Classical swine fever (CSF), caused by the classical swine fever virus (CSFV), remains a significant threat to the global pig industry. Recent advances in mRNA vaccines offered a promising platform for combating CSFV. In this study, we designed and evaluated three lipid nanoparticle (LNP)-encapsulated mRNA vaccine candidates encoding the ectodomain of E2 glycoprotein (E2_EX), E2_EX fused with the transmembrane (TM) region of the PEDV S protein (E2tm), and E2_EX fused with the TM region of the influenza virus HA protein (E2tm-HA). Among these, the E2tm mRNA vaccine induced the most robust antibody responses in pigs. Immunization of piglets with the E2tm mRNA vaccine showed that its immunogenicity was not impaired by maternal antibodies. Comparative analysis of pseudouridine (Ψ)-modified ( ^Ψ E2tm) and unmodified (E2tm) mRNA vaccines revealed that E2tm induced significantly higher antibodies titers than ^Ψ E2tm. All vaccinated pigs survived the CSFV challenge, with the 150 µg E2tm dose providing optimal protection, effectively suppressing viremia and preventing viral dissemination to tissues while also resulting in undetectable viral RNA in swab samples. Our findings provide a promising novel mRNA vaccine that could be used as an alternative vaccination strategy against CSFV infection. IMPORTANCE: Classical swine fever virus (CSFV) remains a significant threat to the global pig industry. While live attenuated and subunit vaccines are currently in use, there is an urgent need for more effective and safer vaccination strategies. Here, we present a novel mRNA vaccine encoding the CSFV E2 glycoprotein, which provides protective immunity against the CSFV challenge in pigs. Our findings underscore the promising efficacy of this mRNA-based vaccine platform and offer an alternative strategy for CSFV prevention and control.

African swine fever virus (ASFV), a highly contagious pathogen characterized by a complex structure and a variety of immunosuppression proteins, causes hemorrhagic, acute, and aggressive infectious disease that severely injures the pork products and industry. However, there is no effective vaccine or treatment. The main reasons are not only the complex mechanisms that lead to immunosuppression but also the unknown functions of various proteins. This review summarizes the interaction between ASFV and the host immune system, along with the involvement of virulence-related genes and proteins, as well as the corresponding molecular mechanism of immunosuppression of ASFV, encompassing pathways such as cGAS-STING, nuclear factor kappa–light-chain-enhancer of activated B cells (NF-κB), Janus Kinase (JAK) and JAK Signal Transducers and Activators of Transcription (STAT), apoptosis, and other modulation. The aim is to summarize the dynamic process during ASFV infection and entry into the host cell, provide a rational insight into development of a vaccine, and provide a better clear knowledge of how ASFV impacts the host.

African swine fever (ASF) has caused a devastating pandemic among domestic and wild swine, leading to significant economic losses in the global swine industry. Recombinant live-attenuated vaccines are a potential option for the control of ASF. However, safe and effective vaccines against the ASF virus (ASFV) are not yet commercially available, and thus, additional vaccine candidates still need to be developed. In this study, we demonstrate that the simultaneous deletion of the ASFV genes CD2v and A137R from the highly virulent isolate ASFV HuB/HH/2019 substantially attenuated the virulence in swine. All pigs (4/4) infected with 10 ⁵ TCID ₅₀ doses of the double gene deletion virus HuB/HH/2019Δ CD2v Δ A137R (HuBΔ CD2v Δ A137R ) remained healthy during a 27-day observation period, with no fevers (>40.5°C) observed. Cases of viremia were mild and cleared by 24 days post-inoculation (dpi). Antibodies against ASFV p30 were induced, and the inoculated pigs were well-protected against homologous challenges. All inoculated pigs survived after being challenged with 10 ² HAD ₅₀ ASFV HuB/HH/2019, and no fever or clinical symptoms developed during the 22-day monitoring period. In contrast, all control group pigs died before 11 dpi (2/2). Cytokine assays and RNA sequencing revealed mild responses elicited by HuBΔ CD2v Δ A137R . Successful innate and passive immune responses were also triggered. The findings suggest that deletion of the CD2v and A137R genes can attenuate ASFV, and the deletion mutant virus HuBΔ CD2v Δ A137R is a promising vaccine candidate. IMPORTANCE: The emergence of ASF has caused substantial economic losses in the global pig industry. In light of this, the development of a safe and effective vaccine is crucial to control the spread of ASF. In this study, a live-attenuated ASFV strain was developed by simultaneously knocking out the viral genes CD2v and A137R . The mutant virus exhibited weakened virulence in pigs, elicited robust humoral and cellular immunity, and conferred protection upon challenge with high doses of the parental virus. Notably, no fever or clinical symptoms were observed during a 27-day monitoring period. Consequently, our research presents a highly promising candidate strain for a live-attenuated vaccine, offering a significant step forward in the quest for effective prevention measures. Additionally, the identification of these specific gene targets opens up avenues for further exploration and refinement of strategies aimed at combating ASF outbreaks.

