Co-infection of turkeys with Escherichia coli (O78) and H6N1 avian influenza virus

Polypharmacology-based approach for screening TCM against coinfection of Mycoplasma gallisepticum and Escherichia coli

Natural products and their unique polypharmacology offer significant advantages for finding novel therapeutics particularly for the treatment of complex diseases. Meanwhile, Traditional Chinese Medicine exerts overall clinical benefits through a multi-component and multi-target approach. In this study, we used the previously established co-infection model of Mycoplasma gallisepticum and Escherichia coli as a representative of complex diseases. A new combination consisting of 6 herbs were obtained by using network pharmacology combined with transcriptomic analysis to reverse screen TCMs from the Chinese medicine database, containing Isatdis Radix, Forsythia Fructus, Ginkgo Folium, Mori Cortex, Licorice, and Radix Salviae. The results of therapeutic trials showed that the Chinese herbal compounds screened by the target network played a good therapeutic effect in the case of co-infection. In summary, these data suggested a new method to validate target combinations of natural products that can be used to optimize their multiple structure-activity relationships to obtain drug-like natural product derivatives.

Vaccination with inactivated virus against low pathogenic avian influenza subtype H9N2 does not prevent virus transmission in chickens

H9N2 subtype avian influenza has spread dramatically in China ever since first reported in the 1990s. A national vaccination program for poultry was initiated in 1998. Field isolation data show that the widely used inactivated H9N2 vaccine does not provide effective control of the transmission of this low pathogenic avian influenza (LPAI) virus in poultry. Current research has focused on two reasons: (i) insufficient immune response triggered by the vaccination with the inactivated virus, (ii) the occurrence of escape mutants selected by vaccine-induced immune pressure. However, the lack of effectivity of the inactivated virus vaccine to sufficiently reduce transmission has been noticed. We mimicked the natural infection and transmission process of the H9N2 virus in vaccinated and non-vaccinated chickens. A statistical model was used to estimate the transmission rate parameters among vaccinated chickens, varying in serum hemagglutinin inhibition titers (HIT) and non-vaccinated chickens. We demonstrate, for the first time, that the transmission is not sufficiently reduced by the H9N2 vaccine, even when vaccinated chickens have an IgG serum titer (HIT>2³), which is considered protective for vaccination against homologous highly pathogenic avian influenza (HPAI) virus. Our study does, on the other hand, cast new light on virus transmission and immune escape of LPAI H9N2 virus in vaccinated chickens populations, and shows that new mitigation strategies against LPAI viruses in poultry are needed.

Pathogenesis of Avian Influenza Virus Subtype H9N2 in Turkeys and Evaluation of Inactivated Vaccine Efficacy

Avian influenza H9N2 viruses circulate in all types of poultry species, including turkeys, and cause significant losses for the poultry industry in many parts of the word. The aim of this study was to assess the pathogenesis of the Moroccan avian influenza virus (AIV) H9N2 under experimental conditions in turkeys and the protection efficacy of an inactivated commercial vaccine against AIV H9N2. Unvaccinated turkeys showed marked depression sinusitis, respiratory distress characterized by bronchiolar and tracheal rales of moderate severity, and a mortality rate of 50%. Postmortem examinations of dead and euthanatized birds revealed the presence of fibrinous tracheitis and airsacculitis lesions. Vaccination reduced the mortality rate to 20%. Vaccinated birds recovered at day 10 postchallenge, and only 12.5% (1/8) and 37.5% of birds still displayed fibrinous and nonfibrinous airsacculitis lesions, respectively, at day 15 postinoculation. Viral shedding in cloacal and tracheal swabs was lower in vaccinated than in control birds. Although viral RNA was detected in the cloacal swabs of all unvaccinated turkeys at day 3 postinoculation, only 50% of the vaccinated turkeys were positive for virus detection. At day 11 postinoculation, no viral RNA was detected in oropharyngeal swabs of vaccinated turkeys, whereas 40% of the unvaccinated turkeys were still shedding virus.

