Recombinant Fowl aviadenovirus E (FAdV-E) penton base vaccination fails to confer protection against inclusion body hepatitis (IBH) in chickens.

Inclusion body hepatitis (IBH) is a metabolic disease affecting chickens, associated with different serotypes of fowl adenovirus (FAdV). Experimentally tested vaccines against IBH include several capsid-based subunit vaccines, but not the penton base protein. In the present study, specific pathogen-free chickens were vaccinated with recombinant penton base expressed from each of two different FAdV serotypes (FAdV-7 and FAdV-8b), followed by challenge with a virulent IBH-causing strain. No protection was observed with either vaccine, possibly due to the low immunogenicity of each protein and their inability to induce neutralizing antibodies in the host.

Local cellular immune response plays a key role in protecting chickens against hepatitis-hydropericardium syndrome (HHS) by vaccination with a recombinant fowl adenovirus (FAdV) chimeric fiber protein.

Fowl adenovirus (FAdV)-induced diseases hepatitis-hydropericardium syndrome (HHS) and inclusion body hepatitis (IBH) have been affecting the poultry industry with increasing severity in the last two decades. Recently, a subunit vaccine based on a chimeric fiber protein with epitopes from different fowl adenovirus serotypes (named crecFib-4/11) has been shown to confer simultaneous protection against both HHS and IBH. However, the underlying immune mechanisms in chickens are still enigmatic, especially because of frequently absent neutralizing response despite high levels of protection. In this study, we investigated the kinetics of the humoral and cellular immune responses in specific pathogen-free chickens after vaccination with crecFib-4/11 and/or challenge with a HHS-causing strain, on a systemic level, as well as locally in target and lymphoid organs. The humoral response was assessed via enzyme-linked immunosorbent assay (ELISA) and virus neutralization test in serum, while the cellular immune response was determined by phenotyping using flow cytometry. Although vaccination induced serum antibodies, as confirmed by ELISA, such antibodies exhibited no pre-challenge neutralizing activity against FAdV-4. Nevertheless, immunized birds experienced a significant B cell increase in the liver upon challenge, remaining high throughout the experiment. Furthermore, vaccination stimulated the proliferation of cytotoxic T lymphocytes, with earlier circulation in the blood compared to the challenge control and subsequent increase in liver and spleen. Overall, these findings imply that protection of chickens from HHS after crecFib-4/11 vaccination relies on a prominent local immune response in the target organs, instead of circulating neutralizing antibodies.

Vaccination with a fowl adenovirus chimeric fiber protein (crecFib-4/11) simultaneously protects chickens against hepatitis-hydropericardium syndrome (HHS) and inclusion body hepatitis (IBH).

In the past decades, fowl adenovirus (FAdV)-related diseases became an increasing concern for the poultry industry worldwide. Various immunization strategies against FAdVs have been experimentally investigated, with a particular focus on subunit vaccines against hepatitis-hydropericardium syndrome (HHS), caused by FAdV serotype 4, and inclusion body hepatitis (IBH), caused by serotypes 2, 8a, 8b and 11. In this study, we extended our innovative concept of recombinant chimeric fiber proteins to design a novel chimera combining epitopes from two distinct serotypes, FAdV-4 and -11, and we investigated its efficacy to simultaneously protect chickens against HHS and IBH. Specific pathogen-free chickens were vaccinated with the novel recombinant chimeric fiber and subsequently challenged with either a HHS- or IBH-causing strain. Vaccinated/challenged birds exhibited a reduction of clinical signs, limited hepatomegaly and lower levels of AST compared to the respective challenge controls. Furthermore, the vaccine prevented atrophy of HHS-affected lymphoid organs, such as thymus and bursa of Fabricius, and viral load in the target organs was significantly reduced. Clinical protection was associated with high levels of pre-challenge antibodies measured on ELISA plates coated with the vaccination antigen. Interestingly, the development of neutralizing antibodies was limited against FAdV-11 and absent against FAdV-4, indicating that protection granted by such an antigen may be linked to different immunization pathways. In conclusion, we proved that the concept of chimeric fiber vaccines can be extended across viral species boundaries and represents the first single-component FAdV subunit vaccine providing comprehensive protection against different FAdV-associated diseases.

