Comparative Pathology and Pathogenesis of African Swine Fever Infection in Swine

Pathogenicity and virulence of African swine fever virus

African swine fever (ASF) is a devastating disease with a high impact on the pork industry worldwide. ASF virus (ASFV) is a very complex pathogen, the sole member of the family Asfaviridae, which induces a state of immune suppression in the host through infection of myeloid cells and apoptosis of lymphocytes. Moreover, haemorrhages are the other main pathogenic effect of ASFV infection in pigs, related to the infection of endothelial cells, as well as the activation and structural changes of this cell population by proinflammatory cytokine upregulation within bystander monocytes and macrophages. There are still many gaps in the knowledge of the role of proteins produced by the ASFV, which is related to the difficulty in producing a safe and effective vaccine to combat the disease, although few candidates have been approved for use in Southeast Asia in the past couple of years.

Replication Characteristics of African Swine Fever Virus (ASFV) Genotype I E70 and ASFV Genotype II Belgium 2018/1 in Perivenous Macrophages Using Established Vein Explant Model

African Swine Fever Virus (ASFV), resulting in strain-dependent vascular pathology, leading to hemorrhagic fever, is an important pathogen in swine. The pathogenesis of ASFV is determined by the array and spatial distribution of susceptible cells within the host. In this study, the replication characteristics of ASFV genotype I E70 (G1-E70) and ASFV genotype II Belgium 2018/1 (G2-B18) in the environment of small veins were investigated in an established vein explant model. Immunofluorescence staining analysis revealed that perivenous macrophages (CD163+ cells) were widely distributed in the explant, with most of them (approximately 2-10 cells/0.03 mm2) being present close to the vein (within a radius of 0-348 µm). Upon inoculation with G1-E70 and G2-B18, we observed an increase in the quantity of cells testing positive for viral antigens over time. G1-E70 replicated more efficiently than G2-B18 in the vein explants (7.6-fold for the ear explant at 72 hpi). The majority of ASFV+ cells were CD163+, indicating that macrophages are the primary target cells. Additional identification of cells infected with ASFV revealed the presence of vimentin+, CD14+, and VWF+ cells, demonstrating the cellular diversity and complexity associated with ASFV infection. By the use of this new vein explant model, the susceptibility of vascular and perivascular cells to an ASFV infection was identified. With this model, it will be possible now to conduct more functional analyses to get better insights into the pathogenesis of ASFV-induced hemorrhages.

Strategic nucleic acid detection approaches for diagnosing African swine fever (ASF): navigating disease dynamics

African swine fever (ASF) is a devastating disease caused by African swine fever virus (ASFV) and leads to significant economic losses in the pig farming industry. Given the absence of an effective vaccine or treatment, the mortality rate of ASF is alarmingly close to 100%. Consequently, the ability to rapidly and accurately detect ASFV on site and promptly identify infected pigs is critical for controlling the spread of this pandemic. The dynamics of the ASF virus load and antibody response necessitate the adoption of various detection strategies at different stages of infection, a topic that has received limited attention to date. This review offers detailed guidance for choosing appropriate ASF diagnostic techniques tailored to the clinical manifestations observed from the acute to chronic phases, including asymptomatic cases. We comprehensively summarize and evaluate the latest advancements in ASFV detection methods, such as CRISPR-based diagnostics, biosensors, and microfluidics. Additionally, we address the challenges of false negatives or positives due to ASF variants or the use of injected live attenuated vaccines. This review provides an exhaustive list of diagnostic tests suitable for detecting each stage of symptoms and potential target genes for developing new detection methods. In conclusion, we highlight the current challenges and future directions in ASFV detection, underscoring the need for continued research and innovation in this field.

Duckweeds as edible vaccines in the animal farming industry

Animal diseases are among the most debilitating issues in the animal farming industry, resulting in decreased productivity and product quality worldwide. An emerging alternative to conventional injectable vaccines is edible vaccines, which promise increased delivery efficiency while maintaining vaccine effectiveness. One of the most promising platforms for edible vaccines is duckweeds, due to their high growth rate, ease of transformation, and excellent nutritional content. This review explores the potential, feasibility, and advantages of using duckweeds as platforms for edible vaccines. Duckweeds have proven to be superb feed sources, as evidenced by numerous improvements in both quantity (e.g., weight gain) and quality (e.g., yolk pigmentation). In terms of heterologous protein production, duckweeds, being plants, are capable of expressing proteins with complex structures and post-translational modifications. Research efforts have focused on the development of duckweed-based edible vaccines, including those against avian influenza, tuberculosis, Newcastle disease, and mastitis, among others. As with any emerging technology, the development of duckweeds as a platform for edible vaccines is still in its early stages compared to well-established injectable vaccines. It is evident that more proof-of-concept studies are required to bring edible vaccines closer to the current standards of conventional vaccines. Specifically, the duckweed expression system needs further development in areas such as yield and growth rate, especially when compared to bacterial and mammalian expression systems. Continued efforts in this field could lead to breakthroughs that significantly improve the resilience of the animal farming industry against disease threats.

Navigating the threat of African swine fever: a comprehensive review

African swine fever (ASF) is caused by Asfivirus and has become one of the most important diseases of swine in recent years. ASF was an endemic disease of the sub-Saharan Africa but later spread to various parts of the world. The infection in ticks and wild swine, alongside global pork trade, drives its spread and persistence. Once introduced to an area, the disease is difficult to eliminate due to sylvatic, domestic, and tick-swine transmission cycles. Because of the existence of various modes of transmission of the ASF virus, biosecurity measures have not been very successful. The line of treatment is not of much use and the outcome of this disease is usually fatal. The prognosis or the recovery of the animal depends on the virulence of the strain involved. Development of vaccines has been attempted but to date has not been very successful. This review focuses on the basic context of ASF, the challenges associated with it, and the options that might be available to prevent its occurrence which includes the different vaccine development strategies tried and tested till now.

Identification of linear B-cell epitope on the structure protein p49 of African Swine Fever Virus (ASFV)

African swine fever (ASF), a viral disease affecting both domestic pigs and wild boars, is caused by the African swine fever virus (ASFV). Currently, an effective vaccine is lacking. The structural protein p49, encoded by the B438L gene, is vital for the virus's capsid structure and architecture. Research indicates its potential as a vaccine target. In this study, mAbs against ASFV p49 were generated using the hybridoma technique. The full-length B438L sequence was divided into 5 segments (B1 ∼ B5) via the overlapping polypeptide method, and an expression vector was constructed for expression and purification. Three hybridoma cell lines recognized epitope regions, with 3B12 and 6F1 recognizing the B4 (aa 234-362) fragment, and 3B12, 6F1, and 7C5 reacting with the B5 (aa 312-438) segment. The amino acid sequence (aa 333-438) was further divided into three segments (B6 ∼ B8) for verification. Results from Dot-ELISA and peptide ELISA confirmed that 333-YQTHYMENIVTLVPR-347 and 383-NNYIPKYTGGIGDSK-397 were the major B cell antigenic, highly conserved across ASFV strains. Interestingly, the motif 333-YQTHYMENIVTLVPR-347 was highly conserved, except for a single substitution (T → S) in three residues. This study identifies the B cell epitope of p49 protein, providing insights into ASFV p49 protein structure and function and supporting the development of ASFV-related vaccine products.

