Phylodynamic analysis of foot-and-mouth disease virus evolution in Mar Chiquita, Argentina

Foot-and-mouth disease is a highly contagious disease affecting cloven-hoofed animals, resulting in considerable economic losses. Its causal agent is foot-and-mouth disease virus (FMDV), a picornavirus. Due to its error-prone replication and rapid evolution, the transmission and evolutionary dynamics of FMDV can be studied using genomic epidemiological approaches. To analyze FMDV evolution and identify possible transmission routes in an Argentinean region, field samples that tested positive for FMDV by PCR were obtained from 21 farms located in the Mar Chiquita district. Whole FMDV genome sequences were obtained by PCR amplification in seven fragments and sequencing using the Sanger technique. The genome sequences obtained from these samples were then analyzed using phylogenetic, phylogeographic, and evolutionary approaches. Three local transmission clusters were detected among the sampled viruses. The dataset was analyzed using Bayesian phylodynamic methods with appropriate coalescent and relaxed molecular clock models. The estimated mean viral evolutionary rate was 1.17 × 10- 2 substitutions/site/year. No significant differences in the rate of viral evolution were observed between farms with vaccinated animals and those with unvaccinated animals. The most recent common ancestor of the sampled sequences was dated to approximately one month before the first reported case in the outbreak. Virus transmission started in the south of the district and later dispersed to the west, and finally arrived in the east. Different transmission routes among the studied herds, such as non-replicating vectors and close contact contagion (i.e., aerosols), may be responsible for viral spread.

Calcium Chloride as a Novel Stabilizer for Foot-and-Mouth Disease Virus and Its Application in the Vaccine Formulation

The thermal stability of the in-house-developed foot-and-mouth disease (FMD) type O and A viruses was evaluated, and the O Jincheon virus was found to exhibit the lowest thermal stability. To overcome this instability, we proposed a novel stabilizer, calcium chloride. The thermal stability of FMDVs increased up to a CaCl2 concentration of 10 mM, and it had a decreasing trend at >30 mM. The O Jincheon virus showed a significant decrease in the amount of antigen over time at 4 °C. In contrast, the samples treated with CaCl2 showed stable preservation of the virus without significant antigen loss. After the CaCl2-formulated vaccine was administered twice to pigs, the virus neutralization titer reached approximately 1:1000, suggesting that the vaccine could protect pigs against the FMDV challenge. In summary, the O Jincheon virus is difficult to utilize as a vaccine given its low stability during storage after antigen production. However, following its treatment with CaCl2, it can be easily utilized as a vaccine. This study evaluated CaCl2 as a novel stabilizer in FMD vaccines and may contribute to the development of stable vaccine formulations, especially for inherently unstable FMDV strains.

Cell Culture Adaptive Amino Acid Substitutions in FMDV Structural Proteins: A Key Mechanism for Altered Receptor Tropism

The foot-and-mouth disease virus is a highly contagious and economically devastating virus of cloven-hooved animals, including cattle, buffalo, sheep, and goats, causing reduced animal productivity and posing international trade restrictions. For decades, chemically inactivated vaccines have been serving as the most effective strategy for the management of foot-and-mouth disease. Inactivated vaccines are commercially produced in cell culture systems, which require successful propagation and adaptation of field isolates, demanding a high cost and laborious time. Cell culture adaptation is chiefly indebted to amino acid substitutions in surface-exposed capsid proteins, altering the necessity of RGD-dependent receptors to heparan sulfate macromolecules for virus binding. Several amino acid substations in VP1, VP2, and VP3 capsid proteins of FMDV, both at structural and functional levels, have been characterized previously. This literature review combines frequently reported amino acid substitutions in virus capsid proteins, their critical roles in virus adaptation, and functional characterization of the substitutions. Furthermore, this data can facilitate molecular virologists to develop new vaccine strains against the foot-and-mouth disease virus, revolutionizing vaccinology via reverse genetic engineering and synthetic biology.

Enhanced antigen-specific CD8 T cells contribute to early protection against FMDV through swine DC vaccination

Foot-and-mouth disease virus (FMDV) remains a challenge for cloven-hooved animals. The currently licensed FMDV vaccines induce neutralizing antibody (NAb)-mediated protection but show defects in the early protection. Dendritic cell (DC) vaccines have shown great potency in inducing rapid T-cell immunity in humans and mice. Whether DC vaccination could enhance early protection against FMDV has not been elaborately explored in domestic pigs. In this study, we employed DC vaccination as an experimental approach to study the roles of cellular immunity in the early protection against FMDV in pigs. Autologous DCs were differentiated from the periphery blood mononuclear cells of each pig, pulsed with inactivated FMDV (iFMDV-DC) and treated with LPS, and then injected into the original pigs. The cellular immune responses and protective efficacy elicited by the iFMDV-DC were examined by multicolor flow cytometry and tested by FMDV challenge. The results showed that autologous iFMDV-DC immunization induced predominantly FMDV-specific IFN-γ-producing CD4+ T cells and cytotoxic CD8+ T cells (CTLs), high NAb titers, compared to the inactivated FMDV vaccine, and accelerated the development of memory CD4 and CD8 T cells, which was concomitantly associated with early protection against FMDV virulent strain in pigs. Such early protection was associated with the rapid proliferation of secondary T-cell response after challenge and significantly contributed by secondary CD8 effector memory T cells. These results demonstrated that rapid induction of cellular immunity through DC immunization is important for improving early protection against FMDV. Enhancing cytotoxic CD8+ T cells may facilitate the development of more effective FMDV vaccines.IMPORTANCEAlthough the currently licensed FMDV vaccines provide NAb-mediated protection, they have defects in early immune protection, especially in pigs. In this study, we demonstrated that autologous swine DC immunization augmented the cellular immune response and induced an early protective response against FMDV in pigs. This approach induced predominantly FMDV-specific IFN-γ-producing CD4+ T cells and cytotoxic CD8+ T cells, high NAb titers, and rapid development of memory CD4 and CD8 T cells. Importantly, the early protection conferred by this DC immunization is more associated with secondary CD8+ T response rather than NAbs. Our findings highlighted the importance of enhancing cytotoxic CD8+ T cells in early protection to FMDV in addition to Th1 response and identifying a strategy or adjuvant comparable to the DC vaccine might be a future direction for improving the current FMDV vaccines.

