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Comparative study of the pathogenicity of SARS-CoV-2 B.1 AND B.1.617.2 lineages for syrian hamsters

BACKGROUND: Syrian hamsters are the most sensitive model for studying the pathogenesis of a new coronavirus infection and testing prophylactic and therapeutic drugs against SARS-CoV-2. Accordingly, it is important to identify pathomorphological indicators of tissue damage in coronavirus-infected animals, which would correlate with the severity of the disease. 
AIM: Comprehensive assessment of the pathogenicity of SARS-CoV-2 viruses of B.1 and B.1.167.2 lineages on the model of Syrian hamsters to identify the most sensitive criteria that correlate with the clinical manifestation of the disease. 
MATERIALS AND METHODS: Intranasal infection of animals with SARS-CoV-2, followed by the assessment of the clinical picture of the disease and detailed pathomorphological studies of various organs collected on the 5th day after infection. 
RESULTS: The SARS-CoV-2 Delta virus (B.1.617.2) was shown to be less pathogenic for Syrian hamsters compared to the ancestral strain that circulated during the first wave of the COVID-19 pandemic (B.1). The histopathological characterization of lung tissue sections of infected animals revealed the most sensitive morphometric indicator that correlates with the severity of SARS-CoV-2-induced pathology, namely, the alveolar wall thickness. 
CONCLUSIONS: The use of this indicator makes it possible to determine even slight differences in the severity of virus-induced pathology in the Syrian hamster model, which can be critical in the preclinical evaluation of prophylactic and therapeutic drugs for COVID-19.