Figure 2.

Simultaneous coinfection of hamsters by higher doses of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and mouse-adapted A/Hongkong/415742/2009 H1N1 (pH1N1). Groups of hamsters were intranasally inoculated with 50 µL of SARS-CoV-2 (10³ plaque-forming units [PFUs]) and pH1N1 (10⁵ PFUs) mixture; the animals were monitored for body weight and clinical sign scores, and killed at 4 days postinfection (dpi). Monoinfection by either viruses were included as controls. A, Body weight changes during the 5-day experimental period. Weight on day 0 before virus inoculation was taken as 100%. n = 3 each group. Error bars indicate mean ± standard deviation. B, Average clinical scores for disease signs including lethargy, ruffled fur, hunchback posture, and rapid breathing. A score of 1 was given to each of these clinical signs. P value was calculated by 2-way analysis of variance. C, SARS-CoV-2 viral load in homogenized lung or nasal turbinate (NT) tissues at 4 dpi after monoinfection or coinfection. Right panels are SARS-CoV-2 RdRp gene copies determined by real-time reverse-transcription polymerase chain reaction (RT-qPCR). The left panels are infectious viral titers determined by plaque assays in Vero E6 cells. P value was calculated by Student t test. Horizontal dashed line indicates detection limit of the assays. D, pH1N1 viral load in lung and nasal turbinate (NT) by RT-qPCR (right panel), or plaque assays in Madin-Darby canine kidney cells (left panel). Horizontal dashed line indicates detection limit of the assays. E, Representative images of lung histopathological changes at 4 dpi after monoinfection or coinfection. Top left image shows the normal lung structure of mock control. SARS-CoV-2 (10³ PFUs) monoinfection showed diffuse alveolitis with massive alveolar space inflammatory cell infiltration, exudation, and pulmonary vasculitis (arrows, top right image). pH1N1 (10⁵ PFUs)–infected lung showed conspicuous bronchiolar luminal cell debris (arrows), mild peribronchiolar infiltration, and perivascular edema; a bronchiole section inside the boxed area filled with cell debris is shown in magnified image. Images in the bottom panels are SARS-CoV-2+pH1N1-coinfected lung tissue, which showed massive exudation of protein-rich fluid (pink color) filling alveolar space (solid arrows), and a large area of alveolar hemorrhage (open arrows). Boxed area is magnified showing endotheliitis in a blood vessel.