A Non-Hemadsorbing Live-Attenuated Virus Vaccine Candidate Protects Pigs against the Contemporary Pandemic Genotype II African Swine Fever Virus

African swine fever (ASF) is a highly contagious and severe hemorrhagic transboundary swine viral disease with up to a 100% mortality rate, which leads to a tremendous socio-economic loss worldwide. The lack of safe and efficacious ASF vaccines is the greatest challenge in the prevention and control of ASF. In this study, we generated a safe and effective live-attenuated virus (LAV) vaccine candidate VNUA-ASFV-LAVL3 by serially passaging a virulent genotype II strain (VNUA-ASFV-L2) in an immortalized porcine alveolar macrophage cell line (3D4/21, 50 passages). VNUA-ASFV-LAVL3 lost its hemadsorption ability but maintained comparable growth kinetics in 3D4/21 cells to that of the parental strain. Notably, it exhibited significant attenuation of virulence in pigs across different doses (103, 104, and 105 TCID50). All vaccinated pigs remained healthy with no clinical signs of African swine fever virus (ASFV) infection throughout the 28-day observation period of immunization. VNUA-ASFV-LAVL3 was efficiently cleared from the blood at 14-17 days post-infection, even at the highest dose (105 TCID50). Importantly, the attenuation observed in vivo did not compromise the ability of VNUA-ASFV-LAVL3 to induce protective immunity. Vaccination with VNUA-ASFV-LAVL3 elicited robust humoral and cellular immune responses in pigs, achieving 100% protection against a lethal wild-type ASFV (genotype II) challenge at all tested doses (103, 104, and 105 TCID50). Furthermore, a single vaccination (104 TCID50) provided protection for up to 2 months. These findings suggest that VNUA-ASFV-LAVL3 can be utilized as a promising safe and efficacious LAV candidate against the contemporary pandemic genotype II ASFV.

Histopathologic evaluation system of African swine fever in wild boar infected with high (Arm07) and low virulence (Lv17/WB/Riel) isolates

To understand the clinicopathological forms of African swine fever (ASF) in wild boar, it is crucial to possess a basic knowledge of the biological characteristics of the currently circulating ASF virus isolates. The aim of this work is to establish an accurate and comprehensive histopathologic grading system to standardize the assessment of the ASF lesions in wild boar. The study evaluated the differences between animals infected with a high virulence genotype II isolate (Arm07) (HVI) through intramuscular (IM) (n = 6) and contact-infected (n = 12) routes, alongside those orally infected with a low virulence isolate (Lv17/WB/Riel) (LVI) (n = 6). The assessment included clinical (CS), macroscopic (MS), and histopathologic (HS) scores, as well as viral loads in blood and tissues by real-time quantitative polymerase chain reaction (qPCR). Tissues examined included skin, lymph nodes, bone marrow, palatine tonsil, lungs, spleen, liver, kidneys, thymus, heart, adrenal glands, pancreas, urinary bladder, brain, and gastrointestinal and reproductive tracts. The HVI group exhibited a 100% mortality rate with elevated CS, MS, and HS values. Animals infected by contact (CS = 12; MS = 58.5; HS = 112) and those intramuscularly infected (CS = 14.8; MS = 47; HS = 104) demonstrated similar values, indicating that the route of infection does not decisively influence the severity of clinical and pathological signs. The LVI group showed a 0% mortality rate, an inconspicuous clinical form, minimal lesions (CS = 0; MS = 12; HS = 29), and a lower viral load. Histopathologic evaluation has proven valuable in advancing our comprehension of ASF pathogenesis in wild boar and paves the groundwork for further research investigating protective mechanisms in vaccinated animals.

ASFV infection induces macrophage necroptosis and releases proinflammatory cytokine by ZBP1-RIPK3-MLKL necrosome activation

African swine fever (ASF) is an infectious disease characterized by hemorrhagic fever, which is highly pathogenic and causes severe mortality in domestic pigs. It is caused by the African swine fever virus (ASFV). ASFV is a large DNA virus and primarily infects porcine monocyte macrophages. The interaction between ASFV and host macrophages is the major reason for gross pathological lesions caused by ASFV. Necroptosis is an inflammatory programmed cell death and plays an important immune role during virus infection. However, whether and how ASFV induces macrophage necroptosis and the effect of necroptosis signaling on host immunity and ASFV infection remains unknown. This study uncovered that ASFV infection activates the necroptosis signaling in vivo and macrophage necroptosis in vitro. Further evidence showed that ASFV infection upregulates the expression of ZBP1 and RIPK3 to consist of the ZBP1-RIPK3-MLKL necrosome and further activates macrophage necroptosis. Subsequently, multiple Z-DNA sequences were predicted to be present in the ASFV genome. The Z-DNA signals were further confirmed to be present and colocalized with ZBP1 in the cytoplasm and nucleus of ASFV-infected cells. Moreover, ZBP1-mediated macrophage necroptosis provoked the extracellular release of proinflammatory cytokines, including TNF-α and IL-1β induced by ASFV infection. Finally, we demonstrated that ZBP1-mediated necroptosis signaling inhibits ASFV replication in host macrophages. Our findings uncovered a novel mechanism by which ASFV induces macrophage necroptosis by facilitating Z-DNA accumulation and ZBP1 necrosome assembly, providing significant insights into the pathogenesis of ASFV infection.

African swine fever virus early protein pI73R suppresses the type-I IFN promoter activities

African swine fever virus is known to suppress type-I interferon (IFN) responses. The main objective of this study was to screen early-expressed viral genes for their ability to suppress IFN production. Out of 16 early genes examined, I73R exhibited robust suppression of cGAS-STING-induced IFN-β promoter activities, impeding the function of both IRF3 and NF-κB transcription factors. As a result, I73R obstructed IRF3 nuclear translocation following the treatment of cells with poly(dA:dT), a strong inducer of the cGAS-STING signaling pathway. Although the I73R protein exhibits structural homology with the Zα domain binding to the left-handed helical form of DNA known as Z-DNA, its ability to suppress cGAS-STING induction of IFN-β was independent of Z-DNA binding activity. Instead, the α3 and β1 domains of I73R played a significant role in suppressing cGAS-STING induction of IFN-β. These findings offer insights into the protein's functions and support its role as a virulence factor.

Antiviral screening of natural, anti-inflammatory compound library against African swine fever virus

BACKGROUND

African swine fever virus (ASFV) is a major threat to pig production and the lack of effective vaccines underscores the need to develop robust antiviral countermeasures. Pathologically, a significant elevation in pro-inflammatory cytokine production is associated with ASFV infection in pigs and there is high interest in identifying dual-acting natural compounds that exhibit antiviral and anti-inflammatory activities.

METHODS

Using the laboratory-adapted ASFV BA71V strain, we screened a library of 297 natural, anti-inflammatory compounds to identify promising candidates that protected Vero cells against virus-induced cytopathic effect (CPE). Virus yield reduction, virucidal, and cell cytotoxicity experiments were performed on positive hits and two lead compounds were further characterized in dose-dependent assays along with time-of-addition, time-of-removal, virus entry, and viral protein synthesis assays. The antiviral effects of the two lead compounds on mitigating virulent ASFV infection in porcine macrophages (PAMs) were also tested using similar methods, and the ability to inhibit pro-inflammatory cytokine production during virulent ASFV infection was assessed by enzyme-linked immunosorbent assay (ELISA).

RESULTS

The screen identified five compounds that inhibited ASFV-induced CPE by greater than 50% and virus yield reduction experiments showed that two of these compounds, tetrandrine and berbamine, exhibited particularly high levels of anti-ASFV activity. Mechanistic analysis confirmed that both compounds potently inhibited early stages of ASFV infection and that the compounds also inhibited infection of PAMs by the virulent ASFV Arm/07 isolate. Importantly, during ASFV infection in PAM cells, both compounds markedly reduced the production of pro-inflammatory cytokines involved in disease pathogenesis while tetrandrine had a greater and more sustained anti-inflammatory effect than berbamine.

CONCLUSIONS

Together, these findings support that dual-acting natural compounds with antiviral and anti-inflammatory properties hold promise as preventative and therapeutic agents to combat ASFV infection by simultaneously inhibiting viral replication and reducing virus-induced cytokine production.

