Mechanisms of Entry and Endosomal Pathway of African Swine Fever Virus

Genome-wide characterization of structure variations in the Xiang pig for genetic resistance to African swine fever

African swine fever (ASF) is a rapidly fatal viral haemorrhagic fever in Chinese domestic pigs. Although very high mortality is observed in pig farms after an ASF outbreak, clinically healthy and antibody-positive pigs are found in those farms, and viral detection is rare from these pigs. The ability of pigs to resist ASF viral infection may be modulated by host genetic variations. However, the genetic basis of the resistance of domestic pigs against ASF remains unclear. We generated a comprehensive set of structural variations (SVs) in a Chinese indigenous Xiang pig with ASF-resistant (Xiang-R) and ASF-susceptible (Xiang-S) phenotypes using whole-genome resequencing method. A total of 53,589 nonredundant SVs were identified, with an average of 25,656 SVs per individual in the Xiang pig genome, including insertion, deletion, inversion and duplication variations. The Xiang-R group harboured more SVs than the Xiang-S group. The F-statistics (FST) was carried out to reveal genetic differences between two populations using the resequencing data at each SV locus. We identified 2,414 population-stratified SVs and annotated 1,152 Ensembl genes (including 986 protein-coding genes), in which 1,326 SVs might disturb the structure and expression of the Ensembl genes. Those protein-coding genes were mainly enriched in the Wnt, Hippo, and calcium signalling pathways. Other important pathways associated with the ASF viral infection were also identified, such as the endocytosis, apoptosis, focal adhesion, Fc gamma R-mediated phagocytosis, junction, NOD-like receptor, PI3K-Akt, and c-type lectin receptor signalling pathways. Finally, we identified 135 candidate adaptive genes overlapping 166 SVs that were involved in the virus entry and virus-host cell interactions. The fact that some of population-stratified SVs regions detected as selective sweep signals gave another support for the genetic variations affecting pig resistance against ASF. The research indicates that SVs play an important role in the evolutionary processes of Xiang pig adaptation to ASF infection.

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.

Challenges in the Application of African Swine Fever Vaccines in Asia

This paper explores the significance of quality vaccines in managing ASF in Asia, where it poses a substantial threat to the pork industry. It emphasizes the risks associated with substandard vaccines, including the emergence of new virus strains that complicate disease control. Highlighting recent advancements in vaccine deployment in Vietnam, the paper calls for rigorous testing and regulations to guarantee vaccine effectiveness and safety. The authors advocate for the implementation of vaccines with the inclusion of differentiating infected from vaccinated animals (DIVA), which enhances disease management strategies in both endemic and non-endemic regions. The conclusion underscores the necessity of stringent standards in vaccine development and strict adherence to regulatory guidelines to ensure successful ASF management and maintain public trust in the vaccines.

Identification of two novel linear epitopes on the E165R protein of African swine fever virus recognized by monoclonal antibodies

African swine fever (ASF) is a highly fatal infectious disease in pigs, caused by the African swine fever virus (ASFV). It is characterized by short disease duration and high morbidity and mortality. In August 2018, ASF was first reported in China and it subsequently spread rapidly throughout the country, causing serious economic losses for the Chinese pig industry. Early detection plays a critical role in preventing and controlling ASF because there is currently no effective vaccine or targeted therapeutic medication available. Additionally, identifying conserved protective antigenic epitopes of ASFV is essential for the development of diagnostic reagents. The E165R protein, which is highly expressed in the early stages of ASFV infection, can serve as an important indicator for early detection. In this study, we successfully obtained high purity soluble prokaryotic expression of the E165R protein. We then utilized the purified recombinant E165R protein for immunization in mice to prepare monoclonal antibodies (mAbs) using the hybridoma fusion technique. After three subclonal screens, we successfully obtained three mAbs against ASFV E165R protein in cells named 1B7, 1B8, and 10B8. Through immunofluorescence assay (IFA) and Western blot, we confirmed that the prepared mAbs specifically recognize the baculovirus-expressed E165R protein. By using overlapping truncated E165R protein and overlapping peptide scanning analysis, we tentatively identified two novel linear B cell epitopes (13EAEAYYPPSV22 and 55VACEHMGKKC64) that are highly conserved in genotype I and genotype II of ASFV. Thus, as a detection antibody, it has the capability to detect ASFV across a wide range of genotypes, providing valuable information for the development of related immunodiagnostic reagents.

Comprehensive Characterization of the Genetic Landscape of African Swine Fever Virus: Insights into Infection Dynamics, Immunomodulation, Virulence and Genes with Unknown Function

African Swine Fever (ASF) is a lethal contagious hemorrhagic viral disease affecting the swine population. The causative agent is African Swine Fever Virus (ASFV). There is no treatment or commercial vaccine available at present. This virus poses a significant threat to the global swine industry and economy, with 100% mortality rate in acute cases. ASFV transmission occurs through both direct and indirect contact, with control measures limited to early detection, isolation, and culling of infected pigs. ASFV exhibits a complex genomic structure and encodes for more than 50 structural and 100 non-structural proteins and has 150 to 167 open reading frames (ORFs). While many of the proteins are non-essential for viral replication, they play crucial roles in mediating with the host to ensure longevity and transmission of virus in the host. The dynamic nature of ASFV research necessitates constant updates, with ongoing exploration of various genes and their functions, vaccine development, and other ASF-related domains. This comprehensive review aims to elucidate the structural and functional roles of both newly discovered and previously recorded genes involved in distinct stages of ASFV infection and immunomodulation. Additionally, the review discusses the virulence genes and genes with unknown functions, and proposes future interventions.

A genome-wide CRISPR/Cas9 knockout screen identifies TMEM239 as an important host factor in facilitating African swine fever virus entry into early endosomes

African swine fever (ASF) is a highly contagious, fatal disease of pigs caused by African swine fever virus (ASFV). The complexity of ASFV and our limited understanding of its interactions with the host have constrained the development of ASFV vaccines and antiviral strategies. To identify host factors required for ASFV replication, we developed a genome-wide CRISPR knockout (GeCKO) screen that contains 186,510 specific single guide RNAs (sgRNAs) targeting 20,580 pig genes and used genotype II ASFV to perform the GeCKO screen in wild boar lung (WSL) cells. We found that knockout of transmembrane protein 239 (TMEM239) significantly reduced ASFV replication. Further studies showed that TMEM239 interacted with the early endosomal marker Rab5A, and that TMEM239 deletion affected the co-localization of viral capsid p72 and Rab5A shortly after viral infection. An ex vivo study showed that ASFV replication was significantly reduced in TMEM239-/- peripheral blood mononuclear cells from TMEM239 knockout piglets. Our study identifies a novel host factor required for ASFV replication by facilitating ASFV entry into early endosomes and provides insights for the development of ASF-resistant breeding.

