African Swine Fever Virus: An Emerging DNA Arbovirus

Advanced Strategies for Developing Vaccines and Diagnostic Tools for African Swine Fever

African swine fever (ASF) is one of the most lethal infectious diseases affecting domestic pigs and wild boars of all ages. Over a span of 100 years, ASF has continued to spread over continents and adversely affects the global pig industry. To date, no vaccine or treatment has been approved. The complex genome structure and diverse variants facilitate the immune evasion of the ASF virus (ASFV). Recently, advanced technologies have been used to design various potential vaccine candidates and effective diagnostic tools. This review updates vaccine platforms that are currently being used worldwide, with a focus on genetically modified live attenuated vaccines, including an understanding of their potential efficacy and limitations of safety and stability. Furthermore, advanced ASFV detection technologies are presented that discuss and incorporate the challenges that remain to be addressed for conventional detection methods. We also highlight a nano-bio-based system that enhances sensitivity and specificity. A combination of prophylactic vaccines and point-of-care diagnostics can help effectively control the spread of ASFV.

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 pF778R Attenuates Type I Interferon Response by Impeding STAT1 Nuclear Translocation

African swine fever virus (ASFV) is an extensive and intricate double-stranded DNA virus with approximately 100% lethality in domestic swine. There is no effective vaccine to combat this virus, and this has led to substantial economic losses in the swine industry. ASFV encodes various proteins that impede interferon-based immune defenses in the host by employing diverse mechanisms. However, the roles of most of these proteins remain unknown. Therefore, understanding the immune evasion mechanisms employed by ASFV may facilitate the development of effective measures against the virus. In this study, we discovered a negative regulation of the type I interferon (IFN) response by the ASFV ribonuclease reductase large subunit pF778R. This novel type Ⅰ IFN response antagonist significantly inhibits IFN-α-induced interferon-stimulated response element promoter activation, precludes the upregulation of various interferon-stimulated genes, and prevents STAT1 nuclear translocation. Mechanistically, pF778R did not affect the protein levels of crucial molecules in the JAK/STAT signaling pathway or engage in direct interactions. However, pF778R expression impedes type I IFN responses mediated by the JAK/STAT signaling pathway. Further investigations revealed that pF778R did not interfere with STAT1 phosphorylation or dimerization, but it inhibited IFN signaling by weakening the nuclear accumulation of activated STAT1. The critical role of the ASFV protein pF778R in evading IFN-I-mediated innate immunity highlights a unique mode of ASFV evasion and provides insights into the pathogenic mechanism of the virus.

A multi-state survey of farm-level preparedness towards African swine fever outbreak in Nigeria

Outbreaks of African Swine Fever (ASF) have severe economic implications for Nigeria and result in significant loss of livelihoods. The non-availability of vaccines makes biosecurity the reliable key to reducing ASF outbreaks. This study evaluated preparedness for ASF outbreaks at the farm level among 247 pig farmers randomly selected from Abia, Akwa-Ibom, Edo, Kwara, and Oyo states. We categorized each pig farmer's ASF preparedness rating (ASF - PR) as "poor", "moderate", and "satisfactory" based on their score on an 11-item scale. Finally, a multivariable logistic regression analysis was conducted to assess the association between the socio-demographic variables and farm-level ASF preparedness. The awareness of ASF among pig farmers was very high (87.9%, n = 217). Most farmers knew the clinical signs of the disease, the modes of transmission of ASF, and correctly identified the risk factors. They also considered the need for thorough cleaning and disinfection of piggeries (87.1%, n = 189), tightened biosecurity (85.7%, n = 186), culling all ASF-affected pigs (77.9%, n = 169) as well as the ban on the transport of pigs and their products (49.8%, n = 108) as very important in ASF control. Conversely, 27.6%, (n = 60) of the farmers thought ASF could affect humans, 12% (n = 27) of them openly discarded the carcasses of dead pigs, and there was a high antibiotic usage. Most of the pig farmers used antibiotics as prophylaxis (63.6%, n = 157), chemotherapeutics (66.4%, n = 164), growth promoters (15.4%, n = 38), and wrongly so, 13% (n = 32) of them thought that antibiotics could be used to prevent and treat ASF. At the farm level, two-thirds (68.8%, n = 170) of the farmers had strict movement restrictions, and 48.6% (n = 120) routinely quarantine new pigs before introduction into their herd. Across the five states, 36% (n = 89) of the farmers had witnessed sudden death with signs consistent with ASF amongst their pigs and only 10.1% (n = 27) had confirmatory ASF diagnosis. The mean score for the farm-level ASF-PR was 6.95 ± 2.7. Approximately one-quarter of the 247 pig farmers had satisfactory ASF - PR that might help to prevent the incursion of ASF into their farms. Most farmers had moderate ASF - PR (59.5%, n = 147) whereas 17% (n = 42) had very poor ASF-PR and were most prone to an ASF outbreak. Of the sociodemographic variables, only age was significantly associated with farm-level ASF preparedness as older pig farmers especially those aged between 50 and 59 years (OR: 4.83; 95% CI: 1.10, 21.22; p = 0.037) were more likely to have satisfactory ASF - PR than the others. Our findings showed pig farmers were not adequately prepared and the next ASF outbreak could pose more significant threat to pig populations across Nigeria. Government should urgently establish minimum biosecurity measures and improve its ASF surveillance mechanisms for commercial and backyard pig production.

Glycerol Monolaurate Inhibits Wild-Type African Swine Fever Virus Infection in Porcine Macrophages

Naturally abundant antimicrobial lipids, such as fatty acids and monoglycerides, that disrupt membrane-enveloped viruses are promising mitigants to inhibit African swine fever virus (ASFV). Among mitigant candidates in this class, glycerol monolaurate (GML) has demonstrated particularly high antiviral activity against laboratory-adapted ASFV strains. However, there is an outstanding need to further determine the effects of GML on wild-type ASFV strains, which can have different virulence levels and sensitivities to membrane-disrupting compounds as compared to laboratory-adapted strains. Herein, we investigated the antiviral effects of GML on a highly virulent strain of a wild-type ASFV isolate (Armenia/07) in an in vitro porcine macrophage model. GML treatment caused a concentration-dependent reduction in viral infectivity, and there was a sharp transition between inactive and active GML concentrations. Low GML concentrations had negligible effect on viral infectivity, whereas sufficiently high GML concentrations caused a >99% decrease in viral infectivity. The concentration onset of antiviral activity matched the critical micelle concentration (CMC) value of GML, reinforcing that GML micelles play a critical role in enabling anti-ASFV activity. These findings validate that GML can potently inhibit wild-type ASFV infection of porcine macrophages and support a biophysical explanation to guide antimicrobial lipid performance optimization for pathogen mitigation applications.

African Swine Fever: The State of the Art in Italy

African swine fever (ASF) is a severe viral disease of domestic pigs and Eurasian wild boars (Sus scrofa) caused by the African swine fever virus (ASFV). ASF is endemic in sub-Saharan Africa, where 24 genotypes of the virus have been reported. Between the late 1950s and the early 1980s, genotype I ASFV emerged in Europe, including Italy. In June 2007, a second ASF epidemic wave caused by genotype II was registered, involving several European and extra-European countries, including Italy in 2022. The present paper aims to provide the state of the art of ASF in Italy, describing the course of ASF in wild boars and domestic pigs as an example of multiple concurring different scenarios. Sardinia is coping with the last phase of the eradication of the disease by applying the exit strategy. Conversely, four clusters of infection located in North, Central, and South Italy are still ongoing. The unique and complex Italian experience in ASF-controlling may be useful to increase know-how on the efficacy of strategies and measures, as well as issues that could be further improved.