Resistance to African swine fever virus among African domestic pigs appears to be associated with a distinct polymorphic signature in the RelA gene and upregulation of RelA transcription

African swine fever virus (ASFV) is a highly contagious and fatal hemorrhagic disease of domestic pigs, which poses a major threat to the swine industry worldwide. Studies have shown that indigenous African pigs tolerate ASFV infection better than European pigs. The porcine v-rel avian reticuloendotheliosis viral oncogene homolog A (RelA) encoding a p65 kD protein, a major subunit of the NF-kB transcription factor, plays important roles in controlling both innate and adaptive immunity during infection with ASFV. In the present study, RelA genes from ASFV-surviving and symptomatic pigs were sequenced and found to contain polymorphisms revealing two discrete RelA amino acid sequences. One was found in the surviving pigs, and the other in symptomatic pigs. In total, 16 nonsynonymous SNPs (nsSNPs) resulting in codon changes were identified using bioinformatics software (SIFT and Polyphen v2) and web-based tools (MutPre and PredictSNP). Seven nsSNPs (P374-S, T448-S, P462-R, V464-P, Q478-H, L495-E, and P499-Q) were predicted to alter RelA protein function and stability, while 5 of these (P374-S, T448-S, P462-R, L495-E, and Q499-P) were predicted as disease-related SNPs.Additionally, the inflammatory cytokine levels of IFN-α, IL-10, and TNF-α at both the protein and the mRNA transcript levels were measured using ELISA and Real-Time PCR, respectively. The resulting data was used in correlation analysis to assess the association between cytokine levels and the RelA gene expression. Higher levels of IFN-α and detectable levels of IL-10 protein and RelA mRNA were observed in surviving pigs compared to healthy (non-infected). A positive correlation of IFN-α cytokine levels with RelA mRNA expression was also obtained. In conclusion, 7 polymorphic events in the coding region of the RelA gene may contribute to the tolerance of ASFV in pigs.

Adaptation of African swine fever virus to MA-104 cells: Implications of unique genetic variations

African swine fever virus (ASFV) is a large, double-stranded DNA virus that causes a fatal, contagious disease specifically in pigs. However, prevention and control of ASFV outbreaks have been hampered by the lack of an effective vaccine or antiviral treatment for ASFV. Although ASFV has been reported to adapt to a variety of continuous cell lines, the phenotypic and genetic changes associated with ASFV adaptation to MA-104 cells remain poorly understood. Here, we adapted ASFV field isolates to efficiently propagate through serial viral passages in MA-104 cells. The adapted ASFV strain developed a pronounced cytopathic effect and robust infection in MA-104 cells. Interestingly, the adapted variant maintained its tropism in primary porcine kidney macrophages. Whole genome analysis of the adapted virus revealed unique gene deletions in the left and right variable regions of the viral genome compared to other previously reported cell culture-adapted ASFV strains. Notably, gene duplications at the 5' and 3' ends of the viral genome were in reverse complementary alignment with their paralogs. Single point mutations in protein-coding genes and intergenic regions were also observed in the viral genome. Collectively, our results shed light on the significance of these unique genetic changes during adaptation, which facilitate the growth of ASFV in MA-104 cells.

Epidemiological investigation of ASF outbreaks in Kerala (India): detection, source tracing and economic implications

This study investigates suspected African swine fever (ASF) outbreaks in two villages of Kannur district in Kerala, India, with the aim of identifying the causative agent and its genotype, the source of infection, and estimating the economic losses due to the outbreaks. Clinically, the disease was acute with high mortality, while gross pathology was characterized by widespread haemorrhages in various organs, especially the spleen, which was dark, enlarged and had friable cut surfaces with diffuse haemorrhages. Notably, histopathological examination revealed multifocal, diffuse haemorrhages in the splenic parenchyma and lymphoid depletion accompanied by lymphoid cell necrosis. The clinico-pathological observations were suggestive of ASF, which was confirmed by PCR. The source of outbreak was identified as swill and it was a likely point source infection as revealed by epidemic curve analysis. The phylogenetic analysis of p72 gene identified the ASFV in the current outbreak as genotype-II and IGR II variant consistent with ASFVs detected in India thus far. However, the sequence analysis of the Central Variable Region (CVR) of the B602L gene showed that the ASFVs circulating in Kerala (South India) formed a separate clade along with those found in Mizoram (North East India), while ASFVs circulating in Arunachal Pradesh and Assam states of India grouped in to different clade. This study represents the first investigation of ASF outbreak in South India, establishing the genetic relatedness of the ASFV circulating in this region with that in other parts of the country. The study also underscores the utility of the CVR of the B602L gene in genetically characterizing highly similar Genotype II ASFVs to understand the spread of ASF within the country.

The transcriptomic insight into the differential susceptibility of African Swine Fever in inbred pigs

African swine fever (ASF) is a global threat to animal health and food security. ASF is typically controlled by strict biosecurity, rapid diagnosis, and culling of affected herds. Much progress has been made in developing modified live virus vaccines against ASF. There is host variation in response to ASF infection in the field and under controlled conditions. To better understand the dynamics underlying this host differential morbidity, whole transcriptome profiling was carried out in twelve immunized and five sham immunized pigs. Seventeen MHC homozygous inbred Large white Babraham pigs were sampled at three time points before and after the challenge. The changes in the transcriptome profiles of infected animals were surveyed over time. In addition, the immunization effect on the host response was studied as well among the contrasts of all protection subgroups. The results showed two promising candidate genes to distinguish between recovered and non-recovered pigs after infection with a virulent African swine fever virus (ASFV) pre-infection: HTRA3 and GFPT2 (padj < 0.05). Variant calling on the transcriptome assemblies showed a two-base pair insertion into the ACOX3 gene closely located to HTRA3 that may regulate its expression as a putative genomic variant for ASF. Several significant DGEs, enriched gene ontology (GO) terms, and KEGG pathways at 1 day and 7 days post-infection, compared to the pre-infection, indicate a significant inflammation response immediately after ASF infection. The presence of the virus was confirmed by the mapping of RNA-Seq reads on two whole viral genome sequences. This was concordant with a higher virus load in the non-recovered animals 7 days post-infection. There was no transcriptome signature on the immunization at pre-infection and 1 day post-infection. More samples and data from additional clinical trials may support these findings.

Pathogenicity and horizontal transmission evaluation of a novel isolated African swine fever virus strain with a three-large-fragment-gene deletion

African swine fever has caused substantial economic losses to China`s pig industry in recent years. Currently, the highly pathogenic African swine fever virus strain of genotype II is predominantly circulating in China, accompanied by a series of emerging isolates displaying unique genetic variations. The pathogenicity of these emerging strains is still unclear. Recently, a novel ASFV strain with a distinguishable three-large-fragment gene deletion was obtained from the field specimens, and its in vivo pathogenicity and transmission were evaluated in this study. The animal experiment involved inoculating a high dose of YNFN202103 and comparing its effects with those of the highly pathogenic strain GZ201801_2. Results showed that pigs infected by YNFN202103 exhibited significantly prolonged onset and survival time, lower viremia levels, and less severe histopathological lesions compared to GZ201801_2. These findings contributed valuable insights into the pathogenicity and transmission of ASFV and its prevention and eradication strategies in practical settings.

Nanoparticle-Based Secretory Granules Induce a Specific and Long-Lasting Immune Response through Prolonged Antigen Release

Developing prolonged antigen delivery systems that mimic long-term exposure to pathogens appears as a promising but still poorly explored approach to reach durable immunities. In this study, we have used a simple technology by which His-tagged proteins can be assembled, assisted by divalent cations, as supramolecular complexes with progressive complexity, namely protein-only nanoparticles and microparticles. Microparticles produced out of nanoparticles are biomimetics of secretory granules from the mammalian hormonal system. Upon subcutaneous administration, they slowly disintegrate, acting as an endocrine-like secretory system and rendering the building block nanoparticles progressively bioavailable. The performance of such materials, previously validated for drug delivery in oncology, has been tested here regarding the potential for time-prolonged antigen release. This has been completed by taking, as a building block, a nanostructured version of p30, a main structural immunogen from the African swine fever virus (ASFV). By challenging the system in both mice and pigs, we have observed unusually potent pro-inflammatory activity in porcine macrophages, and long-lasting humoral and cellular responses in vivo, which might overcome the need for an adjuvant. The robustness of both innate and adaptive responses tag, for the first time, these dynamic depot materials as a novel and valuable instrument with transversal applicability in immune stimulation and vaccinology.