Development and efficacy evaluation of a novel water-in-oil-in-water adjuvant for an inactivated foot-and-mouth disease vaccine

To develop a novel water-in-oil-in-water (W/O/W) adjuvant and evaluate the effect on foot-and-mouth disease (FMD) inactivated vaccine, in this study, we prepared the novel nano-emulsion adjuvant based on QS-21 (BEA) which is composed of the mixture of mineral oil Marcol52, surfactant Tween80, oleate polyoxyethylene ether ester, polyoxyethylene palmitic acid ester and span80, cosurfactant polyethylene glycol and QS-21. The two-step emulsification method formed the W/O/W nano-emulsion with two films and three-phase structures. The effective particle diameter of the BEA was about 184 nm, and it has good thermal stability. Then, BEA was emulsified as an adjuvant to prepare for the inactivated FMDV vaccine, and BALB/c mice and pigs were immunized to evaluate its safety and immunization effect. The results showed that the inactivated BEA-FMDV vaccine significantly increased BALB/c mice and pigs' antibodies and cytokine IFN-γ in serum. Meanwhile, the pig-neutralizing antibodies were higher than control group. Safety tests found no symptoms of FMD or significant toxic reactions. After 28 days of immunization, the protection rate can reach 93.3%. The BEA vaccine had good stability at 4 °C, no stratification after 180 days, and the content of 146S in the vaccine did not decrease. In conclusion, the BEA prepared in this study is suitable for FMDV inactivated vaccine and is an effective adjuvant.

Molecular Epidemiology of Foot-and-Mouth Disease Viruses in the Emirate of Abu Dhabi, United Arab Emirates

Foot-and-mouth disease (FMD) is an endemic disease in the United Arab Emirates (UAE) in both wild and domestic animals. Despite this, no systematic FMD outbreak investigation accompanied by molecular characterisation of FMD viruses (FMDVs) in small ruminants or cattle has been performed, and only a single report that describes sequences for FMDVs in wildlife from the Emirate has been published. In this study, FMD outbreaks that occurred in 2021 in five animal farms and one animal market in the Emirate of Abu Dhabi were investigated. Cases involved sheep, goats, and cattle, as well as Arabian oryx (Oryx leucoryx). Twelve samples were positive for FMDV via RT-qPCR, and four samples (Arabian oryx n = 1, goat n = 2, and sheep n = 1) were successfully genotyped using VP1 nucleotide sequencing. These sequences shared 88~98% identity and were classified within the serotype O, Middle East-South Asia topotype (O/ME-SA). Phylogenetic analysis revealed that the Arabian oryx isolate (UAE/2/2021) belonged to the PanAsia-2 lineage, the ANT-10 sublineage, and was closely related to the FMDVs recently detected in neighbouring countries. The FMDV isolates from goats (UAE/10/2021 and UAE/11/2021) and from sheep (UAE/14/2021) formed a monophyletic cluster within the SA-2018 lineage that contained viruses from Bangladesh, India, and Sri Lanka. This is the first study describing the circulation of the FMDV O/ME-SA/SA-2018 sublineage in the UAE. These data shed light on the epidemiology of FMD in the UAE and motivate further systematic epidemiological studies and genomic sequencing to enhance the ongoing national animal health FMD control plan.

Establishing a molecular toolbox of lineage-specific real-time RT-PCR assays for the characterization of foot-and-mouth disease viruses circulating in Asia

Foot-and-mouth disease (FMD) is endemic in many Asian countries, with outbreaks occurring regularly due to viruses from serotypes O, A, and Asia1 that co-circulate in the region. The ability to rapidly characterize new virus occurrences provides critical information to understand the epidemiology and risks associated with field outbreaks, and helps in the selection of appropriate vaccines to control the disease. FMD lineage-specific characterization is usually determined through sequencing; however, this capacity is not always readily available. In this study, we provide a panel of real-time RT-PCR (rRT-PCR) assays to allow differentiation of the FMD virus (FMDV) lineages known to have been co-circulating in Asia during 2020. This panel included five new rRT-PCR assays designed to detect lineages O/ME-SA/PanAsia-PanAsia-2, O/ME-SA/Ind-2001, O/SEA/Mya-98, O/CATHAY, and A/ASIA/Sea-97, along with three published rRT-PCR assays for A/ASIA/Iran-05, A/ASIA/G-VII, and Asia1 serotypes. Samples of known FMD lineage (n = 85) were tested in parallel with all eight lineage-specific assays and an established 3D pan-FMD rRT-PCR assay, and comparative limit of detection (LOD) experiments were conducted for the five newly developed assays. All samples (85/85) were assigned to the correct serotype, and the correct lineage was assigned for 70 out of 85 samples where amplification only occurred with the homologous assay. For 13 out of 85 of the samples, there was amplification in two assays; however, the correct lineage could be designated based on the strongest Ct values for 12 out of 13 samples. An incorrect lineage was assigned for 3 out of 85 samples. The amplification efficiencies for the five new rRT-PCR assays ranged between 79.7 and 100.5%, with nucleic acid dilution experiments demonstrating broadly equivalent limits of detection when compared to the 3D pan-FMD rRT-PCR assay. These new tests, together with other published lineage-specific rRT-PCR assays, constitute a panel of assays (or molecular toolbox) that can be selected for use in FMD endemic countries (individually or a subset of the assays depending on region/lineages known to be circulating) for rapid characterization of the FMDV lineages circulating in Asia at a relatively low cost. This molecular toolbox will enhance the ability of national laboratories in endemic settings to accurately characterize circulating FMDV strains and facilitate prompt implementation of control strategies, and may be particularly useful in settings where it is difficult to access sequencing capability.

Designing one-step reverse transcriptase loop-mediated isothermal amplification for serotype O foot-and-mouth disease virus detection during the 2022 outbreak in East Java, Indonesia

Background and Aim

Various methods can detect foot-and-mouth disease (FMD) in cows, but they necessitate resources, time, costs, laboratory facilities, and specific clinical specimen submission, often leading to FMD virus (FMDV) diagnosis delays. The 2022 FMD outbreak in East Java, Indonesia, highlighted the need for an easy, inexpensive, rapid, and accurate detection approach. This study aims to devise a one-step reverse transcriptase loop-mediated isothermal amplification (RT-LAMP) technique and phylogenetic analysis to detect the serotype O FMDV outbreak in East Java.

Materials and Methods

Swab samples were collected from the foot vesicles, nasal secretions, and saliva of five suspected FMDV-infected cows in East Java between June and July 2022. The RT-LAMP design used hydroxy naphthol blue dye or SYBR Green I dye, with confirmatory analysis through reverse transcriptase polymerase chain reaction (RT-PCR) targeting 249 base pairs. PCR products underwent purification, sequencing, and nucleotide alignment, followed by phylogenetic analysis.