Influenza A virus infection in turkeys induces respiratory and enteric bacterial dysbiosis correlating with cytokine gene expression

Turkey respiratory and gut microbiota play important roles in promoting health and production performance. Loss of microbiota homeostasis due to pathogen infection can worsen the disease or predispose the bird to infection by other pathogens. While turkeys are highly susceptible to influenza viruses of different origins, the impact of influenza virus infection on turkey gut and respiratory microbiota has not been demonstrated. In this study, we investigated the relationships between low pathogenicity avian influenza (LPAI) virus replication, cytokine gene expression, and respiratory and gut microbiota disruption in specific-pathogen-free turkeys. Differential replication of two LPAI H5N2 viruses paralleled the levels of clinical signs and cytokine gene expression. During active virus shedding, there was significant increase of ileal and nasal bacterial contents, which inversely corresponded with bacterial species diversity. Spearman’s correlation tests between bacterial abundance and local viral titers revealed that LPAI virus-induced dysbiosis was strongest in the nasal cavity followed by trachea, and weakest in the gut. Significant correlations were also observed between cytokine gene expression levels and relative abundances of several bacteria in tracheas of infected turkeys. For example, interferon γ/λ and interleukin-6 gene expression levels were correlated positively with Staphylococcus and Pseudomonas abundances, and negatively with Lactobacillus abundance. Overall, our data suggest a potential relationship where bacterial community diversity and enrichment or depletion of several bacterial genera in the gut and respiratory tract are dependent on the level of LPAI virus replication. Further work is needed to establish whether respiratory and enteric dysbiosis in LPAI virus-infected turkeys is a result of host immunological responses or other causes such as changes in nutritional uptake.

Arachidonic acid metabolism is elevated in Mycoplasma gallisepticum and Escherichia coli co-infection and induces LTC4 in serum as the biomarker for detecting poultry respiratory disease

Outbreaks of multiple respiratory diseases with high morbidity and mortality have been frequently reported in poultry industry. Metabolic profiling has showed widespread usage in metabolic and infectious disease for identifying biomarkers and understanding of complex mechanisms. In this study, the non-targeted metabolomics were used on Mycoplasma gallisepticum (MG) and Escherichia coli (E.coli) co-infection model in serum, which showed that Leukotriene C4 (LTC4), Leukotriene D4 (LTD4), Chenodeoxycholate, Linoleate and numerous energy metabolites were varied significantly. KEGG enrichment analysis revealed that the metabolic pathways of linoleic acid, taurine and arachidonic acid (AA) were upregulated. To further characterize the consequences of co-infection, we performed an AA metabolic network pathway with metabolic products and enzyme genes. The results showed that the expression of LTC4 increased extremely significant and accompanied with different degree of infection. Meanwhile, the AA network performed the changes and differences of various metabolites in the pathway when multiple respiratory diseases occurred. Taken together, co-infection induces distinct alterations in the serum metabolome owing to the activation of AA metabolism. Furthermore, LTC4 in serum could be used as the biomarker for detecting poultry respiratory disease.

Abbreviations

MG: Mycoplasma gallisepticum; E.coli: Escherichia coli; AA: Arachidonic acid; LTC4: Leukotriene C4; CRD: chronic respiratory diseases; KEGG: Kyoto Encyclopedia of Genes and Genomes; LTs: leukotrienes; PGs: prostaglandins; NO: nitric oxide; HIS: histamine; PCA: Principal Component Analysis; PLS-DA: Partial Least Squares Discriminant Analysis; CCU: color change unit; UPLC: ultra-performance liquid chromatography; MS: mass spectrometry; DEMs: differentially expressed metabolites; ELISA: enzyme-linked immunosorbent assay; SD: standard deviation; VIP: Variable importance in the projection

Typhlitis induced by Histomonas meleagridis affects relative but not the absolute Escherichia coli counts and invasion in the gut in turkeys