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.

CA-CAS-01-A: A Permissive Cell Line for Isolation and Live Attenuated Vaccine Development Against African Swine Fever Virus

African swine fever virus (ASFV) is the causative agent of the highly lethal African swine fever disease that affects domestic pigs and wild boars. In spite of the rapid spread of the virus worldwide, there is no licensed vaccine available. The lack of a suitable cell line for ASFV propagation hinders the development of a safe and effective vaccine. For ASFV propagation, primary swine macrophages and monocytes have been widely studied. However, obtaining these cells can be time-consuming and expensive, making them unsuitable for mass vaccine production. The goal of this study was to validate the suitability of novel CA-CAS-01-A (CAS-01) cells, which was identified as a highly permissive cell clone for ASFV replication in the MA-104 parental cell line for live attenuated vaccine development. Through a screening experiment, maximum ASFV replication was observed in the CAS-01 cell compared to other sub-clones of MA-104 with 14.89 and log10 7.5 ± 0.15 Ct value and TCID50/ml value respectively. When CAS-01 cells are inoculated with ASFV, replication of ASFV was confirmed by Ct value for ASFV DNA, HAD50/ml assay, TCID50/ml assay, and cytopathic effects and hemadsoption were observed similar to those in primary porcine alveolar macrophages after 5th passage. Additionally, we demonstrated stable replication and adaptation of ASFV over the serial passage. These results suggest that CAS-01 cells will be a valuable and promising cell line for ASFV isolation, replication, and development of live attenuated vaccines.

Insights into the function of ESCRT complex and LBPA in ASFV infection

The African swine fever virus (ASFV) is strongly dependent on an intact endocytic pathway and a certain cellular membrane remodeling for infection, possibly regulated by the endosomal sorting complexes required for transport (ESCRT). The ESCRT machinery is mainly involved in the coordination of membrane dynamics; hence, several viruses exploit this complex and its accessory proteins VPS4 and ALIX for their own benefit. In this work, we found that shRNA-mediated knockdown of VPS4A decreased ASFV replication and viral titers, and this silencing resulted in an enhanced expression of ESCRT-0 component HRS. ASFV infection slightly increased HRS expression but not under VPS4A depletion conditions. Interestingly, VPS4A silencing did not have an impact on ALIX expression, which was significantly overexpressed upon ASFV infection. Further analysis revealed that ALIX silencing impaired ASFV infection at late stages of the viral cycle, including replication and viral production. In addition to ESCRT, the accessory protein ALIX is involved in endosomal membrane dynamics in a lysobisphosphatydic acid (LBPA) and Ca2+-dependent manner, which is relevant for intraluminal vesicle (ILV) biogenesis and endosomal homeostasis. Moreover, LBPA interacts with NPC2 and/or ALIX to regulate cellular cholesterol traffic, and would affect ASFV infection. Thus, we show that LBPA blocking impacted ASFV infection at both early and late infection, suggesting a function for this unconventional phospholipid in the ASFV viral cycle. Here, we found for the first time that silencing of VPS4A and ALIX affects the infection later on, and blocking LBPA function reduces ASFV infectivity at early and later stages of the viral cycle, while ALIX was overexpressed upon infection. These data suggested the relevance of ESCRT-related proteins in ASFV infection.

Host immune responses against African swine fever virus: Insights and challenges for vaccine development

The African swine fever virus (ASFV) poses a serious threat to global swine populations, underscoring the urgent need for effective preventive strategies. This comprehensive review investigates the intricate interplay between innate, cellular, and humoral immunity against ASFV, with a focus on their relevance to vaccine development. By delving into immunopathogenesis and immunological challenges, this review article aims to provide a holistic perspective on the complexities of ASFV infections and immune evasion. Key findings underscore the critical role of innate immune recognition in shaping subsequent adaptive immune defenses, potential protective antigens, and the multifaceted nature of ASFV-specific antibodies and cytotoxic T-cell responses. Despite advancements, the unique attributes of ASFV present hurdles in the development of a successful vaccine. In conclusion, this review examines the current state of ASFV immune responses and offers insights into future research directions, fostering the development of effective interventions against this devastating pathogen.

Stability of African swine fever virus genome under different environmental conditions

Background and Aim

African swine fever (ASF), a globally transmitted viral disease caused by ASF virus (ASFV), can severely damage the global trade economy. Laboratory diagnostic methods, including pathogen and serological detection techniques, are currently used to monitor and control ASF. Because the large double-stranded DNA genome of the mature virus particle is wrapped in a membrane, the stability of ASFV and its genome is maintained in most natural environments. This study aimed to investigate the stability of ASFV under different environmental conditions from both genomic and antibody perspectives, and to provide a theoretical basis for the prevention and elimination of ASFV.

Materials and Methods

In this study, we used quantitative real-time polymerase chain reaction for pathogen assays and enzyme-linked immunosorbent assay for serological assays to examine the stability of the ASFV genome and antibody, respectively, under different environmental conditions.

Results

The stability of the ASFV genome and antibody under high-temperature conditions depended on the treatment time. In the pH test, the ASFV genome and antibody remained stable in both acidic and alkaline environments. Disinfection tests revealed that the ASFV genome and antibody were susceptible to standard disinfection methods.

Conclusion

Collectively, the results demonstrated that the ASFV genome is highly stable in favorable environments but are also susceptible to standard disinfection methods. This study focuses on the stability of the ASFV genome under different conditions and provides various standard disinfection methods for the prevention and control of ASF.

Molecular breeding of livestock for disease resistance

Animal infectious diseases pose a significant threat to the global agriculture and biomedicine industries, leading to significant economic losses and public health risks. The emergence and spread of viral infections such as African swine fever virus (ASFV), porcine reproductive and respiratory syndrome virus (PRRSV), porcine epidemic diarrhea virus (PEDV), and avian influenza virus (AIV) have highlighted the need for innovative approaches to develop resilient and disease-resistant animal populations. Gene editing technologies, such as CRISPR/Cas9, offer a promising avenue for generating animals with enhanced disease resistance. This review summarizes recent advances in molecular breeding strategies for generating disease-resistant animals, focusing on the development of disease-resistant livestock. We also highlight the potential applications of genome-wide CRISPR/Cas9 library screening and base editors in producing precise gene modified livestock for disease resistance in the future. Overall, gene editing technologies have the potential to revolutionize animal breeding and improve animal health and welfare.

