Effects of immunosuppression on the efficacy of vaccination against Mycoplasma gallisepticum infection in chickens

Effect of co-infection with Newcastle disease virus on Mycoplasma gallisepticum pathogenesis in vivo and in vitro

The co-infection of Newcastle disease virus (NDV) and Mycoplasma gallisepticum (MG) has a detrimental effect on chicken production performance, exerts a deleterious impact on poultry production performance, resulting in substantial economic losses. However, the exact impact and underlying mechanisms remain ambiguous. In this study, co-infection models were established both in vivo and in vitro. Through these models, it was found that the co-infection facilitated the replication of MG and NDV, as well as MG induced pathogenesis. The administration of lentogenic NDV resulted in the suppression of the innate immune response in vivo. At cellular level, co-infection promoted MG induced apoptosis through caspase-dependent mitochondrial endogenous pathway and suppressed the inflammatory secretion. This research contributes novel insights in co-infection.

Evaluation of the safety and efficacy of the novel Mycoplasma gallisepticum vaccine, Vaxsafe MG304, after spray-vaccination of 1-day-old specific pathogen-free chicks

Mycoplasma gallisepticum causes chronic respiratory disease in poultry. A novel vaccine, Vaxsafe MG304 (the ts-304 strain), has greater protective efficacy in chickens than the Vaxsafe MG (strain ts-11) vaccine when delivered by eye drop at 3 weeks of age. Applying this vaccine in the hatchery to 1-day-old birds, using mass administration methods, would improve animal welfare and reduce labour costs associated with handling individual birds. This study assessed the protection provided by vaccination with Vaxsafe MG304 after administration to 1-day-old chicks. Chicks were administered a single dose of the vaccine to assess the efficacy of either a high dose (107.0 colour changing units, CCU) or a low dose (105.7 CCU) after eye drop or spray (in water or gel) administration against experimental challenge with virulent M. gallisepticum strain Ap3AS at 7 weeks of age. The vaccine was able to colonise the palatine cleft of chicks after vaccination by eye drop (at both doses) or by spray (in water or gel) (at the high dose). The high dose of vaccine, when delivered by eye drop or spray, was shown to be safe and induced a serological response and protective immunity (as measured by tracheal mucosal thickness and air sac lesion scores) against challenge. Vaccination of 1-day-old chicks with Vaxsafe MG304 by eye drop induced protective immunity equivalent to vaccination at 3 weeks of age. Vaxsafe MG304 was also protective when applied by both coarse- and gel spray methods at the higher dose and is therefore a suitable live attenuated vaccine for use in 1-day-old chicks.

Novel variant infectious bursal disease virus diminishes FAdV-4 vaccination and enhances pathogenicity of FAdV-4

Infectious bursal disease virus (IBDV) caused an acute and highly contagious infectious disease characterized by severe immunosuppression, causing considerable economic losses to the poultry industry globally. Although this disease was well-controlled under the widely use of commercial vaccines in the past decades, the novel variant IBDV strains emerged recently because of the highly immunized-selection pressure in the field, posting new threats to poultry industry. Here, we reported novel variant IBDV is responsible for a disease outbreak, and assessed the epidemic and pathogenicity of IBDV in this study. Moreover, we constructed a challenge model using Fowl adenovirus serotype 4 (FAdV-4) to study on the immunosuppressive effect. Our findings underscore the importance of IBDV surveillance, and provide evidence for understanding the pathogenicity of IBDV.

Development and evaluation of a multi-epitope subunit vaccine against Mycoplasma synoviae infection

Mycoplasma synoviae is an extremely significant avian pathogen, causing substantial financial harm to poultry farmers worldwide, and impacting both chicken and turkey production. Multi-epitope vaccines offer higher immunity and lower allergenicity compared to conventional vaccines. In this study, our objective is to develop a multi-epitope vaccine for M. synoviae (MSMV) and to evaluate the immune responses and protective efficacy of MSMV in chickens. We successfully identified a total of 14 B-cell, 5 MHC-I, and 16 MHC-II binding epitopes from the immunodominant proteins RS01790, BMP, GrpE, RS00900, and RS00275. Subsequently, we synthesized the multi-epitope vaccine by connecting all conserved epitopes using appropriate linkers. The resulting MSMV demonstrated notable antigenicity, non-allergenic properties, and stability. Notably, the MSMV effectively stimulated high levels of antibody production in chickens. Furthermore, MSMV the vaccine elicited a robust cellular immune response in chickens, characterized by a well-balanced Th1/Th2-type cytokine profile and enhanced lymphocyte proliferation. In immune protection experiments, the vaccinated chickens exhibited reduced air sac lesion scores and tracheal mucosal thickness compared to their non-vaccinated chickens. Additionally, vaccinated chickens displayed lower M. synoviae loads in throat swabs. These findings collectively suggested that the MSMV holds significant potential as a promising vaccine candidate for managing M. synoviae infections.