Recombinantly Expressed Chimeric Fibers Demonstrate Discrete Type-Specific Neutralizing Epitopes in the Fowl Aviadenovirus E (FAdV-E) Fiber, Promoting the Optimization of FAdV Fiber Subunit Vaccines towards Cross-Protection in vivo.

Vaccines against inclusion body hepatitis in chickens are complicated by the involvement of antigenically diverse fowl adenovirus types. Though immunization with fiber protein confers robust protection, type specificity of fiber antibodies is an obstacle for the desired broad coverage. In this study, we utilized information on multiple linear epitopes predicted in the Fowl Aviadenovirus E (FAdV-E) fiber head (knob) to develop chimeric fibers with an exchange between two serotypes' sequences, each containing proposed epitopes. Two consecutive segments pertaining to amino acid positions 1 to 441 and 442 to 525/523 in the fibers of FAdV-8a and -8b, types of Fowl Aviadenovirus E that cause inclusion body hepatitis, were swapped reciprocally to result in novel chimeras, crecFib-8a/8b and crecFib-8b/8a. crecFib was indistinguishable from monospecific recombinant fibers in its eactivity with different FAdV antisera in Western blotting. However, contrary to the results for monospecific fibers, crecFib induced cross-neutralizing antibodies against both serotypes in chickens. This demonstrates three nonidentical epitopes in the FAdV-E fiber, the conserved epitope detected in Western blotting and at least two epitopes participating in neutralization, being type specific and located opposite residue position 441-442. Furthermore, we supply conformational evidence for a site in the fiber knob with accessibility critical for neutralization. With such an extended neutralization spectrum compared to those of individual fibers, crecFib was anticipated to fulfill and even extend the mechanistic basis of fiber-mediated protection toward bivalent coverage. Accordingly, crecFib, administered as a single-antigen component, protected chickens simultaneously against challenge with FAdV-8a or -8b, demonstrated by up-to-complete resistance to clinical disease, prevention of target organ-related changes, and significant reduction of viral load. IMPORTANCE The control of inclusion body hepatitis, a disease of economic importance for chicken production worldwide, is complicated by an etiology involving multiple divergent fowl adenovirus types. The fiber protein is principally efficacious in inducing neutralizing and protective antibodies in vaccinated chickens; however, it faces limitations due to its intrinsic type specificity for neutralization. In this study, based on an in silico-guided prediction of multiple epitopes in the fowl adenovirus fiber head's loops, we designed chimeric proteins, swapping N- and C-distal fiber portions, each containing putative epitopes, between divergent types FAdV-8a and -8b. In in vitro and in vivo studies, the chimeric fiber displayed extended properties compared to those of individual monotype-specific fibers, allowing the number, distribution, functionality, and conformational bearings of epitopes of the fowl adenovirus fiber to be characterized in more detail. Importantly, the chimeric fiber induced cross-neutralizing antibodies and protective responses in chickens against infections by both serotypes, promoting the advancement of broadly protective subunit vaccination strategies against FAdV.

Fowl adenovirus (FAdV) fiber-based vaccine against inclusion body hepatitis (IBH) provides type-specific protection guided by humoral immunity and regulation of B and T cell response.