Developing an Indirect ELISA for the Detection of African Swine Fever Virus Antibodies Using a Tag-Free p15 Protein Antigen

African swine fever (ASF) is one of the most severe diseases caused by the ASF virus (ASFV), causing massive economic losses to the global pig industry. Serological tests are important in ASF epidemiological surveillance, and more antigen targets are needed to meet market demand for ASFV antibody detection. In the present study, ASFV p15 protein was fusion-expressed in Escherichia coli (E. coli) with elastin-like polypeptide (ELP), and the ELP-p15 protein was purified using a simple inverse transition cycling (ITC) process. The ELP tag was cleaved off using tobacco etch virus protease (TEVp), resulting in a tag-free p15 protein. Western blot analysis demonstrated that the p15 protein reacted strongly with ASFV-positive serum. The p15 protein was used as a coating antigen in an indirect ELISA (iELISA) for detecting ASFV antibodies. The p15-iELISA method demonstrated high specificity to ASFV-positive sera, with a maximum detection dilution of 1:1600. Moreover, the method exhibited good reproducibility, with less intra-assay and inter-assay CV values than 10%. Therefore, p15-iELISA offers a novel approach for accurately detecting ASFV antibodies with significant clinical application potential.

Internal Validation of the ASFV MONODOSE dtec-qPCR Kit for African Swine Fever Virus Detection under the UNE-EN ISO/IEC 17025:2005 Criteria

African swine fever virus is considered an emerging virus that causes African swine fever, a disease characterised by high mortality and elevated transmission rates and that, as it is for most other viral diseases, cannot be treated with specific drugs. Effective and reliable detection of the virus is relevant to prevent uncontrolled contagion among boar populations and to reduce economic losses. Moreover, animal health laboratories are demanding standardisation, optimisation and quality assurance of the available diagnostic assays. In the present study, the ASFV MONODOSE dtec-qPCR kit was validated following the UNE-EN ISO/IEC 17025:2005 guidelines. Analytical validation terms include in silico and in vitro specificity, sensitivity, efficiency and reliability (repeatability/reproducibility). Diagnostic validation of the method was assessed through the analysis of a total of 181 porcine samples originating from six different matrix types doped with African swine fever virus DNA received from the European reference laboratory for African Swine Fever (INIA-CISA, Madrid, Spain): whole blood, blood serum, kidney, heart, liver and tonsil. Results agreed with those obtained from a reference detection method also based on real-time PCR, endorsed by WOAH, but the ASFV MONODOSE dtec-qPCR kit incorporates some technical innovations and improvements which may benefit end-users. This kit, available worldwide with full analytical and diagnostic validation, can recognise all known ASFV genotypes and brings additional benefits to the current qPCR technology.

Phylogenomic Comparison of Seven African Swine Fever Genotype II Outbreak Viruses (1998-2019) Reveals the Likely African Origin of Georgia 2007/1

Since the initial report of African swine fever (ASF) in Kenya in 1921, the disease has predominantly been confined to Africa. However, in 2007, an ASF genotype II virus of unknown provenance was introduced to Georgia. This was followed by its rampant spread to 73 countries, and the disease is now a global threat to pig production, with limited effective treatment and vaccine options. Here, we investigate the origin of Georgia 2007/1 through genome sequencing of three viruses from outbreaks that predated the genotype II introduction to the Caucasus, namely Madagascar (MAD/01/1998), Mozambique (MOZ/01/2005), and Mauritius (MAU/01/2007). In addition, genome sequences were generated for viruses from East African countries historically affected by genotype II (Malawi (MAL/04/2011) and Tanzania (TAN/01/2011)) and newly invaded southern African countries (Zimbabwe (ZIM/2015) and South Africa (RSA/08/2019). Phylogenomic analyses revealed that MOZ/01/2005, MAL/04/2011, ZIM/2015 and RSA/08/2019 share a recent common ancestor with Georgia 2007/1 and that none contain the large (~550 bp) deletion in the MGT110 4L ORF observed in the MAD/01/1998, MAU/01/2007 and TAN/01/2011 isolates. Furthermore, MOZ/01/2005 and Georgia 2007/1 only differ by a single synonymous SNP in the EP402R ORF, confirming that the closest link to Georgia 2007/1 is a virus that was circulating in Mozambique in 2005.

Immunogenic response of recombinant pseudorabies virus carrying B646L and B602L genes of African swine fever virus in mice

African swine fever (ASF) is an acute infectious disease that poses a high lethality risk to domestic pigs and wild boars, causing substantial economic losses to the global pig industry. The prevention and control of ASF remain challenging, necessitating the urgent development of a safe and effective vaccine. This study focused on the essential structural protein p72 of ASFV (encoded by the B646L gene) and its chaperone protein pB602L (encoded by the B602L gene) as the target antigenic proteins. Based on CRISPR/Cas9 gene-editing technology, we constructed a live attenuated recombinant pseudorabies virus vector expressing the p72 and pB602L proteins (designated as rPRVXJ-EGFP/B602L/B646L), and assessed its immunization effect in mice. The recombinant virus rPRVXJ-EGFP/B602L/B646L successfully proliferated and demonstrated stable expression of the p72 and pB602L proteins in BHK-21 cells. Moreover, it exhibited excellent safety when used in mice and induced specific humoral and cellular immune responses targeting p72 and pB602L. In addition, it provided complete protection (100%) against the virulent PRV strain (PRV-XJ). These results indicate that the recombinant virus rPRVXJ-EGFP/B602L/B646L possesses robust immunogenicity and safety in mice. In conclusion, PRV represents a promising viral vector for expressing ASFV gene, and our study serves as an essential reference for the development of viral vector vaccines against ASFV.

African swine fever virus MGF-360-10L is a novel and crucial virulence factor that mediates ubiquitination and degradation of JAK1 by recruiting the E3 ubiquitin ligase HERC5

African swine fever virus (ASFV) causes acute hemorrhagic infectious disease in pigs. The ASFV genome encodes various proteins that enable the virus to escape innate immunity; however, the underlying mechanisms are poorly understood. The present study found that ASFV MGF-360-10L significantly inhibits interferon (IFN)-β-triggered STAT1/2 promoter activation and the production of downstream IFN-stimulated genes (ISGs). ASFV MGF-360-10L deletion (ASFV-Δ10L) replication was impaired compared with the parental ASFV CN/GS/2018 strain, and more ISGs were induced by the ASFV-Δ10L in porcine alveolar macrophages in vitro. We found that MGF-360-10L mainly targets JAK1 and mediates its degradation in a dose-dependent manner. Meanwhile, MGF-360-10L also mediates the K48-linked ubiquitination of JAK1 at lysine residues 245 and 269 by recruiting the E3 ubiquitin ligase HERC5 (HECT and RLD domain-containing E3 ubiquitin protein ligase 5). The virulence of ASFV-Δ10L was significantly lower than that of the parental strain in vivo, which indicates that MGF-360-10L is a novel virulence factor of ASFV. Our findings elaborate the novel mechanism of MGF-360-10L on the STAT1/2 signaling pathway, expanding our understanding of the inhibition of host innate immunity by ASFV-encoded proteins and providing novel insights that could contribute to the development of African swine fever vaccines. IMPORTANCE African swine fever outbreaks remain a concern in some areas. There is no effective drug or commercial vaccine to prevent African swine fever virus (ASFV) infection. In the present study, we found that overexpression of MGF-360-10L strongly inhibited the interferon (IFN)-β-induced STAT1/2 signaling pathway and the production of IFN-stimulated genes (ISGs). Furthermore, we demonstrated that MGF-360-10L mediates the degradation and K48-linked ubiquitination of JAK1 by recruiting the E3 ubiquitin ligase HERC5. The virulence of ASFV with MGF-360-10L deletion was significantly less than parental ASFV CN/GS/2018. Our study identified a new virulence factor and revealed a novel mechanism by which MGF-360-10L inhibits the immune response, thus providing new insights into the vaccination strategies against ASFV.

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.

Factors Affecting the Spread, Diagnosis, and Control of African Swine Fever in the Philippines

African Swine Fever (ASF) is a highly contagious disease that threatens the swine industry globally. Since its introduction into the Philippines in 2019, ASF has spread extensively in both commercial and backyard farms. Here, using a mix of qualitative and quantitative methods, including conjoint and SWOT analyses, world café discussions, and multivariable regression models, the most important factors that influence the spread, diagnosis, and control of ASF in the Philippines were identified. Research findings suggest that swill or contaminated feed, inadequate biosecurity protocols, and movement of personnel were the top risk factors favoring ASF spread among farms in general. For commercial farms, contaminated vehicles and personnel were also important, whereas for backyard farms, the introduction of new pigs, environmental contamination, and poor feeding quality were relevant risk factors. Notable clinical signs of ASF in pigs include reduced feed intake, huddled behavior, and reluctance to stand. This study highlights the need for timely reporting, trust-building initiatives, and enhanced biosecurity measures to effectively manage ASF outbreaks in the country. Results here contribute to the knowledge of factors affecting ASF spread in the Philippines and can help design prevention and control measures in ASF-infected countries while enhancing preparedness in countries free from the disease.