Results

The RT-LAMP method using hydroxy naphthol blue dye displayed a positive reaction through a color shift from purple to blue in the tube. Naked-eye observation in standard light or ultraviolet (UV) light at 365 nm, with SYBR Green I stain, also revealed color change. Specifically, using SYBR Green I dye, UV light at 365 nm revealed a color shift from yellow to green, signifying a positive reaction. Nucleotide alignment revealed mutations and deletion at the 15th sequence in the JT-INDO-K3 isolate from the East Java FMDV outbreak. Despite differing branches, the phylogenetic tree placed it in the same cluster as serotype O FMDV from Malaysia and Mongolia.

Conclusion

JT-INDO-K3 exhibited distinctions from Indonesian serotype O FMDV isolates and those documented in GenBank. Then, the RT-LAMP method used in this study has a detection limit 10 times higher latter than the conventional RT-PCR limit, without any cross-reactivity among strains.

Foot-and-Mouth Disease Virus Induces Porcine Gasdermin E-Mediated Pyroptosis through the Protease Activity of 3Cpro

Foot-and-mouth disease (FMD) is an acute, highly contagious disease of cloven-hoofed animals caused by FMD virus (FMDV). Currently, the molecular pathogenesis of FMDV infection remains poorly understood. Here, we demonstrated that FMDV infection induced gasdermin E (GSDME)-mediated pyroptosis independent of caspase-3 activity. Further studies showed that FMDV 3Cpro cleaved porcine GSDME (pGSDME) at the Q271-G272 junction adjacent to the cleavage site (D268-A269) of porcine caspase-3 (pCASP3). The inhibition of enzyme activity of 3Cpro failed to cleave pGSDME and induce pyroptosis. Furthermore, overexpression of pCASP3 or 3Cpro-mediated cleavage fragment pGSDME-NT was sufficient to induce pyroptosis. Moreover, the knockdown of GSDME attenuated the pyroptosis caused by FMDV infection. Our study reveals a novel mechanism of pyroptosis induced by FMDV infection and might provide new insights into the pathogenesis of FMDV and the design of antiviral drugs. IMPORTANCE Although FMDV is an important virulent infectious disease virus, few reports have addressed its relationship with pyroptosis or pyroptosis factors, and most studies focus on the immune escape mechanism of FMDV. GSDME (DFNA5) was initially identified as being associated with deafness disorders. Accumulating evidence indicates that GSDME is a key executioner for pyroptosis. Here, we first demonstrate that pGSDME is a novel cleavage substrate of FMDV 3Cpro and can induce pyroptosis. Thus, this study reveals a previously unrecognized novel mechanism of pyroptosis induced by FMDV infection and might provide new insights into the design of anti-FMDV therapies and the mechanisms of pyroptosis induced by other picornavirus infections.

A highly discriminatory RNA strand-specific assay to facilitate analysis of the role of cis-acting elements in foot-and-mouth disease virus replication

Foot-and-mouth-disease virus (FMDV), the aetiological agent responsible for foot-and-mouth disease (FMD), is a member of the genus Aphthovirus within the family Picornavirus. In common with all picornaviruses, replication of the single-stranded positive-sense RNA genome involves synthesis of a negative-sense complementary strand that serves as a template for the synthesis of multiple positive-sense progeny strands. We have previously employed FMDV replicons to examine viral RNA and protein elements essential to replication, but the factors affecting differential strand production remain unknown. Replicon-based systems require transfection of high levels of RNA, which can overload sensitive techniques such as quantitative PCR, preventing discrimination of specific strands. Here, we describe a method in which replicating RNA is labelled in vivo with 5-ethynyl uridine. The modified base is then linked to a biotin tag using click chemistry, facilitating purification of newly synthesised viral genomes or anti-genomes from input RNA. This selected RNA can then be amplified by strand-specific quantitative PCR, thus enabling investigation of the consequences of defined mutations on the relative synthesis of negative-sense intermediate and positive-strand progeny RNAs. We apply this new approach to investigate the consequence of mutation of viral cis-acting replication elements and provide direct evidence for their roles in negative-strand synthesis.

The Application of the Gibson Assembly Method in the Production of Two pKLS3 Vector-Derived Infectious Clones of Foot-and-Mouth Disease Virus

The construction of a full-length infectious clone, essential for molecular virological study and vaccine development, is quite a challenge for viruses with long genomes or possessing complex nucleotide sequence structures. Herein, we have constructed infectious clones of foot-and-mouth disease virus (FMDV) types O and A by joining each viral coding region with our pKLS3 vector in a single isothermal reaction using Gibson Assembly (GA). pKLS3 is a 4.3-kb FMDV minigenome. To achieve optimal conditions for the DNA joining, each FMDV coding sequence was divided into two overlapping fragments of approximately 3.8 and 3.2 kb, respectively. Both DNA fragments contain the introduced linker sequences for assembly with the linearized pKLS3 vector. FMDV infectious clones were produced upon directly transfecting the GA reaction into baby hamster kidney-21 (BHK-21) cells. After passing in BHK-21 cells, both rescued FMDVs (rO189 and rNP05) demonstrated growth kinetics and antigenicity similar to their parental viruses. Thus far, this is the first report on GA-derived, full-length infectious FMDV cDNA clones. This simple DNA assembly method and the FMDV minigenome would facilitate the construction of FMDV infectious clones and enable genetic manipulation for FMDV research and custom-made FMDV vaccine production.

Diagnostic application of formalin fixed archived tissues for detection of foot-and-mouth disease

Early and definitive disease diagnosis is critical for effective disease control. 50% buffered glycerine is commonly used viral transport medium, which is not always available and required cold chain. Tissues samples archived in 10% neutral buffered formalin (NBF) can preserve nucleic acid that can be used in molecular studies and disease diagnosis. The present study's goal was to detect the foot-and-mouth disease (FMD) viral genome in formalin-fixed archived tissue which may avoid cold chain during transportation. This study used FMD suspected samples preserved in 10% neutral buffered formalin from 0 to 730 days post fixation (DPF). All archived tissues were positive for FMD viral genome by multiplex RT-PCR and RT-qPCR up to 30 DPF, whereas archived epithelium tissues and thigh muscle were positive for FMD vial genome up to 120 DPF. FMD viral genome was detected in cardiac muscle up to 60 DPF and 120 DPF, respectively. The findings suggest that 10% neutral buffered formalin could be used for sample preservation and transportation for timely and accurate FMD diagnosis. More samples need to be tested before implementing the use of 10% neutral buffered formalin as a preservative and transportation medium. The technique may add value in ensuring biosafety measures for creation during disease free zone as well.

