Respiratory phagocytes are implicated in enhanced colibacillosis in chickens co-infected with influenza virus H9N2 and Escherichia coli

ABSTRACT

1. The aim of this study was to determine the most likely time interval after infection with influenza virus H9N2 for co-infection with Escherichia coli to cause colibacillosis, the importance of lung load of E. coli and the involvement of respiratory phagocytes.

2. Specific pathogen free chickens were inoculated intranasally with 10⁶EID₅₀ of influenza virus or uninfected. After specified time intervals, 10⁷ CFU E. coli or phosphate-buffered saline was inoculated. The presence of lesions, the number of respiratory phagocytes in the respiratory lavage fluid and the E. coli load in the lung were determined after different time intervals.

3. Compared with the number of lesions in chickens receiving only E. coli inoculation, the number lesions in co-infected chickens were increased at 0- and 3-d time intervals, but reduced in the groups at 6- and 9-d intervals between co-infection.

4. At 1–3 d after E. coli inoculation, the number of lesions chickens was correlated with the number of respiratory phagocytes harvested and related to the E. coli load in the lungs at 5 d.

5. These results suggest that the lesions caused by E. coli in chickens were increased within a 0–3 d interval following H9N2 virus inoculation and that this effect is related to the number of respiratory phagocytes.

KEYWORDS:

• Chicken
• E. coli
• H9N2 influenza virus
• lesion
• respiratory phagocytes

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Natural Science Foundation of Shandong Province [ZR2013CL022]; Poultry Industry Innovation Team of Modern Agricultural Technology System of Shandong Province [DAIT-13-011-03].