article · Avian Pathology
Co-infection of chickens with Salmonella enteritidis and H9N2 avian influenza virus leads to significantly more severe disease than infection with either pathogen alone. In an experimental trial comparing uninfected, single-infection, and co-infected birds inoculated at 21 days of age, co-infected chickens suffered higher mortality, worse clinical symptoms, and significant body weight changes. The presence of the viral infection suppressed both systemic and mucosal immune defences, lowering antibody and intestinal immunoglobulin A responses while causing greater damage to lymphoid organs such as the spleen and bursa. Consequently, co-infected birds exhibited higher bacterial colonization in organs and increased faecal shedding of Salmonella. In turn, bacterial infection lengthened the shedding duration and increased the shedding titres of the avian influenza virus, pointing to amplified transmission risks.
Both Salmonella and avian influenza virus pose serious threats to agricultural productivity and human public health. Demonstrating that concurrent infections worsen disease severity and prolong pathogen shedding highlights how mixed infections in poultry flocks can aggravate economic losses, accelerate environmental contamination, and raise the risk of zoonotic disease transmission to humans.
This work represents early-stage experimental research that can inform poultry health managers, veterinary diagnostic providers, and vaccine developers. The findings underline the need for combined disease surveillance protocols and potentially multi-pathogen intervention strategies in commercial poultry operations. Because the study focuses on pathogen interactions in an experimental setting, practical applications remain at a pre-commercial, investigative stage rather than near market deployment.
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<i>Salmonella</i> and avian influenza virus are important pathogens affecting the poultry industry and human health worldwide. In this experimental study, we evaluated the consequences of co-infection of <i>Salmonella enteritidis</i> (SE) with H9N2 avian influenza virus (H9N2-AIV) in chickens. Four groups were included: control group, H9N2-AIV group, H9N2-AIV + SE group, and SE group. Infected chickens were intranasally inoculated with H9N2-AIV at 21 days of age and then orally administered SE on the same day. The birds were monitored for clinical signs, mortality rates, and alterations in body weight. Sera, intestinal fluids, oropharyngeal, and cloacal swabs, and tissue samples were collected at 2, 6, 10, and 14 days post-infection (dpi). Significant increases in clinical signs and mortality rates were observed in the H9N2-AIV + SE group. Moreover, chickens with co-infection showed a significant change in body weight. SE faecal shedding and organ colonization were significantly higher in the H9N2-AIV + SE group than in the SE group. H9N2-AIV infection compromised the systemic and mucosal immunity against SE, as evidenced by a significant decrease in lymphoid organ indices as well as systemic antibody and intestinal immunoglobulin A (IgA) responses to SE and a significant increase in splenic and bursal lesion scores. Moreover, SE infection significantly increased shedding titres and duration of H9N2-AIV. In conclusion, this is the first report of co-infection of SE with H9N2-AIV in chickens, which leads to increased pathogenicity, SE faecal shedding and organ colonization, and H9N2-AIV shedding titre and duration, resulting in substantial economic losses and environmental contamination, ultimately leading to increased zoonoses.
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DOI: 10.1080/03079457.2020.1778162
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