Dihydromyricetin inhibits African swine fever virus replication by downregulating toll-like receptor 4-dependent pyroptosis in vitro

African swine fever (ASF), caused by ASF virus (ASFV) infection, poses a huge threat to the pork industry owing to ineffective preventive and control measures. Hence, there is an urgent need to develop strategies, including antiviral drugs targeting ASFV, for preventing ASFV spread. This study aimed to identify novel compounds with anti-ASFV activity. To this end, we screened a small chemical library of 102 compounds, among which the natural flavonoid dihydromyricetin (DHM) exhibited the most potent anti-ASFV activity. DHM treatment inhibited ASFV replication in a dose- and time-dependent manner. Furthermore, it inhibited porcine reproductive and respiratory syndrome virus and swine influenza virus replication, which suggested that DHM exerts broad-spectrum antiviral effects. Mechanistically, DHM treatment inhibited ASFV replication in various ways in the time-to-addition assay, including pre-, co-, and post-treatment. Moreover, DHM treatment reduced the levels of ASFV-induced inflammatory mediators by regulating the TLR4/MyD88/MAPK/NF-κB signaling pathway. Meanwhile, DHM treatment reduced the ASFV-induced accumulation of reactive oxygen species, further minimizing pyroptosis by inhibiting the ASFV-induced NLRP3 inflammasome activation. Interestingly, the effects of DHM on ASFV were partly reversed by treatment with polyphyllin VI (a pyroptosis agonist) and RS 09 TFA (a TLR4 agonist), suggesting that DHM inhibits pyroptosis by regulating TLR4 signaling. Furthermore, targeting TLR4 with resatorvid (a specific inhibitor of TLR4) and small interfering RNA against TLR4 impaired ASFV replication. Taken together, these results reveal the anti-ASFV activity of DHM and the underlying mechanism of action, providing a potential compound for developing antiviral drugs targeting ASFV.

Whole Genome Sequencing Shows that African Swine Fever Virus Genotype IX Is Still Circulating in Domestic Pigs in All Regions of Uganda

Blood samples were collected from pigs at six abattoirs in the Kampala, Uganda metropolitan area from May 2021 through June 2022, and tested for African swine fever virus. Thirty-one samples with cycle threshold values < 26 from pigs with different geographic origins, clinical and pathologic signs, and Ornithodoros moubata exposure underwent whole genome sequencing. The p72 gene was used to genotype the isolates, and all were found to be genotype IX; whole genome sequences to previous genotype IX isolates confirmed their similarity. Six of the isolates had enough coverage to evaluate single nucleotide polymorphisms (SNPs). Five of the isolates differed from historic regional isolates, but had similar SNPs to one another, and the sixth isolate also differed from historic regional isolates, but also differed from the other five isolates, even though they are all genotype IX. Whole genome sequencing data provide additional detail on viral evolution that can be useful for molecular epidemiology, and understanding the impact of changes in genes to disease phenotypes, and may be needed for vaccine targeting should a commercial vaccine become available. More sequencing of African swine fever virus isolates is needed in Uganda to understand how and when the virus is changing.

Refinement of water-based foam depopulation procedures for finisher pigs during field conditions: Welfare implications and logistical aspects

Water-based foam (WBF) depopulation is currently being researched as an alternative for rapid destruction of swine populations under emergency circumstances. Appropriate guidelines are needed to maintain method reliability and depopulation efficacy while minimizing animal distress under field conditions. Finisher pigs were depopulated using WBF with a 7.5-minute dwell time in two trials to evaluate the effect of; trial 1) foam fill level (1.5, 1.75, or 2.0 times the pig's head height) and trial 2) foam fill rate (slow, medium, or fast) on aversive pig responses (surface breaks, vocalization, and escape attempts) and time to cessation of cardiac activity. Activity and cardiac activity were recorded using subcutaneous bio-loggers for swine in trial 2. The average time to cessation of movement (COM) from the start of foam filling was compared for the foam fill rate groups using a generalized linear mixed effect model under Poisson distribution. Foam rate group was used as an independent variable, and replicates as a random effect. For trial 1, the average (mm:ss ± SD) time to fill completion was 01:18 ± 00:00, 00:47 ± 00:05, and 00:54 ± 00:05, for 1.5, 1.75, and 2.0 times the pig's head height, respectively. For trial 2, the average time to fill completion was 03:57 ± 00:32, 01:14 ± 00:23 and 00:44 ± 00:03, and the average time (mm:ss ± SE) to COM was 05:22 ± 00:21, 03:32 ± 00:14, and 03:11 ± 00:13 for slow, medium, and fast fill rate groups, respectively. A higher number of aversive pig responses were observed for the lowest foam fill level and slowest foam fill rate compared to increased fill levels and faster fill rates. For trial 2 the median (mm:ss ± IQR) time to fatal arrhythmia was 09:53 ± 02:48, 11:19 ± 04:04, and 10:57 ± 00:47 post-foam initiation for fast, medium, and slow foam rate groups, respectively. Time to cessation of cardiac activity was significantly shorter for the fast foam rate group compared to medium and slow foam rates groups (P = 0.04). For both trials, vocalizations were absent, and all pigs were unconscious following the 7.5-minute dwell time and no pigs needed a secondary euthanasia method. This WBF study showed that slower fill rates and low foam fill levels may extend the time until cessation of cardiac activity in swine during depopulation. A conservative recommendation with consideration of swine welfare during an emergency scenario would be a minimum foam fill level twice the pig's head height and a foam fill rate capable of covering pigs in foam within 60 s to minimize aversive responses and expedite cessation of cardiac activity.

Target capture sequencing for the first Nigerian genotype I ASFV genome

African swine fever (ASF) is a contagious viral disease that affects domestic pigs and wild boars, causing significant economic losses globally. After the first Nigerian outbreak in 1997, there have been frequent reports of ASF in pig-producing regions in the country. To facilitate control, it is important to understand the genotype and phylogenetic relationship of ASF viruses (ASFVs). Recent genetic analysis of Nigerian ASFV isolates has revealed the presence of both genotypes I and II; this is based on analysis of a few selected genes. Phylogenetic analysis of ASFV whole genomes highlights virus origins and evolution in greater depth. However, there is currently no information on the ASFV genome from Nigerian isolates. Two ASFV-positive samples were detected during a random survey of 150 Nigerian indigenous pig samples collected in 2016. We assembled near-complete genomes of the two ASFV-positive samples using in-solution hybrid capture sequencing. The genome-wide phylogenetic tree assigned these two genomes into p72 genotype I, particularly close to the virulent Benin 97/1 strain. The two ASFVs share 99.94 and 99.92 % genomic sequence identity to Benin97/1. This provides insight into the origin and relationship of ASFV strains from Nigeria and Italy. The study reports for the first time the determination of near-complete genomes of ASFV using in-solution hybrid capture sequencing, which represents an important advance in understanding the global evolutionary landscape of ASFVs.