The pattern of stability of African swine fever virus in leeches

African swine fever virus (ASFV) can accumulate and survive in leeches for a long time. The reasons for the survival of ASFV in leeches are not entirely clear. Here, we elucidate the virus survival pathway in infected leeches. One of the questions reported previously is addressed in this article. How the virus concentration in the body of the leech is equal to or higher than in the water infected with ASFV? Examination of blood swallowed by leeches reveals that the blood cells retain their morphological characteristics for several weeks. It can explain the long-term persistence of the high levels of ASFV in the leeches that ingested ASFV-infected pig blood. qRT-PCR assay showed the transcription of ASFV genes in infected leeches. However, the infectious particles of the virus measured by HADU haven't increased. Quantitative studies of the ASFV revealed a high content of both viral genes and infectious particles in the skin of leeches compared with other body parts. Electron microscopy analysis revealed the ability of the ASFV to effectively bind to the skin surface of the leeches, which explained the high concentrations of ASFV in the leeches' skin. A significant difference in the transcriptional activity between early and late viral genes indicates that the virus entered the initial stage of replication, but for some reason failed to complete it, which is typical of abortive infections.

Coreceptor AXL Facilitates African Swine Fever Virus Entry via Apoptotic Mimicry

African swine fever (ASF) is an acute and hemorrhagic infectious disease caused by African swine fever virus (ASFV), which is listed as an animal epidemic disease that must be reported by The World Organization for Animal Health and that causes serious economic losses to China and even the whole world. Currently, the entry mechanism of ASFV is not fully understood. Especially in the early stages of virus entry, the host factors required for ASFV entry have not yet been identified and characterized. In this study, we demonstrated that ASFV externalized phosphatidylserine (PS) on the envelope functioned as viral apoptotic mimicry, which interacts with AXL, a tyrosine kinase receptor, to mediate ASFV entry into porcine alveolar macrophages (PAMs). We found that AXL was the most pronounced phosphatidylserine receptor (PSR) affecting ASFV entry in PAMs by RNA interference screening. Knockout AXL gene expression remarkably decreased ASFV internalization and replication in MA104 cells. Furthermore, the antibody against AXL extracellular domains effectively inhibited the ASFV entry. Consistent with these results, the deletion of the intracellular kinase domain of AXL and the treatment of the AXL inhibitor, R428, significantly inhibited the internalization of ASFV. Mechanistically, AXL facilitated the internalization of ASFV virions via macropinocytosis. Collectively, we provide evidence that AXL is a coreceptor for ASFV entry into PAMs, which expands our knowledge of ASFV entry and provides a theoretical basis for identifying new antiviral targets. IMPORTANCE African swine fever (ASF) is a highly contagious infectious disease caused by the ASF virus (ASFV), with a mortality rate of up to 100%. ASFV has caused huge economic losses to pig farming worldwide. Specific cellular surface receptors are considered crucial determinants of ASFV tropism. However, the host factors required for ASFV entry have not yet been identified, and the molecular mechanism of its entry remains unclear. Here, we found that ASFV utilized phosphatidylserine (PS) on the surface of virions to masquerade as apoptotic mimicry and facilitated virus entry by interacting with host factor AXL. We found that knockout of AXL remarkably decreased ASFV internalization and replication. The antibody against AXL extracellular domains and AXL inhibitor R428 significantly inhibited the internalization of ASFV via macropinocytosis. The current work deepens our understanding of ASFV entry and provides clues for the development of antiviral drugs to control ASFV infection.

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

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

Human SCARB2 Acts as a Cellular Associator for Helping Coxsackieviruses A10 Infection

Coxsackievirus A10 (CVA10) causes hand, foot, and mouth disease (HFMD) and herpangina, which can result in severe neurological symptoms in children. CVA10 does not use the common enterovirus 71 (EV71) receptor, human SCARB2 (hSCARB2, scavenger receptor class B, member 2), for infection but instead uses another receptor, such as KREMEN1. Our research has shown that CVA10 can infect and replicate in mouse cells expressing human SCARB2 (3T3-SCARB2) but not in the parental NIH3T3 cells, which do not express hSCARB2 for CVA10 entry. Knocking down endogenous hSCARB2 and KREMEN1 with specific siRNAs inhibited CVA10 infection in human cells. Co-immunoprecipitation confirmed that VP1, a main capsid protein where virus receptors for attaching to the host cells, could physically interact with hSCARB2 and KREMEN1 during CVA10 infection. It is the efficient virus replication following virus attachment to its cellular receptor. It resulted in severe limb paralysis and a high mortality rate in 12-day-old transgenic mice challenged with CVA10 but not in wild-type mice of the same age. Massive amounts of CVA10 accumulated in the muscles, spinal cords, and brains of the transgenic mice. Formalin inactivated CVA10 vaccine-induced protective immunity against lethal CVA10 challenge and reduced the severity of disease and tissue viral loads. This is the first report to show that hSCARB2 serves as an associate to aid CVA10 infection. hSCARB2-transgenic mice could be useful in evaluating anti-CVA10 medications and studying the pathogenesis induced by CVA10.

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.

Nucleotide and codon usage biases involved in the evolution of African swine fever virus: A comparative genomics analysis

Since African swine fever virus (ASFV) replication is closely related to its host's machinery, codon usage of viral genome can be subject to selection pressures. A better understanding of codon usage can give new insights into viral evolution. We implemented information entropy and revealed that the nucleotide usage pattern of ASFV is significantly associated with viral isolation factors (region and time), especially the usages of thymine and cytosine. Despite the domination of adenine and thymine in the viral genome, we found that mutation pressure alters the overall codon usage pattern of ASFV, followed by selective forces from natural selection. Moreover, the nucleotide skew index at the gene level indicates that nucleotide usages influencing synonymous codon bias of ASFV are significantly correlated with viral protein hydropathy. Finally, evolutionary plasticity is proved to contribute to the weakness in synonymous codons with A- or T-end serving as optimal codons of ASFV, suggesting that fine-tuning translation selection plays a role in synonymous codon usages of ASFV for adapting host. Taken together, ASFV is subject to evolutionary dynamics on nucleotide selections and synonymous codon usage, and our detailed analysis offers deeper insights into the genetic characteristics of this newly emerging virus around the world.

