Structures and Functional Diversities of ASFV Proteins

Discovery of a potent inhibitor, D-132, targeting AsfvPolX, via protein-DNA complex-guided pharmacophore screening and in vitro molecular characterizations

The heightened transmissibility and capacity of African swine fever virus (ASFV) induce fatal diseases in domestic pigs and wild boars, posing significant economic repercussions and global threats. Despite extensive research efforts, the development of potent vaccines or treatments for ASFV remains a persistent challenge. Recently, inhibiting the AsfvPolX, a key DNA repair enzyme, emerges as a feasible strategy to disrupt viral replication and control ASFV infections. In this study, a comprehensive approach involving pharmacophore-based inhibitor screening, coupled with biochemical and biophysical analyses, were implemented to identify, characterize, and validate potential inhibitors targeting AsfvPolX. The constructed pharmacophore model, Phar-PolX-S, demonstrated efficacy in identifying a potent inhibitor, D-132 (IC50 = 2.8 ± 0.2 µM), disrupting the formation of the AsfvPolX-DNA complex. Notably, D-132 exhibited strong binding to AsfvPolX (KD = 6.9 ± 2.2 µM) through a slow-on-fast-off binding mechanism. Employing molecular modeling, it was elucidated that D-132 predominantly binds in-between the palm and finger domains of AsfvPolX, with crucial residues (R42, N48, Q98, E100, F102, and F116) identified as hotspots for structure-based inhibitor optimization. Distinctively characterized by a 1,2,5,6-tetrathiocane with modifications at the 3 and 8 positions involving ethanesulfonates, D-132 holds considerable promise as a lead compound for the development of innovative agents to combat ASFV infections.

Development of a quantum dots based immunochromatographic strip for rapid and on-site detection of African swine fever virus

African swine fever (ASF) is a lethal disease caused by ASF virus (ASFV), severely impacting the global swine industry. Though nuclear acid-based detection methods are reliable, they are laboratory-dependent. In this study, we developed a device-independent, user friendly and cost-effective quantum dots based immunochromatographic strip (QDs-ICS) with high specificity and sensitivity for the rapid and on-site detection of ASFV antigen. For the preparation of the QDs-ICS, we generated a monoclonal antibody (mAb) mAb-8G8 and polyclonal antibody (pAb) against ASFV-p72 protein. The pAb was labelled with QDs to be used as the detection probe and the mAb-8G8 was coated on the nitrocellulose membrane as the test line. Our results proved that the strip displayed no cross-reactivity with other swine viruses and detection limit of the QDs-ICS was down to 1 ng/mL for the ASFV-p72 protein with great reproducibility. The strip also exhibited high stability with a storage period up to 12 months under room temperature. Twenty blind samples and one hundred clinical samples were examined by the QDs-ICS, conventional PCR and real-time PCR method, respectively. Results showed that the agreement rate between the QDs-ICS and PCR method was 100%, and the agreement rate between the strip and real-time PCR was 94%. The novel QDs-ICS developed here would be an effective tool for on-site detection of ASFV.

Development of novel monoclonal antibodies for blocking NF-κB activation induced by CD2v protein in African swine fever virus

Background

CD2v, a critical outer envelope glycoprotein of the African swine fever virus (ASFV), plays a central role in the hemadsorption phenomenon during ASFV infection and is recognized as an essential immunoprotective protein. Monoclonal antibodies (mAbs) targeting CD2v have demonstrated promise in both diagnosing and combating African swine fever (ASF). The objective of this study was to develop specific monoclonal antibodies against CD2v.

Methods

In this investigation, Recombinant CD2v was expressed in eukaryotic cells, and murine mAbs were generated through meticulous screening and hybridoma cloning. Various techniques, including indirect enzyme-linked immunosorbent assay (ELISA), western blotting, immunofluorescence assay (IFA), and bio-layer interferometry (BLI), were employed to characterize the mAbs. Epitope mapping was conducted using truncation mutants and epitope peptide mapping.

Results

An optimal antibody pair for a highly sensitive sandwich ELISA was identified, and the antigenic structures recognized by the mAbs were elucidated. Two linear epitopes highly conserved in ASFV genotype II strains, particularly in Chinese endemic strains, were identified, along with a unique glycosylated epitope. Three mAbs, 2B25, 3G25, and 8G1, effectively blocked CD2v-induced NF-κB activation.

Conclusions

This study provides valuable insights into the antigenic structure of ASFV CD2v. The mAbs obtained in this study hold great potential for use in the development of ASF diagnostic strategies, and the identified epitopes may contribute to vaccine development against ASFV.

Label-Free Detection of African Swine Fever and Classical Swine Fever in the Point-of-Care Setting Using Photonic Integrated Circuits Integrated in a Microfluidic Device

Swine viral diseases have the capacity to cause significant losses and affect the sector's sustainability, a situation further exacerbated by the lack of antiviral drugs and the limited availability of effective vaccines. In this context, a novel point-of-care (POC) diagnostic device incorporating photonic integrated circuits (PICs), microfluidics and information, and communication technology into a single platform was developed for the field diagnosis of African swine fever (ASF) and classical swine fever (CSF). The device targets viral particles and has been validated using oral fluid and serum samples. Sensitivity, specificity, accuracy, precision, positive likelihood ratio (PLR), negative likelihood ratio (NLR), and diagnostic odds ratio (DOR) were calculated to assess the performance of the device, and PCR was the reference method employed. Its sensitivities were 80.97% and 79%, specificities were 88.46% and 79.07%, and DOR values were 32.25 and 14.21 for ASF and CSF, respectively. The proposed POC device and PIC sensors can be employed for the pen-side detection of ASF and CSF, thus introducing novel technological advancements in the field of animal diagnostics. The need for proper validation studies of POC devices is highlighted to optimize animal biosecurity.

Analysis of the Immunogenicity of African Swine Fever F317L Protein and Screening of T Cell Epitopes

The African swine fever virus (ASFV) encodes numerous proteins characterized by complex immune escape mechanisms. At present, the structure and function of these proteins, including the F317L protein, have yet to be fully elucidated. In this study, we examined the immunogenicity of the F317L protein. Mice were subcutaneously immunized with the F317L protein using initial and subsequent booster doses, and, at the 28th day post-treatment, we assessed the humoral and cellular immune responses of mice. The F317L protein stimulated production of specific antibodies and activated humoral immune responses. In addition, F317L stimulated the production of large amounts of IFN-γ by splenic lymphocytes, thereby activating cellular immune responses. Using informatics technology, we predicted and synthesized 29 F317L protein T cell epitopes, which were screened using IFN-γ ELISpot. Among these, the F25 (246SRRSLVNPWT255) peptide was identified as having a stronger stimulatory effect than the full-length protein. Collectively, our findings revealed that the ASFV F317L protein can stimulate both strong humoral and cellular immunity in mice, and that the F25 (246SRRSLVNPWT255) peptide may be a potential active T cell epitope. These findings will provide a reference for further in-depth studies of the F317L protein and screening of antigenic epitopes.