Unlike in chickens, dynamics of the gut microbiome in turkeys is limitedly understood and no data were yet published in context of pathological changes following experimental infection. Thus, the impact of Histomonas meleagridis-associated inflammatory changes in the caecal microbiome, especially the Escherichia coli population and their caecal wall invasion in turkeys was investigated. Birds experimentally inoculated with attenuated and/or virulent H. meleagridis and non-inoculated negative controls were divided based on the severity of macroscopic caecal lesions. The high throughput amplicon sequencing of 16SrRNA showed that the species richness and diversity of microbial community significantly decreased in severely affected caeca. The relative abundances of operational taxonomic units belonging to Anaerotignum lactatifermentans, E. coli, and Faecalibacterium prausnitzii were higher and paralleled with a decreased abundances of those belonging to Alistipes putredinis, Streptococcusalactolyticus, Lactobacillus salivarius and Lactobacillus reuteri in birds with the highest lesion scores. Although the relative abundance of E. coli was higher, the absolute count was not affected by the severity of pathological lesions. Immunohistochemistry showed that E. coli was only present in the luminal content of caecum and did not penetrate even severely inflamed and necrotized caecal wall. Overall, it was demonstrated that the fundamental shift in caecal microbiota of turkeys infected with H. meleagridis was attributed to the pathology induced by the parasite, which only led to relative but not absolute changes in E. coli population. Furthermore, E. coli cells did not show tendency to penetrate the caecal tissue even when the intestinal mucosal barriers were severely compromised.

Regulated delayed attenuation improves vaccine efficacy in preventing infection from avian pathogenic Escherichia coli O78 and Salmonella typhimurium

Avian pathogenic Escherichia coli (APEC) O₇₈ and Salmonella typhimurium (S. Typhimurium) are two leading bacterial pathogens that cause significant economic loss in the poultry industry. O-antigen is an important immunogen of these two bacteria to induce host protective immune responses during infection. To develop a bivalent vaccine against APEC O₇₈ and S. Typhimurium, the attenuated Salmonella ST01 (Δasd ΔrfbP Δcrp) was genetically constructed to deliver APEC O₇₈ O-antigen polysaccharide (OPS), which stably expresses OPS with asd⁺ balanced-lethal system in vitro and in vivo. After oral immunization, the recombinant attenuated Salmonella vaccine (RASV) strain ST01 (pSS26-O₇₈) provided insufficient protection against the APEC O₇₈ challenge. Therefore, the regulated delayed attenuation strain ST02 (Δasd ΔrfbP ΔPcrp::TTaraC P_BADcrp) was further constructed by regulating cyclic AMP receptor protein (crp) with araC P_BAD cassette to better present the heterologous O-antigen to the host immune system. The innovative recombinant strain ST02 (pSS26-O₇₈) stimulated robust antibody responses against APEC O₇₈ and S. Typhimurium OPS, with serum titers over 1:800 for both IgG and IgA, thereby providing the complement-mediated bactericidal activity and stronger protection against APEC O₇₈ and S. Typhimurium infection. Collectively, this study demonstrates a biologically-conjugated polysaccharide vaccine candidate that can enhance homologous protection against APEC O₇₈ and S. Typhimurium.

Concurrent infection of Avibacterium paragallinarum and fowl adenovirus in layer chickens

The diagnosis of a concurrent infection of Avibacterium paragallinarum and fowl adenovirus (FAdV) in an infectious coryza–like outbreak in the outskirt of Beijing is reported. The primary signs of the infection were acute respiratory signs, a drop in egg production, and the presence of hydropericardium–hepatitis syndrome–like gross lesions. Laboratory examination confirmed the presence of A. paragallinarum by bacterial isolation and a species-specific PCR test. In addition, conventional serotyping identified the isolates as Page serovar A. Fowl adenovirus was isolated from chicken liver specimen and identified by hexon gene amplification. In addition, histopathologic analysis and transmission electron microscopy examination further confirmed the presence of the virus. Both hexon gene sequencing and phylogenetic analysis defined the viral isolate as FAdV-4. The pathogenic role of A. paragallinarum and FAdV was evaluated by experimental infection of specific-pathogen-free chickens. The challenge trial showed that combined A. paragallinarum and FAdV infection resulted in more severe clinical signs than that by FAdV infection alone. The concurrent infection caused 50% mortality compared with 40% mortality by FAdV infection alone and zero mortality by A. paragallinarum infection alone. To our knowledge, this is the first report of A. paragallinarum coinfection with FAdV. The case implies that concurrent infections with these 2 agents do occur and more attention should be given to the potential of multiple agents during disease diagnosis and treatment.

