Characterization of Virus Replication, Pathogenesis, and Cytokine Responses in Syrian Hamsters Inoculated with SARS-CoV-2

Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel coronavirus which caused a global respiratory disease pandemic beginning in December 2019. Understanding the pathogenesis of infection and the immune responses in a SARS-CoV-2-infected animal model is urgently needed for vaccine development. Methods: Syrian hamsters (Mesocricetus auratus) were intranasally inoculated with 10(5), 5x10(5), and 10(6) TCID50 of SARS-CoV-2 per animal and studied for up to 14 days. Body weight, viral load and real-time PCR amplification of the SARS-CoV-2 N gene were measured. On days 3, 6 and 9, lung, blood, liver, pancreas, heart, kidney, and bone marrow were harvested and processed for pathology, viral load, and cytokine expression. Results: Body weight loss, increased viral load, immune cell infiltration, upregulated cytokine expression, viral RNA, SARS-CoV-2 nucleoprotein, and mucus were detected in the lungs, particularly on day 3 post-infection. Extremely high expression of the proinflammatory cytokines MIP-1 and RANTES was detected in lung tissue, as was high expression of IL-1 beta, IL-6, IL-12, and PD-L1. The glutamic oxalacetic transaminase/glutamic pyruvic transaminase (GOT/GPT) ratio in blood was significantly increased at 6 days postinfection, and plasma amylase and lipase levels were also elevated in infected hamsters. Conclusion: Our results provide new information on immunological cytokines and biological parameters related to the pathogenesis and immune response profile in the Syrian hamster model of SARS-CoV-2 infection.