Structural Insights into the Assembly of the African Swine Fever Virus Inner Capsid

African swine fever virus (ASFV), the cause of a highly contagious hemorrhagic and fatal disease of domestic pigs, has a complex multilayer structure. The inner capsid of ASFV located underneath the inner membrane enwraps the genome-containing nucleoid and is likely the assembly of proteolytic products from the virally encoded polyproteins pp220 and pp62. Here, we report the crystal structure of ASFV p150△NC, a major middle fragment of the pp220 proteolytic product p150. The structure of ASFV p150△NC contains mainly helices and has a triangular plate-like shape. The triangular plate is approximately 38 Å in thickness, and the edge of the triangular plate is approximately 90 Å long. The structure of ASFV p150△NC is not homologous to any of the known viral capsid proteins. Further analysis of the cryo-electron microscopy maps of the ASFV and the homologous faustovirus inner capsids revealed that p150 or the p150-like protein of faustovirus assembles to form screwed propeller-shaped hexametric and pentametric capsomeres of the icosahedral inner capsids. Complexes of the C terminus of p150 and other proteolytic products of pp220 likely mediate interactions between the capsomeres. Together, these findings provide new insights into the assembling of ASFV inner capsid and provide a reference for understanding the assembly of the inner capsids of nucleocytoplasmic large DNA viruses (NCLDV). IMPORTANCE African swine fever virus has caused catastrophic destruction to the pork industry worldwide since it was first discovered in Kenya in 1921. The architecture of ASFV is complicated, with two protein shells and two membrane envelopes. Currently, mechanisms involved in the assembly of the ASFV inner core shell are less understood. The structural studies of the ASFV inner capsid protein p150 performed in this research enable the building of a partial model of the icosahedral ASFV inner capsid, which provides a structural basis for understanding the structure and assembly of this complex virion. Furthermore, the structure of ASFV p150△NC represents a new type of fold for viral capsid assembly, which could be a common fold for the inner capsid assembly of nucleocytoplasmic large DNA viruses (NCLDV) and would facilitate the development of vaccine and antivirus drugs against these complex viruses.

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.

Identification and Characterization of Nanobodies from a Phage Display Library and Their Application in an Immunoassay for the Sensitive Detection of African Swine Fever Virus

African swine fever (ASF) is one of the most lethal and devastating diseases of domestic and wild swine. The continual spread and frequent outbreaks of ASF have seriously threatened the pig and pig-related industries, causing great socioeconomic losses at unprecedented proportions. Although ASF has been documented for a century, no effective vaccine or antiviral treatment is currently available. Nanobodies (Nbs) derived from heavy-chain-only antibodies in camelids have been discovered to be effective as therapeutics and robust biosensors in imaging and diagnostic applications. In the present study, a high-quality phage display library containing specific Nbs raised against ASFV proteins was successfully constructed, and 19 nanobodies specific to ASFV p30 were preliminarily identified by phage display technology. After extensive evaluation, nanobodies Nb17 and Nb30 were employed as immunosensors and applied to develop a sandwich enzyme-linked immunosorbent assay (ELISA) for the detection of ASFV in clinical specimens. This immunoassay showed a detection limit of approximately 1.1 ng/mL target protein and 102.5 hemadsorption (HAD50/mL) of ASFV and exhibited high specificity with no cross-reaction with the other porcine viruses tested. The performances of the newly developed assay and a commercial kit in testing 282 clinical swine samples were very similar (93.62% agreement). However, the novel sandwich Nb-ELISA showed higher sensitivity than the commercial kit when serial dilutions of ASFV-positive samples were tested. The present study describes a valuable alternative technique for the detection and surveillance of ASF in endemic regions. Furthermore, additional nanobodies specific to ASFV may be developed using the generated VHH library and employed in different biotechnology fields.

Identification of a Linear B Cell Epitope on p54 of African Swine Fever Virus Using Nanobodies as a Novel Tool

African swine fever (ASF) has received great attention from the swine industry due to the pandemic and the lack of vaccines or effective treatments. In the present study, 13 African swine fever virus (ASFV) p54-specific nanobodies (Nbs) were successfully screened based on Bactrian camel immunization of p54 protein and phage display technology, and their reactivity with the p54 C-terminal domain (p54-CTD) was determined; however, only Nb8-horseradish peroxidase (Nb8-HRP) exhibited the best reactivity. Immunoperoxidase monolayer assay (IPMA) and immunofluorescence assay (IFA) results indicated that Nb8-HRP specifically reacted with ASFV-infected cells. Then, the possible epitopes of p54 were identified using Nb8-HRP. The results showed that Nb8-HRP could recognize p54-CTD truncated mutant p54-T1. Then, 6 overlapping peptides covering p54-T1 were synthesized to determine the possible epitopes. Dot blot and peptide-based enzyme-linked immunosorbent assay (ELISA) results suggested that one novel minimal linear B cell epitope, 76QQWVEV81, which had never been reported before, was identified. Alanine-scanning mutagenesis revealed that 76QQWV79 was the core binding site for Nb8. Epitope 76QQWVEV81 was highly conserved among genotype II ASFV strains and could react with inactivated ASFV antibody-positive serum from naturally infected pigs, indicating that it was a natural linear B cell epitope. These findings provide valuable insights for vaccine design and p54 as an effective diagnostic tool. IMPORTANCE The ASFV p54 protein plays an important role in inducing neutralization antibodies in vivo after viral infection and is often used as a candidate protein for subunit vaccine development. The full understanding of the p54 protein epitope provides a sufficient theoretical basis for p54 as a vaccine candidate protein. The present study uses a p54-specific nanobody as a probe to identify a highly conserved antigenic epitope, 76QQWVEV81, among different ASFV strains, and it can induce humoral immune responses in pigs. This is the first report using virus-specific nanobodies as a tool to identify some special epitopes that cannot be recognized by conventional monoclonal antibodies. This study opens up nanobodies as a new tool for identifying epitopes and also provides a theoretical basis for understanding p54-induced neutralizing antibodies.

Swine Backyard Production Systems in Central Chile: Characterizing Farm Structure, Animal Management, and Production Value Chain

Backyard production systems (BPS) are highly distributed in central Chile. While poultry BPS have been extensively characterized, there remains a notable gap in the characterization of swine BPS in central Chile. In addition, there is evidence that zoonotic pathogens, such as influenza A virus and Salmonella spp., are circulating in backyard poultry and pigs. A total of 358 BPS located in central Chile were evaluated between 2013 and 2015 by interviewing farm owners. Severe deficiencies in biosecurity measures were observed. The value chain of swine backyard production identified food, veterinary care (visits and products), and replacement or breeding animals as the primary inputs to the backyard. The most common origin of swine replacements was from outside the BPS (63%). The main outputs of the system were identified as meat and live animals, including piglets and breeding animals. In 16% of BPS, breeding animals were lent to other BPS, indicating the existence of animals and animal product movement in and out of backyard farms. Results from this study indicate that swine BPS in central Chile represents an animal-human interface that demands special attention for implementing targeted preventive measures to prevent the introduction and spread of animal pathogens and the emergence of zoonotic pathogens.

I329L protein-based indirect ELISA for detecting antibodies specific to African swine fever virus

African swine fever (ASF) is a disease that causes severe economic losses to the global porcine industry. As no vaccine or drug has been discovered for the prevention and control of ASF virus (ASFV), accurate diagnosis and timely eradication of infected animals are the primary measures, which necessitate accurate and effective detection methods. In this study, the truncated ASFV I329L (amino acids 70-237), was induced using IPTG and expressed in Escherichia coli cells. The highly antigenic viral protein I329L was used to develop an indirect enzyme-linked immunosorbent assay (iELISA), named I329L-ELISA, which cut-off value was 0.384. I329L-ELISA was used to detect 186 clinical pig serum samples, and the coincidence rate between the indirect ELISA developed here and the commercial kit was 96.77%. No cross-reactivity was observed with CSFV, PRRSV, PCV2, or PRV antibody-positive pig sera, indicating good specificity. Both intra- assay and inter-assay coefficients were below 10%, and the detection sensitivity of the iELISA reached 1:3200. In this study, an iELISA for ASFV antibody detection was developed based on the truncated ASFV I329L protein. Overall, the I329L-ELISA is a user-friendly detection tool that is suitable for ASFV antibody detection and epidemiological surveillance.

Improving African Swine Fever Surveillance Using Fluorescent Rapid Tests

African swine fever (ASF) is a viral disease of swine with a huge impact due to its high mortality. Lately, the disease has actively spread around the world, affecting new areas from which it had been eradicated long ago. To date, ASF control is carried out by the implementation of strict biosecurity measures such as the early identification of infected animals. In this work, two fluorescent rapid tests were developed to improve the sensitivity of point-of-care diagnosis of ASF. For antigen (Ag) detection in blood, a double-antibody sandwich fluorescent lateral flow assay (LFA) was developed, employing a newly developed recombinant antibody to the VP72 of the virus. To complement the diagnosis, a double-recognition fluorescent LFA was developed using the VP72 for the detection of specific antibodies (Ab) in sera or blood. Both assays statistically improved the detection of the disease when compared to the commercial colorimetric assays INgezim^® ASFV CROM Ag and INgezim^® PPA CROM Anticuerpo, respectively, with higher statistical significance between 11 and 39 days post-infection. From the observation of results, it can be concluded that the combination of both Ag-LFA and Ab-LFA assays would facilitate the identification of infected animals, regardless of post-infection time.

