Infectious Bursal Disease (IBD) is an immunosuppressive viral disease caused by the Infectious Bursal Disease Virus (IBDV). It primarily affects young chickens, targeting the bursa of Fabricius, and poses significant economic threats to the poultry industry. To date, in addition to strict biosecurity measures, large-scale immunization is the optimal strategy and effective method to prevent and control IBDV infection. The emergence of new variant strains has made it more urgent to develop new vaccination strategies against IBD. Over the past few decades, many high-quality vaccines have been available on the market for the control of IBD, which can provide solid protection against the infections and diseases caused by classic IBDV to very virulent IBDV that had been continuously evolving and were endemic worldwide. However, viruses are not static. As they continue to circulate and evolve in the fields, novel antigenic variant viruses have been emerged in the last few years, and vaccines need to keep up with their pace. Collectively, this review summarizes the strategic evolution of IBDV vaccines from traditional methods to cutting-edge molecular platforms, providing promising strategies for developing the next-generation vaccines with higher safety, efficacy, and the ability to keep pace with the antigenic drift in IBDV.

Pasteurella multocida (Pm) is a zoonotic pathogen that poses a significant threat to animal health and causes substantial economic losses, further aggravated by rising tetracycline resistance. To restore the efficacy of tetracyclines to Pm, we evaluated the synergistic antibacterial activity of doxycycline combined with metformin, an FDA-approved antidiabetic agent. Among several non-antibiotic adjuvant candidates, metformin exhibited the most potent in vitro synergy with doxycycline, especially against capsular serogroup A strain (PmA). The combination demonstrated minimal cytotoxicity and hemolysis in both mammalian and avian cells and effectively inhibited resistance development under doxycycline pressure. At 50 mg/kg each, the combination of metformin and doxycycline significantly reduced mortality in mice and ducks acutely infected with PmA (from 100% to 60%), decreased pulmonary bacterial burdens, and alleviated tissue inflammation and damage. Mechanistic validation confirmed that metformin enhances membrane permeability in Pm without compromising membrane integrity, dissipates membrane potential, increases intracellular doxycycline accumulation, and downregulates the transcription of the tetracycline efflux gene tet(B). Morphological analyses further revealed pronounced membrane deformation and possible leakage of intracellular contents. These findings highlight metformin as a potent, low-toxicity tetracycline adjuvant with cross-species efficacy, offering a promising therapeutic approach for managing tetracycline-resistant Pm infections.

Riemerella anatipestifer (RA) is the primary causative agent of infectious serositis in ducks, causing significant economic losses. In this study, a rapid and visual loop-mediated isothermal amplification (LAMP) assay targeting the conserved region of the ompA gene was developed. Specific primers and a FAM-labeled probe were designed, and amplification products were visualized using phenol red-based colorimetric detection and a lateral flow dipstick (LFD) system. Among the five candidate primer sets, primer set 2 was selected because it showed the highest amplification efficiency and specificity, with no cross-reactivity detected against 12 common waterfowl pathogens. Under optimal conditions, the phenol red-based LAMP assay yielded visible results after incubation at 65 °C for 30 min, while the LAMP-LFD assay required an additional 3~5 min probe hybridization step, with detection limits of 7.76 × 10² copies/μL for the phenol red-based method and 7.76 × 10⁰ copies/μL for the LAMP-LFD method. Thirty clinical samples suspected of RA infection were analyzed using conventional PCR and the developed visual LAMP assays. The positive detection rates obtained with the LAMP-LFD and phenol red-based LAMP methods were 63.3% and 60%, respectively, showing high concordance with conventional PCR (56.7%). In conclusion, the LAMP assay integrating phenol red visualization and lateral flow dipstick detection is rapid, sensitive, and easy to perform, and both detection formats show potential for point-of-care or on-site applications, and can be used for the early diagnosis and detection of RA.

Avian metapneumovirus subtype C (aMPV/C) has re-emerged as a widespread pathogen in China, causing hydrosalpinx fluid syndrome (HFS) in laying ducks and resulting in substantial economic losses, highlighting the urgent need for a reliable immunological detection method. In the present study, a non-invasive indirect enzyme-linked immunosorbent assay (iELISA) was developed and optimized for detecting aMPV/C-specific immunoglobulin Y (IgY) in egg yolks of laying ducks, using purified novel aMPV/C as the coating antigen. Checkerboard titration established the optimal conditions as an antigen concentration of 1.25 μg/mL and an IgY dilution of 1:200. The cut-off value, determined by receiver operating characteristic curve analysis, was 0.3268, enabling a detection limit of 1:3200 for IgY antibodies. The assay showed no cross-reactivity with IgY positive for other duck pathogens, and both intra-assay and inter-assay coefficients of variation were less than 10%, demonstrating good specificity and reproducibility. Clinical evaluation of 151 duck egg yolk samples yielded an overall aMPV/C-specific IgY positivity rate of 58.3% (88/151). The concordance rate between the iELISA and an indirect immunofluorescence assay (IFA) was 97.8% (45/46). These results indicate that the established iELISA for detecting aMPV/C-specific IgY is a reliable and practical tool for large-scale detection of aMPV/C exposure in clinical duck egg yolk samples.

The increasing serotypic diversity and multidrug resistance of Riemerella anatipestifer pose a serious threat to the poultry industry, necessitating novel antimicrobial agents. Although phage-derived endolysins offer rapid and specific bactericidal activity with low resistance potential, their efficacy against this Gram-negative pathogen is severely constrained by the outer membrane barrier, driving the need for strategies to enhance endolysin penetration. In this study, the native endolysin NA of phages vB_RanS_CRP2 was verified to lack antibacterial activity. To overcome this barrier, we constructed three chimeric proteins—ALC001, ALC005, and ALC007—by fusing a receptor-binding protein, a cell-penetrating peptide, or a polycationic nonapeptide, respectively. All three chimeras exhibited dose-dependent antibacterial activity, with ALC005 demonstrating the best performance. ALC005 achieved a lytic rate of 72.2% against the tested Riemerella anatipestifer strains, remained stable at 0–40 °C and pH 6–9, and was shown by transmission electron microscopy to exert its bactericidal effect by disrupting the bacterial cell envelope and inducing cell lysis. Collectively, cell-penetrating peptide fusion is a reliable and effective strategy to potentiate endolysin activity against Riemerella anatipestifer.