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

Age-based host response to Turkey arthritis reovirus in commercial Turkeys in the presence of maternally derived antibodies

BACKGROUND

Turkey arthritis reovirus (TARV) causes arthritic lameness in market-age turkeys. Since 2011, highly pathogenic TARV strains have caused significant economic losses in the turkey industry due to increased culling, reduced market weights, and decreased carcass quality, necessitating more effective control measures. Autogenous vaccine prevention strategies have been inefficacious partly due to a limited understanding of age-related susceptibility of turkeys to TARV. This study investigated age-related host and gut microbiota responses to TARV infection in commercial turkeys derived from vaccinated breeder hens. Poults with known maternally derived antibody titers were orally challenged with TARV O'Neil strain at 1-, 3-, and 7- weeks of age (WOA) and monitored for cloacal virus shedding, gastrocnemius tendon viral tropism, tendon inflammation, weight gain, and changes in gut microbiota.

RESULTS

A transient TARV-induced weight gain suppression was evident in poults infected at 1- and 3- WOA during the first 3 weeks post-infection. Age-dependent variations in cloacal viral shedding, virus isolation from tendons, and tendon inflammation severity were also observed. There was significant dissimilarity in ileal and cecal bacterial communities between mock and infected groups, but the effect of age of infection was unclear.

CONCLUSIONS

Age dependent host response was observed to TARV based on cloacal virus shedding, weight gain suppression and viral tendon tropism. Our study also indicates that maternally derived antibodies appeared insufficient to prevent virus translocation to the tendons and subsequent pathological changes. This study lays the groundwork for future investigations of better vaccines/vaccination strategies and alternative preventive measures.

IMPORTANCE

Turkey arthritis reovirus (TARV) causes lameness due to arthritis and tenosynovitis, commonly in market-age turkeys, resulting in significant economic losses. As a control strategy, the turkey industry used autogenous vaccines, prepared from field TARV isolates in breeder hens, to protect the poults in the early stage of life through maternally derived antibodies (MDAs). This study establishes the level of protection provided by MDAs in young poults with age-based responses to TARV O'Neil reovirus strain. Additionally, this study reveals the dynamics of gut dysbiosis in infected poults at different timepoints, paving the way to ground-breaking investigations into gut microbiome modulation interventions that could potentially improve vaccine efficacy and reduce virus transmission and disease severity.

Influenza a virus subtype H9N2 infection induces respiratory microbiota dysbiosis in chickens via type-I interferon-mediated mechanisms

Avian influenza virus (AIV) poses significant threats to poultry and human health. This study investigates the impact of H9N2 AIV infection on the respiratory microbiota of chickens using 16S rRNA gene sequencing. Total 48 one-day-old specific pathogen-free chickens were assigned to six groups: a control and five post-infection groups (days 1, 3, 5, 7, and 9). After a 15-day microbiota stabilization period, the infected chickens received a viral inoculum (107 TCID50/ml) via ocular, intra-nasal, and intra-tracheal routes. Tracheal and broncho-alveolar lavage samples were analyzed. Significant reductions in microbiota diversity were observed on days 5, 7, and 9 post-infection, compared to d0 controls. Permutational Multivariate Analysis of Variance confirmed significant beta diversity differences (P = 0.001) between infected and uninfected groups. The microbial shifts from d5 to d9 were marked by increased Proteobacteria, decreased Actinobacteria and Firmicutes, and a rise in Dickeya. Elevated type-I interferon (IFN-β) and viperin gene expression at d5 coincided with reduced microbiota diversity, highlighting the respiratory microbiota's role in modulating host responses to AIV H9N2 infection and suggesting potential biomarkers for respiratory dysbiosis.

Human Infant Fecal Microbiota Differentially Influences the Mucosal Immune Pathways Upon Influenza Infection in a Humanized Gnotobiotic Pig Model

In this study, we evaluated the impact of human gut microbiota on the immune pathways in the respiratory tract using a gnotobiotic (Gn) piglet model. We humanized piglets with rural and urban infant fecal microbiota (RIFM and UIFM, respectively) and then infected them with a H1N1 swine influenza virus. We analyzed the microbial diversity and structure of the intestinal and respiratory tracts of the piglets before and after the influenza virus infection and measured the viral load and immune responses. We found that the viral load in the upper respiratory tract of UIFM transplanted piglets was higher than their rural cohorts (RIFM), while virus-specific antibody responses were comparable. The relative cytokine gene expression in the tracheobronchial (respiratory tract) and mesenteric (gastrointestinal) lymph nodes, lungs, blood, and spleen of RIFM and UIFM piglets revealed a trend in reciprocal regulation of proinflammatory, innate, and adaptive immune-associated cytokines as well as the frequency of T-helper/memory cells, cytotoxic T cells, and myeloid immune cell subsets. We also observed different phylum-level shifts of the fecal microbiota in response to influenza virus infection between the two piglet groups, suggesting the potential impact of the gut microbiota on the immune responses to influenza virus infection and lung microbiota. In conclusion, Gn piglets humanized with diverse infant fecal microbiota had differential immune regulation, with UIFM favoring the activation of proinflammatory immune mediators following an influenza virus infection compared to their rural RIFM cohorts. Furthermore, Gn piglets can be a useful model in investigating the impact of diverse human microbiota of the gastrointestinal tract, probably also the respiratory tract, on respiratory health and testing specific probiotic- or prebiotic-based therapeutics.

