Susceptibility to SARS-CoV-2 Virus Variants of Concern in Mouse Models

The aim of the research was to assess the susceptibility of mice of different lines to newly emerging variants of SARS-CoV-2. Materials and methods . The SARS-CoV-2 virus strains belonging to variants of concern (VOC) circulating in the territory of the Russian Federation were used in the study. Experiments involved three inbred mouse lines (BALB/c, CBA and C57Bl/6z) and CD1 outbred mice taken from the nursery of the SSC VB “Vector” of the Rospotrebnadzor. The infectious titer of coronavirus in tissue samples obtained from the laboratory animals was determined on a Vero E6 cell culture. The (Ct) threshold value in RT-PCR was considered an additional parameter for monitoring the viral load in the samples. The severity of lung tissue damage was assessed using histological preparations. Results and discussion . The susceptibility of various mouse lines to the genetic variant Beta of the SARS-CoV-2 virus has been investigated. During intranasal infection of the inbred and outbred mice with strains of VOC at a dose of 2·10 3 TCID 50 , the virus replicated in the lungs with maximum concentrations 72 hours after infection. The pathogenicity of genetic variants of the SARS-CoV-2 virus for BALB/c mice has been assessed, a 50 % infectious dose for intranasal infection (ID 50 ) determined. Histological analysis showed COVID-19-specific lung tissue lesions in infected animals. Our study proves that BALB/c mice can be used as a model animal in screening studies when evaluating the effectiveness of therapeutic, vaccine preparations and studying the pathogenesis caused by VOC of the SARS-CoV-2 virus: Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1), Omicron (B.1.1.529) and the like.