The Microvillar and Solitary Chemosensory Cells as the Novel Targets of Infection of SARS-CoV-2 in Syrian Golden Hamsters.

Patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019, suffer from respiratory and non-respiratory symptoms. Among these symptoms, the loss of smell has attracted considerable attention. The objectives of this study were to determine which cells are infected, what happens in the olfactory system after viral infection, and how these pathologic changes contribute to olfactory loss. For this purpose, Syrian golden hamsters were used. First, we verified the olfactory structures in the nasal cavity of Syrian golden hamsters, namely the main olfactory epithelium, the vomeronasal organ, and their cellular components. Second, we found angiotensin-converting enzyme 2 expression, a receptor protein of SARS-CoV-2, in both structures and infections of supporting, microvillar, and solitary chemosensory cells. Third, we observed pathological changes in the infected epithelium, including reduced thickness of the mucus layer, detached epithelia, indistinct layers of epithelia, infiltration of inflammatory cells, and apoptotic cells in the overall layers. We concluded that a structurally and functionally altered microenvironment influences olfactory function. We observed the regeneration of the damaged epithelium, and found multilayers of basal cells, indicating that they were activated and proliferating to reconstitute the injured epithelium.

Zika virus infection in chemosensory cells.

Zika virus (ZIKV) is an emerging virus belonging to the genus Flavivirus. ZIKV infection is a significant health concern, with increasing numbers of reports of microcephaly cases in fetuses and Guillain-Barré syndrome (GBS) in adults. Interestingly, chemosensory disturbances are also reported as one of the manifestations of GBS. ZIKV infects several human tissues and cell types in vitro and in vivo. However, there is no study demonstrating ZIKV infection and replication in chemosensory cells, including olfactory and taste cells. Taste papilla and olfactory cells are chemosensory receptor cells with unique histological, molecular, and physiological characteristics. Here we examined ZIKV infection (PRVABC59) in cultured human olfactory epithelial cells (hOECs) and fungiform taste papilla (HBO) cells in vitro, as well as in vivo mouse taste and olfactory epithelial and olfactory bulb tissues. Interestingly, while HBO cells showed resistance to ZIKV replication, hOECs were highly susceptible for ZIKV infection and replication. Further, we demonstrated the presence of ZIKV particles and expression of viral proteins in olfactory epithelium, as well as in olfactory bulb, but not in taste papillae, of immunocompromised mice (ifnar/-) infected with the PRVABC59 strain of ZIKV. These observations suggest that chemosensory cells in the olfactory neuroepithelium and olfactory bulb may be important tissues for ZIKV replication and dissemination.