A triplex crystal digital PCR for the detection of genotypes I and II African swine fever virus

African swine fever (ASF) is a highly contagious and lethal viral disease that causes severe hemorrhagic fever in pigs. It keeps spreading around the world, posing a severe socioeconomic risk and endangering biodiversity and domestic food security. ASF first outbroke in China in 2018, and has spread to most provinces nationwide. Genotypes I and II ASF virus (ASFV) as the etiological pathogens have been found in China. In this study, three pairs of specific primers and probes targeting the ASFV B646L gene, F1055L gene, and E183L gene were designed to detect universal, genotype I, and genotype II strains, respectively. A triplex crystal digital PCR (cdPCR) was established on the basis of optimizing various reaction conditions. The assay demonstrated remarkably sensitive with low limits of detection (LODs) of 5.120, 4.218, 4.588 copies/reaction for B646L, F1055L, and E183L gene, respectively; excellent repeatability with 1.24-2.01% intra-assay coefficients of variation (CVs) and 1.32-2.53% inter-assay CVs; good specificity for only detection of genotypes I and II ASFV, without cross-reactivity with PCV2, PRV, SIV, PRRSV, PEDV, FMDV, and CSFV. The triplex cdPCR was used to test 1,275 clinical samples from Guangxi province of China, and the positivity rates were 5.05, 3.22, and 1.02% for genotype I, genotype II, and co-infection of genotypes I and II, respectively. These 1,275 clinical samples were also detected using a reported reference triplex real-time quantitative PCR (qPCR), and the agreements of detection results between these two methods were more than 98.98%. In conclusion, the developed triplex cdPCR could be used as a rapid, sensitive, and accurate method to detect and differentiate genotypes I and II strains of ASFV.

In silico identification of multi-target inhibitors from medicinal fungal metabolites against the base excision repair pathway proteins of African swine fever virus

African swine fever virus (ASFV) has emerged as a serious threat to the pork industry resulting in significant economic losses and heightened concerns about food security. With no known cure presently available, existing control measures center on animal quarantine and culling. Considering the severity and challenges posed by ASFV, it is imperative to discover new treatment strategies and implement additional measures to prevent its further spread. This study recognized the potential of 1830 fungal metabolites from medicinal fungi as antiviral compounds against base excision repair (BER) proteins of ASFV, specifically ASFVAP, ASFVPolX, and ASFVLig. A wide array of computer-aided drug discovery techniques were employed to carry out the virtual screening process: ADMET profiling revealed 319 molecules with excellent bioavailability and toxicity properties; consensus docking identified the 10 best-scoring ligands against all targets; molecular dynamics simulation elucidated the stability of the protein-ligand complexes; and MM/PB(GB)SA energy calculations predicted the binding energies of the compounds as well as the key residues integral to binding. Through in silico methods, we identified two theoretical lead candidates against ASFVAP, four against ASFVLig, and five against ASFVPolX. Two compounds, methyl ganoderate E and antcamphin M, exhibited potential multi-target inhibitory characteristics against ASFVPolX and ASFVLig, while compound cochlactone A showed promising antagonistic results against all three BER proteins. It is recommended to prioritize these hit compounds in future in vitro and in vivo studies to validate their potential as antiviral drugs against ASFV.

A unified view on enzyme catalysis by cryo-EM study of a DNA topoisomerase

The theories for substrate recognition in enzyme catalysis have evolved from lock-key to induced fit, then conformational selection, and conformational selection followed by induced fit. However, the prevalence and consensus of these theories require further examination. Here we use cryogenic electron microscopy and African swine fever virus type 2 topoisomerase (AsfvTop2) to demonstrate substrate binding theories in a joint and ordered manner: catalytic selection by the enzyme, conformational selection by the substrates, then induced fit. The apo-AsfvTop2 pre-exists in six conformers that comply with the two-gate mechanism directing DNA passage and release in the Top2 catalytic cycle. The structures of AsfvTop2-DNA-inhibitor complexes show that substantial induced-fit changes occur locally from the closed apo-conformer that however is too far-fetched for the open apo-conformer. Furthermore, the ATPase domain of AsfvTop2 in the MgAMP-PNP-bound crystal structures coexist in reduced and oxidized forms involving a disulfide bond, which can regulate the AsfvTop2 function.

The p30 protein of the African swine fever virus behaves as an RNase

The African Swine Fever Virus (ASFV) is responsible for causing African Swine Fever (ASF), a severe contagious disease characterized by hemorrhagic symptoms. The p30 protein of ASFV is the most abundantly expressed viral protein. It is reported to be antigenic and has recognized phosphorylation, glycosylation, and membrane attachment sites, which also shows that the C-terminal region of p30 is more active than the N-terminal region. The present study reports the unique RNase activity of recombinant p30. The RNase activity of p30 was stable at an optimum temperature of 37 °C, and the maximum activity was recorded at pH 7-9 in the presence of monovalent salts. The mutant of p30 (p30m), where cysteine was mutated to alanine at position 109, showed a loss of RNase activity. Our understanding of ASFV biology is significantly less; until now, we have little knowledge about the functions of its proteins. The results of the present study will assist in exploring the biology of ASFV and the role of its protein in counteracting the host immune response.

SNX32 is a host restriction factor that degrades African swine fever virus CP204L via the RAB1B-dependent autophagy pathway

African swine fever virus (ASFV) causes a highly contagious and deadly disease in domestic pigs and European wild boars, posing a severe threat to the global pig industry. ASFV CP204L, a highly immunogenic protein, is produced during the early stages of ASFV infection. However, the impact of CP204L protein-interacting partners on the outcome of ASFV infection is poorly understood. To accomplish this, coimmunoprecipitation and mass spectrometry analysis were conducted in ASFV-infected porcine alveolar macrophages (PAMs). We have demonstrated that sorting nexin 32 (SNX32) is a CP204L-binding protein and that CP204L interacted and colocalized with SNX32 in ASFV-infected PAMs. ASFV growth and replication were promoted by silencing SNX32 and suppressed by overexpressing SNX32. SNX32 degraded CP204L by recruiting the autophagy-related protein Ras-related protein Rab-1b (RAB1B). RAB1B overexpression inhibited ASFV replication, while knockdown of RAB1B had the opposite effect. Additionally, RAB1B, SNX32, and CP204L formed a complex upon ASFV infection. Taken together, this study demonstrates that SNX32 antagonizes ASFV growth and replication by recruiting the autophagy-related protein RAB1B. This finding extends our understanding of the interaction between ASFV CP204L and its host and provides new insights into exploring the relationship between ASFV infection and autophagy.IMPORTANCEAfrican swine fever (ASF) is a highly contagious and acute hemorrhagic viral disease with a high mortality near 100% in domestic pigs. ASF virus (ASFV), which is the only member of the family Asfarviridae, is a dsDNA virus of great complexity and size, encoding more than 150 proteins. Currently, there are no available vaccines against ASFV. ASFV CP204L represents the most abundantly expressed viral protein early in infection and plays an important role in regulating ASFV replication. However, the mechanism by which the interaction between ASFV CP204L and host proteins affects ASFV replication remains unclear. In this study, we demonstrated that the cellular protein SNX32 interacted with CP204L and degraded CP204L by upregulating the autophagy-related protein RAB1B. In summary, this study will help us understand the interaction mechanism between CP204L and its host upon infection and provide new insights for the development of vaccines and antiviral drugs.