ASFV transcription reporter screening system identifies ailanthone as a broad antiviral compound

African swine fever (ASF) is an acute, highly contagious and deadly viral disease in swine that jeopardizes the worldwide pig industry. Unfortunately, there are no authoritative vaccine and antiviral drug available for ASF control. African swine fever virus (ASFV) is the etiological agent of ASF. Among the ASFV proteins, p72 is the most abundant component in the virions and thus a potential target for anti-ASFV drug design. Here, we constructed a luciferase reporter system driven by the promoter of p72, which is transcribed by the co-transfected ASFV RNA polymerase complex. Using this system, we screened over 3200 natural product compounds and obtained three potent candidates against ASFV. We further evaluated the anti-ASFV effects and proved that among the three candidates, ailanthone (AIL) inhibits the replication of ASFV at the nanomolar concentration (IC50 ​= ​15 ​nmol/L). Our in vitro experiments indicated that the antiviral effect of AIL is associated with its inhibition of the HSP90-p23 cochaperone. Finally, we showed the antiviral activity of AIL on Zika virus and hepatitis B virus (HBV), which supports that AIL is a potential broad-spectrum antiviral agent.

Crystal structure of African swine fever virus pE301R reveals a ring-shaped trimeric DNA sliding clamp

African swine fever virus (ASFV) is an important animal pathogen that is causing a current ASF pandemic and affecting pork industry globally. ASFV encodes at least 150 proteins, and the functions of many of them remain to be clarified. The ASFV protein E301R (pE301R) was predicted to be a DNA sliding clamp protein homolog working as a DNA replication processivity factor. However, structural evidence was lacking to support the existence of a ring-shaped sliding clamp in large eukaryotic DNA viruses. Here we have solved a high-resolution crystal structure of pE301R and identified a canonical ring-shaped clamp comprising a pE301R trimer. Interestingly, this complete-toroidal structure is different from those of the monomeric clamp protein homolog, herpes simplex virus UL42, and the C-shaped dimeric human cytomegalovirus UL44, but highly homologous to that of the eukaryotic clamp homolog proliferating cell nuclear antigen. Moreover, pE301R has a unique N-terminal extension (NE) that is important in maintaining the trimeric form of the protein in solution, while specific features in length and surface electrostatic potential of its inter-domain connector (IDC) implies specificity in interactions with binding partners such as the viral DNA polymerase. Thus, our data pave the way for further dissection of the processivity clamp protein structural and functional diversity and ASFV DNA replication mechanisms.

Recombinant porcine interferon cocktail delays the onset and lessens the severity of African swine fever

African swine fever (ASF) is a highly contagious and deadly disease that affects domestic and wild pigs. No commercial vaccine or antiviral is currently available against ASF. The control of ASF primarily relies on implementing effective biosecurity measures during the breeding process. Here, we evaluated the preventive and therapeutic potential of the interferon (IFN) cocktail (a mixture of recombinant porcine IFN α and γ) on ASF. The IFN cocktail treatment delayed the onset of ASF symptoms and ASF virus (ASFV) replication for approximately one week. However, IFN cocktail treatment could not prevent the death of the pigs. Further analysis showed that IFN cocktail treatment increased the expression of multiple IFN-stimulated genes (ISGs) in porcine peripheral blood mononuclear cells in vivo and in vitro. Additionally, IFN cocktail modulated the expression of pro- and anti-inflammatory cytokines and reduced tissue injury in the ASFV-infected pigs. Collectively, the results suggest that the IFN cocktail restricts the progression of acute ASF by inducing high levels of ISGs, contributing to the pre-establishment of antiviral status, and modulating the balance of pro- and anti-inflammatory mediators to lessen cytokine storm-mediated tissue damage.

New perspective on African swine fever: a bibliometrics study and visualization analysis

Introduction

African swine fever (ASF) is a contagious viral disease that can have devastating effects on domestic pigs and wild boars. Over the past decade, there has been a new wave of this ancient disease spreading around the world, prompting many scholars to dedicate themselves to researching this disease. This research aims to use bibliometric methods to organize, analyze and summarize the scientific publications on ASF that have been amassed in the past two decades.

Methods

This paper used VOSviewer, CiteSpace, and a bibliometric online analysis platform to conduct performance analysis and visualization studies on 1,885 academic papers about ASF in the Web of Science from January 2003 to December 2022.

Results

The amount of literature published on ASF has increased exponentially in recent years, and the development trend of related research is good. A group of representative scholars have appeared in this research field, and some cooperative networks have been formed. Transboundary and Emerging Diseases is the journal with the most publications in this field, while Virus Research is the journal with the most citation per article. High-productivity countries are led by China in terms of the number of articles published followed by the United States and Spain. In regard to the average number of citations, the scholars in the UK are in the lead. The institution with the most articles was the Chinese Academy of Agricultural Sciences. The analysis of high-frequency keywords showed that the pathogens and epidemiology of ASF were the research hotspots in this field, and the research content was closely related to molecular biology and immunology. The burst keywords "transmission", "identification", "virulence", "replication", and "gene" reflects the research frontier. In addition, by collating and analyzing highly cited journals and highly co-cited references, we explored the knowledge structure and theoretical basis of this field.

Discussion

This is the first bibliometric analysis report on ASF research, which highlights the key characteristics of ASF research and presents the research status and evolution trend in this field from a new perspective. It provides a valuable reference for further research.

African swine fever virus QP383R dampens type I interferon production by promoting cGAS palmitoylation

Cyclic GMP-AMP synthase (cGAS) recognizes viral DNA and synthesizes cyclic GMP-AMP (cGAMP), which activates stimulator of interferon genes (STING/MITA) and downstream mediators to elicit an innate immune response. African swine fever virus (ASFV) proteins can antagonize host immune responses to promote its infection. Here, we identified ASFV protein QP383R as an inhibitor of cGAS. Specifically, we found that overexpression of QP383R suppressed type I interferons (IFNs) activation stimulated by dsDNA and cGAS/STING, resulting in decreased transcription of IFNβ and downstream proinflammatory cytokines. In addition, we showed that QP383R interacted directly with cGAS and promoted cGAS palmitoylation. Moreover, we demonstrated that QP383R suppressed DNA binding and cGAS dimerization, thus inhibiting cGAS enzymatic functions and reducing cGAMP production. Finally, the truncation mutation analysis indicated that the 284-383aa of QP383R inhibited IFNβ production. Considering these results collectively, we conclude that QP383R can antagonize host innate immune response to ASFV by targeting the core component cGAS in cGAS-STING signaling pathways, an important viral strategy to evade this innate immune sensor.

African swine fever virus I73R is a critical virulence-related gene: A potential target for attenuation

African swine fever virus (ASFV) is a large, double-stranded DNA virus that causes a fatal disease in pigs, posing a threat to the global pig industry. Whereas some ASFV proteins have been found to play important roles in ASFV-host interaction, the functional roles of many proteins are still largely unknown. In this study, we identified I73R, an early viral gene in the replication cycle of ASFV, as a key virulence factor. Our findings demonstrate that pI73R suppresses the host innate immune response by broadly inhibiting the synthesis of host proteins, including antiviral proteins. Crystallization and structural characterization results suggest that pI73R is a nucleic-acid-binding protein containing a Zα domain. It localizes in the nucleus and inhibits host protein synthesis by suppressing the nuclear export of cellular messenger RNA (mRNAs). While pI73R promotes viral replication, the deletion of the gene showed that it is a nonessential gene for virus replication. In vivo safety and immunogenicity evaluation results demonstrate that the deletion mutant ASFV-GZΔI73R is completely nonpathogenic and provides effective protection to pigs against wild-type ASFV. These results reveal I73R as a virulence-related gene critical for ASFV pathogenesis and suggest that it is a potential target for virus attenuation. Accordingly, the deletion mutant ASFV-GZΔI73R can be a potent live-attenuated vaccine candidate.