Seneca Valley Virus Enters PK-15 Cells via Caveolae-Mediated Endocytosis and Macropinocytosis Dependent on Low-pH, Dynamin, Rab5, and Rab7

Seneca Valley virus (SVV), a new pathogen resulting in porcine vesicular disease, is prevalent in pig herds worldwide. Although an understanding of SVV biology pathogenesis is crucial for preventing and controlling this disease, the molecular mechanisms for the entry and post-internalization of SVV, which represent crucial steps in viral infection, are not well characterized. In this study, specific inhibitors, Western blotting, and immunofluorescence detection revealed that SVV entry into PK-15 cells depends on low-pH conditions and dynamin. Furthermore, results showed that caveolae-mediated endocytosis (CavME) contributes crucially to the internalization of SVV, as evidenced by cholesterol depletion, downregulation of caveolin-1 expression by small interfering RNA knockdown, and overexpression of a caveolin-1 dominant negative (caveolin-1-DN) in SVV-infected PK-15 cells. However, SVV entry into PK-15 cells did not depend on clathrin-mediated endocytosis (CME). Furthermore, treatment with specific inhibitors demonstrated that SVV entry into PK-15 cells via macropinocytosis depended on the Na+/H+ exchanger (NHE), p21-activated kinase 1 (Pak1), and actin rearrangement, but not phosphatidylinositol 3-kinase (PI3K). Electron microscopy showed that SVV particles or proteins were localized in CavME and macropinocytosis. Finally, knockdown of GTPase Rab5 and Rab7 by siRNA significantly inhibited SVV replication, as determined by measuring viral genome copy numbers, viral protein expression, and viral titers. In this study, our results demonstrated that SVV utilizes caveolae-mediated endocytosis and macropinocytosis to enter PK-15 cells, dependent on low pH, dynamin, Rab5, and Rab7. IMPORTANCE Entry of virus into cells represents the initiation of a successful infection. As an emerging pathogen of porcine vesicular disease, clarification of the process of SVV entry into cells enables us to better understand the viral life cycle and pathogenesis. In this study, patterns of SVV internalization and key factors required were explored. We demonstrated for the first time that SVV entry into PK-15 cells via caveolae-mediated endocytosis and macropinocytosis requires Rab5 and Rab7 and is independent of clathrin-mediated endocytosis, and that low-pH conditions and dynamin are involved in the process of SVV internalization. This information increases our understanding of the patterns in which all members of the family Picornaviridae enter host cells, and provides new insights for preventing and controlling SVV infection.

Modulation of Host Antiviral Innate Immunity by African Swine Fever Virus: A Review

African swine fever (ASF), caused by African swine fever virus (ASFV), is a highly contagious and fatal disease found in swine. However, the viral proteins and mechanisms responsible for immune evasion are poorly understood, which has severely hindered the development of vaccines. This review mainly focuses on studies involving the innate antiviral immune response of the host and summarizes the latest studies on ASFV genes involved in interferon (IFN) signaling and inflammatory responses. We analyzed the effects of candidate viral proteins on ASFV infection, replication and pathogenicity and identified potential molecular targets for novel ASFV vaccines. These efforts will contribute to the construction of novel vaccines and wonder therapeutics for ASF.

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.

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.

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.

COVID-19 2022 update: transition of the pandemic to the endemic phase

COVID-19, which is caused by the SARS-CoV-2, has ravaged the world for the past 2 years. Here, we review the current state of research into the disease with focus on its history, human genetics and genomics and the transition from the pandemic to the endemic phase. We are particularly concerned by the lack of solid information from the initial phases of the pandemic that highlighted the necessity for better preparation to face similar future threats. On the other hand, we are gratified by the progress into human genetic susceptibility investigations and we believe now is the time to explore the transition from the pandemic to the endemic phase. The latter will require worldwide vigilance and cooperation, especially in emerging countries. In the transition to the endemic phase, vaccination rates have lagged and developed countries should assist, as warranted, in bolstering vaccination rates worldwide. We also discuss the current status of vaccines and the outlook for COVID-19.

High mobility group protein B1 decreases surface localization of PD-1 to augment T-cell activation

High-mobility group protein B1 (HMGB1) is a danger signaling molecule that has been found to trigger an effective antitumor immune response. However, the mechanisms underlying its antitumor effects are not fully understood. Here, we found that HMGB1 release induced by chemotherapy in patients with non-small cell lung cancer (NSCLC) was negatively correlated with PD-1 expression on CD8+ T cells. In vitro analysis indicated that treatment with HMGB1 led to a significant decrease in the level of expression of PD-1 on CD8+ T cells. Further analysis demonstrated that HMGB1 reduced PD-1 expression by inducing dynamin-mediated internalization of the protein, leading to early endocytosis in the cytoplasm, and subsequently degradation in the lysosomes. In a xenograft model, HER2-targeted chimeric-antigen receptor (CAR) T cells had enhanced function in the presence of HMGB1. These data identify a role for HMGB1 as a negative regulator of PD-1 signaling in lung cancer cells and the observed antitumor effect of HMGB1 on chimeric-antigen receptor (CAR) T cells may provide a theoretical foundation for a new immunotherapy combination.

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.

Immune Escape Mechanism and Vaccine Research Progress of African Swine Fever Virus

African swine fever virus (ASFV) is the causative agent of the epidemic of African swine fever (ASF), with virulent strains having a mortality rate of up to 100% and presenting devastating impacts on animal farming. Since ASF was first reported in China in 2018, ASFV still exists and poses a potential threat to the current pig industry. Low-virulence and genotype I strains of ASFV have been reported in China, and the prevention and control of ASF is more complicated. Insufficient understanding of the interaction of ASFV with the host immune system hinders vaccine development. Physical barriers, nonspecific immune response and acquired immunity are the three barriers of the host against infection. To escape the innate immune response, ASFV invades monocytes/macrophages and dendritic cells, thereby inhibiting IFN expression, regulating cytokine expression and the body’s inflammatory response process. Meanwhile, in order to evade the adaptive immune response, ASFV inhibits antigen presentation, induces the production of non-neutralizing antibodies, and inhibits apoptosis. Recently, significant advances have been achieved in vaccine development around the world. Live attenuated vaccines (LAVs) based on artificially deleting specific virulence genes can achieve 100% homologous protection and partial heterologous protection. The key of subunit vaccines is identifying the combination of antigens that can effectively provide protection and selecting carriers that can effectively deliver the antigens. In this review, we introduce the epidemic trend of ASF and the impact on the pig industry, analyze the interaction mechanism between ASFV and the body’s immune system, and compare the current status of potential vaccines in order to provide a reference for the development of effective ASF vaccines.

Modulation of Macrophage Polarization by Viruses: Turning Off/On Host Antiviral Responses

Macrophages are professional antigen-presenting cells and serve as the first line of defense against invading pathogens. Macrophages are polarized toward the proinflammatory classical (M1) or anti-inflammatory alternative (M2) phenotype upon viral infections. M1-polarized macrophages exert critical roles in antiviral responses via different mechanisms. Within the long competitive history between viruses and hosts, viruses have evolved various immune evasion strategies, inhibiting macrophage acquisition of an antiviral phenotype, impairing the antiviral responses of activated macrophages, and/or exploiting macrophage phenotypes for efficient replication. This review focuses on the sophisticated regulation of macrophage polarization utilized by viruses and is expected to provide systematic insights into the regulatory mechanisms of macrophage polarization by viruses and further facilitate the design of therapeutic targets for antivirals.