Preparation and epitope mapping of monoclonal antibodies against African swine fever virus p22 protein

African swine fever (ASF), caused by the African swine fever virus (ASFV), is now widespread in many countries and severely affects the commercial rearing of swine. Rapid and early diagnosis is crucial for the prevention of ASF. ASFV mature virions comprise the inner envelope protein, p22, making it an excellent candidate for the serological diagnosis and surveillance of ASF. In this study, the prokaryotic-expressed p22 recombinant protein was prepared and purified for immunization in mice. Four monoclonal antibodies (mAbs) were identified using hybridoma cell fusion, clone purification, and immunological assays. The epitopes of mAbs 14G1 and 22D8 were further defined by alanine-scanning mutagenesis. Our results showed that amino acids C39, K40, V41, D42, C45, G48, E49, and C51 directly bound to 14G1, while the key amino acid epitope for 22D8 included K161, Y162, G163, D165, H166, I167, and I168. Homologous and structural analysis revealed that these sites were highly conserved across Asian and European ASFV strains, and the amino acids identified were located on the surface of p22. Thus, our study contributes to a better understanding of the antigenicity of the ASFV p22 protein, and the results could facilitate the prevention and control of ASF.

Current detection methods of African swine fever virus

African swine fever (ASF), caused by the African swine fever virus (ASFV), is a highly contagious and notifiable animal disease in domestic pigs and wild boars, as designated by the World Organization for Animal Health (WOAH). The effective diagnosis of ASF holds great importance in promptly controlling its spread due to its increasing prevalence and the continuous emergence of variant strains. This paper offers a comprehensive review of the most common and up-to-date methods established for various genes/proteins associated with ASFV. The discussed methods primarily focus on the detection of viral genomes or particles, as well as the detection of ASFV associated antibodies. It is anticipated that this paper will serve as a reference for choosing appropriate diagnostic methods in diverse application scenarios, while also provide direction for the development of innovative technologies in the future.

The E301R protein of African swine fever virus functions as a sliding clamp involved in viral genome replication

IMPORTANCE

Sliding clamp is a highly conserved protein in the evolution of prokaryotic and eukaryotic cells. The sliding clamp is required for genomic replication as a critical co-factor of DNA polymerases. However, the sliding clamp analogs in viruses remain largely unknown. We found that the ASFV E301R protein (pE301R) exhibited a sliding clamp-like structure and similar functions during ASFV replication. Interestingly, pE301R is assembled into a unique ring-shaped homotetramer distinct from sliding clamps or proliferating cell nuclear antigens (PCNAs) from other species. Notably, the E301R gene is required for viral life cycle, but the pE301R function can be partially restored by the porcine PCNA. This study not only highlights the functional role of the ASFV pE301R as a viral sliding clamp analog, but also facilitates the dissection of the complex replication mechanism of ASFV, which provides novel clues for developing antivirals against ASF.

Structural Insight into Polymerase Mechanism via a Chiral Center Generated with a Single Selenium Atom

DNA synthesis catalyzed by DNA polymerase is essential for all life forms, and phosphodiester bond formation with phosphorus center inversion is a key step in this process. Herein, by using a single-selenium-atom-modified dNTP probe, we report a novel strategy to visualize the reaction stereochemistry and catalysis. We capture the before- and after-reaction states and provide explicit evidence of the center inversion and in-line attacking SN2 mechanism of DNA polymerization, while solving the diastereomer absolute configurations. Further, our kinetic and thermodynamic studies demonstrate that in the presence of Mg2+ ions (or Mn2+), the binding affinity (Km) and reaction selectivity (kcat/Km) of dGTPαSe-Rp were 51.1-fold (or 19.5-fold) stronger and 21.8-fold (or 11.3-fold) higher than those of dGTPαSe-Sp, respectively, indicating that the diastereomeric Se-Sp atom was quite disruptive of the binding and catalysis. Our findings reveal that the third metal ion is much more critical than the other two metal ions in both substrate recognition and bond formation, providing insights into how to better design the polymerase inhibitors and discover the therapeutics.

Sensitive and Specific Exonuclease III-Assisted Recombinase-Aided Amplification Colorimetric Assay for Rapid Detection of Nucleic Acids

The development of a contamination-free and on-site nucleic acid detection platform with high sensitivity and specificity but low-cost for the detection of pathogenic nucleic acids is critical for infectious disease diagnosis and surveillance. In this study, we combined the recombinase-aided amplification (RAA) with the exonuclease III (Exo III)-assisted signal amplification into a platform for sensitive and specific detection of nucleic acids of African swine fever virus (ASFV). We found that this platform enabled a naked eye visual detection of ASFV at a detection limit as low as 2 copies/μL in 30 min. As expected, no cross-reactivity was observed with other porcine viruses. In addition, to avoid aerosol contamination, a one-tube RAA-Exo III colorimetric assay was also established for the accurate detection of ASFV in clinical samples. Taken together, we developed a rapid, instrument-free, and low-cost Exo III-assisted RAA colorimetric-assay-based nucleic acid detection platform.

Development of a triplex real-time quantitative PCR for detection and differentiation of genotypes I and II African swine fever virus

African swine fever virus (ASFV) was first identified in 1921 and is extensively prevalent around the world nowadays, which has a significant negative impact on the swine industry. In China, genotype II ASFV was first discovered in 2018, and has spread quickly to different provinces in a very short time; genotype I ASFV was first found in 2020, and has been reported in several provinces since then. To establish an accurate method for detection and differentiation of genotypes I and II ASFV, three primers and probes were designed targeting the ASFV B646L gene for different genotypes, the F1055L gene for genotype I, and the E183L gene for genotype II, and a triplex real-time quantitative PCR (qPCR) for differential detection of genotypes I and II ASFV was developed after optimizing the reaction conditions. The assay showed high sensitivity, and the limits of detection (LOD) of the B646L, F1055L, and E183L genes were 399.647 copies/reaction, 374.409 copies/reaction, and 355.083 copies/reaction, respectively; the coefficients of variation (CVs) of the intra-assay and the inter-assay were 0.22-1.88% and 0.16-1.68%, respectively, showing that this method had good repeatability; the assay could detect only ASFV, without cross-reactivity with other swine viruses including PRRSV, PEDV, PDCoV, CSFV, PRV, and PCV2, showing excellent specificity of this method. A total of 3,519 clinical samples from Guangxi province, southern China, were tested by the developed assay, and 8.16% (287/3,519) samples were found to be positive for ASFV, of which 0.17% (6/3,519) samples were positive for genotype I, 7.19% (253/3,519) samples for genotype II, and 0.80% (28/3,519) samples for genotypes I and II. At the same time, these clinical samples were also tested by a previously reported multiplex qPCR, and the agreement between these two methods was more than 99.94%. In summary, the developed triplex qPCR provided a fast, specific and accurate method for detection and differentiation of genotypes I and II ASFV.