Preparation and characterization of monoclonal antibodies against porcine gasdermin D protein

Pyroptosis is a newly discovered type of pro-inflammatory programmed cell death that plays a vital role in various processes such as inflammations, immune responses, and pathogen infections. As one of the main executioners of pyroptosis, gasdermin D (GSDMD) is a membrane pore-forming protein that typically exists in a self-inhibitory state. Once activated, GSDMD will be cleaved into an N-terminal fragment with pore-forming activity, becoming the key indicator of pyroptosis activation, and a C-terminal fragment. Although commercial antibodies against human and murine GSDMD proteins are currently available, their reactivity with porcine GSDMD (pGSDMD) is poor, which limits research on the biological functions of pGSDMD and pyroptosis in pigs in vivo and in vitro. Here, five monoclonal antibodies (mAbs) were prepared by immunizing BALB/c mice with procaryotically expressed full-length pGSDMD, all of which did not cross react with human and murine GSDMD proteins. Epitope mapping demonstrated that 15H6 recognizes amino acids (aa) at positions 28-34 of pGSDMD (LQTSDRF), 19H3 recognizes 257-260aa (PPQF), 23H10 and 27A10 recognize 78-82aa (GPFYF), and 25E2 recognizes 429-435aa (PPTLLGS). The affinity constant and isotype of 15H6, 19H3, 23H10, 27A10, and 25E2 mAbs were determined to be 1.32 × 10-9, 3.66 × 10-9, 9.04 × 10-9, 1.83 × 10-9, and 8.00 × 10-8 mol/L and IgG1/κ, IgG2a/κ, IgG2a/κ, IgG1/κ, and IgG1/κ, respectively. Heavy- and light-chain variable regions sequencing showed that the heavy-chain complementarity-determining region (CDR) sequences of all five mAbs are completely different, while the light-chain CDR sequences of the four mAbs that recognize the N-terminus of pGSDMD are identical. Our prepared mAbs provide valuable materials for studying pGSDMD function and pyroptosis. KEY POINTS: • A total of five mouse anti-pGSDMD mAbs were prepared, of which four recognize the N-terminus of pGSDMD and one recognize its C-terminus. • The main performance parameters of the five mAbs, including epitope, antibody titer, affinity constant, isotype, and heavy- and light-chain CDR, were characterized. • All five mAbs specifically recognize pGSDMD protein and do not cross react with human and murine GSDMD proteins.

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.

The Long-Jumping of African Swine Fever: First Genotype II Notified in Sardinia, Italy

African swine fever (ASF) is a devastating infectious disease of domestic pigs and wild boar that is spreading quickly around the world and causing huge economic losses. Although the development of effective vaccines is currently being attempted by several labs, the absence of globally recognized licensed vaccines makes disease prevention and early detection even more crucial. ASF has spread across many countries in Europe and about two years ago affected the Italian susceptible population. In Italy, the first case of ASF genotype II in wild boar dates back to January 2022, while the first outbreak in a domestic pig farm was notified in August 2023. Currently, four clusters of infection are still ongoing in northern (Piedmont-Liguria and Lombardy), central (Lazio), and southern Italy (Calabria and Campania). In early September 2023, the first case of ASFV genotype II was detected in a domestic pig farm in Sardinia, historically affected by genotype I and in the final stage of eradication. Genomic characterization of p72, p54, and I73R/I329L genome regions revealed 100% similarity to those obtained from isolates that have been circulating in mainland Italy since January 2022 and also with international strains. The outbreak was detected and confirmed due to the passive surveillance plan on domestic pig farms put in place to provide evidence on genotype I's absence. Epidemiological investigations suggest 24 August as the most probable time of ASFV genotype II's arrival in Sardinia, likely due to human activities.

Clinicopathological and ultrastructural study of African swine fever outbreak in North-East India

The present investigation focuses on examining the clinical, histopathological, and ultrastructural changes that occurred in pig, during an outbreak of African swine fever (ASF) in 2022 in Assam, India. The disease initially manifested as a per-acute case with high mortality but without any evident clinical signs. Subsequently, some animals exhibited an acute form of the disease characterized by high fever (104-106 °F), anorexia, vomiting, respiratory distress, and bleeding from the anal and nasal orifices. During acute African swine fever virus (ASFV) infections, elevated levels of pro-inflammatory IL-1α, IL-1β, IL-6, TNF, CCL2, CCL5, and CXCL10 were detected in the palatine tonsil, lymph nodes, spleen, and kidney using qPCR assay. These molecular changes were associated with haemorrhages, edemas, and lymphoid depletion. Postmortem examinations revealed prominent features such as splenomegaly with haemorrhages, haemorrhagic lymphadenitis, severe petechial haemorrhage in the kidney, pneumonia in the lungs, and necrotic palatine tonsil. Histopathological analysis demonstrated lymphocyte depletion in lymphoid organs, multi-organ haemorrhages, and interstitial pneumonia in the lungs. Scanning electron microscopy (SEM) further confirmed lymphocyte depletion in lymphoid organs through lymphocyte apoptosis and kidney damage with distorted tubules due to red blood cell destruction. Transmission electron microscopy reaffirmed lymphocyte apoptosis by observing chromatin condensation and nucleus margination in lymphocytes of lymphoid organs. These findings provide comprehensive insights into the clinical, histopathological, and ultrastructural aspects of ASF outbreak in pigs. Understanding the pathological changes associated with ASF can contribute to improved diagnosis, prevention, and control measures for this highly contagious and economically devastating viral disease.

Increased Presence of Circulating Cell-Free, Fragmented, Host DNA in Pigs Infected with Virulent African Swine Fever Virus

African swine fever virus (ASFV) causes severe hemorrhagic disease in domestic pigs and wild boar, often with high case fatality rates. The virus replicates in the circulating cells of the monocyte-macrophage lineage and within lymphoid tissues. The infection leads to high fever and a variety of clinical signs. In this study, it was observed that ASFV infection in pigs resulted in a >1000-fold increase in the level of circulating cell-free DNA (cfDNA), derived from the nuclei of host cells in the serum. This change occurred in parallel with the increase in circulating ASFV DNA. In addition, elevated levels (about 30-fold higher) of host mitochondrial DNA (mtDNA) were detected in the serum from ASFV-infected pigs. For comparison, the release of the cellular enzyme, lactate dehydrogenase (LDH), a commonly used marker of cellular damage, was also found to be elevated during ASFV infection, but later and less consistently. The sera from pigs infected with classical swine fever virus (CSFV), which causes a clinically similar disease to ASFV, were also tested but, surprisingly, this infection did not result in the release of cfDNA, mtDNA, or LDH. It was concluded that the level of cfDNA in the serum is a sensitive host marker of virulent ASFV infection.

Transcriptome analysis reveals gene expression changes of pigs infected with non-lethal African swine fever virus

African swine fever (ASF) is an important viral disease of swine caused by the African swine fever virus (ASFV), which threatens swine production profoundly. To better understand the gene expression changes when pig infected with ASFV, RNA sequencing was performed to characterize differentially expressed genes (DEGs) of six tissues from Kenya domestic pigs and Landrace × Yorkshire (L/Y) pigs infected with ASFV Kenya1033 in vivo. As results, a total of 209, 522, 34, 505, 634 and 138 DEGs (q-value < 0.05 and |Log2foldchange| values >2) were detected in the kidney, liver, mesenteric lymph node, peripheral blood mononuclear cell, submandibular lymph node and spleen, respectively. The expression profiles of DEGs shared in the multiple tissues illustrated variation in regulation function in the different tissues. Functional annotation analysis and interaction of proteins encoded by DEGs revealed that genes including IFIT1, IFITM1, MX1, OASL, ISG15, SAMHD1, IFINA1, S100A12 and S100A8 enriched in the immune and antivirus pathways were significantly changed when the hosts were infected with ASFV. The genes mentioned could play crucial roles in the process of the reaction to non-lethal ASF infection, which may will help to improve the ASF tolerance in the pig population through molecular breeding strategies.

