. These effects were demonstrated with both a low and high dose.

Application of Syrian Hamsters for Studying SARS-CoV-2 Virology

This hypothesis proposes that infection of olfactory epithelium (OE)-related cells, such as sustentacular and basal cells, is the basis of anosmia-related symptoms  in COVID-19 patients (Ref #1)

1) Gene expression profiles of human nasal biopsy samples revealed that neither ACE2 nor TMPRSS2 were detected in OSNs, which would be necessary for SARS-CoV-2 infection. This was confirmed by immunostaining of human biopsy tissue.

2) Immunostaining revealed, however, that OE cells such as sustentacular and basal cells express ACE2. This suggests that the MOA for COVID-19-mediated anosmia may be from damage of these OE cells.

3) These findings are confirmed by experiments performed in Syrian hamster models of SARS-CoV-2 infection (Ref #2)

Non-Neuronal Infection As a Potential Cause of Anosmia and Ageusia in COVID-19 Patients

Bryche, B., St Albin, A., Murri, S., Lacôte, S., Pulido, C., Ar Gouilh, M., ... & Meunier, N. (2020). Massive transient damage of the olfactory epithelium associated with infection of sustentacular cells by SARS-CoV-2 in golden Syrian hamsters. https://www.sciencedirect.com/science/article/pii/S0889159120313581

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