Lateral Flow Assay for the Detection of African Swine Fever Virus Antibodies Using Gold Nanoparticle-Labeled Acid-Treated p72

African swine fever is a widespread and highly contagious disease in the porcine population, which is caused by African swine fever virus (ASFV). The PCR and ELISA detection methods are the main conventional diagnostic methods for ASFV antigen/antibody detection in the field. However, these methods have limitations of expensive equipment, trained technicians, and time-consuming results. Thus, a rapid, inexpensive, accurate and on-site detection method is urgently needed. Here we describe a double-antigen-sandwich lateral-flow assay based on gold nanoparticle-conjugated ASFV major capsid protein p72, which can detect ASFV antibody in serum samples with high sensitivity and specificity in 10 min and the results can be determined by naked eyes. A lateral flow assay was established by using yeast-expressed and acid-treated ASFV p72 conjugated with gold nanoparticles, which are synthesized by seeding method. A high coincidence (97.8%) of the assay was determined using clinical serum compared to a commercial ELISA kit. In addition, our lateral flow strip can detect as far as 1:10,000 diluted clinically positive serum for demonstration of high sensitivity. In summary, the assay developed here was shown to be rapid, inexpensive, accurate and highly selective. It represents a reliable method for on-site ASFV antibody detection and may help to control the ASFV pandemic.

Spatiotemporally Orchestrated Interactions between Viral and Cellular Proteins Involved in the Entry of African Swine Fever Virus

African swine fever (ASF) is a highly contagious hemorrhagic disease in domestic pigs and wild boars with a mortality of up to 100%. The causative agent, African swine fever virus (ASFV), is a member of the Asfarviridae family of the nucleocytoplasmic large DNA viruses. The genome size of ASFV ranges from 170 to 194 kb, encoding more than 50 structural and 100 nonstructural proteins. ASFV virions are 260–300 nm in diameter and composed of complex multilayered structures, leading to an intricate internalization pathway to enter host cells. Currently, no commercial vaccines or antivirals are available, due to the insufficient knowledge of the viral receptor(s), the molecular events of ASFV entry into host cells, and the functions of virulence-associated genes. During the early stage of ASFV infection, the fundamental aspects of virus-host interactions, including virus internalization, intracellular transport through the endolysosomal system, and membrane fusion with endosome, are precisely regulated and orchestrated via a series of molecular events. In this review, we summarize the currently available knowledge on the pathways of ASFV entry into host cells and the functions of viral proteins involved in virus entry. Furthermore, we conclude with future perspectives and highlight areas that require further investigation. This review is expected to provide unique insights for further understanding ASFV entry and facilitate the development of vaccines and antivirals.

Endocytosis of abiotic nanomaterials and nanobiovectors: Inhibition of membrane trafficking

Humans are exposed to nanoscopical nanobiovectors (e.g. coronavirus SARS-CoV-2) as well as abiotic metal/carbon-based nanomaterials that enter cells serendipitously or intentionally. Understanding the interactions of cell membranes with these abiotic and biotic nanostructures will facilitate scientists to design better functional nanomaterials for biomedical applications. Such knowledge will also provide important clues for the control of viral infections and the treatment of virus-induced infectious diseases. In the present review, the mechanisms of endocytosis are reviewed in the context of how nanomaterials are uptaken into cells. This is followed by a detailed discussion of the attributes of man-made nanomaterials (e.g. size, shape, surface functional groups and elasticity) that affect endocytosis, as well as the different human cell types that participate in the endocytosis of nanomaterials. Readers are then introduced to the concept of viruses as nature-derived nanoparticles. The mechanisms in which different classes of viruses interact with various cell types to gain entry into the human body are reviewed with examples published over the last five years. These basic tenets will enable the avid reader to design advanced drug delivery and gene transfer nanoplatforms that harness the knowledge acquired from endocytosis to improve their biomedical efficacy. The review winds up with a discussion on the hurdles to be addressed in mimicking the natural mechanisms of endocytosis in nanomaterials design.

Porcine deltacoronavirus enters porcine IPI-2I intestinal epithelial cells via macropinocytosis and clathrin-mediated endocytosis dependent on pH and dynamin

Porcine deltacoronavirus (PDCoV), an emerging enteropathogenic coronavirus, causes serious diarrhoea in suckling piglets and has the potential for cross-species transmission. Although extensive studies have been reported on the biology and pathogenesis of PDCoV, the mechanisms by which PDCoV enters cells are not well characterized. In this study, we investigated how PDCoV enters IPI-2I cells, a line of porcine intestinal epithelial cells derived from pig ileum. Immunofluorescence assays, siRNA interference, specific pharmacological inhibitors and dominant-negative mutation results revealed that PDCoV entry into IPI-2I cells depended on clathrin, dynamin and a low-pH environment, but was independent of caveolae. Specific inhibition of phosphatidylinositol 3-kinase (PI3K) and the Na⁺/H⁺ exchanger (NHE) revealed that PDCoV entry involves macropinocytosis and depends on NHE rather than on PI3K. Additionally, Rab5 and Rab7, but not Rab11, regulated PDCoV endocytosis. This is the first study to demonstrate that PDCoV uses clathrin-mediated endocytosis and macropinocytosis as alternative endocytic pathways to enter porcine intestinal epithelial cells. We also discussed the entry pathways of PDCoV into other porcine cell lines. Our findings reveal the entry mechanisms of PDCoV and provide new insight into the PDCoV life cycle. IMPORTANCE An emerging enteropathogenic coronavirus, PDCoV has the potential for cross-species transmission, attracting extensive attenuation. Characterizing the detailed process of PDCoV entry into cells will deepen our understanding of the viral infection and pathogenesis, and provide the clues for therapeutic intervention against PDCoV. With the objective, we used complementary approaches to dissect the process in PDCoV-infected IPI-2I cells, a line of more physiologically relevant intestinal epithelial cells to PDCoV infection in vivo. Here, we demonstrate that PDCoV enters IPI-2I cells via macropinocytosis that does not require a specific receptor and clathrin-mediated endocytosis that requires a low-pH environment and dynamin, while a caveola-mediated endocytic pathway is used by PDCoV to enter swine testicular (ST) cells and porcine kidney (LLC-PK1) cells. These findings provide a molecular detail of the cellular entry pathways of PDCoV and may direct us toward novel antiviral drug development.

