Canine influenza virus coinfection with Staphylococcus pseudintermedius enhances bacterial colonization, virus load and clinical presentation in mice.
BACKGROUND
Canine influenza virus (CIV) and Staphylococcus pseudintermedius (Sp) are pathogens that cause respiratory disease in dogs. Considering bacterial infections following influenza are a leading cause of illness and death, it is of particular meaning to investigate the interaction between these two pathogens. In this study, BALB/c mice were used as a mouse model to assess whether inoculation with CIV H3N2 followed by S. pseudintermedius 72 h later resulted in exacerbation of disease. Disease was characterized by assessment of body weight loss, titration of virus and bacteria, histopathology, and cytokine production.


RESULTS
There was a significantly greater decrease in body weight in the co-infected group compared with the CIV-only and SP-only groups. CIV inoculation increased bacterial colonization, whereas secondary infection with S. pseudintermedius elevated the viral RNA load of CIV in tissues. The histological lesions in the brain, spleen and lung were more severe in the CIV/Sp group than in the singly treated groups. Infection with CIV alone, Sp alone or coinfection stimulated a significantly higher release of cytokines, such as interferon-gamma (IFN)-γ, interleukin 6 (IL)-6, tumor necrosis factor (TNF-α) and lymphotactin (Lptn), than was observed in the mock-infected group (PBS). Moreover, the levels of IFN-γ in the spleen and lung were higher in the CIV/Sp group compared with the CIV-only and Sp-only groups.


CONCLUSIONS
Our findings provide the first demonstration that the secondary infection of mice with Sp leads to increased clinical signs and lesions during canine influenza.
College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China.
Dildar Hussain
DH
Kalhoro
College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China.
Shanshan
S
Gao
College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China.
Xing
X
Xie
College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China.
Shan
S
Liang
College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China.
Su
S
Luo
College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China.
Yanbing
Y
Zhao
College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China. liuyongjie@njau.edu.cn.
Yongjie
Y
Liu
D000818:Animals; D001921:Brain / Q000473:pathology; D060085:Coinfection; D016207:Cytokines / Q000378:metabolism; D004195:Disease Models, Animal; D053122:Influenza A Virus, H3N2 Subtype; D008168:Lung / Q000473:pathology; D051379:Mice; D008807:Mice, Inbred BALB C; D009976:Orthomyxoviridae Infections / Q000150:complications* / Q000473:pathology; D013154:Spleen / Q000473:pathology; D013203:Staphylococcal Infections / Q000150:complications* / Q000473:pathology; D013210:Staphylococcus; D019562:Viral Load; D015431:Weight Loss
D016207:Cytokines
Staphylococcus pseudintermedius; canine influenza virus; coinfection; mice; pathological lesions