The E2 subunit vaccine has been considered a promising alternative to an attenuated classical swine fever (CSF) vaccine. However, it fails to induce a good

Classical swine fever (CSF) is a highly contagious and lethal disease caused by classical swine fever virus (CSFV), and it is also a notifiable disease according to the World Organization for Animal Health. Owing to the continuous growth of the international trade in pigs and pig products, pig farming has become the pillar industry of the global livestock industry and is the most important source of animal protein for mankind. As a single-stranded RNA virus, CSFV can avoid being recognized and cleared by the host immune system through a variety of immune evasion strategies so that it persists in the host body and causes multisystemic pathology. CSF has also become one of the most serious infectious diseases affecting the pig industry, resulting in considerable economic losses to the pig industry. Therefore, understanding the main immune evasion mechanism of CSFV is very important for the prevention and control of CSF infection. This article reviews the main immune evasion mechanisms of CSFV, including the suppression of nonspecific immune responses; evasion of adaptive immune responses; and the regulation of host cell apoptosis and cell autophagy. CSFV affects type I interferon regulatory signals; the JAK-STAT signaling pathway; the RIG-I and NF-κB signaling pathways; immune cell function; the mitochondrial apoptosis pathway; and the endoplasmic reticulum stress apoptosis pathway; the PI3K-Akt signaling mediated AMPK-mTOR macroautophagy pathway through its structural proteins E^rns and E1 and E2; and the nonstructural proteins N^pro, NS4B, and NS5A to achieve immune evasion. As our understanding of CSFV immune strategies continues to deepen, we believe that this understanding will provide new strategies for the development of new vaccines and novel diagnostic methods in the future.

The continuous emergence of circular Rep‐encoding single‐stranded (CRESS) DNA viruses across diverse hosts has been closely associated with the occurrence of severe diseases. Four circoviruses within the genus Circovirus have been identified in pigs, including porcine circovirus Type 1 (PCV1), PCV2, PCV3, PCV4, and PCV5. In late 2021, a large pig farm experienced an outbreak of reproductive disorders that were undiagnosed by standard tests. Subsequent viral metagenomic analysis of stillborn piglets identified a novel single‐stranded circular DNA virus, designated porcine megalocircovirus (PMCV). PMCV has a large genome of 9426 nt and encodes nine open reading frames. Biochemical analyses of Rep confirm PMCV as a CRESS DNA virus. However, PMCV Rep showed low amino acid sequence identities to the four PCV species and several human CRESS DNA viruses, with the highest identity of 23.6% to PCV4 Rep. The genetic evolutionary tree indicates that PMCV belongs to an unknown family of the CRESS DNA viruses. The positive detection rate for PMCV in tested samples was 24% (30/125), while the positive rate regarding pig farms was 41.18% (14/34) in China. The emergence of PMCV warrants further investigation.