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.
Highlights
Bacillus cereus (B. cereus) is among the microorganisms most often isolated from cases of food spoilage and gastrointestinal diseases as well as non-gastrointestinal infections due to its ability to produce several enterotoxins such as the heat-stable emetic toxin i.e., cereulide and tissue-destructive enzymes[1]
When compared to the breathing difficulty of birds in the H9N2 group on day 3, the breathing difficulty in birds inoculated with H9N2/B. cereus con-infection persisted for one week
A primary infection with H9N2 followed by inoculation with B. cereus caused birds to develop more severe breathing difficulty in comparison with H9N2 infection alone
Summary
Bacillus cereus (B. cereus) is among the microorganisms most often isolated from cases of food spoilage and gastrointestinal diseases as well as non-gastrointestinal infections due to its ability to produce several enterotoxins such as the heat-stable emetic toxin i.e., cereulide and tissue-destructive enzymes[1]. This opportunistic pathogen leads to vomiting and diarrhea syndromes in livestock and human beings, which is associated with rapidly fatal clinical infections, especially in neonates and immunocompromised individuals. Our hypothesis is that immune suppression by B. cereus causes aggravation of the respiratory distress after avian influenza subtype H9N2 infection. The experiments in our study were designed to evaluate both humoral and mucosal responses post inoculation with the combinations of B. cereus and H9N2 or H9N2 alone
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