Structure of African Swine Fever Virus and Associated Molecular Mechanisms Underlying Infection and Immunosuppression: A Review

African swine fever (ASF) is an acute, highly contagious, and deadly infectious disease. The mortality rate of the most acute and acute ASF infection is almost 100%. The World Organization for Animal Health [Office International des épizooties (OIE)] lists it as a legally reported animal disease and China lists it as class I animal epidemic. Since the first diagnosed ASF case in China on August 3, 2018, it has caused huge economic losses to animal husbandry. ASF is caused by the African swine fever virus (ASFV), which is the only member of Asfarviridae family. ASFV is and the only insect-borne DNA virus belonging to the Nucleocytoplasmic Large DNA Viruses (NCLDV) family with an icosahedral structure and an envelope. Till date, there are still no effective vaccines or antiviral drugs for the prevention or treatment of ASF. The complex viral genome and its sophisticated ability to regulate the host immune response may be the reason for the difficulty in developing an effective vaccine. This review summarizes the recent findings on ASFV structure, the molecular mechanism of ASFV infection and immunosuppression, and ASFV-encoded proteins to provide comprehensive proteomic information for basic research on ASFV. In addition, it also analyzes the results of previous studies and speculations on the molecular mechanism of ASFV infection, which aids the study of the mechanism of clinical pathological phenomena, and provides a possible direction for an intensive study of ASFV infection mechanism. By summarizing the findings on molecular mechanism of ASFV- regulated host cell immune response, this review provides orientations and ideas for fundamental research on ASFV and provides a theoretical basis for the development of protective vaccines against ASFV.

Recent insights into anti-WSSV immunity in crayfish

White spot syndrome virus (WSSV) is currently the most severely viral pathogen for farmed crustaceans such as shrimp and crayfish, which has been causing huge economic losses for crustaceans farming worldwide every year. Unfortunately, study on the molecular mechanisms of WSSV has been restricted by the lack of crustacean cell lines for WSSV propagation as well as the incompletely annotated genomes for host species, resulting in limited elucidation for WSSV pathogenesis at present. In addition to the findings of anti-WSSV response in shrimp, some of novel cellular events involved in WSSV infection have been recently revealed in crayfish, including endocytosis and intracellular transport of WSSV, innate immune pathways in response to WSSV infection, and regulation of viral gene expression by host genes. Despite these advances, many fundamental gaps in WSSV pathogenesis are still remaining, for example, how WSSV genome enters into nucleus and how the progeny virions are fully assembled in the host cell nucleus. In this review, recent findings in WSSV infection mechanism and the antiviral immunity against WSSV in crayfish are summarized and discussed, which may provide us a better understanding of the WSSV pathogenesis as well as new ideas for the target design of antiviral drugs against WSSV in crustaceans farming.

A novel function of African Swine Fever Virus pE66L in inhibition of host translation by the PKR/eIF2α pathway

African swine fever virus (ASFV) is one of the most contagious and lethal viruses infecting pigs. This virus is endemic in many countries and has very recently spread to China, but no licensed vaccines or treatments are currently available. Despite extensive research, the basic question of how ASFV-encoded proteins inhibit host translation remains. Here, we examined how ASFV interfered with host translation and optimized viral gene expression. We found that 14 ASFV proteins inhibited Renilla luciferase (Rluc) activity greater than 5-fold, and the protein with the strongest inhibitory effect was pE66L, which was not previously reported. Combined with bioinformatical analysis and biochemical experiment, we determined that the transmembrane (TM) domain (amino acids 13-34) of pE66L was required for the inhibition of host gene expression. Notably, we constructed a recombinant plasmid with the TM domain linked to enhanced green fluorescent protein (EGFP) and further demonstrated that this domain broadly inhibited protein synthesis. Confocal and biochemical analyses indicated that the TM domain might help proteins locate to the endoplasmic reticulum (ER) to suppress translation though the PKR/eIF2α pathway. Deletion of the E66L gene had little effect on virus replication in macrophages, but significantly recovered host gene expression. Taken together, our findings complement studies on the host translation of ASFV proteins and suggest that ASFV pE66L induces host translation shutoff, which is dependent on activation of the PKR/eIF2α pathway.Importance African swine fever virus (ASFV) is a member of the nucleocytoplasmic large DNA virus superfamily that predominantly replicates in the cytoplasm of infected cells. The ASFV double-stranded DNA genome varies in length from approximately 170 to 193 kbp depending on the isolate and contains between 150 and 167 open reading frames (ORFs), of which half the encoded proteins have not been explored. Our study showed that 14 proteins had an obvious inhibitory effect on Renilla luciferase (Rluc) gene synthesis, with pE66L showing the most significant effect. Furthermore, the transmembrane (TM) domain of pE66L broadly inhibited host protein synthesis in a PKR/eIF2a pathway-dependent manner. Loss of pE66L during ASFV infection had little effect on virus replication, but significantly recovered host protein synthetic. Based on the above results, our findings expand our view of ASFV in determining the fate of host-pathogen interactions.

The recombinant pseudorabies virus expressing African swine fever virus CD2v protein is safe and effective in mice

Background

African swine fever (ASF) leads to high mortality in domestic pigs and wild boar and is caused by the African swine fever virus (ASFV). Currently, no vaccine is commercially available for prevention, and the epidemic is still spreading. Here, we constructed a recombinant pseudorabies virus (PRV) (PRV-ΔgE/ΔgI/ΔTK-(CD2v)) that expresses the CD2v protein of ASFV and evaluated its effectiveness and safety as a vaccine candidate in mice.

Methods

A homologous recombination fragment containing ASFV CD2v was synthesized and co-transfected into HEK 293 T cells, a knockout vector targeting the PRV TK gene. The transfected cells were infected with PRV-ΔgE/ΔgI, and the recombinant strain (PRV-ΔgE/ΔgI/ΔTK-(CD2v)) was obtained by plaque purification in Vero cells. The expression of ASFV CD2v in the recombinant virus was confirmed by sequencing, Western blotting, and immunofluorescence analysis, and the genetic stability was tested in Vero cells over 20 passages. The virulence, immunogenicity and protective ability of the recombinant virus were further tested in a mouse model.

Results

The PRV-ΔgE/ΔgI/ΔTK-(CD2v) recombinant strain is stable in Vero cells, and the processing of CD2v does not depend on ASFV infection. The vaccination of PRV-ΔgE/ΔgI/ΔTK-(CD2v) causes neither pruritus, not a systemic infection and inflammation (with the high expression of interleukin-6 (IL6)). Besides, the virus vaccination can produce anti-CD2v specific antibody and activate a specific cellular immune response, and 100% protect mice from the challenge of the virulent strain (PRV-Fa). The detoxification occurs much earlier upon the recombinant virus vaccination and the amount of detoxification is much lower as well.

