Severe acute respiratory syndrome coronavirus 2 and influenza A virus co-infection alters viral tropism and haematological composition in Syrian hamsters

Abstract

The ongoing coronavirus disease 2019 pandemic and its overlap with the influenza season lead to concerns over severe disease caused by the influenza virus and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) co-infections. Using a Syrian hamster co-infection model with SARS-CoV-2 and the pandemic influenza virus A/California/04/2009 (H1N1), we found (a) more severe disease in co-infected animals, compared to those infected with influenza virus alone but not SARS-CoV-2 infection alone; (b) altered haematological changes in only co-infected animals and (c) altered influenza virus tropism in the respiratory tracts of co-infected animals. Overall, our study revealed that co-infection with SARS-CoV-2 and influenza virus is associated with altered disease severity and tissue tropism, as well as haematological changes, compared to infection with either virus alone.

Keywords: SARS-CoV-2; co-infection; haematological change; influenza A virus; viral tropism.

FIGURE 1

Disease severity and tissue tropism in hamsters inoculated or co‐inoculated with severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) and/or CA04. (a) Timeline of experiments showing groups and viruses used to inoculate animals. (b) Mean body weight changes in the experimental groups. Titers of SARS‐CoV‐2 and CA04 measured in the nasal turbinates (c and f), tracheas (d and g) and lungs (e and h) are shown. The bars and error bars in Panels (c–h) represent the mean ± standard error of the mean for each group at each time point. The results are shown as the mean ± s.d. *p < .05 and ** p < .01

FIGURE 2

Lung pathological changes showing early differences in the disease course of hamsters inoculated or co‐inoculated with SARS‐CoV‐2 and/or CA04. (a) Representative H&E staining and IHC staining with specific antibodies against the SARS‐CoV‐2 N and influenza A virus N proteins in lung sections obtained from animals at 2, 4 and 7 DPI (scale bar = 100 μm). (b) Representative gross pathological changes in the lungs of inoculated animals. Lungs are representative of the gross pathological changes observed at 2, 4 and 7 DPI. (c) Pathological changes scoring of haemorrhaging, inflammation, bronchiolitis and pulmonary oedema observed in lung sections. DPI, days post inoculation; H&E, haematoxylin and eosin; IHC, immunohistochemistry

FIGURE 3

Scoring of lung haematology showing early differences in the disease course of hamsters inoculated or co‐inoculated with SARS‐CoV‐2 and/or CA04. Numbers of white blood cells and percentages of the cell population comprising granulocytes and lymphocytes in whole blood samples at 2, 4 and 7 DPI. Bars and error bars represent the mean ± standard error of the mean for each group at each time point. The results are shown as the mean ± s.d. *p < .05, **p < .01 and **p < .001

FIGURE 4

Immunological profiling of hamsters inoculated with SARS‐CoV‐2 and/or CA04. (a) Concomitant upregulation of type 1 and 2 cytokines in the lungs of hamsters inoculated with SARS‐CoV‐2 and/or CA04. Mean mRNA expression of IFN‐γ, TNF‐α, IL‐6, IL‐21, IL‐12p40, CCR4, CCL17 and CCL22 at 2, 4 and 7 DPI. Bars and error bars represent the mean ± standard error of the mean for each group at each time point. The results are shown as the mean ± s.d. *p < .05 and **p < .01. (b) T‐cell response in the lungs of hamsters inoculated with SARS‐CoV‐2 and/or CA04. Flow cytometry analysis of the T‐cell response in inoculated hamsters. FACS analysis of splenocytes collected at 2, 4 and 7 DPI using specific antibodies targeting CD4+ and CD8+ T cells and B cells. Data were analysed using FlowJo software (Treestar). CCR4, CC chemokine receptor 4; CCL17, C‐C motif chemokine ligand 17; IFN‐γ, interferon‐gamma; TNF‐α), tumor necrosis factor‐alpha