Identification of Potential miRNA-mRNA Regulatory Network Associated with Regulating Immunity and Metabolism in Pigs Induced by ASFV Infection

African swine fever (ASF) is a devastating infectious disease in domestic pigs caused by African swine fever virus (ASFV) with a mortality rate of about 100%. However, the understanding of the interaction between ASFV and host is still not clear. In this study, the expression differences and functional analysis of microRNA (miRNA) in porcine peripheral blood lymphocytes of ASFV infected pigs and healthy pigs were compared based on Illumina high-throughput sequencing, then the GO and KEGG signal pathways were analyzed. The miRNA related to immunity and inflammation were screened, and the regulatory network of miRNA-mRNA was drawn. A total of 70 differentially expressed miRNAs were found (p ≤ 0.05). Of these, 45 were upregulated and 25 were downregulated in ASFV-infected pigs vs. healthy pigs. A total of 8179 mRNA genes targeted by these 70 differentially expressed miRNA were predicted, of which 1447 mRNA genes were targeted by ssc-miR-2320-5p. Five differentially expressed miRNA were validated by RT-qPCR, which were consistent with the RNA-Seq results. The GO analysis revealed that a total of 30 gene functions were significantly enriched, including 7 molecular functions (MF), 13 cellular components (CC), and 10 biological processes (BP). The KEGG enrichment analysis revealed that the differentially expressed genes were significantly enriched in pathways related to immunity, inflammation, and various metabolic processes, in which a total of two downregulated miRNAs after infection and eight upregulated miRNAs related to immunity and inflammation were screened in ASFV-infected pigs vs. healthy pigs. The network of miRNA-mRNA showed that the mRNA target genes were strongly regulated by ssc-miR-214, ssc-miR-199b-3p, and ssc-miR-199a-3p. The mRNA target genes were enriched into the MAPK signaling pathway, Toll-like receptor signaling pathway, TNF signaling pathway, and IL-17 signaling pathway by using a KEGG enrichment analysis. Therefore, ASFV could regulate immunity and metabolism-related pathways in infected pigs by inducing differential expression of miRNAs. These results provided a new basis for further elucidating the interactions between ASFV and the host as well as the immunity regulation mechanisms of ASFV, which will be conducive to better controlling ASF.

Evaluation of African Swine Fever Virus E111R Gene on Viral Replication and Porcine Virulence

African swine fever (ASF) is an acute infectious disease of domestic pigs and wild boars caused by the African swine fever virus (ASFV), with up to a 100% case fatality rate. The development of a vaccine for ASFV is hampered by the fact that the function of many genes in the ASFV genome still needs to be discovered. In this study, the previously unreported E111R gene was analyzed and identified as an early-expressed gene that is highly conserved across the different genotypes of ASFV. To further explore the function of the E111R gene, a recombinant strain, SY18ΔE111R, was constructed by deleting the E111R gene of the lethal ASFV SY18 strain. In vitro, the replication kinetics of SY18ΔE111R with deletion of the E111R gene were consistent with those of the parental strain. In vivo, high-dose SY18ΔE111R (105.0 TCID50), administered intramuscularly to pigs, caused the same clinical signs and viremia as the parental strain (102.0 TCID50), with all pigs dying on days 8–11. After being infected with a low dose of SY18ΔE111R (102.0 TCID50) intramuscularly, pigs showed a later onset of disease and 60% mortality, changing from acute to subacute infection. In summary, deletion of the E111R gene has a negligible effect on the lethality of ASFV and does not affect the viruses’ ability to replicate, suggesting that E111R could not be the priority target of ASFV live-attenuated vaccine candidates.

Rapid Identification of ASFV, CSFV and FMDV from Mongolian Outbreaks with MinION Short Amplicon Sequencing

African swine fever virus (ASFV), classical swine fever virus (CSFV), and foot-and-mouth disease virus (FMDV) cause important transboundary animal diseases (TADs) that have a significant economic impact. The rapid and unequivocal identification of these pathogens and distinction from other animal diseases based on clinical symptoms in the field is difficult. Nevertheless, early pathogen detection is critical in limiting their spread and impact as is the availability of a reliable, rapid, and cost-effective diagnostic test. The purpose of this study was to evaluate the feasibility to identify ASFV, CSFV, and FMDV in field samples using next generation sequencing of short PCR products as a point-of-care diagnostic. We isolated nucleic acids from tissue samples of animals in Mongolia that were infected with ASFV (2019), CSFV (2015), or FMDV (2018), and performed conventional (RT-) PCR using primers recommended by the Terrestrial Animal Health Code of the World Organization for Animal Health (WOAH). The (RT-) PCR products were then sequenced in Mongolia using the MinION nanopore portable sequencer. The resulting sequencing reads successfully identified the respective pathogens that exhibited 91-100% nucleic acid similarity to the reference strains. Phylogenetic analyses suggest that the Mongolian virus isolates are closely related to other isolates circulating in the same geographic region. Based on our results, sequencing short fragments derived by conventional (RT-) PCR is a reliable approach for rapid point-of-care diagnostics for ASFV, CSFV, and FMDV even in low-resource countries.

A Novel Linear B-Cell Epitope on the P54 Protein of African Swine Fever Virus Identified Using Monoclonal Antibodies

The African swine fever virus (ASFV) is a highly infectious viral pathogen that presents a major threat to the global pig industry. No effective vaccine is available for the virus. The p54 protein, a major structural component of ASFV, is involved in virus adsorption and entry to target cells and also plays a key role in ASFV vaccine development and disease prevention. Here, we generated species-specific monoclonal antibodies (mAbs), namely 7G10A7F7, 6E8G8E1, 6C3A6D12, and 8D10C12C8 (subtype IgG1/kappa type), against the ASFV p54 protein and characterized the specificity of these mAbs. Peptide scanning techniques were used to determine the epitopes that are recognized by the mAbs, which defined a new B-cell epitope, TMSAIENLR. Amino acid sequence comparison showed that this epitope is conserved among all reference ASFV strains from different regions of China, including the widely prevalent, highly pathogenic strain Georgia 2007/1 (NC_044959.2). This study reveals important signposts for the design and development of ASFV vaccines and also provides critical information for the functional studies of the p54 protein via deletion analysis.

Diversity and emergence of new variants of African swine fever virus Genotype I circulating in domestic pigs in Nigeria (2016-2018)

BACKGROUND

African swine fever (ASF) is the most lethal disease of pigs caused by ASF virus (ASFV) with severe economic implications and threat to the swine industry in endemic countries. Between 2016 and 2018, several ASF outbreaks were reported throughout pig producing states in Nigeria.

OBJECTIVES

Thereafter, this study was designed to identify the ASFV genotypes responsible for these outbreaks within the study period (2016-2018).

METHODS

Twenty-two ASFV-positive samples by polymerase chain reaction were selected. The samples were collected during passive surveillance in eight states of Nigeria were characterised using 3 partial genes sequences of the virus namely, p72 capsid protein of the B646L, p54 envelope protein of E183L and the central variable region (CVR) within B602L of ASFV.

RESULTS

Phylogenetic and sequences analysis based on p72 and p54 revealed ASFV genotype I as the circulating virus. Sequence analysis of the CVR of B602L revealed genetic variations with six ASFV tandem repeat sequence (TRS) variants namely, Tet-15, Tet-20a, Tet-21b, Tet-27, Tet-31 and Tet-34, thus increasing the overall genetic diversity of ASFV in Nigeria. Three of the TRS variants, Tet-21b, Tet-31 and Tet-34, were identified for the first time in Nigeria. The new TRS variants of ASFV genotype I were identified in Enugu, Imo, Plateau and Taraba states, while co-circulation of multiple variants of ASFV genotype I was recorded in Plateau and Benue states.

CONCLUSIONS

The high genetic diversity, emergence and increasing recovery of new variants of genotype I in Nigeria should be a concern given that ASFV is a relatively stable DNA virus. The epidemiological implications of these findings require further investigation.