A Cell-Adapted Live-Attenuated Vaccine Candidate Protects Pigs against the Homologous Strain VNUA-ASFV-05L1, a Representative Strain of the Contemporary Pandemic African Swine Fever Virus

African swine fever (ASF) is a lethal and highly contagious transboundary animal disease with the potential for rapid international spread. Currently, there is no ASF vaccine commercially available. All infected animals must be isolated and culled immediately upon the confirmation of the presence of the virus. Studies leading to the rational development of protective ASF vaccines are urgently needed. Here, we generated a safe and efficacious live-attenuated vaccine (LAV) VNUA-ASFV-LAVL2 by serially passaging a field isolate (VNUA-ASFV-05L1, genotype II) in porcine alveolar macrophages (PAMs, 65 passages) and an immortalized porcine alveolar macrophage cell line (3D4/21, 55 passages). VNUA-ASFV-LAVL2 can efficiently replicate in both PAMs and 3D4/21 cells. It provides 100% protection, even with the low dose of 102 HAD50, to the vaccinated pigs against the challenge of contemporary pandemic ASFV field isolate. Pigs vaccinated with this LAV in a dose range of 102 to 105 HAD50 remained clinically healthy during both the 28-day observation period of immunization and the 28-day observation period of challenge. VNUA-ASFV-LAVL2 was eliminated from blood by 28 days post-inoculation (DPI), and from feces or oral fluids by 17 DPI. Although the vaccine strain in serum remained a safe and attenuated phenotype after five passages in swine, a reversion-to-virulence study using blood or tissue homogenates at peak viremia will be conducted in the future. ASFV-specific IgG antibodies and significant cellular immunity were detected in vaccinated pigs before the ASFV challenge. These results indicate that the VNUA-ASFV-LAVL2 strain is a safe and efficacious LAV against the genotype II ASFV strain responsible for current ASF outbreaks in Asia.

Mucosal and cellular immune responses elicited by nasal and intramuscular inoculation with ASFV candidate immunogens

African swine fever (ASF) is an infectious disease caused by African swine fever virus (ASFV) that is highly contagious and has an extremely high mortality rate (infected by virulent strains) among domestic and wild pigs, causing huge economic losses to the pig industry globally. In this study, SDS-PAGE gel bands hybridized with ASFV whole virus protein combined with ASFV-convalescent and ASFV-positive pig serum were identified by mass spectrometry. Six antigens were detected by positive serum reaction bands, and eight antigens were detected in ASFV-convalescent serum. In combination with previous literature reports and proteins corresponding to MHC-II presenting peptides screened from ASFV-positive pig urine conducted in our lab, seven candidate antigens, including KP177R (p22), K78R (p10), CP204L (p30), E183L (p54), B602L (B602L), EP402R-N (CD2V-N) and F317L (F317L), were selected. Subunit-Group 1 was prepared by mixing above-mentioned seven ASFV recombinant proteins with MONTANIDETM1313 VG N mucosal adjuvant and immunizing pigs intranasally and intramuscularly. Subunit-Group 2 was prepared by mixing four ASFV recombinant proteins (p22, p54, CD2V-N1, B602L) with Montanide ISA 51 VG adjuvant and immunizing pigs by intramuscular injection. Anticoagulated whole blood, serum, and oral fluid were collected during immunization for flow cytometry, serum IgG as well as secretory sIgA antibody secretion, and cytokine expression testing to conduct a comprehensive immunogenicity assessment. Both immunogen groups can effectively stimulate the host to produce ideal humoral, mucosal, and cellular immune responses, providing a theoretical basis for subsequent functional studies, such as immunogens challenge protection and elucidation of the pathogenic mechanism of ASFV.

A survey of biosecurity practices of pig farmers in selected districts affected by African swine fever in Uganda

Introduction

In Uganda, pig production is an important source of livelihood for many people and contributes to food security. African swine fever (ASF) is a major constraint to pig production in Uganda, threatening the food supply and sustainable livelihoods. Prevention of ASF primarily relies on good biosecurity practices along the pig value chain. Previous studies showed that biosecurity along the pig value chain and on farms in Uganda is poor. However, the biosecurity practices of pig farmers in ASF affected areas of Uganda and their opinions on on-farm ASF morbidity and mortality were previously not comprehensively characterized. The objectives of this study were to document pig farmers' experiences with ASF in their farms and to describe the pig biosecurity practices in districts of Uganda that were highly affected by ASF.

Methods

A total of 99 farmers were interviewed in five districts. Data were collected by way of triangulation through farmer interviews, field observations during the farmer interviews, and a survey of key informants. However, farmer interviews were considered the primary source of data for this study. Farmers' biosecurity practices were scored using a biosecurity scoring algorithm.

Results

Forty-one out of 96 (42.7%) farmers reported having pigs with ASF in the past 12 months. The level of pig farming experience (p = 0.0083) and herd size (p < 0.0001) were significantly associated with the reported occurrence of ASF. Overall, the biosecurity scores for the respondents were considered poor with 99% (98/99) scoring <70% and just one farmer obtaining a fair score of 72.2%. District (p = 0.0481), type of husbandry system (p = 0.014), and type of pig breed raised (p = 0.004) were significantly associated with farmer's biosecurity score.

Conclusion

Continued farmer education on ASF and the importance of good biosecurity practices is necessary. More in-depth scientific inquiry into the factors influencing the biosecurity practices among pig farmers in Uganda is necessary.

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.

Susceptibility of perivenous macrophages to PRRSV-1 subtype 1 LV and PRRSV-1 subtype 3 Lena using a new vein explant model

Vessel pathology such as increased permeability and blue discoloration is frequently observed with highly pathogenic PRRSV strains. However, data concerning the viral replication in the environment of blood vessels are absent. In the present study, ex vivo models with swine ear and hind leg vein explants were established to study the interaction of PRRSV-1 subtype 1 reference strain LV and highly pathogenic subtype 3 strain Lena with perivenous macrophages. The replication characteristics of these two strains were compared in vein explants by immunofluorescence analysis. The explants maintained a good viability during 48 hours of in vitro culture. We found that CD163-positive macrophages were mainly present around the veins and their number gradually decreased with increasing distance from the veins and longer incubation time. More CD163+Sn- cells than CD163+Sn+ cells (6.6 times more) were observed in the vein explants. The Lena strain demonstrated a higher replication level than the LV strain, with approximately 1.4-fold more infected cells in the surrounding areas of the ear vein and 1.1-fold more infected cells in the leg vein explants at 48 hours post inoculation. In both LV and Lena inoculated vein explants, most infected cells were identified as CD163+Sn+ (> 94%). In this study, an ex vivo vein model was successfully established, and our findings will contribute to a better understanding of the vein pathology during viral infections (e.g., PRRS, classical and African swine fever).

Immunization of pigs with replication-incompetent adenovirus-vectored African swine fever virus multi-antigens induced humoral immune responses but no protection following contact challenge

Introduction

African swine fever virus (ASFV) is a pathogen of great economic importance given that continues to threaten the pork industry worldwide, but there is no safe vaccine or treatment available. Development of a vaccine is feasible as immunization of pigs with some live attenuated ASFV vaccine candidates can confer protection, but safety concerns and virus scalability are challenges that must to be addressed. Identification of protective ASFV antigens is needed to inform the development of efficacious subunit vaccines.

Methods

In this study, replication-incompetent adenovirus-vectored multicistronic ASFV antigen expression constructs that covered nearly 100% of the ASFV proteome were generated and validated using ASFV convalescent serum. Swine were immunized with a cocktail of the expression constructs, designated Ad5-ASFV, alone or formulated with either Montanide ISA-201™ (ASFV-ISA-201) or BioMize^® adjuvant (ASFV-BioMize).

Results

These constructs primed strong B cell responses as judged by anti-pp62-specific IgG responses. Notably, the Ad5-ASFV and the Ad5-ASFV ISA-201, but not the Ad5-ASFV BioMize^®, immunogens primed significantly (p < 0.0001) higher anti-pp62-specific IgG responses compared with Ad5-Luciferase formulated with Montanide ISA-201™ adjuvant (Luc-ISA-201). The anti-pp62-specific IgG responses underwent significant (p < 0.0001) recall in all the vaccinees after boosting and the induced antibodies strongly recognized ASFV (Georgia 2007/1)-infected primary swine cells. However, following challenge by contact spreaders, only one pig nearly immunized with the Ad5-ASFV cocktail survived. The survivor had no typical clinical symptoms, but had viral loads and lesions consistent with chronic ASF.