African swine fever virus MGF360-9L promotes viral replication by degrading the host protein HAX1

African swine fever virus (ASFV) infection causes African swine fever (ASF), a virulent infectious disease that threatens the safety of livestock worldwide. Studies have shown that MGF360-9 L is important for the virulence of ASFV and the host protein HS1-associated protein X-1 (HAX1) plays an important role in viral pathogenesis. This study aimed to clarify the mechanism by which HAX1 mediates ASFV replication through interactions with MGF360-9 L. The regions of interaction between MGF360-9 L and HAX1 were predicted and validated. HAX1 overexpression and RNA interference studies revealed that HAX1 is a host restriction factor that suppresses ASFV replication. Moreover, HAX1 expression was inhibited in ASFV-infected mature bone marrow-derived macrophages, and infection with the virulent MGF360-9 L gene deletion strain (∆MGF360-9 L) attenuated the inhibitory effect of the wild-type strain (WT) on HAX1 expression, suggesting a complex regulatory relationship between MGF360-9 L and HAX1. Furthermore, the E3 ubiquitin ligase RNF114 interacted with MGF360-9 L and HAX1, MGF360-9 L degraded HAX1 through the ubiquitin-proteasome pathway, and RNF114 facilitated the degradation of HAX1 by MGF360-9L-linked K48 ubiquitin chains through the ubiquitin-proteasome pathway, thereby facilitating ASFV replication. In conclusion, this study has enriched our understanding of the regulatory networks between ASFV proteins and host proteins and provided a reference for investigation into the pathogenesis and immune escape mechanism of ASFV.

The African swine fever virus I10L protein inhibits the NF-κB signaling pathway by targeting IKKβ

Proinflammatory factors play important roles in the pathogenesis of African swine fever virus (ASFV), which is the causative agent of African swine fever (ASF), a highly contagious and severe hemorrhagic disease. Efforts in the prevention and treatment of ASF have been severely hindered by knowledge gaps in viral proteins responsible for modulating host antiviral responses. In this study, we identified the I10L protein (pI10L) of ASFV as a potential inhibitor of the TNF-α- and IL-1β-triggered NF-κB signaling pathway, the most canonical and important part of host inflammatory responses. The ectopically expressed pI10L remarkably suppressed the activation of NF-κB signaling in HEK293T and PK-15 cells. The ASFV mutant lacking the I10L gene (ASFVΔI10L) induced higher levels of proinflammatory cytokines production in primary porcine alveolar macrophages (PAMs) compared with its parental ASFV HLJ/2018 strain (ASFVWT). Mechanistic studies suggest that pI10L inhibits IKKβ phosphorylation by reducing the K63-linked ubiquitination of NEMO, which is necessary for the activation of IKKβ. Morever, pI10L interacts with the kinase domain of IKKβ through its N-terminus, and consequently blocks the association of IKKβ with its substrates IκBα and p65, leading to reduced phosphorylation. In addition, the nuclear translocation efficiency of p65 was also altered by pI10L. Further biochemical evidence supported that the amino acids 1-102 on pI10L were essential for the pI10L-mediated suppression of the NF-κB signaling pathway. The present study clarifies the immunosuppressive activity of pI10L, and provides novel insights into the understanding of ASFV pathobiology and the development of vaccines against ASF. IMPORTANCE African swine fever (ASF), caused by the African swine fever virus (ASFV), is now widespread in many countries and severely affects the commercial rearing of swine. To date, few safe and effective vaccines or antiviral strategies have been marketed due to large gaps in knowledge regarding ASFV pathobiology and immune evasion mechanisms. In this study, we deciphered the important role of the ASFV-encoded I10L protein in the TNF-α-/IL-1β-triggered NF-κB signaling pathway. This study provides novel insights into the pathogenesis of ASFV and thus contributes to the development of vaccines against ASF.

Establishment of a Dual-Antigen Indirect ELISA Based on p30 and pB602L to Detect Antibodies against African Swine Fever Virus

African swine fever (ASF) is an acute, virulent, and highly fatal infectious disease caused by the African swine fever virus (ASFV). There is no effective vaccine or diagnostic method to prevent and control this disease currently, which highlights the significance of ASF early detection. In this study, we chose an early antigen and a late-expressed antigen to co-detect the target antibody, which not only helps in early detection but also improves accuracy and sensitivity. CP204L and B602L were successfully expressed as soluble proteins in an Escherichia coli vector system. By optimizing various conditions, a dual-antigen indirect ELISA for ASFV antibodies was established. The assay was non-cross-reactive with antibodies against the porcine reproductive and respiratory syndrome virus, classical swine fever virus, porcine circovirus type 2, and pseudorabies virus. The maximum serum dilution for detection of ASFV-positive sera was 1:1600. The intra-batch reproducibility coefficient of variation was <5% and the inter-batch reproducibility coefficient of variation was <10%. Compared with commercial kits, the dual-antigen indirect ELISA had good detection performance. In conclusion, we established a detection method with low cost, streamlined production process, and fewer instruments. It provides a new method for the serological diagnosis of ASF.

Triplex Crystal Digital PCR for the Detection and Differentiation of the Wild-Type Strain and the MGF505-2R and I177L Gene-Deleted Strain of African Swine Fever Virus

African swine fever (ASF) is a severe and highly contagious viral disease that affects domestic pigs and wild boars, characterized by a high fever and internal bleeding. The disease is caused by African swine fever virus (ASFV), which is prevalent worldwide and has led to significant economic losses in the global pig industry. In this study, three pairs of specific primers and TaqMan probes were designed for the ASFV B646L, MGF505-2R and I177L genes. After optimizing the reaction conditions of the annealing temperature, primer concentration and probe concentration, triplex crystal digital PCR (cdPCR) and triplex real-time quantitative PCR (qPCR) were developed for the detection and differentiation of the wild-type ASFV strain and the MGF505-2R and/or I177L gene-deleted ASFV strains. The results indicate that both triplex cdPCR and triplex qPCR were highly specific, sensitive and repeatable. The assays could detect only the B646L, MGF505-2R and I177L genes, without cross-reaction with other swine viruses (i.e., PRRSV, CSFV, PCV2, PCV3, PEDV, PDCoV and PRV). The limit of detection (LOD) of triplex cdPCR was 12 copies/reaction, and the LOD of triplex qPCR was 500 copies/reaction. The intra-assay and inter-assay coefficients of variation (CVs) for repeatability and reproducibility were less than 2.7% for triplex cdPCR and less than 1.8% for triplex qPCR. A total of 1510 clinical tissue samples were tested with both methods, and the positivity rates of ASFV were 14.17% (214/1510) with triplex cdPCR and 12.98% (196/1510) with triplex qPCR, with a coincidence rate of 98.81% between the two methods. The positivity rate for the MGF505-2R gene-deleted ASFV strains was 0.33% (5/1510), and no I177L gene-deleted ASFV strain was found. The results indicate that triplex cdPCR and triplex qPCR developed in this study can provide rapid, sensitive and accurate methods for the detection and differentiation of the ASFV B646L, MGF505-2R and I177L genes.

