Foundations and advances in recombinant, subunit, and conjugate vaccine development against Pasteurella multocida: A review of the 2015-2025 decade.

Pasteurella multocida is a major veterinary pathogen causing severe diseases such as fowl cholera, hemorrhagic septicemia, and atrophic rhinitis, leading to substantial global losses in livestock production. Conventional bacterins and live-attenuated vaccines remain limited by serotype specificity, variable safety, and short-lived immunity, prompting the need for molecularly defined alternatives. Genomic and proteomic analyses have driven the identification of conserved outer membrane proteins (OMPs), including PlpE, OmpH, OmpA, Omp87, and VacJ as leading antigen candidates capable of eliciting robust humoral and cellular responses with promising cross-protective potential. Parallel progress in antigen engineering and delivery technologies have supported the emergence of multi-epitope constructs, DNA vaccines, and innovative platforms such as outer membrane vesicles (OMVs), bacterial ghosts, nanoparticles, and viral vectors, each enhancing antigen presentation and immunomodulation. Despite these advances, major challenges persist, particularly the extensive antigenic diversity of P. multocida, inconsistent cross-protection across serogroups, and translational gaps between murine models and target livestock species. This review presents key advances from 2015 to 2025 in recombinant, subunit, and conjugate vaccine development aimed at overcoming these limitations, with the conjugate vaccine section focusing on the structural, genetic, and conformational foundations required for future CPS-based glycoconjugate design.". This review outlines the field's transition toward rational, multi-antigen vaccine design and highlights the need for optimized adjuvants, improved delivery systems, and rigorous efficacy studies in natural hosts to achieve broad-spectrum and long-lasting protection against P. multocida.