Screening of immunogenic proteins and evaluation of vaccine candidates against Mycoplasma synoviae

Mycoplasma synoviae (M. synoviae) is a serious avian pathogen that causes significant economic losses to chicken and turkey producers worldwide. The currently available live attenuated and inactivated vaccines provide limited protection. The objective of this study was to identify potential subunit vaccine candidates using immunoproteomics and reverse vaccinology analyses and to evaluate their preliminary protection. Twenty-four candidate antigens were identified, and five of them, namely RS01790 (a putative sugar ABC transporter lipoprotein), BMP (a substrate-binding protein of the BMP family ABC transporter), GrpE (a nucleotide exchange factor), RS00900 (a putative nuclease), and RS00275 (an uncharacterized protein), were selected to evaluate their immunogenicity and preliminary protection. The results showed that all five antigens had good immunogenicity, and they were localized on the M. synoviae cell membrane. The antigens induced specific humoral and cellular immune responses, and the vaccinated chickens exhibited significantly greater body weight gain and lower air sac lesion scores and tracheal mucosal thicknesses. Additionally, the vaccinated chickens had lower M. synoviae loads in throat swabs than non-vaccinated chickens. The protective effect of the RS01790, BMP, GrpE, and RS00900 vaccines was better than that of the RS00275 vaccine. In conclusion, our study demonstrates the potential of subunit vaccines as a new approach to developing M. synoviae vaccines, providing new ideas for controlling the spread of M. synoviae worldwide.

Effects of administration of tylosin on the duration of protective immunity induced by the novel Mycoplasma gallisepticum vaccine strain, Vaxsafe MG ts-304, in chickens

Prophylactic use of antimicrobials after administration of live vaccines is a common practice in the poultry industry, but the impact of this on the efficacy and duration of protection induced by the vaccines is unknown. The effect of treatment with tylosin on the efficacy of vaccination with the live attenuated M. gallisepticum strain, Vaxsafe MG ts-304, was examined. This vaccine has previously been shown to provide protection for at least 57 weeks. Ten-week-old specific-pathogen-free chickens were vaccinated with Vaxsafe MG ts-304 and then treated with tylosin at a therapeutic dose in drinking water from 6 weeks after vaccination. Tylosin was withdrawn 5 days before challenge with M. gallisepticum strain Ap3AS at 6, 10, 14, 18 or 22 weeks after vaccination. Air sac lesions, tracheal mucosal thickening and the concentrations of serum antibodies against M. gallisepticum were assessed at 2 weeks after challenge. The protection induced by the vaccine in the 6 weeks before initiation of tylosin treatment persisted for 18 weeks after vaccination, with lesions only observed in the air sacs of vaccinated birds that had been treated with tylosin after challenge at 22 weeks after vaccination. Concentrations of serum antibodies against M. gallisepticum began to decrease in vaccinated birds that had been treated with tylosin from 16 weeks after vaccination. This study has suggested that treatment of chickens with tylosin after vaccination with a live attenuated mycoplasma vaccine reduces the duration of protective immunity afforded by the vaccine.