SY18ΔL60L: a new recombinant live attenuated African swine fever virus with protection against homologous challenge

Introduction

African swine fever (ASF) is an acute and highly contagious disease and its pathogen, the African swine fever virus (ASFV), threatens the global pig industry. At present, management of ASF epidemic mainly relies on biological prevention and control methods. Moreover, due to the large genome of ASFV, only half of its genes have been characterized in terms of function.

Methods

Here, we evaluated a previously uncharacterized viral gene, L60L. To assess the function of this gene, we constructed a deletion strain (SY18ΔL60L) by knocking out the L60L gene of the SY18 strain. To evaluate the growth characteristics and safety of the SY18ΔL60L, experiments were conducted on primary macrophages and pigs, respectively.

Results

The results revealed that the growth trend of the recombinant strain was slower than that of the parent strain in vitro. Additionally, 3/5 (60%) pigs intramuscularly immunized with a 105 50% tissue culture infectious dose (TCID50) of SY18ΔL60L survived the 21-day observation period. The surviving pigs were able to protect against the homologous lethal strain SY18 and survive. Importantly, there were no obvious clinical symptoms or viremia.

Discussion

These results suggest that L60L could serve as a virulence- and replication-related gene. Moreover, the SY18ΔL60L strain represents a new recombinant live-attenuated ASFV that can be employed in the development of additional candidate vaccine strains and in the elucidation of the mechanisms associated with ASF infection.

Functional Landscape of African Swine Fever Virus-Host and Virus-Virus Protein Interactions

Viral replication fully relies on the host cell machinery, and physical interactions between viral and host proteins mediate key steps of the viral life cycle. Therefore, identifying virus-host protein-protein interactions (PPIs) provides insights into the molecular mechanisms governing virus infection and is crucial for designing novel antiviral strategies. In the case of the African swine fever virus (ASFV), a large DNA virus that causes a deadly panzootic disease in pigs, the limited understanding of host and viral targets hinders the development of effective vaccines and treatments. This review summarizes the current knowledge of virus-host and virus-virus PPIs by collecting and analyzing studies of individual viral proteins. We have compiled a dataset of experimentally determined host and virus protein targets, the molecular mechanisms involved, and the biological functions of the identified virus-host and virus-virus protein interactions during infection. Ultimately, this work provides a comprehensive and systematic overview of ASFV interactome, identifies knowledge gaps, and proposes future research directions.

Polygalic acid inhibits african swine fever virus polymerase activity: findings from machine learning and in vitro testing

African swine fever virus (ASFV), an extremely contagious virus with high mortality rates, causes severe hemorrhagic viral disease in both domestic and wild pigs. Fortunately, ASFV cannot be transmitted from pigs to humans. However, ongoing ASFV outbreaks could have severe economic consequences for global food security. Although ASFV was discovered several years ago, no vaccines or treatments are commercially available yet; therefore, the identification of new anti-ASFV drugs is urgently warranted. Using molecular docking and machine learning, we have previously identified pentagastrin, cangrelor, and fostamatinib as potential antiviral drugs against ASFV. Here, using machine learning combined with docking simulations, we identified natural products with a high affinity for AsfvPolX proteins. We selected five natural products (NPs) that are located close in chemical space to the six known natural flavonoids that possess anti-ASFV activity. Polygalic acid markedly reduced AsfvPolX polymerase activity in a dose-dependent manner. We propose an efficient protocol for identifying NPs as potential antiviral drugs by identifying chemical spaces containing high-affinity binders against ASFV in NP databases.

B602L-Fc fusion protein enhances the immunogenicity of the B602L protein of the African swine fever virus

African swine fever (ASF) is an acute, highly contagious, and deadly infectious disease caused by the African swine fever virus (ASFV) and has a huge impact on the pig industry. A lack of vaccines and effective therapeutic drugs has brought great challenges to the prevention and control of ASF. In this study, insect baculovirus expression system was used to express ASFV B602L protein (B602L) alone and the IgG FC-fused B602L protein (B602L-Fc), and evaluate the immune effect of B602L-Fc in mice model. To be specific, the ASFV B602L protein and B602L-Fc fusion protein were successfully expressed by the insect baculovirus expression system. Then, Functional analysis in vitro revealed that the B602L-Fc fusion protein bound and interacted with the FcRI receptor of antigen-presenting cells and significantly promoted the expression of proteins involved in antigen presentation and various cytokines at mRNA levels in porcine alveolar macrophages. Additionally, immunization using B602L-Fc fusion protein remarkably promoted the Th1-biased cellular immune response and humoral immune response in mice. In conclusion, The B602L-Fc fusion protein could up-regulate the expression of molecules involved in antigen presentation in APCs and enhance the humoral and cellular immune responses in mice. These results suggest that ASFV B602L-Fc recombinant fusion protein may be a promising candidate for subunit vaccine. This study provided useful data for the development of subunit vaccines for ASF.

An Intracellular Epitope of ASFV CD2v Protein Elicits Humoral and Cellular Immune Responses

The African swine fever virus (ASFV) causes high mortality in domestic pigs. ASFV encodes an important protein target for subunit vaccine development, CD2v, but its most effective immunological regions are not known. Herein, we generated a monoclonal antibody (mAb) named IF3 by immunizing mice against the intracellular region of the CD2v protein (CD2v-IR). 1F3 specifically recognized CD2v, which is expressed transiently in transfected Sf9 cells and also in inactivated ASFV-infected porcine alveolar macrophage (PAM) cells. The epitope recognized by 1F3 is ²⁶⁴EPSPREP²⁷⁰, which is highly conserved in ASFV genotypes. Immunization of mice with this epitope elicited an increased IgG response, including IgG1 and IgG2a subtypes, and also increased CD8⁺ T cells and cytokine expression. Overall, these results indicate that this epitope induces both humoral and cellular immune responses that may be used for ASFV-related subunit vaccine design and development.