Conclusions

The PRV-ΔgE/ΔgI/ΔTK-(CD2v) recombinant strain has strong immunogenicity, is safe and effective, and maybe a potential vaccine candidate for the prevention of ASF and Pseudorabies.

Identification of a Functional Small Noncoding RNA of African Swine Fever Virus

African swine fever virus (ASFV) causes a lethal hemorrhagic disease of domestic pigs, against which no vaccine is available. ASFV has a large, double-stranded DNA genome that encodes over 150 proteins. Replication takes place predominantly in the cytoplasm of the cell and involves complex interactions with host cellular components, including small noncoding RNAs (sncRNAs). A number of DNA viruses are known to manipulate sncRNA either by encoding their own or disrupting host sncRNA. To investigate the interplay between ASFV and sncRNAs, a study of host and viral small RNAs extracted from ASFV-infected primary porcine macrophages (PAMs) was undertaken. We discovered that ASFV infection had only a modest effect on host miRNAs, with only 6 miRNAs differentially expressed during infection. The data also revealed 3 potential novel small RNAs encoded by ASFV, ASFVsRNA1-3. Further investigation of ASFVsRNA2 detected it in lymphoid tissue from pigs with ASF. Overexpression of ASFVsRNA2 led to an up to 1-log reduction in ASFV growth, indicating that ASFV utilizes a virus-encoded small RNA to disrupt its own replication.IMPORTANCE African swine fever (ASF) poses a major threat to pig populations and food security worldwide. The disease is endemic to Africa and Eastern Europe and is rapidly emerging into Asia, where it has led to the deaths of millions of pigs in the last 12 months. The development of safe and effective vaccines to protect pigs against ASF has been hindered by lack of understanding of the complex interactions between ASFV and the host cell. We focused our work on characterizing the interactions between ASFV and sncRNAs. Although comparatively modest changes to host sncRNA abundances were observed upon ASFV infection, we discovered and characterized a novel functional ASFV-encoded sncRNA. The results from this study add important insights into ASFV host-pathogen interactions. This knowledge may be exploited to develop more effective ASFV vaccines that take advantage of the sncRNA system.

African swine fever: Etiology, epidemiological status in Korea, and perspective on control

African swine fever (ASF), caused by the ASF virus, a member of the Asfarviridae family, is one of the most important diseases in the swine industry due to its clinical and economic impacts. Since the first report of ASF a century ago, ample information has become available, but prevention and treatment measures are still inadequate. Two waves of epizootic outbreaks have occurred worldwide. While the first wave of the epizootic outbreak was controlled in most of the infected areas, the second wave is currently active in the European and Asian continents, causing severe economic losses to the pig industry. There are different patterns of spreading in the outbreaks between those in European and Asian countries. Prevention and control of ASF are very difficult due to the lack of available vaccines and effective therapeutic measures. However, recent outbreaks in South Korea have been successfully controlled on swine farms, although feral pigs are periodically being found to be positive for the ASF virus. Therefore, we would like to share our story regarding the preparation and application of control measures. The success in controlling ASF on farms in South Korea is largely due to the awareness and education of swine farmers and practitioners, the early detection of infected animals, the implementation of strict control policies by the government, and widespread sharing of information among stakeholders. Based on the experience gained from the outbreaks in South Korea, this review describes the current understanding of the ASF virus and its pathogenic mechanisms, epidemiology, and control.

Coronavirus Interplay With Lipid Rafts and Autophagy Unveils Promising Therapeutic Targets

Coronaviruses are enveloped, single-stranded, positive-sense RNA viruses that can infect animal and human hosts. The infection induces mild or sometimes severe acute respiratory diseases. Nowadays, the appearance of a new, highly pathogenic and lethal coronavirus variant, SARS-CoV-2, responsible for a pandemic (COVID-19), represents a global problem for human health. Unfortunately, only limited approaches are available to treat coronavirus infections and a vaccine against this new coronavirus variant is not yet available. The plasma membrane microdomain lipid rafts have been found by researchers to be involved in the replication cycle of numerous viruses, including coronaviruses. Indeed, some pathogen recognition receptors for coronaviruses as for other viruses cluster into lipid rafts, and it is therefore conceivable that the first contact between virus and host cells occurs into these specialized regions, representing a port of cell entry for viruses. Recent data highlighted the peculiar pro-viral or anti-viral role played by autophagy in the host immune responses to viral infections. Coronaviruses, like other viruses, were reported to be able to exploit the autophagic machinery to increase their replication or to inhibit the degradation of viral products. Agents known to disrupt lipid rafts, such as metil-β-cyclodextrins or statins, as well as autophagy inhibitor agents, were shown to have an anti-viral role. In this review, we briefly describe the involvement of lipid rafts and autophagy in coronavirus infection and replication. We also hint how lipid rafts and autophagy may represent a potential therapeutic target to be investigated for the treatment of coronavirus infections.

Toxoplasma gondii Mechanisms of Entry Into Host Cells

Toxoplasma gondii, the causative agent of toxoplasmosis, is an obligate intracellular protozoan parasite. Toxoplasma can invade and multiply inside any nucleated cell of a wide range of homeothermic hosts. The canonical process of internalization involves several steps: an initial recognition of the host cell surface and a sequential secretion of proteins from micronemes followed by rhoptries that assemble a macromolecular complex constituting a specialized and transient moving junction. The parasite is then internalized via an endocytic process with the establishment of a parasitophorous vacuole (PV), that does not fuse with lysosomes, where the parasites survive and multiply. This process of host cell invasion is usually referred to active penetration. Using different cell types and inhibitors of distinct endocytic pathways, we show that treatment of host cells with compounds that interfere with clathrin-mediated endocytosis (hypertonic sucrose medium, chlorpromazine hydrochloride, and pitstop 2 inhibited the internalization of tachyzoites). In addition, treatments that interfere with macropinocytosis, such as incubation with amiloride or IPA-3, increased parasite attachment to the host cell surface but significantly blocked parasite internalization. Immunofluorescence microscopy showed that markers of macropinocytosis, such as the Rab5 effector rabankyrin 5 and Pak1, are associated with parasite-containing cytoplasmic vacuoles. These results indicate that entrance of T. gondii into mammalian cells can take place both by the well-characterized interaction of parasite and host cell endocytic machinery and other processes, such as the clathrin-mediated endocytosis, and macropinocytosis.