Preventive effects of quercetin against foot-and-mouth disease virus in vitro and in vivo by inducing type I interferon

Foot-and-mouth disease (FMD) is an acute contagious infectious disease that affects cloven-hoofed animals. Although current emergency FMD vaccines only take effect 7 days after vaccination, antiviral agents, such as quercetin, which is a common flavonoid, could reduce the spread of FMD virus (FMDV) during outbreaks. We investigated the in vitro and in vivo antiviral effects of quercetin against FMDV. Analysis of viral copy numbers showed that quercetin had a dose-dependent inhibitory effect on FMDV at concentrations between 19.5 and 1,250 μM in porcine cells. In addition, we observed a quercetin-induced interferon (IFN)-α protein and interferon-stimulated gene (ISG) upregulation in swine cells. Enzyme-linked immunosorbent assay of sera revealed that quercetin induces the production of IFN-α, IFN-β, IFN-γ, interleukin (IL)-12, and IL-15 in mice. Inoculation of mice with quercetin or a combination of quercetin with an inactivated FMD vaccine enhanced both the survival rate and neutralizing antibody titer. Therefore, we suggest the use of quercetin as a novel and effective antiviral agent for controlling FMDV infection; however, further investigation of its application in livestock is required.

Insights into Polyprotein Processing and RNA-Protein Interactions in Foot-and-Mouth Disease Virus Genome Replication

Foot-and-mouth disease virus (FMDV) is a picornavirus, which infects cloven-hoofed animals to cause foot-and-mouth disease (FMD). The positive-sense RNA genome contains a single open reading frame, which is translated as a polyprotein that is cleaved by viral proteases to produce the viral structural and nonstructural proteins. Initial processing occurs at three main junctions to generate four primary precursors; L^pro and P1, P2, and P3 (also termed 1ABCD, 2BC, and 3AB_1,2,3CD). The 2BC and 3AB_1,2,3CD precursors undergo subsequent proteolysis to generate the proteins required for viral replication, including the enzymes 2C, 3C^pro, and 3D^pol. These precursors can be processed through both cis and trans (i.e., intra- and intermolecular proteolysis) pathways, which are thought to be important for controlling virus replication. Our previous studies suggested that a single residue in the 3B₃-3C junction has an important role in controlling 3AB_1,2,3CD processing. Here, we use in vitro based assays to show that a single amino acid substitution at the 3B₃-3C boundary increases the rate of proteolysis to generate a novel 2C-containing precursor. Complementation assays showed that while this amino acid substitution enhanced production of some nonenzymatic nonstructural proteins, those with enzymatic functions were inhibited. Interestingly, replication could only be supported by complementation with mutations in cis acting RNA elements, providing genetic evidence for a functional interaction between replication enzymes and RNA elements. IMPORTANCE Foot-and-mouth disease virus (FMDV) is responsible for foot-and-mouth disease (FMD), an important disease of farmed animals, which is endemic in many parts of the world and can results in major economic losses. Replication of the virus occurs within membrane-associated compartments in infected cells and requires highly coordinated processing events to produce an array of nonstructural proteins. These are initially produced as a polyprotein that undergoes proteolysis likely through both cis and trans alternative pathways (i.e., intra- and intermolecular proteolysis). The role of alternative processing pathways may help coordination of viral replication by providing temporal control of protein production and here we analyze the consequences of amino acid substitutions that change these pathways in FMDV. Our data suggest that correct processing is required to produce key enzymes for replication in an environment in which they can interact with essential viral RNA elements. These data further the understanding of RNA genome replication.

Heterogeneity and Recombination of Foot-and-Mouth Disease Virus during Multi-Strain Coinfection of Cattle

Superinfection of cattle persistently infected with foot-and-mouth disease virus (FMDV), with a heterologous FMDV strain has been shown to generate novel recombinant viruses. In this study, we investigated the pathogenesis events within specific tissues associated with FMDV coinfections in cattle subjected to either simultaneous or serial exposure to two distinct strains of FMDV. Both strains of FMDV (one each of serotypes O and A) were similarly localized to the nasopharyngeal mucosa during the early stages of infection. However, while no recombinant FMDV genomes were recovered from simultaneously coinfected cattle, interserotypic recombinants were isolated from nasopharyngeal tissue samples obtained at 48 h after heterologous superinfection of a persistently infected FMDV carrier. Additionally, analysis of FMDV genomes obtained from replicate nasopharyngeal tissue samples demonstrated that adjacent segments of the mucosa were sometimes infected by distinct viruses, demonstrating a multifocal and heterogeneous distribution of FMDV infection during primary and persistent phases of infection. This work indicates that superinfection of FMDV carriers may be an important source of emergent recombinant strains of FMDV in areas where multiple strains are co-circulating. IMPORTANCE Foot-and-mouth disease (FMD) is a socioeconomically impactful livestock disease with a complex epidemiology and ecology. Although recombinant viruses have been identified in field samples, the mechanisms of emergence of those viruses have never been elucidated. This current study demonstrates how serial infection of cattle with two distinct serotypes of FMD virus (FMDV) leads to rapid generation of recombinant viruses in the upper respiratory tracts of infected animals. This finding is particularly relevant in relation to the management of persistently infected FMDV carrier cattle that can maintain subclinical FMDV infection for months to years after an initial infection. Such carrier animals may function as mixing vessels that facilitate the emergence of novel recombinant FMDV strains in areas where multiple virus strains are in circulation.

B and T Cell Epitopes of the Incursionary Foot-and-Mouth Disease Virus Serotype SAT2 for Vaccine Development

Failure of cross-protection among interserotypes and intratypes of foot-and-mouth disease virus (FMDV) is a big threat to endemic countries and their prevention and control strategies. However, insights into practices relating to the development of a multi-epitope vaccine appear as a best alternative approach to alleviate the cross-protection-associated problems. In order to facilitate the development of such a vaccine design approach, identification and prediction of the antigenic B and T cell epitopes along with determining the level of immunogenicity are essential bioinformatics steps. These steps are well applied in Eurasian serotypes, but very rare in South African Territories (SAT) Types, particularly in serotype SAT2. For this reason, the available scattered immunogenic information on SAT2 epitopes needs to be organized and clearly understood. Therefore, in this review, we compiled relevant bioinformatic reports about B and T cell epitopes of the incursionary SAT2 FMDV and the promising experimental demonstrations of such designed and developed vaccines against this serotype.