A study of African swine fever virus in Regional VI of the Disease Investigation Center of Denpasar Bali in Indonesia

Background and Aims

African swine fever (ASF) is a highly contagious viral disease that causes major economic losses due to morbidity and fatality rates of up to 100% in wild boar and domestic pigs. The disease emerged in Africa in 1921 and then entered several European countries by 1957. In Indonesia, the first outbreak of ASF in 2019 in North Sumatra killed thousands of pigs and quickly spread to 10 out of 34 pig-producing provinces, including Bali and Eastern Nusa Tenggara. As no commercial ASF vaccine is available, the disease has become endemic and continues killing pigs. This study aimed to investigate the epidemiological and virological studies of ASF virus (ASFV) conducted in 2020 and 2021 by the Disease Investigation Center Regional VI of Denpasar Bali, which covers three provinces in Indonesia, including Bali, Western Nusa Tenggara, and Eastern Nusa Tenggara.

Materials and Methods

A total of 5402 blood samples were sent to the laboratory to detect ASFV infection using quantitative polymerase chain reaction (qPCR) and enzyme-linked immunosorbent assay tests. The virological studies were performed by culturing local ASFV isolates obtained from field cases in primary macrophages and confirmation of viral growth by qPCR.

Results

The qPCR results show that only 156/4528 (3.4%) of samples originating from Bali and Eastern Nusa Tenggara were ASFV-positive with cycle threshold value of 18 to 23, while the virus was not detected in Western Nusa Tenggara. Of 874 serum samples tested, 114 (13%) were antibody positive and were all collected from the two ASFV-affected provinces in 2020. A Bali ASFV isolate (BL21) was isolated and characterized molecularly.

Conclusion

These findings suggest that during the time of sampling, ASFV was detected only in Bali and East Nusa Tenggara but not in Western Nusa Tenggara. These findings support the symptomology of ASFV reported in the two regions. Moreover, BL21 may be useful for developing subculture-attenuated vaccines using commercial cell lines. However, the current study has some limitations namely the investigation was not performed during the initial outbreak and no pathological examination of internal organs was conducted.

Antagonisms of ASFV towards Host Defense Mechanisms: Knowledge Gaps in Viral Immune Evasion and Pathogenesis

African swine fever (ASF) causes high morbidity and mortality of both domestic pigs and wild boars and severely impacts the swine industry worldwide. ASF virus (ASFV), the etiologic agent of ASF epidemics, mainly infects myeloid cells in swine mononuclear phagocyte system (MPS), including blood-circulating monocytes, tissue-resident macrophages, and dendritic cells (DCs). Since their significant roles in bridging host innate and adaptive immunity, these cells provide ASFV with favorable targets to manipulate and block their antiviral activities, leading to immune escape and immunosuppression. To date, vaccines are still being regarded as the most promising measure to prevent and control ASF outbreaks. However, ASF vaccine development is delayed and limited by existing knowledge gaps in viral immune evasion, pathogenesis, etc. Recent studies have revealed that ASFV can employ diverse strategies to interrupt the host defense mechanisms via abundant self-encoded proteins. Thus, this review mainly focuses on the antagonisms of ASFV-encoded proteins towards IFN-I production, IFN-induced antiviral response, NLRP3 inflammasome activation, and GSDMD-mediated pyroptosis. Additionally, we also make a brief discussion concerning the potential challenges in future development of ASF vaccine.

Structure and function of African swine fever virus proteins: Current understanding

African swine fever virus (ASFV) is a highly infectious and lethal double-stranded DNA virus that is responsible for African swine fever (ASF). ASFV was first reported in Kenya in 1921. Subsequently, ASFV has spread to countries in Western Europe, Latin America, and Eastern Europe, as well as to China in 2018. ASFV epidemics have caused serious pig industry losses around the world. Since the 1960s, much effort has been devoted to the development of an effective ASF vaccine, including the production of inactivated vaccines, attenuated live vaccines, and subunit vaccines. Progress has been made, but unfortunately, no ASF vaccine has prevented epidemic spread of the virus in pig farms. The complex ASFV structure, comprising a variety of structural and non-structural proteins, has made the development of ASF vaccines difficult. Therefore, it is necessary to fully explore the structure and function of ASFV proteins in order to develop an effective ASF vaccine. In this review, we summarize what is known about the structure and function of ASFV proteins, including the most recently published findings.

Combination of Fe(OH)3 modified diatomaceous earth and qPCR for the enrichment and detection of African swine fever virus in water

Water is one of the primary vectors for African swine fever virus (ASFV) transmission among swine herds. However, the low concentrations of ASFV in water represent a challenge for the detection of the virus by conventional PCR methods, and enrichment of the virus would increase the test sensitivity. In this study, aiming to enrich ASFV in water quickly and efficiently, a rapid and efficient water-borne virus enrichment system (MDEF, modified diatomaceous earth by ferric hydroxide colloid) was used to enrich ASFV in water. After enrichment by MDEF, conventional real-time PCR (qPCR) was used for ASFV detection. ASFV were inactivated and diluted in 10 L of water, of which 4 mL were collected after 60 min treatment using the MDEF system. Two thousand five hundred times reduction of the sample volume was achieved after enrichment. A high adsorption rate of about 99.99 (±0.01)% and a high recovery rate of 64.01 (±10.20)% to 179.65 (±25.53)% was achieved by using 1g modified diatomaceous earth for 10 L ASFV contaminated water. The limit of qPCR detection of ASFV decreased to 1 × 10^-1.11 GU ml^-1 (genomic units per milliliter) from 1 × 10^2.71 GU ml^-1 after concentrating the spiked water from 10 L to 4 ml. Preliminary application of MDEF allowed successful detection of African swine fever virus (ASFV), porcine circovirus type 2 (PCV2), and pseudorabies virus (PRV) in sewage. Thus, the combination of modified diatomaceous earth and real-time PCR is a promising strategy for the detection of viruses in water.

Indirect ELISA Using Multi-Antigenic Dominants of p30, p54 and p72 Recombinant Proteins to Detect Antibodies against African Swine Fever Virus in Pigs

African swine fever (ASF) caused by ASF virus (ASFV) is a fatal disease in pigs and results in great economic losses. Due to the lack of available vaccines and treatments, serological diagnosis of ASF plays a key role in the surveillance program, but due to the lack of knowledge and the complexity of the ASFV genome, the candidate target viral proteins are still being researched. False negativity is still a big obstacle during the diagnostic process. In this study, the high antigenic viral proteins p30, p54 and p72 were screened to find the antigenic dominant domains and the tandem His-p30-54-72 was derived. An indirect enzyme-linked immunosorbent assay (iELISA) coated with His-p30-54-72 was developed with a cut-off value of 0.371. A total of 192 clinical samples were detected by His-p30-54-72-coated indirect ELISA (iELISA) and commercial ASFV antibody kits. The results showed that the positive rate of His-p30-54-72-coated iELISA was increased by 4.7% and 14.6% compared with a single viral protein-based commercial ASFV antibody kits. These results provide a platform for future ASFV clinical diagnosis and vaccine immune effect evaluation.