E190V substitution of H6 hemagglutinin is one of key factors for binding to sulfated sialylated glycan receptor and infection to chickens

Avian influenza viruses (AIVs) recognize sialic acid linked α2,3 to galactose (SAα2,3Gal) glycans as receptors. In this study, the interactions between hemagglutinins (HAs) of AIVs and sulfated SAα2,3Gal glycans were analyzed to clarify the molecular basis of interspecies transmission of AIVs from ducks to chickens. It was revealed that E190V and N192D substitutions of the HA increased the recovery of viruses derived from an H6 duck virus isolate, A/duck/Hong Kong/960/1980 (H6N2), in chickens. Recombinant HAs from an H6 chicken virus, A/chicken/Tainan/V156/1999 (H6N1), bound to sulfated SAα2,3Gal glycans, whereas the HAs from an H6 duck virus did not. Binding preference of mutant HAs revealed that an E190V substitution is critical for the recognition of sulfated SAα2,3Gal glycans. These results suggest that the binding of the HA from H6 AIVs to sulfated SAα2,3Gal glycans explains a part of mechanisms of interspecies transmission of AIVs from ducks to chickens.

Co-infection of Mycoplasma gallisepticum and Escherichia coli Triggers Inflammatory Injury Involving the IL-17 Signaling Pathway

Mycoplasma gallisepticum and Escherichia coli are well known respiratory disease-inducing pathogens. Previous studies have reported that co-infection by MG and E.coli causes significant economic loss in the poultry industry. In order to assess the respiratory toxicity of co-infection in chicken lung, we established a co-infection model to investigate changes in the inflammatory cytokines, lung tissue structure, and transcriptome profiles of chicken lung. The results showed that co-infection caused a wider range of immune damage and more severe tissue lesions than single-pathogen infection. Differentially expressed gene (DEG) analysis indicated that 3,115/1,498/1,075 genes were significantly expressed among the three infection groups, respectively. Gene ontology and KEGG analysis showed genes enriched in response to immune response, cytokine-cytokine receptor interaction, and inflammation-related signaling pathways. Among these pathways, IL-17 signaling was found to be significantly enriched only in co-infection. The expression of IL-17C, CIKS, TRAF6, NFκB, C/EBPβ, and inflammatory chemokines were significantly up-regulated in response to co-infection. Taken together, we concluded that co-infection increased the expression of inflammatory chemokines in lungs through IL-17 signaling, leading to cilia loss and excessive mucus secretion. These results provide new insights into co-infection and reveal target proteins for drug therapy.

Immunization with outer membrane vesicles of avian pathogenic Escherichia coli O78 induces protective immunity in chickens

Avian pathogenic Escherichia coli (APEC) typically causes colibacillosis and is a major concern for the poultry industry and public health. As a vaccine platform, the outer membrane vesicles (OMVs) derived from various gram-negative bacteria and even some gram-positive bacteria have been reported to be immunogenic in laboratories or upon commercial usage worldwide. Here, we purified OMVs from APEC serotype O78 strain by ultracentrifugation and gradient isolation. By SDS-PAGE and LC-MS/MS analysis, the 20 most abundant proteins located on OMVs were identified and analyzed; the lipopolysaccharide (LPS) profiles of OMVs were not different from those of the bacteria. Moreover, three groups of chickens were immunized with OMV-, outer membrane protein (OMP)- and PBS, with the latter two serving as positive and negative controls, respectively. By analyzing the anti-OMP and anti-LPS IgG titers stimulated by the tested vaccine candidates, the macrophage opsonophagocytic activity and the bactericidal activity mediated by serum antibodies in vaccinated chickens, we found that the OMV-vaccinated chicken group was superior to the two other groups. These findings were confirmed by additional chicken challenge tests, in which all OMV-vaccinated group chickens obtained complete protection but those of the other two groups were barely protected. Our data demonstrate that native APEC O78 OMVs can induce protective immunity in chickens and therefore be used as a candidate vaccine for APEC serotype O78 strain infections.