Abstract:
Avian influenza virus subtype H9N2 is identified in chickens with respiratory disease while Bacillus
cereus (B. cereus) has been frequently isolated from chicken feed in China. However, the roles
of co-infection with these two pathogens remain unclear. In the present study, SPF chicks were
intragastrically administered with 108 CFU/mL of B. cereus for 7 days and then inoculated intranasally
with 100 EID50 of H9N2 three days later. Alternatively, chickens were initially inoculated with H9N2 and
then with B. cereus for one week. Post administration, typical respiratory distress persisted for 5 days
in both co-infection groups. Gizzard erosions developed in the groups B. cereus/H9N2 and B. cereus
group on 7th day while in group H9N2/B. cereus on 14th day. More importantly, both air-sac lesions and
lung damage increased significantly in the co-infection group. Significant inflammatory changes were
observed in the B. cereus group from day 7 to day 21. Moreover, higher loads of H9N2 virus were found
in the co-infected groups than in the H9N2 group. Newcastle Disease Virus (NDV) specific antibodies
were decreased significantly in the H9N2/B. cereus group compared to the B. cereus and the B. cereus/
H9N2 groups. Nonspecific IgA titers were reduced significantly in the B. cereus group and the H9N2/B.
cereus group compared to the control group. In addition to this, lower lymphocyte proliferation was
found in the con-infection groups and the H9N2 group. Hence, feed-borne B. cereus contamination
potentially exacerbates gizzard ulceration and aggravates H9N2-induced respiratory distress by
inhibiting antibody-mediated immunity and pathogen clearance. Thus controlling the B. cereus
contamination in poultry feed is immediately needed.