Deletion of African Swine Fever Virus (ASFV) H240R Gene Attenuates the Virulence of ASFV by Enhancing NLRP3-Mediated Inflammatory Responses

African swine fever (ASF) is a highly contagious infectious disease of domestic pigs and wild boars caused by African swine fever virus (ASFV), with a mortality rate of up to 100%. In order to replicate efficiently in macrophages and monocytes, ASFV has evolved multiple strategies to evade host antiviral responses. However, the underlying molecular mechanisms by which ASFV-encoded proteins execute immune evasion are not fully understood. In this study, we found that ASFV pH240R strongly inhibits transcription, maturation, and secretion of interleukin-1β (IL-1β). Importantly, pH240R not only targeted NF-κB signaling but also impaired NLRP3 inflammasome activation. In this mechanism, pH240R interacted with NF-kappa-B essential modulator (NEMO), a component of inhibitor of kappa B kinase (IKK) complex and subsequently reduced phosphorylation of IκBα and p65. In addition, pH240R bonded to NLRP3 to inhibit NLRP3 inflammasome activation, resulting in reduced IL-1β production. As expected, infection with H240R-deficient ASFV (ASFV-ΔH240R) induced more inflammatory cytokine expression both in vitro and in vivo than its parental ASFV HLJ/18 strain. Consistently, H240R deficiency reduced the viral pathogenicity in pigs compared with its parental strain. These findings reveal that the H240R gene is an essential virulence factor, and deletion of the H240R gene affects the pathogenicity of ASFV HLJ/18 by enhancing antiviral inflammatory responses, which provides insights for ASFV immune evasion mechanisms and development of attenuated live vaccines and drugs for prevention and control of ASF. IMPORTANCE African swine fever (ASF), caused by African swine fever virus (ASFV), is a highly contagious and acute hemorrhagic viral disease of domestic pigs, with a high mortality approaching 100%. ASFV has spread rapidly worldwide and caused huge economic losses and ecological consequences. However, the pathogenesis and immune evasion mechanisms of ASFV are not fully understood, which limits the development of safe and effective ASF attenuated live vaccines. Therefore, investigations are urgently needed to identify virulence factors that are responsible for escaping the host antiviral innate immune responses and provide a new target for development of ASFV live-attenuated vaccine. In this study, we determined that the H240R gene is an essential virulence factor, and its depletion affects the pathogenicity of ASFV by enhancing NLRP3-mediated inflammatory responses, which provides theoretical support for the development of an ASFV attenuated live vaccine.

Dynamics of Serological and Mucosal Antibody Responses against African Swine Fever Viruses in Experimentally Infected Pigs

African swine fever virus (ASFV) is a lethal swine pathogen, and there is no effective vaccine or treatment available for ASFV infection. Recently, the occurrence of ASFV genotype I and genotype II natural mutants that manifest as subacute, longer-incubation, or persistent infections poses threats to preventing ASFV infection. The dynamics of antibody responses to ASFV are still completely unrevealed, especially the secretion of mucosal antibodies in oral fluid. Here, a systematic analysis was performed of serological and mucosal antibody secretion against 6 ASFV antigens after direct or indirect infection with four different ASFV strains or genotypes, namely, the field virulent genotype II isolate ASFV HLJ/18, the artificially attenuated genotype II strain HLJ/18-7GD, the naturally attenuated genotype II isolate HLJ/HRB1/20, and genotype I isolate SD/DY-I/21. Severe clinical signs of HLJ/18 infection were observed in pigs from 4 days postinoculation. However, no clinical signs were observed in HLJ/18-7GD-infected pigs. The contact pigs cohoused with the pigs intramuscularly infected with the isolate SD/DY-I/21 or HLJ/HRB1/20 only showed chronic clinical signs. Interestingly, the oral fluid sIgA responses to all the selected antigens were significantly stronger and earlier than the serum IgG responses in both HLJ/18- and HLJ/18-7GD-challenged pigs. Although significant fluctuations and individual differences appeared in oral swab sIgA responses in the contact transmission group, they were earlier than the corresponding serological IgG responses. Moreover, according to the comparative analysis of the three infection groups, P54 was proposed to be a dominant target for serological IgG diagnosis, while P30, CD2v, P54, P22, and P10 were more advantageous as mucosal sIgA diagnosis targets. These results highlight the important role of mucosal antibodies in the early diagnosis of ASFV infection and can provide references to screen appropriate targets for ASFV detection.

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.

Transmission of African Swine Fever Virus to the Wild Boars of Northeast India

BACKGROUND

India recorded the first outbreak of African swine fever (ASF) in North-eastern region (NER) in the year 2020.

AIM

The current study was undertaken to investigate the transmission of African swine fever virus (ASFV) in the wild boars of Northeast India, particularly of Assam.

MATERIAL AND METHODS

ASF suspected mortal tissue remains and blood samples of wild boars collected from different locations of Assam were screened for molecular detection of swine viruses which includes Classical swine fever virus, Porcine Circovirus 2, Porcine reproductive and respiratory syndrome virus and ASFV.

RESULTS

One sample each from Manas and Nameri National Parks were detected positive for ASFV. Besides this, one of the samples was positive for CSFV and one of the ASFV positive samples was also positive for PCV2. Several striking gross and microscopic alterations were noticed in different organs of ASFV infected animals. Sequencing and phylogenetic analysis of B646L gene confirmed the presence of ASFV genotype-II in wild boars. Circulation of similar genotype in domestic pigs of NER in the contemporary period as well as locations near to the aforementioned national parks indicates the transmission of ASFV from domestic to wild boars.

CLINICAL RELEVANCE

The detection of ASFV in the wild boars of Assam is alarming as it is an impending threat to pig population and other endangered species (particularly Pygmy hog), making it increasingly daunting to control the disease.

CONCLUSION

Chances are high for ASFV to become endemic in Assam region if stringent measures are not taken at proper time.

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.

Novel p22 and p30 dual-proteins combination based indirect ELISA for detecting antibodies against African swine fever virus

Introduction

African swine fever virus (ASFV) infection is one of the most complex and fatal hemorrhagic viral diseases, causing a devastating loss to the swine industry. Since no effective vaccine is available, prevention and control of ASFV heavily depends on early diagnostic detection.

Methods

In this study, a novel indirect ELISA was established for detecting antibodies against ASFV using dual-proteins, p22 and p30. Recombinants p22 and p30 were expressed and purified from E.coli vector system by recombined plasmids pET-KP177R and pET-CP204L. p22 and p30 were mixed as antigens for developing the indirect ELISA.

Results

Through optimizing coating concentrations of p30 and p22, coating ratio (p30: p22 = 1:3), and serum dilution (as 1:600), the established ELISA performed higher specificity, sensitivity, and repeatability against ASFV-positive serum. Furthermore, 184 clinical serum samples from suspected diseased pigs were verified the established ELISA in clinical diagnosis. The results showed that compared with two commercial ELISA kits, the established ELISA possessed higher sensitivity and almost uniform coincidence rate.

Conclusion

The novel indirect ELISA based on dual-proteins p30 and p22 performed a valuable role in diagnostic detection of ASFV, providing a broad insight into serological diagnostic methods of ASFV.

Identification of p72 epitopes of African swine fever virus and preliminary application

African swine fever virus (ASFV) causes a highly lethal hemorrhagic viral disease (ASF) of pigs that results in serious losses in China and elsewhere. The development of a vaccine and diagnosis technology for ASFV is essential to prevent and control the spread of ASF. The p72 protein of ASFV is highly immunogenic and reactive, and is a dominant antigen in ASF vaccine and diagnostic research. In this study, 17 p72 monoclonal antibodies (mAbs) were generated. Epitope mapping by a series of overlapping peptides expressed in Escherichia coli showed that these mAbs recognized a total of seven (1-7) linear B cell epitopes. These mAbs did not show significant neutralizing activity. Epitopes 1 (²⁴⁹HKPHQSKPIL²⁵⁸), 2 (⁶⁹PVGFEYENKV⁷⁷), 5 (¹⁹⁵VNGNSLDEYSS²⁰⁵), and 7 (²²³GYKHLVGQEV²³³) are novel. Sequence alignment analysis revealed that the identified epitopes were highly conserved among 27 ASFV strains from nine genotypes. Preliminary screening using known positive and negative sera indicated the diagnostic potential of mAb-2B8D7. The results provide new insights into the antigenic regions of ASFV p72 and will inform the diagnosis of ASFV.

