Fig 2. The KR mt enhances SARS-CoV-2 pathogenesis and fitness.

(A) Schematic of the infection of hamsters with SARS-CoV-2. (B-E) Three- to four-week-old male hamsters were mock-infected (gray) or inoculated with 10⁴ PFU of WT SARS-CoV-2 (black) or the KR mt (red). Animals were then monitored for weight loss (B). On days 2 and 4 post infection, viral titers in the lung (C), trachea (D), and from nasal washes (E) were determined. (F) Schematic of competition/transmission experiment. (G-H) Three- to four-week-old male donor hamsters were inoculated with 10⁴ PFU of WT SARS-CoV-2 and the KR mt at a 1:1 ratio. On day 1 of the experiment, donor and recipient hamsters were co-housed for 8 hours, then separated, and the donor hamsters underwent nasal washing. On day 2, recipient hamsters were nasal washed. Hamsters were then monitored and nasal washes and lung tissue harvested on days 4 (donors) and 5 (recipients). The ratio of WT (gray) to KR mt (red) was then determined by NGS of all donor (G) and recipient (H) samples. For weight loss data, mean percent weight loss was graphed ± s.e.m. For titer data, individuals were graphed with means ± s.d. indicated by lines. For competition studies, individual replicates are graphed as points, while bars represent the mean. Statistical significance was between WT and the KR mt was determined by student’s T-Test with p≤0.05 (*), p≤0.01 (**), and p≤ 0.001 (***). Grey dotted lines are equal to LOD.