Discussion

Besides the limited sample size used, the outcome suggests that in vivo antigen expression, but not the antigen content, might be the limitation of this immunization approach as the replication-incompetent adenovirus does not amplify in vivo to effectively prime and expand protective immunity or directly mimic the gene transcription mechanisms of attenuated ASFV. Addressing the in vivo antigen delivery limitations may yield promising outcomes.

Development of a Novel Indirect ELISA for the Serological Diagnosis of African Swine Fever Using p11.5 Protein as a Target Antigen

African swine fever is a hemorrhagic viral disease with a mortality rate of nearly 100% in pigs. Hence, it is classified as a notifiable disease by the World Organization for Animal Health. Because no field-available vaccine exists, African swine fever virus (ASFV) control and eradication solely depend on good farm biosecurity management and rapid and accurate diagnosis. In this study, we developed a new indirect serological enzyme-linked immunosorbent assay (ELISA) using recombinant p11.5 protein from ASFV as a solid-phase target antigen. The cutoffs were determined by receiver operating curve analysis performed with serum samples obtained from naïve and infected pigs. Based on the results of a commercially available serological ELISA, the relative sensitivity and specificity of our assay were 93.4% and 94.4% (N = 166; area under the curve = 0.991; 95% confidence interval = 0.982-0.999), respectively. Furthermore, to compare the performance of the serological ELISAs, we conducted the assays on a panel of sera collected from pigs and boars experimentally infected with different ASFV isolates. The results indicated the greater sensitivity of the newly developed assay and its ability to detect anti-ASFV antibodies earlier after virus inoculation.

Alteration of the Gut Microbiota in Pigs Infected with African Swine Fever Virus

The factors that influence the pathogenicity of African swine fever (ASF) are still poorly understood, and the host's immune response has been indicated as crucial. Although an increasing number of studies have shown that gut microbiota can control the progression of diseases caused by viral infections, it has not been characterized how the ASF virus (ASFV) changes a pig's gut microbiome. This study analyzed the dynamic changes in the intestinal microbiome of pigs experimentally infected with the high-virulence ASFV genotype II strain (N = 4) or mock strain (N = 3). Daily fecal samples were collected from the pigs and distributed into the four phases (before infection, primary phase, clinical phase, and terminal phase) of ASF based on the individual clinical features of the pigs. The total DNA was extracted and the V4 region of the 16 s rRNA gene was amplified and sequenced on the Illumina platform. Richness indices (ACE and Chao1) were significantly decreased in the terminal phase of ASF infection. The relative abundances of short-chain-fatty-acids-producing bacteria, such as Ruminococcaceae, Roseburia, and Blautia, were decreased during ASFV infection. On the other hand, the abundance of Proteobacteria and Spirochaetes increased. Furthermore, predicted functional analysis using PICRUSt resulted in a significantly reduced abundance of 15 immune-related pathways in the ASFV-infected pigs. This study provides evidence for further understanding the ASFV-pig interaction and suggests that changes in gut microbiome composition during ASFV infection may be associated with the status of immunosuppression.

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.

Development of a sensitive, high-throughput extraction protocol for qPCR detection of African swine fever virus in formalin-fixed, paraffin-embedded tissues

African swine fever (ASF) causes fatal disease in pigs and is an escalating threat to the global swine industry. ASF has re-emerged from Africa as a transcontinental epidemic spreading through the Caucasus into Europe, Russia, China, numerous Asian countries, and the Caribbean. ASF virus (ASFV) is a U.S. select agent requiring handling in high-containment biosafety level 3 (BSL-3) laboratories for pathogen work. Formalin-fixation eliminates infectivity and preserves the genome, providing noninfectious specimens for BSL-2 work. Recovery of DNA from formalin-fixed, paraffin-embedded tissue (FFPET) is challenging and cumbersome. A reliable and easy-to-perform method for DNA recovery from FFPET would facilitate surveillance. To meet this objective, we developed a high-throughput protocol for the recovery of ASFV DNA from FFPET. Deparaffinization, tissue lysis, and reversal of cross-linking were performed in a single tube, followed by DNA purification via automated magnetic bead extraction. Quantitative PCR (qPCR) detection was used to determine the copy number of the B646L gene that encodes for the ASFV p72 protein in tissues (5 pigs, 4 tissues) from pigs with lesions consistent with acute ASF. Copy numbers obtained from FFPET were within one log of copy numbers obtained from fresh tissue, thus enabling ASF qPCR surveillance from formalin-inactivated and preserved tissues at BSL-2 at diagnostic sensitivity similar to fresh tissues tested at BSL-3.

Characterization of a Novel African Swine Fever Virus p72 Genotype II from Nigeria

African swine fever (ASF) is a high-consequence transboundary hemorrhagic fever of swine. It continues to spread across the globe causing socio-economic issues and threatening food security and biodiversity. In 2020, Nigeria reported a major ASF outbreak, killing close to half a million pigs. Based on the partial sequences of the genes B646L (p72) and E183L (p54), the virus responsible for the outbreak was identified as an African swine fever virus (ASFV) p72 genotype II. Here, we report further characterization of ASFV RV502, one of the isolates obtained during the outbreak. The whole genome sequence of this virus revealed a deletion of 6535 bp between the nucleotide positions 11,760–18,295 of the genome, and an apparent reverse complement duplication of the 5′ end of the genome at the 3′ end. Phylogenetically, ASFV RV502 clustered together with ASFV MAL/19/Karonga and ASFV Tanzania/Rukwa/2017/1 suggesting that the virus responsible for the 2020 outbreak in Nigeria has a South-eastern African origin.

Pathological Characteristics of Domestic Pigs Orally Infected with the Virus Strain Causing the First Reported African Swine Fever Outbreaks in Vietnam

African swine fever (ASF) is currently Vietnam’s most economically significant swine disease. The first ASF outbreak in Vietnam was reported in February 2019. In this study, VNUA/HY/ASF1 strain isolated from the first ASF outbreak was used to infect 10 eight-week-old pigs orally with 103 HAD50 per animal. The pigs were observed daily for clinical signs, and whole blood samples were collected from each animal for viremia detection. Dead pigs were subjected to full post-mortem analyses. All 10 pigs displayed acute or subacute clinical signs and succumbed to the infection between 10 to 27 (19.8 ± 4.66) days post-inoculation (dpi). The onset of clinical signs started around 4–14 dpi. Viremia was observed in pigs from 6–16 dpi (11.2 ± 3.55). Enlarged, hyperemic, and hemorrhagic lymph nodes, enlarged spleen, pneumonia, and hydropericardium were observed at post-mortem examinations.

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.

Community engagement strengthens pig disease knowledge and passive surveillance in Timor-Leste

Smallholder pig production in Timor-Leste is culturally and economically important for most households. However, regular and ongoing disease surveillance and pig husbandry training for farmers are limited. This article describes collaborative social and diagnostic research followed by a pilot community engagement program to improve farmer and technician knowledge, skills, and working relationships. There were three phases: (1) A qualitative study in 2020 to explore the experiences and knowledge of 133 pig farmers, 6 village leaders, and 16 district veterinary technicians on pig diseases and reporting, treatment methods, and access to information or assistance. (2) A pilot community engagement program in 3 villages in 2021 with the diagnostic investigation with samples analyzed from 27 dead pigs, and (3) Evaluation of community engagement and training outcomes. Results of the qualitative study revealed limited reporting of sick or dead pigs by farmers to veterinary technicians due to a lack of trust in the veterinary diagnostic system. Most technicians lacked experience with sampling or post-mortems so diagnostic training was undertaken for the pilot disease investigation. Evaluation results showed improved knowledge, motivation, and confidence of government staff and farmers. The credibility of veterinary technicians improved and gave them more confidence to work with communities. Farmers felt supported because all aspects of pig husbandry were addressed, and they were more willing to report dead or sick pigs. The project indicates that improved passive disease surveillance can be achieved by engaging communities in smallholder pig farming in Timor-Leste. Further research and testing of the approach in other districts and countries is recommended.