Evaluation of DNA Vaccine Candidates against Foot-and-Mouth Disease Virus in Cattle

We evaluated four DNA vaccine candidates for their ability to produce virus-like particles (VLPs) and elicit a protective immune response against Foot-and-mouth disease virus (FMDV) in cattle. Two traditional DNA plasmids and two DNA minicircle constructs were evaluated. Both the pTarget O1P1-3C plasmid and O1P1-3C minicircle encoded a wild-type FMDV 3C protease to process the P1-2A polypeptide, whereas the O1P1-HIV-3C^T minicircle used an HIV-1 ribosomal frameshift to down-regulate expression of a mutant 3C protease. A modified pTarget plasmid with a reduced backbone size, mpTarget O1P1-3C^LT, used a 3C protease containing two mutations reported to enhance expression. All constructs produced mature FMDV P1 cleavage products in transfected cells, as seen by western blot analysis. Three constructs, O1P1-3C minicircles, pTarget O1P1-3C, and mpTarget O1P1-3C^LT plasmids, produced intracellular VLP crystalline arrays detected by electron microscopy. Despite VLP formation in vitro, none of the DNA vaccine candidates elicited protection from clinical disease when administered independently. Administration of pTarget O1P1-3C plasmid enhanced neutralizing antibody titers when used as a priming dose prior to administration of a conditionally licensed adenovirus-vectored FMD vaccine. Further work is needed to develop these DNA plasmid-based constructs into standalone FMD vaccines in cattle.

Local and systemic immune responses induced by intranasal immunization with biomineralized foot-and-mouth disease virus-like particles

Introduction

Foot-and-mouth disease virus (FMDV) infects the host by invading mucosal epithelial cells of the respiratory or digestive tract. Therefore, establishing a specific antiviral mucosal immune barrier can effectively block viral invasion.

Methods

We evaluated local mucosal and systemic immune responses elicited by intranasal immunization of mice with foot-and-mouth disease (FMD) calcium phosphate mineralized virus-like particles (CaP-VLPs) and tested whether three commercial mucosal adjuvants enhanced the immunogenicity of the antigen. The biosafety of the vaccine was verified through gross observation and pathological analysis of the lungs.

Results

CaP-VLPs effectively induced secretion of IgA (sIgA) from multiple sites in mouse mucosa and produced anti-FMD-specific IgG in the serum. Splenic lymphocytes specifically proliferated and secreted IFN-γ following antigen stimulation, indicating the vaccine can induce a certain level of cellular immune response. Finally, the pathological examination confirmed that CaP-VLPs did not cause substantial damage to the lungs of animals after immunization via mucosal administration. Notably, the vaccine mixed with S adjuvant increased the content of sIgA and serum IgG, and the high level of IgG in serum was maintained at least 7 weeks.

Discussion

Overall, this study reveals that FMD CaP-VLPs can induce good local mucosal immune and systemic immune response through intranasal immunization, and the immune response was specifically enhanced by S adjuvant. These data support that CaP-VLPs-S as a candidate mucosal vaccine for the prevention of FMD vaccine infection.

Antiviral Effect of Manganese against Foot-and-Mouth Disease Virus Both in PK15 Cells and Mice

Foot-and-mouth disease (FMD) is an acute contagious disease of cloven-hoofed animals such as cattle, pigs, and sheep. Current emergency FMD vaccines are of limited use for early protection because their protective effect starts 7 days after vaccination. Therefore, antiviral drugs or additives are used to rapidly stop the spread of the virus during FMD outbreaks. Manganese (Mn²⁺) was recently found to be an important substance necessary for the host to protect against DNA viruses. However, its antiviral effect against RNA viruses remains unknown. In this study, we found that Mn²⁺ has antiviral effects on the FMD virus (FMDV) both in PK15 cells and mice. The inhibitory effect of Mn²⁺ on FMDV involves NF-κB activation and up-regulation of interferon-stimulated genes. Animal experiments showed that Mn²⁺ can be highly effective in protecting C57BL/6N mice from being infected with FMDV. Overall, we suggest Mn²⁺ as an effective antiviral additive for controlling FMDV infection.

Phylogeography as a Proxy for Population Connectivity for Spatial Modeling of Foot-and-Mouth Disease Outbreaks in Vietnam

Bayesian space-time regression models are helpful tools to describe and predict the distribution of infectious disease outbreaks and to delineate high-risk areas for disease control. In these models, structured and unstructured spatial and temporal effects account for various forms of non-independence amongst case counts across spatial units. Structured spatial effects capture correlations in case counts amongst neighboring provinces arising from shared risk factors or population connectivity. For highly mobile populations, spatial adjacency is an imperfect measure of connectivity due to long-distance movement, but we often lack data on host movements. Phylogeographic models inferring routes of viral dissemination across a region could serve as a proxy for patterns of population connectivity. The objective of this study was to investigate whether the effects of population connectivity in space-time regressions of case counts were better captured by spatial adjacency or by inferences from phylogeographic analyses. To compare these two approaches, we used foot-and-mouth disease virus (FMDV) outbreak data from across Vietnam as an example. We identified that accounting for virus movement through phylogeographic analysis serves as a better proxy for population connectivity than spatial adjacency in spatial-temporal risk models. This approach may contribute to design surveillance activities in countries lacking movement data.

Efficacy of a Novel Multiepitope Vaccine Candidate against Foot-and-Mouth Disease Virus Serotype O and A

Foot-and-mouth disease (FMD) is a highly contagious and economically devastating disease in cloven-hoofed animals. To prevent the spread of FMD virus (FMDV), traditional inactivated vaccines are used to immunize susceptible animals in disease-endemic countries. However, the inactivated FMD vaccine has several limitations, including safety concerns. To overcome these limitations, subunit proteins have been studied as alternative vaccine candidates. In this study, we designed two multiepitope recombinant proteins (OVM and AVM) containing antigenic sites (residue of VP1 132-162 and residue of VP1 192-212) of three topotypes of FMDV serotype O or three topotypes of FMDV serotype A. Each recombinant protein was efficiently expressed in Escherichia coli with high solubility, and the immunogenicity and protective efficacy of the proteins as FMD vaccine candidates were evaluated. The results showed that OVM and AVM emulsified with ISA201 adjuvant induced effective antigen-specific humoral and cell-mediated immune responses and successfully protected mice from O/Jincheon/SKR/2014, O/VET/2013, and A/Malaysia/97 viruses. In addition, intramuscular immunization of pigs with the OVM and AVM emulsified with ISA201 elicited effective levels of neutralizing antibodies to the viruses with homologous epitopes. Importantly, OVM-AVM emulsified with CAvant^®SOE-X adjuvant conferred 100% protection against the O/Jincheon/SKR/2014 virus with homologous residues and 75% protection against A/SKR/GP/2018 with heterologous residues. The results presented in this study suggest that the combination of OVM and AVM protein with an effective adjuvant could yield an effective and safe vaccine candidate for the prevention and control of foot-and-mouth disease. In addition, our results provide a vaccine platform that can safely, cost-efficiently, and rapidly generate protective vaccine candidates against diverse FMDVs.

