In the prevention and treatment of infectious diseases, mRNA vaccines hold great promise because of their low risk of insertional mutagenesis, high potency, accelerated development cycles, and potential for low-cost manufacture. In past years, several mRNA vaccines have entered clinical trials and have shown promise for offering solutions to combat emerging and re-emerging infectious diseases such as rabies, Zika, and influenza. Recently, the successful application of mRNA vaccines against COVID-19 has further validated the platform and opened the floodgates to mRNA vaccine’s potential in infectious disease prevention, especially in the veterinary field. In this review, we describe our current understanding of the mRNA vaccines and the technologies used for mRNA vaccine development. We also provide an overview of mRNA vaccines developed for animal infectious diseases and discuss directions and challenges for the future applications of this promising vaccine platform in the veterinary field.

Mucosal immunization represents a promising strategy for preventing enteric infections. Rotavirus (RV), a leading gastrointestinal pathogen distinguished by its remarkable stability and segmented double-stranded RNA genome, has been engineered into a versatile oral vaccine vector through advanced reverse genetics systems. The clinical efficacy of live-attenuated RV vaccines highlights their unique capacity to concurrently induce mucosal IgA responses and systemic neutralizing antibodies, positioning them as a multiple action vector for multiple immune protection. In this review, we summarize the RV colonization of the intestine and stimulation of intestinal immunity, as well as recent advancements in RV reverse genetics, and focus on their application in the rational design of a multivalent mucosal vaccine vector targeting enteric pathogens considering the advantages and challenges of RV as a vector. We further propose molecular strategies to overcome genetic instability in recombinant RV vectors, including the codon optimization of heterologous inserts. These insights provide a theoretical foundation for developing next-generation mucosal immunization platforms with enhanced safety, stability, and cross-protective efficacy.

Unveiling the molecular mechanisms underlying rotavirus replication and pathogenesis has been hampered by the lack of a reverse genetics (RG) system in the past. Since 2017, multiple plasmid-based RG systems for simian, human, and murine-like rotaviruses have been established. However, none of the described methods have supported the recovery of bovine rotaviruses (BRVs). Here, we established an optimized plasmid-based RG system for BRV culture-adapted strain (BRV G10P [15] BLR) and clinical isolates (BRV G6P [1] C73, G10P [11] HM26) based on a BHK-T7 cell clone stably expressing T7 polymerase. Furthermore, using this optimized RG system, we successfully rescued the reporter virus BRV rC73/Zs, rHM26/Zs and rBLR/Zs, harboring a genetically modified 1.8-kb segment 7 encoding full-length nonstructural protein 3 (NSP3) fused to ZsGreen, a 232-amino acid green fluorescent protein. Analysis of the stability of genomic insertions showed that the rC73/Zs and rBLR/Zs replicated efficiently and were genetically stable in seven rounds of serial passaging, while rHM26/Zs can be stabilized only up to the third generation, indicating that the BRV segment composition may influence the viral fitness. In addition, we adopted the recombinant reporter viruses for high-throughput screening application and discovered 12 candidates out of 1440 compounds with potential antiviral activities against rotavirus. In summary, this improved RG system of BRVs represents an important tool with great potential for understanding the molecular biology of BRV and facilitates the development of novel therapeutics and vaccines for BRV.

The segmented genome of live-attenuated rotavirus (RV) vaccines provides an ideal platform for developing multivalent vaccines against enteric pathogens. Here, we engineered the commercial human RV vaccine strain LLR as a vector to deliver Clostridium perfringens alpha-toxin (CPA), a critical virulence factor associated with gastroenteritis. A screen of four 2A peptide sequences identified that porcine teschovirus-1 2A (P2A) preceded by an N-terminal GSG spacer enabled optimal cleavage and antigen expression. In mice, the resulting recombinant virus elicited potent systemic antibody responses against both RV and CPA following oral administration. When tested in a maternal immunization model, intramuscular immunization of cows generated high titers of neutralizing antibodies in colostrum, demonstrating its potential utility for passive immunization. By integrating a key bacterial antigen into a licensed RV vaccine backbone, we establish a versatile strategy to combat viral-bacterial co-infections and polymicrobial enteric diseases, offering a promising new approach to reduce the global burden of diarrheal mortality. IMPORTANCE: The lack of vaccines targeting polymicrobial enteric infections represents a critical gap in the fight against diarrheal diseases, a leading cause of infant mortality worldwide. To bridge this gap, we engineered a novel bivalent vaccine designed to provide dual protection against rotavirus and Clostridium perfringens alpha-toxin (CPA)-mediated disease. Leveraging an enhanced reverse genetics system, we successfully utilized the commercialized rotavirus vaccine strain LLR as a viral vector to express the key C. perfringens virulence factor, CPA. This strategy not only offers a path to broader protection against diarrheal disease but also establishes a versatile platform for developing vaccines against other viral-bacterial co-infections.