Experimental Infection of Domestic Pigs with African Swine Fever Virus Isolated in 2019 in Mongolia

African swine fever (ASF) is an infectious viral disease caused by African swine fever virus (ASFV), that causes high mortality in domestic swine and wild boar (Sus scrofa). Currently, outbreaks are mitigated through strict quarantine measures and the culling of affected herds, resulting in massive economic losses to the global pork industry. In 2019, an ASFV outbreak was reported in Mongolia, describing a rapidly progressing clinical disease and gross lesions consistent with the acute form of ASF; the virus was identified as a genotype II virus. Due to the limited information on clinical disease and viral dynamics within hosts available from field observations of the Mongolian isolates, we conducted the present study to further evaluate the progression of clinical disease, virulence, and pathology of an ASFV Mongolia/2019 field isolate (ASFV-MNG19), by experimental infection of domestic pigs. Intramuscular inoculation of domestic pigs with ASFV-MNG19 resulted in clinical signs and viremia at 3 days post challenge (DPC). Clinical disease rapidly progressed, resulting in the humane euthanasia of all pigs by 7 DPC. ASFV-MNG19 infected pigs had viremic titers of 10⁸ TCID₅₀/mL by 5 DPC and shed virus in oral secretions late in disease, as determined from oropharyngeal swabs. Whole-genome sequencing confirmed that the ASFV-MNG19 strain used in this study was a genotype II strain highly similar to other regional strains. In conclusion, we demonstrate that ASFV-MNG19 is a virulent genotype II ASFV strain that causes acute ASF in domestic swine.

African Swine Fever Vaccinology: The Biological Challenges from Immunological Perspectives

African swine fever virus (ASFV), a nucleocytoplasmic large DNA virus (NCLDV), causes African swine fever (ASF), an acute hemorrhagic disease with mortality rates up to 100% in domestic pigs. ASF is currently epidemic or endemic in many countries and threatening the global swine industry. Extensive ASF vaccine research has been conducted since the 1920s. Like inactivated viruses of other NCLDVs, such as vaccinia virus, inactivated ASFV vaccine candidates did not induce protective immunity. However, inactivated lumpy skin disease virus (poxvirus) vaccines are protective in cattle. Unlike some experimental poxvirus subunit vaccines that induced protection, ASF subunit vaccine candidates implemented with various platforms containing several ASFV structural genes or proteins failed to protect pigs effectively. Only some live attenuated viruses (LAVs) are able to protect pigs with high degrees of efficacy. There are currently several LAV ASF vaccine candidates. Only one commercial LAV vaccine is approved for use in Vietnam. LAVs, as ASF vaccines, have not yet been widely tested. Reports thus far show that the onset and duration of protection induced by the LAVs are late and short, respectively, compared to LAV vaccines for other diseases. In this review, the biological challenges in the development of ASF vaccines, especially subunit platforms, are discussed from immunological perspectives based on several unusual ASFV characteristics shared with HIV and poxviruses. These characteristics, including multiple distinct infectious virions, extremely high glycosylation and low antigen surface density of envelope proteins, immune evasion, and possible apoptotic mimicry, could pose enormous challenges to the development of ASF vaccines, especially subunit platforms designed to induce humoral immunity.

Examination of immunogenic properties of recombinant antigens based on p22 protein from African swine fever virus

Introduction

The single member of the Asfarviridae family is African swine fever virus (ASFV). This double-stranded DNA virus infects wild and farmed swine and loses the pig industry large sums of money. An inner envelope, capsid, and outer envelope are parts of the ASFV particle containing structural proteins playing different roles in the process of infection or host immune defence evasion. When expressed by the baculovirus system, the p22 protein from the inner envelope was found to induce partial protection against a virulent virus strain. This study aimed to express a part of this protein in a different system and evaluate its immunogenicity.

Material and Methods

We designed two proteins, the extracellular (C terminal) part of the p22 protein (p22Ct) and its fusion with the heat-labile enterotoxin B subunit from Escherichia coli (LTB-p22Ct), which is supposed to be a potent enhancer of the immune response. Both proteins were produced in the E. coli expression system and subsequently used for mice immunisation to analyse their safety and immunogenicity.

Results

The protein fused with LTB did not show the expected adjuvant properties and did not prove safe, because abscess formation was observed after immunisation. In contrast, immunisation with the p22Ct protein alone induced a higher antibody titre but caused no adverse symptoms.

Conclusion

These results show the high potential of the p22Ct region as an immunogenic protein for ASFV serological detection purposes.

African Swine Fever Virus: A Review

African swine fever (ASF) is a viral disease with a high fatality rate in both domestic pigs and wild boars. ASF has greatly challenged pig-raising countries and also negatively impacted regional and national trade of pork products. To date, ASF has spread throughout Africa, Europe, and Asia. The development of safe and effective ASF vaccines is urgently required for the control of ASF outbreaks. The ASF virus (ASFV), the causative agent of ASF, has a large genome and a complex structure. The functions of nearly half of its viral genes still remain to be explored. Knowledge on the structure and function of ASFV proteins, the mechanism underlying ASFV infection and immunity, and the identification of major immunogenicity genes will contribute to the development of an ASF vaccine. In this context, this paper reviews the available knowledge on the structure, replication, protein function, virulence genes, immune evasion, inactivation, vaccines, control, and diagnosis of ASFV.

The study of antigen carrying and lesions observed in pigs that survived post African swine fever virus infection

African swine fever (ASF) is a dangerous infectious disease of domestic pigs and wild boar caused by African swine fever virus (ASFV). In Vietnam, the ASF epidemic is gradually turning into an endemic status with several recovered pigs post infection, but there were not many studies evaluating the role of these pigs in the epidemiological context in Vietnam. The aim of this study was to evaluate the viral antigen distribution and lesions in recovered pigs post ASFV infection. Ten pigs recovered from ASF at 6 weeks of age were monitored and assessed for anti-ASFV antibodies and viremia until slaughter. The five major organs (lung, liver, spleen, kidney, and lymph nodes) of these pigs were evaluated for microscopic lesions and viral antigen distribution. Anti-ASFV antibody was consistently observed to be high (S/P% ≥ 80) until slaughter, while viremia levels were very high (7 log₁₀ copies/mL) at 6 weeks of age and gradually decreased to undetectable levels at 12 weeks of age (6th week post-infection). At slaughter, the ASFV-associated lesions in the organs of these pigs were mild and nonspecific. Seven out of ten pigs recovering from ASF still carried the virus in surveyed organ tissues, although not in the serum. These findings suggest that ASF-recovered pigs may be potential carriers of the virus, contributing to the increased complexity in the current endemic status in Vietnam.

Impact of human behavior on the spread of African swine fever virus: what every veterinarian should know

African swine fever virus was first identified and characterized in Africa in the early 1900s, but it has spread exponentially in Europe, Asia, and the Caribbean since 2018. While it is a disease that exclusively affects swine, thus posing no infectious risk to human health, the virus's resiliency and human behavior have facilitated the rapid global dissemination of the virus over the past 4 years. In this Currents in One Health, we will review its epidemiology, viral characteristics, host range, and current prevention strategies; the current perspective on what a response would look like and who would be affected; and if the virus was ever found in the US. Due to the fact that the virus affects all breeds of Sus scrofa, including those used for food and companionship, it is vital for all veterinarians to work together to keep the virus out of the US. It is only through the collaborative efforts of multiple disciplines working locally, nationally, and globally that we can contain the spread of this virus.

Research progress on the proteins involved in African swine fever virus infection and replication

African swine fever (ASF) is an acute, hemorrhagic and highly contagious infectious disease caused by African swine fever virus (ASFV), which infects domestic pigs or wild boars. It is characterized by short course of disease, high fever and hemorrhagic lesions, with mortality of up to 100% from acute infection. Up to now, the lack of commercial vaccines and effective drugs has seriously threatened the healthy economic development of the global pig industry. ASFV is a double-stranded DNA virus and genome varies between about 170-194 kb, which encodes 150-200 viral proteins, including 68 structural proteins and more than 100 non-structural proteins. In recent years, although the research on structure and function of ASFV-encoded proteins has been deepened, the structure and infection process of ASFV are still not clear. This review summarizes the main process of ASFV infection, replication and functions of related viral proteins to provide scientific basis and theoretical basis for ASFV research and vaccine development.