The Parallel Presentation of Two Functional CTL Epitopes Derived from the O and Asia 1 Serotypes of Foot-and-Mouth Disease Virus and Swine SLA-2*HB01: Implications for Universal Vaccine Development

Foot-and-mouth disease virus (FMDV) poses a significant threat to the livestock industry. Through their recognition of the conserved epitopes presented by the swine leukocyte antigen (SLA), T cells play a pivotal role in the antiviral immunity of pigs. Herein, based on the peptide binding motif of SLA-2*HB01, from an original SLA-2 allele, a series of functional T-cell epitopes derived from the dominant antigen VP1 of FMDV with high binding capacity to SLA-2 were identified. Two parallel peptides, Hu64 and As64, from the O and Asia I serotypes, respectively, were both crystallized with SLA-2*HB01. Compared to SLA-1 and SLA-3, the SLA-2 structures showed the flexibility of residues in the P4, P6, and P8 positions and in their potential interface with TCR. Notably, the peptides Hu64 and As64 adopted quite similar overall conformation when bound to SLA-2*HB01. Hu64 has two different conformations, a more stable 'chair' conformation and an unstable 'boat' conformation observed in the two molecules of one asymmetric unit, whereas only a single 'chair' conformation was observed for As64. Both Hu64 and As64 could induce similar dominant T-cell activities. Our interdisciplinary study establishes a basis for the in-depth interpretation of the peptide presentation of SLA-I, which can be used toward the development of universal vaccines.

Development of Monoclonal Antibody to Specifically Recognize VP0 but Not VP4 and VP2 of Foot-and-Mouth Disease Virus

Foot-and-mouth disease (FMD) is a highly contagious vesicular disease that affects cloven-hoofed animals and often causes enormous economic loss in the livestock industry. The capsid of FMD virus (FMDV) consists of four structural proteins. Initially, one copy each of the proteins VP0, VP3, and VP1 are folded together into a protomer, and five copies of the protomer compose a pentamer. Finally, 12 pentamers are assembled into an icosahedral capsid. At the maturation stage during RNA encapsidation, VP0 is cleaved into VP4 and VP2. The mechanism underlying VP0 maturation remains unclear. While monoclonal antibodies (mAbs) against VP2 have been developed in previous studies, a mAb specific to VP0 has not yet been reported. In this study, we generated VP0-specific mAbs by immunizing mice with peptides spanning the C-terminal amino acids of VP4 and N-terminal amino acids of VP2. We verified that these mAbs displayed specificity to VP0 with no reactivity to VP4 or VP2. Therefore, these mAbs could prove useful in identifying the role of VP0 in FMDV replication and elucidating the mechanism underlying VP0 cleavage into VP4 and VP2.

A single amino acid substitution in the VP2 protein of Indian foot-and-mouth disease virus serotype O vaccine strain confers thermostability and protective immunity in cattle

Foot-and-mouth disease (FMD) is a significant threat to animal health globally. Prophylactic vaccination using inactivated FMD virus (FMDV) antigen is being practised for the control in endemic countries. A major limitation of the current vaccine is its susceptibility to high environmental temperature causing loss of immunogenicity, thus necessitating the cold chain for maintenance of its efficacy. Hence, the FMD vaccine with thermostable virus particles will be highly useful in sustaining the integrity of whole virus particle (146S) during storage at 4°C. In this study, 12 recombinant mutants of Indian vaccine strain of FMDV serotype O (O/IND/R2/1975) were generated through reverse genetics approach and evaluated for thermostability. One of the mutant viruses, VP2_Y98F was more thermostable than other mutants and the parent FMDV. The oil-adjuvanted vaccine formulated with the inactivated VP2_Y98F mutant FMDV was stable up to 8 months when stored at 4°C and induced protective antibody response till dpv 180 after primary vaccination. It is concluded that the VP2_Y98F mutant FMDV was thermostable and has the potential to replace the parent vaccine strain.

Micro-Players of Great Significance-Host microRNA Signature in Viral Infections in Humans and Animals

Over time, more and more is becoming known about micro-players of great significance. This is particularly the case for microRNAs (miRNAs; miR), which have been found to participate in the regulation of many physiological and pathological processes in both humans and animals. One such process is viral infection in humans and animals, in which the host miRNAs—alone or in conjunction with the virus—interact on two levels: viruses may regulate the host’s miRNAs to evade its immune system, while the host miRNAs can play anti- or pro-viral roles. The purpose of this comprehensive review is to present the key miRNAs involved in viral infections in humans and animals. We summarize the data in the available literature, indicating that the signature miRNAs in human viral infections mainly include 12 miRNAs (i.e., miR-155, miR-223, miR-146a, miR-122, miR-125b, miR-132, miR-34a, miR -21, miR-16, miR-181 family, let-7 family, and miR-10a), while 10 miRNAs are commonly found in animals (i.e., miR-155, miR-223, miR-146a, miR-145, miR-21, miR-15a/miR-16 cluster, miR-181 family, let-7 family, and miR-122) in this context. Knowledge of which miRNAs are involved in different viral infections and the biological functions that they play can help in understanding the pathogenesis of viral diseases, facilitating the future development of therapeutic agents for both humans and animals.

Morphological and Phenotypic Characteristics of the Bovine Nasopharyngeal Mucosa and Associated Lymphoid Tissue

The mammalian nasopharynx is an anatomically complex region of the upper respiratory tract that directly communicates with the nasal cavity, laryngopharynx, oesophagus and trachea. The nasopharyngeal mucosa contains moderate quantities of mucosa-associated lymphoid tissue (MALT) that is appropriately located for immunological sampling but also creates vulnerability to pathogens. In recent years, the nasopharynx has been inculpated in the pathogenesis of important diseases of cattle (foot-and-mouth disease) and humans (COVID-19), yet the tissue has never been described in detail in any species. In order to characterize the morphology and cellular composition of the bovine nasopharynx, samples of mucosa were collected from the nasopharynx of five 8-13-month-old steers and examined using light microscopy, immunohistochemistry and multichannel immunofluorescence. Morphologically, the nasopharyngeal epithelium was highly heterogeneous, with a continuum ranging from stratified squamous epithelium to highly attenuated, follicle-associated epithelium (FAE). Distribution of MALT was similarly regionally variable ranging from absent to clusters of multiple lymphoid follicles. Phenotypic characterization demonstrated dense distributions of dendritic cells and T lymphocytes surrounding lymphoid follicles, which comprised mostly B lymphocytes. The FAE overlaying the lymphoid follicles also contained higher numbers of dendritic cells and lymphocytes compared with the adjacent non-lymphoid epithelium, although cytotoxic T cells were notably scarce in the FAE. The bovine nasopharyngeal lymphoid tissue had comparable elements to other MALTs with specific differences that may help to elucidate the pathogenesis of infectious agents that have specific tropism for this tissue.

