• Anna Jinxia Zhang, Andrew Chak-Yiu Lee, Hin Chu, Jasper Fuk-Woo Chan, Zhimeng Fan, Can Li, Feifei Liu, Yanxia Chen, Shuofeng Yuan, Vincent Kwok-Man Poon, Chris Chung-Sing Chan, Jian-Piao Cai, Kenneth Lap-Kei Wu, Siddharth Sridhar, Ying-Shing Chan, and Kwok-Yung Yuen.
• State Key Laboratory of Emerging Infectious Diseases, University of Hong Kong, Pokfulam, Hong Kong Special Administrative Region, China.
• Clin. Infect. Dis. 2021 Jul 15; 73 (2): e503-e512.

BackgroundCoronavirus disease 2019 (COVID-19) is primarily an acute respiratory tract infection. Distinctively, a substantial proportion of COVID-19 patients develop olfactory dysfunction. Especially in young patients, loss of smell can be the first or only symptom. The roles of inflammatory obstruction of the olfactory clefts, inflammatory cytokines affecting olfactory neuronal function, destruction of olfactory neurons or their supporting cells, and direct invasion of olfactory bulbs in causing olfactory dysfunction are uncertain.MethodsWe investigated the location for the pathogenesis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from the olfactory epithelium (OE) to the olfactory bulb in golden Syrian hamsters.ResultsAfter intranasal inoculation with SARS-CoV-2, inflammatory cell infiltration and proinflammatory cytokine/chemokine responses were detected in the nasal turbinate tissues. The responses peaked between 2 and 4 days postinfection, with the highest viral load detected at day 2 postinfection. In addition to the pseudo-columnar ciliated respiratory epithelial cells, SARS-CoV-2 viral antigens were also detected in the mature olfactory sensory neurons labeled by olfactory marker protein, in the less mature olfactory neurons labeled by neuron-specific class III β-tubulin at the more basal position, and in the sustentacular cells, resulting in apoptosis and severe destruction of the OE. During the entire course of infection, SARS-CoV-2 viral antigens were not detected in the olfactory bulb.ConclusionsIn addition to acute inflammation at the OE, infection of mature and immature olfactory neurons and the supporting sustentacular cells by SARS-CoV-2 may contribute to the unique olfactory dysfunction related to COVID-19, which is not reported with SARS-CoV-2.© The Author(s) 2020. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.

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