A recombinant fowl adenovirus (FAdV) fiber protein, derived from a FAdV-8a strain, was tested for its efficacy to protect chickens against inclusion body hepatitis (IBH). FAdV-E field isolates belonging to both a homotypic (FAdV-8a) and heterotypic (-8b) serotype were used as challenge. Mechanisms underlying fiber-induced protective immunity were investigated by fiber-based ELISA, virus neutralization assays and flow cytometry of peripheral blood mononuclear cells, monitoring the temporal developments of humoral and cellular responses after vaccination and challenge exposure. Birds were clinically protected from the homologous challenge and showed a significant reduction of viral load in investigated target organs, whereas fiber-based immunity failed to counteract the heterologous serotype infection. These findings were supported in vitro by the strictly type-specific neutralizing activity of fiber immune sera. In protected birds, fiber vaccination prevented a post-challenge drop of peripheral B cells in blood. Furthermore, fiber immunization stimulated CD4+ T lymphocyte proliferation while moderating the CD8α+ T cell response and prevented challenge-induced changes in systemic monocytes/macrophages and γδ+ T cell subpopulations. Both vaccinated and adjuvant-only injected birds experienced a priming of systemic B cells and TCRγδ+ T lymphocytes, which masked possible pre-challenge effects due to the antigen. In conclusion, within FAdV-E, recombinant fiber represents a vaccine candidate to control the adverse effects of homotypic infection by eliciting an effective humoral immunity and regulating B and T cell response, whereas the failure of heterotypic protection suggests a primordial role of humoral immunity for this vaccine.

Occurrence and diversity of Campylobacter species in captive chelonians.

The aim of this study was to investigate the occurrence and diversity of Campylobacter species in chelonians. From July 2016 to September 2017, a total of 452 individuals from a large variety of tortoises (n = 366) and turtles/terrapins (n = 86) kept in private collections and breeding centres, wildlife rescue centres, zoos, pet shops, and veterinary clinics from Northern Italy was sampled and subjected to microbiological examination. Campylobacter genus and species confirmation was performed by single and multiplex PCRs. Out of 452 samples, five (1.1%) tested positive: three for C. iguaniorum (two Testudo graeca and one Testudo hermanni), one for C. fetus subsp. testudinum (Stigmochelys pardalis) and one for C. geochelonis (Testudo hermanni). This study suggests that Campylobacter spp. are not common in chelonians, but a variety of species can be detected in these hosts, including those potentially pathogenic for humans. Further studies are needed to understand the epidemiology and the pathogenic potential for both animals and humans of reptile-associated Campylobacter spp.

Multilocus sequence typing of Campylobacter jejuni and Campylobacter coli to identify potential sources of colonization in commercial turkey farms.

Poultry are the main reservoir for thermophilic Campylobacter spp., which is the most common causative agent of human bacterial gastroenteritis. The epidemiology of Campylobacter in poultry, particularly in turkeys, is not completely understood. This study aimed at identifying potential sources and transmission routes of thermophilic Campylobacter spp. in commercial turkey farms. C. jejuni and C. coli isolates from breeders (n = 29, 20 C. jejuni and 9 C. coli) and their progeny (n = 51, 18 C. jejuni and 33 C. coli) reared in two different farms for three sequential production cycles were analysed by multilocus sequence typing (MLST). Strains (n = 88, 42 C. jejuni and 46 C. coli) isolated from environmental (i.e. anteroom and in-house overshoes), water (i.e. drinkers and water line), and pest (i.e. flies, Alphitobius diaperinus, and mice) sources were also examined. MLST of C. jejuni and C. coli isolates resulted in 13 and 12 different sequence types (STs) belonging to six and one previously-described clonal complexes (CCs), respectively. Three novel STs were identified. Genetic similarities were detected between isolates from fattening turkeys and the considered environmental, water, and pest sources, and with the breeders to a lesser extent. Source attribution analysis estimated that environmental and water sources accounted for most (∼75%) of fattening turkey isolates and were therefore identified as the most likely sources of flock colonization, followed by pests (∼20%) and breeders (∼5%). These sources may thus be targeted by control measures to mitigate the risk of Campylobacter colonization in commercial turkeys. RESEARCH HIGHLIGHTS High occurrence of C. jejuni and C. coli in commercial turkey flocks. High genetic diversity of C. jejuni and C. coli in commercial turkey flocks. Horizontal transmission responsible for Campylobacter colonization of commercial turkey flocks. Environmental and water sources involved in Campylobacter colonization of commercial turkey flocks. Strategies for prevention and control of Campylobacter colonization of commercial turkey flocks are needed.