Enhanced detection and serotyping of foot-and-mouth disease virus serotype O, A, and Asia1 using a novel multiplex real-time RT-PCR

Rapid and accurate detection and serotyping of foot-and-mouth disease (FMD) virus (FMDV) is essential for implementing control policies against emergent FMD outbreaks. Current serotyping assays, such as VP1 reverse transcription-polymerase chain reaction (RT-PCR)/sequencing (VP1 RT-PCR/sequencing) and antigen detection enzyme-linked immunosorbent assay (ELISA), have problems with increasing serotyping failure of FMDVs from FMD outbreaks. This study was conducted to develop a multiplex real-time RT-PCR for specific detection and differential serotyping of FMDV serotype O, A, and Asia 1 directly from field clinical samples. Primers and probes were designed based on 571 VP1 coding region sequences originated from seven pools. Multiplex real-time RT-PCR using these primers and probes demonstrated serotype-specific detection with enhanced sensitivity compared to VP1 RT-PCR/sequencing for reference FMDV (n = 24). Complete serotyping conformity between the developed multiplex real-time RT-PCR and previous VP1 RT-PCR/sequencing was demonstrated using FMDV field viruses (n = 113) prepared in cell culture. For FMDV field clinical samples (n = 55), the serotyping rates of multiplex real-time RT-PCR and VP1 RT-PCR/sequencing were 92.7% (51/55) and 72.7% (40/55), respectively. Moreover, the developed multiplex real-time RT-PCR demonstrated improved FMDV detection (up to 33.3%) and serotyping (up to 67.7%) capabilities for saliva samples when compared with 3D real-time RT-PCR and VP1 RT-PCR/sequencing, during 10 days of challenge infection with FMDV serotype O, A, and Asia 1. Collectively, this study suggests that the newly developed multiplex real-time RT-PCR assay may be useful for the detection and differential serotyping of FMDV serotype O, A, and Asia 1 in the field.

Full-Length Genomic RNA of Foot-and-Mouth Disease Virus Is Infectious for Cattle by Injection

Safe sample transport is of great importance for infectious diseases diagnostics. Various treatments and buffers are used to inactivate pathogens in diagnostic samples. At the same time, adequate sample preservation, particularly of nucleic acids, is essential to allow an accurate laboratory diagnosis. For viruses with single-stranded RNA genomes of positive polarity, such as foot-and-mouth disease virus (FMDV), however, naked full-length viral RNA can itself be infectious. In order to assess the risk of infection from inactivated FMDV samples, two animal experiments were performed. In the first trial, six cattle were injected with FMDV RNA (isolate A22/IRQ/24/64) into the tongue epithelium. All animals developed clinical disease within two days and FMDV was reisolated from serum and saliva samples. In the second trial, another group of six cattle was exposed to FMDV RNA by instilling it on the tongue and spraying it into the nose. The animals were observed for 10 days after exposure. All animals remained clinically unremarkable and virus isolation as well as FMDV genome detection in serum and saliva were negative. No transfection reagent was used for any of the animal inoculations. In conclusion, cattle can be infected by injection with naked FMDV RNA, but not by non-invasive exposure to the RNA. Inactivated FMDV samples that contain full-length viral RNA carry only a negligible risk of infecting animals.

Establishing an In Vitro System to Assess How Specific Antibodies Drive the Evolution of Foot-and-Mouth Disease Virus

Viruses can evolve to respond to immune pressures conferred by specific antibodies generated after vaccination and/or infection. In this study, an in vitro system was developed to investigate the impact of serum-neutralising antibodies upon the evolution of a foot-and-mouth disease virus (FMDV) isolate. The presence of sub-neutralising dilutions of specific antisera delayed the onset of virus-induced cytopathic effect (CPE) by up to 44 h compared to the untreated control cultures. Continued virus passage with sub-neutralising dilutions of these sera resulted in a decrease in time to complete CPE, suggesting that FMDV in these cultures adapted to escape immune pressure. These phenotypic changes were associated with three separate consensus-level non-synonymous mutations that accrued in the viral RNA-encoding amino acids at positions VP2⁶⁶, VP2⁸⁰ and VP1¹⁵⁵, corresponding to known epitope sites. High-throughput sequencing also identified further nucleotide substitutions within the regions encoding the leader (L^pro), VP4, VP2 and VP3 proteins. While association of the later mutations with the adaptation to immune pressure must be further verified, these results highlight the multiple routes by which FMDV populations can escape neutralising antibodies and support the application of a simple in vitro approach to assess the impact of the humoral immune system on the evolution of FMDV and potentially other viruses.

Cross-Serotype Reactivity of ELISAs Used to Detect Antibodies to the Structural Proteins of Foot-and-Mouth Disease Virus

Antibodies to the foot-and-mouth disease virus (FMDV) capsid induced by infection or vaccination can provide serotype-specific protection and be measured using virus neutralization tests and viral structural-protein (SP-)ELISAs. Separate tests are needed for each serotype, but cross-serotype reactions complicate serotyping. In this study, inter-serotypic responses were quantified for five SP-ELISA formats by testing 294 monovalent mainly bovine sera collected following infection, vaccination, or vaccination and infection with one of five serotypes of FMDV. Over half of the samples, representing all three immunization categories, scored positive for at least one heterologous serotype and some scored positive for all serotypes tested. A comparative approach to identifying the strongest reaction amongst serotypes O, A and Asia 1 improved the accuracy of serotyping to 73–100% depending on the serotype and test system, but this method will be undermined where animals have been infected and/or vaccinated with multiple FMDV serotypes. Preliminary studies with stabilized recombinant capsid antigens of serotypes O and A that do not expose internal epitopes showed reduced cross-reactivity, supporting the hypothesis that capsid integrity can affect the serotype-specificity of the SP-ELISAs. The residual cross-reactivity associated with capsid surface epitopes was consistent with the evidence of cross-serotype virus neutralization.