Identification of novel linear epitopes in P72 protein of African swine fever virus recognized by monoclonal antibodies

African swine fever (ASF) is one of the highly contagious and lethal diseases among domestic pigs and wild boars. The capsid protein P72 of African swine fever virus (ASFV) is very important for the diagnosis and vaccine development. However, the epitope of the protein is not clear. In this study, capsid protein P72 was expressed in Sf9 cells along with its chaperone B602L. A total of ten monoclonal antibodies (mAbs) specific to P72 protein were developed by fusions between SP2/0 cells and spleen cells of mice immunized with the recombinant-P72&B602L proteins expressed in Sf9 cells. Four linear B cell epitopes 31SNIKNVNKSY40, 41GKPDP45, 56HLVHFNAH63 and 185ERLYE189 were identified. Biological information analysis illustrated that epitopes 31SNIKNVNKSY40, 41GKPDP45 and 185ERLYE189 were highly conserved within different ASFV strains. These findings may lead to a better understanding of the antibody-antigen interaction and provide new insights into the vaccine research and serological diagnosis of ASF.

Development of an indirect ELISA for the identification of African swine fever virus wild-type strains and CD2v-deleted strains

African swine fever (ASF) is a potent infectious disease with detrimental effects on the global swine industry and no currently vaccine available. The emergence of low-virulence CD2v-deleted mutants manifested as non-hemadsorption (non-HAD) strains represents a significant challenge to the prevention and control of ASF. In this study, we aimed to establish an indirect ELISA (IELISA) method for the identification of ASFV wild-type and CD2v-deleted strains. We integrated the CD2v protein extracellular domain sequence (CD2v-Ex, 1–588 bp) of the highly pathogenic strain China/2018/AnhuiXCGQ into the genome of suspension culture-adapted Chinese hamster Ovary-S (CHO-S) cells using lentivirus vectors (LVs). By screening, we identified a monoclonal CHO-S cell line that stably expressed secretory CD2v-Ex Protein. We then used the purified CD2v-Ex Protein as the detection antigen to establish an indirect ELISA method (CD2v-IELISA) for identification of the ASFV wild-type and CD2v-Deleted (CD2v−) strains. The CD2v-IELISA method showed excellent specificity with no cross-reaction with serum samples infected with ASFV (CD2v−), porcine reproductive and respiratory syndrome virus (PRRSV), classical swine fever virus (CSFV), porcine circovirus (PCV), porcine pseudorabies virus (PRV), swine foot and mouth disease virus (FMDV) and porcine epidemic diarrhea virus (PEDV). Furthermore, this method showed high sensitivity, allowing identification of ASFV-infected clinical serum samples up to a dilution of 1:2,560. The coefficient of variation both in and between batches was &lt;10% with good reproducibility and a high compliance rate of 99.4%. This CD2v-IELISA method developed here is of great significance for the prevention, control and purification of ASFV.

Flavonoids as Potential Antiviral Agents for Porcine Viruses

Flavonoids are types of natural substances with phenolic structures isolated from a variety of plants. Flavonoids have antioxidant, anti-inflammatory, anticancer, and antiviral activities. Although most of the research or applications of flavonoids are focused on human diseases, flavonoids also show potential applicability against porcine virus infection. This review focuses on the recent progress in antiviral mechanisms of potential flavonoids against the most common porcine viruses. The mechanism discussed in this paper may provide a theoretical basis for drug screening and application of natural flavonoid compounds and flavonoid-containing herbs to control porcine virus infection and guide the research and development of pig feed additives.

Clinical sequencing uncovers the genomic characteristics and mutation spectrum of the 2018 African swine fever virus in Guangdong, China

African swine fever (ASF) outbreak have caused tremendous economic loss to the pig industry in China since its emergence in August 2018. Previous studies revealed that many published sequences are not suitable for detailed analyses due to the lack of data regarding quality parameters and methodology, and outdated annotations. Thus, high-quality genomes of highly pathogenic strains that can be used as references for early Chinese ASF outbreaks are still lacking, and little is known about the features of intra-host variants of ASF virus (ASFV). In this study, a full genome sequencing of clinical samples from the first ASF outbreak in Guangdong in 2018 was performed using MGI (MGI Tech Co., Ltd., Shenzhen, China) and Nanopore sequencing platforms, followed by Sanger sequencing to verify the variations. With 22 sequencing corrections, we obtained a high-quality genome of one of the earliest virulent isolates, GZ201801_2. After proofreading, we improved (add or modify) the annotations of this isolate using the whole genome alignment with Georgia 2007/1. Based on the complete genome sequence, we constructed the methylation profiles of early ASFV strains in China and predicted the potential 5mC and 6mA methylation sites, which are likely involved in metabolism, transcription, and replication. Additionally, the intra-host single nucleotide variant distribution and mutant allele frequency in the clinical samples of early strain were determined for the first time and found a strong preference for A and T substitution mutation, non-synonymous mutations, and mutations that resulted in amino acid substitutions into Lysine. In conclusion, this study provides a high-quality genome sequence, updated genome annotation, methylation profile, and mutation spectrum of early ASFV strains in China, thereby providing a reference basis for further studies on the evolution, transmission, and virulence of ASFV.

Interaction network of African swine fever virus structural protein p30 with host proteins

African swine fever virus (ASFV) is a complex nucleocytoplasmic large DNA virus (NCLDV) that causes a lethal hemorrhagic disease that is currently threatening the global pig industry. ASFV structural protein p30 is a membrane phosphoprotein that suggests it may play a regulatory role, possibly in signal transduction. Despite its significance in internalization into host cells, the interaction between p30 and host proteins is relatively unknown. In this study, we describe the application of a DUALmembrane yeast two-hybrid assay to screen a primary porcine alveolar macrophages cDNA library and analyze the interactome of p30 protein. Our data identify seven host cellular proteins (DAB2, RPSA, OAS1, PARP9, CAPG, ARPC5, and VBP1) that putatively interact with the p30. We further verified the interaction between p30 and host proteins by laser confocal microscopy, co-immunoprecipitation, and GST-pulldown assay. To further understand the relationship between host proteins and p30, we drew the interaction network diagram and analyzed the functional enrichment of each host protein. Enrichment analysis of Gene Ontology and Kyoto Encyclopedia of Genes and Genomes indicated that host proteins were mainly related to endocytosis, actin cytoskeleton regulation, and innate immunity. Collectively, we identified the interaction between p30 and host cell protein using a membrane protein yeast two-hybrid system, which increases our knowledge of the interaction between ASFV and the host and informs future research on antiviral strategies.