The challenges of pig farming in Hong Kong: a study of farmers' perceptions and attitudes towards a pig health and production management service

BACKGROUND

Pig farming in Hong Kong differs markedly from other places in the world, with a highly urbanised population, the majority of pigs being imported for slaughter, and limited on-farm veterinary support. Little is known about the barriers and attitudes of pig farmers in Hong Kong and their expectations of a new pig health and production management service provided by veterinarians. We collected qualitative and quantitative data to 1) describe pig farms, 2) identify barriers to pig farming in Hong Kong and 3) describe the perceptions of the new service. Thematic analysis was conducted to identify barriers and attitudes.

RESULTS

Eight and nine out of 38 pig farmers agreed to participate in the qualitative and quantitative components, respectively. All farms were farrow-to-finish farms with a median of 2800 (range 950 to 7000) pigs per farm. Three themes were identified during the interview analysis and could be ranked based on their importance to the farmers: the regulatory environment (Theme 1), veterinary support structures (Theme 2), and the sustainability of the pig industry (Theme 3). Farmers expressed dissatisfaction with the regulation of the industry and veterinary services on offer within Hong Kong. However, farmers did note that the provision of a new pig health and production management service was as a positive development. The public perception of pig farming, market forces, and competition from mainland pig farmers have resulted in sustainability challenges for the industry.

CONCLUSIONS

Farmers identified very specific local systems and challenges unique to pig farming in Hong Kong. The lack of veterinary support was one of these challenges and although a certain level of scepticism towards the new pig health and production service was expressed, farmers indicated their interest and listed areas where they would benefit from improved veterinary support. Prior experiences of veterinary services clouded farmers perceptions of the usefulness of a new service. To be successful in this environment, clear communication about the goals, role and limitations of the new on farm service is crucial, as is the alignment with the needs of farmers. Despite the small sample size, the qualitative methodology used allows us to assume that these themes give a general idea of what Hong Kong farmers' concerns and attitudes are.

OGG1 inhibition suppresses African swine fever virus replication

African swine fever virus (ASFV) is an important pathogen that causes a highly contagious and lethal disease in swine, for which neither a vaccine nor treatment is available. The DNA repair enzyme 8-oxoguanine DNA glycosylase 1 (OGG1), which excises the oxidative base lesion 8-oxo-7,8-dihydroguanine (8-oxoG), has been linked to the pathogenesis of different diseases associated with viral infections. However, the role of OGG1-base excision repair (BER) in ASFV infection has been poorly investigated. Our study aimed to characterize the alteration of host reactive oxygen species (ROS) and OGG1 and to analyse the role of OGG1 in ASFV infection. We found that ASFV infection induced high levels and dynamic changes in ROS and 8-oxoG and consistently increased the expression of OGG1. Viral yield, transcription level, and protein synthesis were reduced in ASFV-infected primary alveolar macrophages (PAMs) treated by TH5487 or SU0268 inhibiting OGG1. The expression of BER pathway associated proteins of ASFV was also suppressed in OGG1-inhibited PAMs. Furthermore, OGG1 was found to negatively regulate interferon β (IFN-β) production during ASFV infection and IFN-β could be activated by OGG1 inhibition with TH5487 and SU0268, which blocked OGG1 binding to 8-oxoG. Additionally, the interaction of OGG1 with viral MGF360-14-L protein could disturb IFN-β production to further affect ASFV replication. These results suggest that OGG1 plays the crucial role in successful viral infection and OGG1 inhibitors SU0268 or TH5487 could be used as antiviral agents for ASFV infection.

Diversity of RNA viruses of three dominant tick species in North China

Background

A wide range of bacterial pathogens have been identified in ticks, yet the diversity of viruses in ticks is largely unexplored.

Methods

Here, we used metagenomic sequencing to characterize the diverse viromes in three principal tick species associated with pathogens, Haemaphysalis concinna, Dermacentor silvarum, and Ixodes persulcatus, in North China.

Results

A total of 28 RNA viruses were identified and belonged to more than 12 viral families, including single-stranded positive-sense RNA viruses (Flaviviridae, Picornaviridae, Luteoviridae, Solemoviridae, and Tetraviridae), negative-sense RNA viruses (Mononegavirales, Bunyavirales, and others) and double-stranded RNA viruses (Totiviridae and Partitiviridae). Of these, Dermacentor pestivirus-likevirus, Chimay-like rhabdovirus, taiga tick nigecruvirus, and Mukawa virus are presented as novel viral species, while Nuomin virus, Scapularis ixovirus, Sara tick-borne phlebovirus, Tacheng uukuvirus, and Beiji orthonairovirus had been established as human pathogens with undetermined natural circulation and pathogenicity. Other viruses include Norway mononegavirus 1, Jilin partitivirus, tick-borne tetravirus, Pico-like virus, Luteo-like virus 2, Luteo-likevirus 3, Vovk virus, Levivirus, Toti-like virus, and Solemo-like virus as well as others with unknown pathogenicity to humans and wild animals.

Conclusion

In conclusion, extensive virus diversity frequently occurs in Mononegavirales and Bunyavirales among the three tick species. Comparatively, I. persulcatus ticks had been demonstrated as such a kind of host with a significantly higher diversity of viral species than those of H. concinna and D. silvarum ticks. Our analysis supported that ticks are reservoirs for a wide range of viruses and suggested that the discovery and characterization of tick-borne viruses would have implications for viral taxonomy and provide insights into tick-transmitted viral zoonotic diseases.

Orally administered recombinant Lactobacillus expressing African swine fever virus antigens that induced immunity responses

African swine fever (ASF) is a highly contagious, acute, febrile disease caused by the African swine fever virus (ASFV), with morbidity and mortality rates approaching 100% in domestic and wild swine, resulting in massive economic losses to the pig industry worldwide. This study aimed to express the p30, p54, and p72 proteins encoded by ASFV in vitro using the Lactobacillus lactis (L. lactis) expression system. Here, six new functional recombinant L. lactis were constructed, and the expression of the p30 protein, p54 protein, p72 protein, p30-LTB (heat-labile enterotoxin B, LTB) fusion protein, p54-LTB fusion protein, and the p72-LTB fusion protein was successfully detected by Western blot analysis. Following oral immunization of rabbits with recombinant L. lactis, serum IgG, intestinal mucosal sIgA, cytokines (IL-4 and INF-γ), and splenocyte viability were higher than in the control group via ELISA. Notably, without the LTB adjuvant group, humoral and Th1 cellular immunity were promoted, whereas, with the LTB adjuvant group, local mucosal immunity, humoral immunity, and Th2 cellular immunity were promoted, providing new insights into the design and development of an ASFV subunit vaccine.

Development and validation of a fast quantitative real-time PCR assay for the detection of African swine fever virus

African swine fever virus (ASFV) is a double-stranded DNA virus that causes African swine fever (ASF), a lethal hemorrhagic fever that is highly contagious among domestic pigs and wild boars. Due to the high mortality rates and highly contagious nature of the ASF, it is important to develop a fast detection method for ASFV with high sensitivity and specificity to take an immediate action to stop wide spread of the virulent disease. Therefore, a fast and quantitative molecular detection method of ASFV is presented in this study. A total of 24 genotypes of ASFV have been identified based on nucleic acid sequences of the major capsid protein p72. The primers and probe of the present assay was designed to detect all of the p72-based genotypes of ASFV. The turnaround time for PCR detection was within 50 min which is at least about two-times faster compared to other PCR assays. Limit of detection (LoD) was 6.91 genomic copies/reaction for the most virulent genotype II. LoD values for other genotypes were within 10-20 copies/reaction. Cross-reactivity of the assay was validated using a panel of pathogens related to swine disease, and no cross-reactivity was observed. Positive and negative clinical samples (50 samples each) obtained from sick and healthy animals, were used to validate the assay. The results showed that 100% agreement for both positive and negative samples. In summary, the assay described in this study offers the advantage of rapid detection of all genotypes of ASFV with high sensitivity and specificity. The assay is a valuable tool both in clinical and laboratory uses for sensitive and fast detection of ASFV.