Measures of tracheal lesions are more discriminatory and reproducible indications of chronic respiratory disease caused by Mycoplasma gallisepticum in poultry

Mycoplasma gallisepticum is the primary causative agent of chronic respiratory disease in poultry and vaccination is the measure most commonly used for its control. Pathological changes caused by M. gallisepticum are mainly observed in the trachea and air sacs, but assessment of air sac lesions is subjective. Standardised parameters for evaluation of pathological changes, and their reproducibility and discrimination in uninfected and infected groups, are critical when assessing the efficacy of M. gallisepticum vaccination. This study reviewed and critically appraised the published literature on evaluation of vaccine efficacy against pathological changes caused by M. gallisepticum in poultry in the trachea and air sacs. A search of four electronic databases, with subsequent manual filtering, identified 23 eligible papers published since 1962 describing the assessment of histopathological changes in the trachea using tracheal lesion scores and/or measurement of tracheal mucosal thicknesses and assessment of gross air sac lesions using lesion scores. Measurement of tracheal lesions proved a more reliable and robust method of assessing disease induced by M. gallisepticum when compared to assessment of air sac lesions, highlighting the importance of including assessment of tracheal lesions as the primary outcome variable in vaccine efficacy studies. In addition, this study also identified the necessity for use of a standardised model for evaluation and reporting on M. gallisepticum vaccines to minimise variations between vaccine efficacy studies and to allow direct comparisons between them.

Comparative pathogenicity of infectious bursal disease viruses of three different genotypes

Infectious bursal disease (IBD) is a highly immunosuppressive and often fatal viral disease of young chickens. The causal agent IBD virus (IBDV) is an avian Birnavirus having two genome segments that have evolved independently and contributed to the emergence of many genotypes with different pathogenic profile. The present study aimed at genetic and pathogenic characterization of IBDVs from Bangladesh. We performed phylogenetic analysis of 15 IBDV isolates recovered from field outbreaks in chickens during 2020-2021 and compared the pathogenicity of three selected isolates belonging to different genotypes on experimental infection in chickens. Out of 15 isolates, one was the typical vvIBDV of genotype A3B2, 13 were reassortant vvIBDV of genotype A3B3 having very virulent-like segment A and early Australian-like segment B, and the remaining one isolate was a classical virulent IBDV of A1aB1 genotype. A few amino acid substitutions were observed between the genotypes in four putative antigenic sites on VP2. In a comparative pathogenicity study, the typical vvIBDV isolate BD-25(A3B2) appeared to be the most virulent with 100% morbidity and 90% mortality, followed by the segment-reassortant vvIBDV isolate BD-28(A3B3) with 50% morbidity and 30% mortality. However, the gross and histopathological lesions in the bursa of Fabricius were similar. The classical virulent isolate BD-26(A1aB1) did not cause any clinical disease. In conclusion, three genotypes of IBDV are co-circulating in poultry of Bangladesh and the typical vvIBDV of A3B2 genotype was more virulent than the reassortant vvIBDV of A3B3 genotype. Further studies are required to assess the country-wide distribution of IBDV of different genotypes and the efficacy of the currently available vaccines in protecting chickens against different genotypes of IBDV in Bangladesh.

Infectious bursal disease virus' interferences with host immune cells: What do we know?

AbstractInfectious bursal disease virus (IBDV) induces one of the most important immunosuppressive diseases in chickens leading to high economic losses due increased mortality and condemnation rates, secondary infections and the need for antibiotic treatment. Over 400 publications have been listed in PubMed.gov in the last five years pointing out the research interest in this disease and the development of improved preventive measures. While B cells are the main target cells of the virus, also other immune and non-immune cell populations are affected leading a multifaceted impact on the normally well orchestrated immune system in IBDV-infected birds. Recent studies clearly revealed the contribution of innate immune cells as well as T cells to a cytokine storm and subsequent death of affected birds in the acute phase of the disease. Transcriptomics identified differential regulation of immune related genes between different chicken genotypes as well as virus strains, which may be associated with a variable disease outcome. The recent availability of primary B cell culture systems allowed a closer look into virus-host interactions during IBDV-infection. The new emerging field of research with transgenic chickens will open up new opportunities to understand the impact of IBDV on the host also under in vivo conditions, which will help to understand the complex virus-host interactions further.