The Development of a Multiplex Real-Time Quantitative PCR Assay for the Differential Detection of the Wild-Type Strain and the MGF505-2R, EP402R and I177L Gene-Deleted Strain of the African Swine Fever Virus

Simple Summary

African swine fever (ASF) was first reported in August 2018 in China, and the naturally gene-deleted ASFV strain was first identified in 2020 in this country. The vaccine candidates that deleted some virulent genes from the virulent parental strains have also been reported in many countries. To differentiate the wild-type and gene-deleted ASFV strains, four pairs of specific primers and TaqMan probes targeting the ASFV B646L (p72), I177L, MGF505-2R and EP402R (CD2v) genes were designed. After optimizing the reaction conditions, a multiplex real-time qPCR assay for the differential detection of the wild-type and gene-deleted ASFV strains was developed. The assay was further used to test 4239 clinical samples, and 534 samples were positive for ASFV, of which 30 samples lacked B646L, I177L, MGF505-2R and/or EP402R genes. The assay showed high specificity, sensitivity and repeatability, and it provided a reliable method for evaluating ASFV in clinical samples.

Abstract

African swine fever virus (ASFV) causes African swine fever (ASF), a devastating hemorrhagic disease of domestic pigs and wild boars. Currently, the MGF505R, EP402R (CD2v) and I177L gene-deleted ASFV strains were confirmed to be the ideal vaccine candidate strains. To develop an assay for differentiating the wild-type and gene-deleted ASFV strains, four pairs of specific primers and TaqMan probes targeting the ASFV B646L (p72), I177L, MGF505-2R and EP402R (CD2v) genes were designed. A multiplex real-time qPCR assay for the differential detection of the wild-type and gene-deleted ASFV strains was developed after optimizing the reaction conditions, including the annealing temperature, primer concentration and probe concentration. The results showed that the multiplex real-time qPCR assay can specifically test the ASFV B646L (p72), I177L, MGF505-2R and EP402R (CD2v) genes with a limit of detection (LOD) of 32.1 copies/μL for the B646L (p72) gene, and 3.21 copies/μL for the I177L, MGF505-2R and EP402R (CD2v) genes. However, the assay cannot test for the classical swine fever virus (CSFV), porcine reproductive and respiratory syndrome virus (PRRSV), porcine epidemic diarrhea virus (PEDV), porcine deltacoronavirus (PDCoV), porcine circovirus type 2 (PCV2), PCV3 and pseudorabies virus (PRV). The assay demonstrated good repeatability and reproducibility with coefficients of variation (CV) less than 1.56% for both the intra- and inter-assay. The assay was used to test 4239 clinical samples, and the results showed that 12.60% (534/4239) samples were positive for ASFV, of which 10 samples lacked the EP402R gene, 6 samples lacked the MGF505-2R gene and 14 samples lacked the EP402R and MGF505-2R genes. The results indicated that the multiplex real-time qPCR developed in this study can provide a rapid, sensitive and specific diagnostic tool for the differential detection of the ASFV B646L, I177L, MGF505-2R and EP402R genes.

Molecular Characterization of African Swine Fever Virus From 2019-2020 Outbreaks in Guangxi Province, Southern China

African swine fever virus (ASFV) causes contagious hemorrhagic disease of pigs with high morbidity and mortality. To identify the molecular characteristics of ASFV strains circulating in Guangxi province, southern China, a total of 336 tissue samples collected from 336 domestic pigs that died as a result of severe hemorrhagic disease during 2019–2020 were tested for ASFV. Furthermore, 66 ASFV strains were genetically characterized by sequence analysis of the C-terminal region of B646L (p72) gene, the complete E183L (p54) gene, the variable region of EP402R (CD2v) gene, the central variable region (CVR) of B602L gene, the full MGF505-2R gene, and the tandem repeat sequence (TRS) within intergenic region (IGR) between the I73R and I329L (I73R/I329L) genes. Phylogenetic analysis revealed that the ASFV strains from Guangxi province belonged to genotypes I and II based on the B646L (p72) and E183L (p54) genes, and there were eight different tetrameric TRS variants based on the CVR of B602L gene. Phylogenetic analysis of the EP402R (CD2v) gene revealed that these ASFV strains belonged to serogroups 4 and 8. Eight of the 66 strains belonged to genotype I and serogroup 4, and showed deletion of whole MGF505-2R gene. The sequence analysis of the IGR between the I73R/I329L genes showed that IGR II and III variants were co-circulating in Guangxi province. The results indicated that ASFV strains circulating in Guangxi province during 2019–2020 outbreaks showed high genetic diversity, of which genotypes I and II, as well as serogroups 4 and 8, were simultaneously circulating in Guangxi province, and there existed wild-type and naturally gene-deleted strains in the field. This is the first detailed report on the molecular characterization of the ASFV strains circulating in southern China, and serogroup 4 in China.

Synergistic Inactivation of African Swine Fever Virus by a Highly Complexed Iodine Combined with Compound Organic Acids

African swine fever (ASF) is a highly contagious disease of domestic pigs and wild boar with high morbidity and mortality caused by African swine fever virus (ASFV). Due to the lack of commercial vaccines and treatments for ASF, cleaning and disinfection remain one of the most effective biosecurity measures to control ASF. Our previous studies have shown that ASFV can be inactivated by 0.25 to 5% highly complexed iodine (HPCI) in 5 to 30 min. This study evaluated the synergistic inactivation effects of HPCI combined with compound organic acids (COAs) against ASFV. The results showed that the inactivation rates of HPCI, COAs, and HPCI+COAs on the reporter ASFV expressing the green fluorescent protein increased in dose- and time-dependent manners. The best inactivation effects were obtained when the compatibility ratio of HPCI and COAs was 5:1, and the ideal temperature was 25°C. Furthermore, there were no significant differences when comparing the efficacy of HPCI combined with COAs (HPCI+COAs) in inactivating wild-type ASFV and the reporter ASFV (P > 0.05). ASFV of 10^4.0 50% tissue culture infective dose (TCID₅₀)/mL was completely inactivated by 0.13% HPCI (0.0065% effective iodine), 0.06% COAs, or 0.13% HPCI+COAs (approximately 0.0054% effective iodine), respectively, while 10^6.0 TCID₅₀/mL ASFV was completely inactivated by 1.00% HPCI (0.05% effective iodine), 0.50% COAs, or 1.00% HPCI+COAs (0.042% effective iodine), respectively. It was found that the combination index (CI) of HPCI and COAs was less than 1 under different conditions. This study demonstrated that HPCI+COAs could synergistically inactivate ASFV and represent an effective compound disinfectant for the control of ASF. IMPORTANCE African swine fever (ASF) is a highly contagious disease of swine with high morbidity and mortality caused by African swine fever virus (ASFV). Due to the lack of commercial vaccines and treatment available for ASF, effective disinfectants and the proper use of them are essential to inactivate ASFV. The significance of this research is in searching for an ideal disinfectant that has the advantages of low toxicity and nonpollution and can inactivate ASFV efficiently. In this study, we demonstrated that HPCI+COAs had synergistic effects on inactivating ASFV. Thus, HPCI+COAs could be used as an effective disinfectant for the control of ASF.