Abstract
H9N2 avian influenza virus (AIV) infection in chickens is often accompanied by secondary bacterial infection, but the mechanism is unclear. The aim of the present study was to reveal that mechanism and explore non-antibiotic treatment. 16s rRNA sequencing and metabonomics were performed in the intestinal contents of chickens infected with H9N2 AIV or H9N2 AIV and fed with ageratum-liquid (AL) to reveal the metabolite that promote intestinal Escherichia coli (E. coli) proliferation caused by H9N2 AIV, as well as to determine the regulatory effect of AL. It was found that H9N2 AIV infection led E. coli to become the dominant gut microbe and promoted E. coli translocation from the intestinal tract to the visceral tissue through the damaged intestinal barrier. H9N2 AIV infection induces inflammation in the intestinal mucosa and promotes the secretion and release of nitrate from the host intestinal epithelium. In addition, nitrate promoted E. coli proliferation in the inflamed intestinal tract following H9N2 AIV infection. Furthermore, Chinese herbal medicine AL can restore intestinal homeostasis, inhibit the production of nitrate in the intestinal epithelium and effectively prevent the proliferation and translocation of E. coli in the intestines. This is the first report on the mechanism of E. coli secondary infection induced by H9N2 AIV, where herbal medicine AL was shown to have a good preventive effect on the secondary infection.
Highlights
Avian influenza virus (AIV) belongs to the influenza virus A genus of the Orthomyxoviridae family (Marc, 2016)
Results showed that the cloacal swabs collected from specific pathogen free (SPF) chickens infected with the virus can be amplified into HA fragments of H9N2 AIV, indicating that SPF chickens were infected successfully in this experiment (Supplementary Figure 1)
Our results showed that H9N2 AIV could upregulate the mRNA level of tumor necrosis factor (TNF)-α, IFNγ and iNOS, and the nitrate content in the intestinal epithelium was significantly increased, indicating that E. coli may proliferate through nitrate metabolism in the inflamed intestinal tract
Summary
Avian influenza virus (AIV) belongs to the influenza virus A genus of the Orthomyxoviridae family (Marc, 2016). Due to the different pathogenicity of the different subtypes, AIV can have high and low pathogenicity. The biggest harm of H9N2 AIV infection in poultry is the induction of immunosuppression and destruction of their immune system. H9N2 AIV can be isolated from host tissues, including the trachea, lung, brain, spleen, pancreas, cloacal cavity and intestinal tract, and causes inflammation and enteric problems to the hosts (Li et al, 2018). H9N2 AIV is prone to secondary infection of bacteria and other pathogens, the most common of which is Escherichia coli (E. coli) infection, which is associated with high mortality in poultry (Barbour et al, 2009; Samy and Naguib, 2018; Nguyen et al, 2019). The H9N2 AIV subtype poses a significant public health threat, as it can replicate in permissive mammalian tissues without prior adaptation (Samir et al, 2019). Several influenza viruses that infect humans all originate from variants of H9N2 AIV (Lam et al, 2013; Chen et al, 2014); the potential harmful effects of H9N2 AIV on aquaculture and human health and safety cannot be ignored
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