Inhibition of African Swine Fever Virus Replication by Porcine Type I and Type II Interferons

Interferons (IFNs) are proteins produced by a variety of cells during the process of virus infection. It can activate the transcription of multiple functional genes in cells, regulate the synergistic effect of multiple signaling pathways, and mediate a variety of biological functions such as antiviral activity and immune regulation. The symptoms of hosts infected with African swine fever virus (ASFV) depend on the combined interaction between viruses and the host. However, it is unclear whether IFNs can be used as an emergency preventive treatment for ASFV. This study focused on the use of recombinant porcine IFNs, produced by Escherichia coli, to inhibit the replication of ASFV. The activity of IFN against ASFV was detected using primary alveolar macrophages at different doses through immunofluorescence assays and quantitative real-time PCR. We found that both 1000 and 100 U/mL doses significantly inhibited the replication of ASFV. Meanwhile, we found that IFNs could significantly trigger the production of a variety of IFN-induced genes (IFIT1, IFITM3, Mx-1, OASL, ISG15, PKR, GBP1, Viperin, BST2, IRF-1, and CXCL10) and MHC molecules, which play key roles in resistance to virus infection. Peripheral blood samples were also obtained from surviving pigs treated with IFNs, and the viral load was determined. Consistent with in vitro tests, low-dose (10⁵ U/kg) recombinant porcine IFNs (PoIFN-α and PoIFN-γ) significantly reduced viral load compared to that with high-dose (10⁶ U/kg) treatment. Our results suggest that recombinant porcine IFNs have high antiviral activity against ASFV, providing a new strategy for the prevention of African swine fever.

African Swine Fever Virus: An Emerging DNA Arbovirus

African swine fever virus (ASFV) is the sole member of the family Asfarviridae, and the only known DNA arbovirus. Since its identification in Kenya in 1921, ASFV has remained endemic in Africa, maintained in a sylvatic cycle between Ornithodoros soft ticks and warthogs (Phacochoerus africanus) which do not develop clinical disease with ASFV infection. However, ASFV causes a devastating and economically significant disease of domestic (Sus scrofa domesticus) and feral (Sus scrofa ferus) swine. There is no ASFV vaccine available, and current control measures consist of strict animal quarantine and culling procedures. The virus is highly stable and easily spreads by infected swine, contaminated pork products and fomites, or via transmission by the Ornithodoros vector. Competent Ornithodoros argasid soft tick vectors are known to exist not only in Africa, but also in parts of Europe and the Americas. Once ASFV is established in the argasid soft tick vector, eradication can be difficult due to the long lifespan of Ornithodoros ticks and their proclivity to inhabit the burrows of warthogs or pens and shelters of domestic pigs. Establishment of endemic ASFV infections in wild boar populations further complicates the control of ASF. Between the late 1950s and early 1980s, ASFV emerged in Europe, Russia and South America, but was mostly eradicated by the mid-1990s. In 2007, a highly virulent genotype II ASFV strain emerged in the Caucasus region and subsequently spread into the Russian Federation and Europe, where it has continued to circulate and spread. Most recently, ASFV emerged in China and has now spread to several neighboring countries in Southeast Asia. The high morbidity and mortality associated with ASFV, the lack of an efficacious vaccine, and the complex makeup of the ASFV virion and genome as well as its lifecycle, make this pathogen a serious threat to the global swine industry and national economies. Topics covered by this review include factors important for ASFV infection, replication, maintenance, and transmission, with attention to the role of the argasid tick vector and the sylvatic transmission cycle, current and future control strategies for ASF, and knowledge gaps regarding the virus itself, its vector and host species.

Crystal Structure of African Swine Fever Virus pS273R Protease and Implications for Inhibitor Design

African swine fever (ASF) is a highly contagious hemorrhagic viral disease of domestic and wild pigs that is responsible for serious economic and production losses. It is caused by the African swine fever virus (ASFV), a large and complex icosahedral DNA virus of the Asfarviridae family. Currently, there is no effective treatment or approved vaccine against the ASFV. pS273R, a specific SUMO-1 cysteine protease, catalyzes the maturation of the pp220 and pp62 polyprotein precursors into core-shell proteins. Here, we present the crystal structure of the ASFV pS273R protease at a resolution of 2.3 Å. The overall structure of the pS273R protease is represented by two domains named the "core domain" and the N-terminal "arm domain." The "arm domain" contains the residues from M1 to N83, and the "core domain" contains the residues from N84 to A273. A structure analysis reveals that the "core domain" shares a high degree of structural similarity with chlamydial deubiquitinating enzyme, sentrin-specific protease, and adenovirus protease, while the "arm domain" is unique to ASFV. Further, experiments indicated that the "arm domain" plays an important role in maintaining the enzyme activity of ASFV pS273R. Moreover, based on the structural information of pS273R, we designed and synthesized several peptidomimetic aldehyde compounds at a submolar 50% inhibitory concentration, which paves the way for the design of inhibitors to target this severe pathogen.IMPORTANCE African swine fever virus, a large and complex icosahedral DNA virus, causes a deadly infection in domestic pigs. In addition to Africa and Europe, countries in Asia, including China, Vietnam, and Mongolia, were negatively affected by the hazards posed by ASFV outbreaks in 2018 and 2019, at which time more than 30 million pigs were culled. Until now, there has been no vaccine for protection against ASFV infection or effective treatments to cure ASF. Here, we solved the high-resolution crystal structure of the ASFV pS273R protease. The pS273R protease has a two-domain structure that distinguishes it from other members of the SUMO protease family, while the unique "arm domain" has been proven to be essential for its hydrolytic activity. Moreover, the peptidomimetic aldehyde compounds designed to target the substrate binding pocket exert prominent inhibitory effects and can thus be used in a potential lead for anti-ASFV drug development.

An Update on African Swine Fever Virology

Animal diseases constitute a continuing threat to animal health, food safety, national economy, and the environment. Among those, African swine fever (ASF) is one of the most devastating viruses affecting pigs and wild suids due to the lack of vaccine or effective treatment. ASF is endemic in countries in sub-Saharan Africa, but since its introduction to the Caucasus region in 2007, a highly virulent strain of ASF virus (ASFV) has continued to circulate and spread into Eastern Europe and Russia, and most recently into Western Europe, China, and various countries of Southeast Asia. Given the importance of this disease, this review will highlight recent discoveries in basic virology with special focus on proteomic analysis, replication cycle, and some recent data on genes involved in cycle progression and viral–host interactions, such as I215L (E2 ubiquitin-conjugating enzyme), EP402R (CD2v), A104R (histone-like protein), QP509L, and Q706L (RNA helicases) or P1192R (Topoisomerase II). Taking into consideration the large DNA genome of ASFV and its complex interactions with the host, more studies and new approaches are to be taken to understand the basic virus–host interaction for ASFV. Proteomic studies are just paving the way for future research.