Experimental co-infection of infectious bronchitis and low pathogenic avian influenza H9N2 viruses in commercial broiler chickens

Abstract

In this study, commercial broilers were experimentally infected with single (classical IBV, variant IBV or AIV-H9N2) or mixed AIV-H9N2 with classical, variant or vaccine strains of IBV. Birds were monitored for clinical and pathological outcomes and virus shedding for 10days post infection (DPI). Clinical signs were limited to the respiratory tract in all challenged groups and varied from mild to moderate mouth breathing to severe respiratory signs with snorting sound and extended head. Mortalities were only recorded in mixed AIV-H9N2/variant IBV challenge group. AIV-H9N2 challenge caused tracheal petechial hemorrhage that progressed to tracheal congestion and caseation. In mixed AIV-H9N2/IBV vaccine challenge, severe tracheitis with bronchial cast formation was observed. In mixed AIV-H9N2/variant IBV challenge severe congestion of the tracheal mucosa and excessive exudates with a tendency to form tubular casts were observed. Kidney ureate deposition was only observed in variant IBV challenge group. Histopathologically, tracheal congestion, severe degeneration, and deciliation were noticed in all groups of mixed infection. Interestingly, hemorrhage and atrophy were observed in thymus gland of birds challenged with single AIV-H9N2 or mixed AIV-H9N2/IBV. There was no difference in the tracheal shedding level of variant IBV between single and mixed infected groups while classical IBV shedding increased in mixed infection group. Interestingly, the AIV-H9N2 showed constantly high shedding titers till 7DPI with variant or vaccine IBV co-infection. In conclusion, co-infection of IBV and AIV-H9N2 induced severe clinical outcome and high mortality. Also, IBV co-infection increased the shedding of AIV-H9N2 in experimentally infected birds.

Keywords: Avian influenza virus; Broiler chickens; Co-infection; H9N2; IBV.

Fig. 1

Thymus lesions in single and mixed infection groups; At 2 normal thymus of control negative group (A), thymus showing severe congestion with petechie in single AIV-H9N2 infection (B), few petechial hemorrhage AIV-H9N2 and variant IBV infection (C), petechial hemorrhage in AIV-H9N2 and classical IBV infection (D), and slight petechial hemorrhage in AIV-H9N2 and IBV vaccine infection (E). At 7 DPI normal thymus of control negative group (F) atrophied hemorrhagic thymus in AIV-H9N2 infection (G), slight petechial hemorrhage in AIV-H9N2 and variant IBV infection (H), atrophy with petechial hemorrhage in AIV-H9N2 and classical IBV (I) and AIV-H9N2 and IBV vaccine strain infection (J).

Fig. 2

Thymus histopathology in infected broiler chickens; Negative control group (A), severe congestion of medulla blood vessels and hemorrhages, blood vessels were ruptured leaving blood-filled spaces and slight to moderate thymus atrophy in the single AIV-H9N2 (B), AIV-H9N2 and classical IBV (C), AIV-H9N2 and classical IBV (D), AIV-H9N2 and variant IBV (E), and AIV-H9N2 and IBV vaccine (E) infections. Magnification 10 × and scale bar = 100 μM.

Fig. 3

Kidney histopathology in infected broiler chickens. Normal kidney (A), congestion, severe degeneration and necrosis, and interstitial nephritis in variant IBV (B), Massive infiltration of leucocytes blood vessel congestion in AIV-H9N2 and classical IBV (C), severe degenerative changes and hemorrhages in AIV-H9N2 and variant IBV (D), and in AIV-H9N2 and IBV vaccine (E). Magnification 10 × and scale bar = 100 μM.

Fig. 4

The AIV-H9N2 (A) and IBV (B) viruses shedding titers in experimentally infected broilers in both single AIV-H9N2 and AIV-H9N2 with IBV mixed infections.