Heterologous Expression, Purification, and Immunomodulatory Effects of Recombinant Lipoprotein GUDIV-103 Isolated from Ureaplasma diversum

Ureaplasma diversum is a bacterial pathogen that infects cattle and can cause severe inflammation of the genital and reproductive systems. Lipid-associated membrane proteins (LAMPs), including GUDIV-103, are the main virulence factors in this bacterium. In this study, we heterologously expressed recombinant GUDIV-103 (rGUDIV-103) in Escherichia coli, purified it, and evaluated its immunological reactivity and immunomodulatory effects in bovine peripheral blood mononuclear cells (PBMCs). Samples from rabbits inoculated with purified rGUDIV-103 were analysed using indirect enzyme-linked immunosorbent assay and dot blotting to confirm polyclonal antibody production and assess kinetics, respectively. The expression of this lipoprotein in field isolates was confirmed via Western blotting with anti-rGUDIV-103 serum and hydrophobic or hydrophilic proteins from 42 U. diversum strains. Moreover, the antibodies produced against the U. diversum ATCC 49783 strain recognised rGUDIV-103. The mitogenic potential of rGUDIV-103 was evaluated using a lymphoproliferation assay in 5(6)-carboxyfluorescein diacetate succinimidyl ester−labelled bovine PBMCs, where it induced lymphocyte proliferation. Quantitative polymerase chain reaction analysis revealed that the expression of interleukin-1β, toll-like receptor (TLR)-α, TLR2, TLR4, inducible nitric oxide synthase, and caspase-3−encoding genes increased more in rGUDIV-103−treated PBMCs than in untreated cells (p < 0.05). Treating PBMCs with rGUDIV-103 increased nitric oxide and hydrogen peroxide levels. The antigenic and immunogenic properties of rGUDIV-103 suggested its suitability for immunobiological application.

Sheep Infection Trials with 'Phase-Locked' Vpma Expression Variants of Mycoplasma agalactiae-Towards Elucidating the Role of a Multigene Family Encoding Variable Surface Lipoproteins in Infection and Disease

The significance of large multigene families causing high-frequency surface variations in mycoplasmas is not well-understood. Previously, VpmaY and VpmaU clonal variants of the Vpma family of lipoproteins of M. agalactiae were compared via experimental sheep infections using the two corresponding ‘Phase-Locked Mutants’. However, nothing is known about the infectivity of the remaining four Vpma expression variants VpmaX, VpmaW, VpmaZ and VpmaV as they were never evaluated in vivo. Here, in vivo infection and disease progression of all six Vpma expressers constituting the Vpma family of type strain PG2 were compared using the corresponding xer1-disrupted PLMs expressing single well-characterized Vpmas. Each of the six PLMs were separately evaluated using the intramammary sheep infection model along with the control phase-variable wildtype strain PG2. Thorough bacteriological, pathological and clinical examinations were performed, including assessment of milk quality, quantity and somatic cell counts. Altogether, the results indicated that the inability to vary the Vpma expression phase does not hamper the initiation of infection leading to mastitis for all six PLMs, except for PLMU, which showed a defect in host colonization and multiplication for the first 24 h p.i. and pathological/bacteriological analysis indicated a higher potential for systemic spread for PLMV and PLMX. This is the first study in which all isogenic expression variants of a large mycoplasma multigene family are tested in the natural host.

Glycyrrhizic Acid against Mycoplasma gallisepticum-Induced Inflammation and Apoptosis Through Suppressing the MAPK Pathway in Chickens

Mycoplasma gallisepticum (MG) is the primary pathogen of chronic respiratory diseases (CRDs) in chickens. In poultry production, antibiotics are mostly used to prevent and control MG infection, but the drug resistance and residue problems caused by them cannot be ignored. Glycyrrhizic acid (GA) is derived from licorice, a herb traditionally used to treat various respiratory diseases. Our study results showed that GA significantly inhibited the mRNA and protein expression of pMGA1.2 and GapA in vitro and in vivo. Furthermore, the network pharmacology study revealed that GA most probably resisted MG infection through the MAPK signaling pathway. Our results demonstrated that GA inhibited MG-induced expression of MMP2/MMP9 and inflammatory factors through the p38 and JUN signaling pathways, but not the ERK pathway in vitro. Besides, histopathological sections showed that GA treatment obviously attenuated tracheal and lung damage caused by MG invasion. In conclusion, GA can inhibit MG-triggered inflammation and apoptosis by suppressing the expression of MMP2/MMP9 through the JNK and p38 pathways and inhibit the expression of virulence genes to resist MG. Our results suggest that GA might serve as one of the antibiotic alternatives to prevent MG infection.