FIG 6 .
BtCoV HKU5-SE MA replication in young and aged BALB/c mice. (A) Weight loss curves of young (10-week-old) and aged (1-year-old) mice infected intranasally with 1 × 105 PFU of BtCoV HKU5-SE MA through 4 days p.i. (B) Viral titers in lungs of mice at days 2 and 4 p.i. Error bars indicate SD. (C) Representative H&E-stained sections of lungs from a young and an aged mouse harvested at 4 days p.i., showing severe inflammatory infiltration and hyaline membrane formation (black arrow) in the aged mouse.