Exploring the complexities of poultry respiratory microbiota: colonization, composition, and impact on health

An accurate understanding of the ecology and complexity of the poultry respiratory microbiota is of utmost importance for elucidating the roles of commensal or pathogenic microorganisms in the respiratory tract, as well as their associations with health or disease outcomes in poultry. This comprehensive review delves into the intricate aspects of the poultry respiratory microbiota, focusing on its colonization patterns, composition, and impact on poultry health. Firstly, an updated overview of the current knowledge concerning the composition of the microbiota in the respiratory tract of poultry is provided, as well as the factors that influence the dynamics of community structure and diversity. Additionally, the significant role that the poultry respiratory microbiota plays in economically relevant respiratory pathobiologies that affect poultry is explored. In addition, the challenges encountered when studying the poultry respiratory microbiota are addressed, including the dynamic nature of microbial communities, site-specific variations, the need for standardized protocols, the appropriate sequencing technologies, and the limitations associated with sampling methodology. Furthermore, emerging evidence that suggests bidirectional communication between the gut and respiratory microbiota in poultry is described, where disturbances in one microbiota can impact the other. Understanding this intricate cross talk holds the potential to provide valuable insights for enhancing poultry health and disease control. It becomes evident that gaining a comprehensive understanding of the multifaceted roles of the poultry respiratory microbiota, as presented in this review, is crucial for optimizing poultry health management and improving overall outcomes in poultry production.

Evidence for Different Virulence Determinants and Host Response after Infection of Turkeys and Chickens with Highly Pathogenic H7N1 Avian Influenza Virus

Wild birds are the reservoir for all avian influenza viruses (AIV). In poultry, the transition from low pathogenic (LP) AIV of H5 and H7 subtypes to highly pathogenic (HP) AIV is accompanied mainly by changing the hemagglutinin (HA) monobasic cleavage site (CS) to a polybasic motif (pCS). Galliformes, including turkeys and chickens, succumb with high morbidity and mortality to HPAIV infections, although turkeys appear more vulnerable than chickens. Surprisingly, the genetic determinants for virulence and pathogenesis of HPAIV in turkeys are largely unknown. Here, we determined the genetic markers for virulence and transmission of HPAIV H7N1 in turkeys, and we explored the host responses in this species compared to those of chickens. We found that recombinant LPAIV H7N1 carrying pCS was avirulent in chickens but exhibited high virulence in turkeys, indicating that virulence determinants vary in these two galliform species. A transcriptome analysis indicated that turkeys mount a different host response than do chickens, particularly from genes involved in RNA metabolism and the immune response. Furthermore, we found that the HA glycosylation at residue 123, acquired by LP viruses shortly after transmission from wild birds and preceding the transition from LP to HP, had a role in virus fitness and virulence in chickens, though it was not a prerequisite for high virulence in turkeys. Together, these findings indicate variable virulence determinants and host responses in two closely related galliformes, turkeys and chickens, after infection with HPAIV H7N1. These results could explain the higher vulnerability to HPAIV of turkeys compared to chickens. IMPORTANCE Infection with HPAIV in chickens and turkeys, two closely related galliform species, results in severe disease and death. Although the presence of a polybasic cleavage site (pCS) in the hemagglutinin of AIV is a major virulence determinant for the transition of LPAIV to HPAIV, there are knowledge gaps on the genetic determinants (including pCS) and the host responses in turkeys compared to chickens. Here, we found that the pCS alone was sufficient for the transformation of a LP H7N1 into a HPAIV in turkeys but not in chickens. We also noticed that turkeys exhibited a different host response to an HPAIV infection, namely, a widespread downregulation of host gene expression associated with protein synthesis and the immune response. These results are important for a better understanding of the evolution of HPAIV from LPAIV and of the different outcomes and the pathomechanisms of HPAIV infections in chickens and turkeys.