Changes in Estimating the Wild Boar Carcasses Sampling Effort: Applying the EFSA ASF Exit Strategy by Means of the WBC-Counter Tool

African swine fever (ASF) is a devastating disease, resulting in the high mortality of domestic and wild pigs, spreading quickly around the world. Ensuring the prevention and early detection of the disease is even more crucial given the absence of licensed vaccines. As suggested by the European Commission, those countries which intend to provide evidence of freedom need to speed up passive surveillance of their wild boar populations. If this kind of surveillance is well-regulated in domestic pig farms, the country-specific activities to be put in place for wild populations need to be set based on wild boar density, hunting bags, the environment, and financial resources. Following the indications of the official EFSA opinion 2021, a practical interpretation of the strategy was implemented based on the failure probabilities of wrongly declaring the freedom of an area even if the disease is still present but undetected. This work aimed at providing a valid, applicative example of an exit strategy based on two different approaches: the first uses the wild boar density to estimate the number of carcasses need to complete the exit strategy, while the second estimates it from the number of wild boar hunted and tested. A practical free access tool, named WBC-Counter, was developed to automatically calculate the number of needed carcasses. The practical example was developed using the ASF data from Sardinia (Italian island). Sardinia is ASF endemic from 43 years, but the last ASFV detection dates back to 2019. The island is under consideration for ASF eradication declaration. The subsequent results provide a practical example for other countries in approaching the EFSA exit strategy in the best choices for its on-field application.

Serum Neutralizing and Enhancing Effects on African Swine Fever Virus Infectivity in Adherent Pig PBMC

African swine fever virus (ASFV) causes hemorrhagic fever with mortality rates of up to 100% in domestic pigs. Currently, there are no commercial vaccines for the disease. Only some live-attenuated viruses have been able to protect pigs from ASFV infection. The immune mechanisms involved in the protection are unclear. Immune sera can neutralize ASFV but incompletely. The mechanisms involved are not fully understood. Currently, there is no standardized protocol for ASFV neutralization assays. In this study, a flow cytometry-based ASFV neutralization assay was developed and tested in pig adherent PBMC using a virulent ASFV containing a fluorescent protein gene as a substrate for neutralization. As with previous studies, the percentage of infected macrophages was approximately five time higher than that of infected monocytes, and nearly all infected cells displayed no staining with anti-CD16 antibodies. Sera from naïve pigs and pigs immunized with a live-attenuated ASFV and fully protected against parental virus were used in the assay. The sera displayed incomplete neutralization with MOI-dependent neutralizing efficacies. Extracellular, but not intracellular, virions suspended in naïve serum were more infectious than those in the culture medium, as reported for some enveloped viruses, suggesting a novel mechanism of ASFV infection in macrophages. Both the intracellular and extracellular virions could not be completely neutralized.

Adenovirus-Vectored African Swine Fever Virus pp220 Induces Robust Antibody, IFN-γ, and CTL Responses in Pigs

African Swine Fever Virus (ASFV) poses a serious threat to the pork industry worldwide; however, there is no safe vaccine or treatment available. The development of an efficacious subunit vaccine will require the identification of protective antigens. The ASFV pp220 polyprotein is essential for virus structural integrity. This polyprotein is processed to generate p5, p34, p14, p37, and p150 individual proteins. Immunization of pigs with a cocktail of adenoviruses expressing the proteins induced significant IgG, IFN-γ-secreting cells, and cytotoxic T lymphocyte responses. Four predicted SLA-I binding nonamer peptides, namely p34161−169, p37859−867, p1501363−1371, and p1501463−1471, recalled strong IFN-γ+ PBMC and splenocyte responses. Notably, peptide p34161−169 was recognized by PBMCs isolated from 7/10 pigs and by splenocytes isolated from 8/10 pigs. Peptides p37859−867 and p1501363−1371 stimulated recall IFN-γ+ responses in PBMCs and splenocytes isolated from 8/10 pigs, whereas peptide p1501463−1471 recalled responses in PBMCs and splenocytes isolated from 7/10 to 9/10 pigs, respectively. The results demonstrate that the pp220 polyprotein contains multiple epitopes that induce robust immune responses in pigs. Importantly, these epitopes are 100% conserved among different ASFV genotypes and were predicted to bind multiple SLA-I alleles. The outcomes suggest that pp220 is a promising candidate for inclusion in a prototype subunit vaccine.

Development of a Blocking ELISA Kit for Detection of ASFV Antibody Based on a Monoclonal Antibody against Full Length p72

BACKGROUND

African swine fever virus (ASFV) is the etiologic agent of African swine fever (ASF), a disease of highly contagious and significant threat to pork production. At present, the sensitive detection methods are the keys to the disease control.

OBJECTIVE

Full length p72 is produced by eukaryotic system and its monoclonal antibody (mAb) 34C10 is subsequently recovered. A blocking ELISA kit for detection of ASFV antibody is developed based on p72 trimers and 34C10.

METHODS

Full length p72 is expressed and is used as immunogen to prepare a panel of monoclonal antibodies. The mAb 34C10 is verified by immunofluorescent and tested by ELISAs with positive serums. The constant affinity of 34C10 is then confirmed. A blocking ELISA kit is further developed and is compared with two commercial kits.

RESULTS

The mAb 34C10 is specifically bound to p72 protein, and it exhibits blocking affection to positive serum. IFA experiment shows that 34C10 could bind to p72 expressed by baculoviruses and the binding affinity of 34C10 is found to be as high as 1.85 × 1011 L/mol. The blocking ELISA kit shows high coincidence with a commercial ELISA kit. The sensitivity between these two kits is 97.6% (95%, CI: 90.65-99.58) and the specificity between them is 100% (95%, CI: 98.34-100).

CONCLUSION

The blocking ELISA developed in this study may have great potential for diagnosis of ASF. The structure of the antigen p72 is found to be a key factor for the performance of the kit.

HIGHLIGHTS

For the first time, the eukaryotic expressed full-length p72 protein is utilized to recover the monoclonal antibody and it is coated as antigen during the development of the blocking ELISA kit. This study sheds new light on the development of the blocking ELISA kits, especially for the development of diagnostic kit for the contagious virus with bio-safety problems.

Cell Lines for the Development of African Swine Fever Virus Vaccine Candidates: An Update

African swine fever virus (ASFV) is the etiological agent of a highly lethal disease in both domestic and wild pigs. The virus has rapidly spread worldwide and has no available licensed vaccine. An obstacle to the construction of a safe and efficient vaccine is the lack of a suitable cell line for ASFV isolation and propagation. Macrophages are the main targets for ASFV, and they have been widely used to study virus-host interactions; nevertheless, obtaining these cells is time-consuming and expensive, and they are not ethically suitable for the production of large-scale vaccines. To overcome these issues, different virulent field isolates have been adapted on monkey or human continuous cells lines; however, several culture passages often lead to significant genetic modifications and the loss of immunogenicity of the adapted strain. Thus, several groups have attempted to establish a porcine cell line able to sustain ASFV growth. Preliminary data suggested that some porcine continuous cell lines might be an alternative to primary macrophages for ASFV research and for large-scale vaccine production, although further studies are still needed. In this review, we summarize the research to investigate the most suitable cell line for ASFV isolation and propagation.

Detection of African swine fever virus in neonatal piglets with congenital tremors

African swine fever virus (ASF) has circulated in Vietnam since 2018, causing significant losses to the pig industry. Quick, accurate diagnosis of African swine fever virus (ASFV) infection is crucial for controlling the disease. The detection of the virus in piglets with congenital tremors is described in this paper. ASFV was detected in brain tissues by polymerase chain reaction (PCR) and immunohistochemistry. Classical swine fever virus, porcine parvovirus, porcine reproductive and respiratory syndrome virus, and pseudorabies virus were not detected by PCR, suggesting that the ASFV was the cause of these neurological signs.