FMDV 3A Antagonizes the Effect of ANXA1 to Positively Modulate Viral Replication

The RIG-I-like receptor signaling pathway is crucial for producing type I interferon (IFN-I) against RNA viruses. The present study observed that viral infection increased annexin-A1 (ANXA1) expression, and ANXA1 then promoted RNA virus-induced IFN-I production. Compared to ANXA1 wild-type cells, ANXA1^−/− knockout cells showed IFN-β production decreasing after viral stimulation. RNA virus stimulation induced ANXA1 to regulate IFN-β production through the TBK1-IRF3 axis but not through the NF-κB axis. ANXA1 also interacted with JAK1 and STAT1 to increase signal transduction induced by IFN-β or IFN-γ. We assessed the effect of ANXA1 on the replication of foot-and-mouth disease virus (FMDV) and found that ANXA1 inhibits FMDV replication dependent on IFN-I production. FMDV 3A plays critical roles in viral replication and host range. The results showed that FMDV 3A interacts with ANXA1 to inhibit its ability to promote IFN-β production. We also demonstrated that FMDV 3A inhibits the formation of ANXA1-TBK1 complex. These results indicate that ANXA1 positively regulates RNA virus-stimulated IFN-β production and FMDV 3A antagonizes ANXA1-promoted IFN-β production to modulate viral replication.

IMPORTANCE FMDV is a pathogen that causes one of the world’s most destructive and highly contagious animal diseases. The FMDV 3A protein plays a critical role in viral replication and host range. Although 3A is one of the viral proteins that influences FMDV virulence, its underlying mechanisms remain unclear. ANXA1 is involved in immune activation against pathogens. The present study demonstrated that FMDV increases ANXA1 expression, while ANXA1 inhibits FMDV replication. The results also showed that ANXA1 promotes RNA virus-induced IFN-I production through the IRF3 axis at VISA and TBK1 levels. ANXA1 was also found to interact with JAK1 and STAT1 to strengthen signal transduction induced by IFN-β and IFN-γ. 3A interacted with ANXA1 to inhibit ANXA1-TBK1 complex formation, thereby antagonizing the inhibitory effect of ANXA1 on FMDV replication. This study helps to elucidate the mechanism underlying the effect of the 3A protein on FMDV replication.

BacMam Expressing Highly Glycosylated Porcine Interferon Alpha Induces Robust Antiviral and Adjuvant Effects against Foot-and-Mouth Disease Virus in Pigs

Foot-and-mouth disease (FMD) is an acute contagious disease that affects cloven-hoofed animals and has severe global economic consequences. FMD is most commonly controlled by vaccination. Currently available commercial FMD vaccines contain chemically inactivated whole viruses, which are thought to be slow acting as they are effective only 4 to 7 days following vaccination. Hence, the development of a novel rapid vaccine or alternative measures, such as antiviral agents or the combination of vaccines and antiviral agents for prompt FMD virus (FMDV) outbreak containment, is desirable. Here, we constructed a recombinant baculovirus (BacMam) expressing consensus porcine interferon alpha (IFN-α) that has three additional N-glycosylation sites driven by a cytomegalovirus immediate early (CMV-IE) promoter (Bac-Con3N IFN-α) for protein expression in mammalian cells. Bac-Con3N IFN-α expressing highly glycosylated porcine IFN-α protein increased the duration of antiviral effects. We evaluated the antiviral effects of Bac-Con3N IFN-α in swine cells and mice and observed sustained antiviral effects in pig serum; additionally, Bac-Con3N IFN-α exhibited sustained antiviral effects in vivo as well as adjuvant effects in combination with an inactivated FMD vaccine. Pigs injected with a combination of Bac-Con3N IFN-α and the inactivated FMD vaccine were protected against FMDV at 1, 3, and 7 days postvaccination. Furthermore, we observed that in combination with the inactivated FMD vaccine, Bac-Con3N IFN-α increased neutralizing antibody levels in mice and pigs. Therefore, we suggest that Bac-Con3N IFN-α is a strong potential antiviral and adjuvant candidate for use in combination with inactivated FMD vaccines to protect pigs against FMDV. IMPORTANCE Early inhibition of foot-and-mouth disease (FMD) virus (FMDV) replication in pigs is highly desirable as FMDV transmission and shedding rates are higher in pigs than in cattle. However, commercial FMD vaccines require at least 4 to 7 days postvaccination (dpv) for protection, and animals are vulnerable to heterologous viruses before acquiring high antibody levels after the second vaccination. Therefore, the development of antiviral agents for use in combination with FMD vaccines is essential. We developed a novel antiviral and immunostimulant, Bac-Con3N IFN-α, which is a modified porcine IFN-α-expressing recombinant baculovirus, to improve IFN stability and allow its direct delivery to animals. We present a promising candidate for use in combination with inactivated FMD vaccines as pigs applied to the strategy had early protection against FMDV at 1 to 7 dpv, and their neutralizing antibody levels were higher than those in pigs administered the vaccine only.

Chemical inactivation of foot-and-mouth disease virus in bovine tongue epithelium for safe transport and downstream processing

Epithelial tissue or vesicular fluid from an unruptured or recently ruptured vesicle is the sample of choice for confirmatory laboratory diagnosis of foot-and-mouth disease (FMD). However, in 'FMD-free' countries the transport and downstream processing of such samples from potentially infected animals present a biosafety risk, particularly during heightened surveillance, potentially involving decentralised testing in laboratories without adequate biocontainment facilities. In such circumstances, rapid inactivation of virus, if present, prior to transport becomes a necessity, while still maintaining the integrity of diagnostic analytes. Tongue epithelium collected from cattle infected with FMD virus (FMDV) of serotype O (O/ALG/3/2014 - Lineage O/ME-SA/Ind-2001d) or A (A/IRN/22/2015 - Lineage A/ASIA/G-VII) was incubated in the PAXGene Tissue System Fixative (pH 4) and Stabiliser (pH 6.5) components respectively, in McIlvaine's citrate-phosphate buffer (pH 2.6) or in phosphate-buffered saline (PBS, pH 7.4) at room temperature for 2, 6, 24 or 48h. Following incubation, tissues were homogenised and tested by virus isolation and titration using LFBK_αVβ6 cells. The integrity of FMD viral RNA was assessed by RT-qPCR (3D^pol coding region), Sanger sequencing of the VP1 region and transfection of LFBK_αVβ6 cells to recover infectious virus. Viable virus could be recovered from samples incubated in PBS for at least 48hours. The PAXgene Tissue System Stabiliser component yielded variable results dependent on virus serotype, requiring at least 6hours of incubation to inactivate A/IRN/22/2015 in most samples, whereas the Fixative component required up to 2hours in some samples. McIlvaine's citrate-phosphate buffer rapidly inactivated both viruses within 2hours of incubation. There was no demonstrable degradation of FMD viral RNA resulting from incubation in any of the buffers for up to 48hours, as assessed by RT-qPCR, and 24hours by sequencing and transfection to recover infectious virus. McIlvaine's citrate-phosphate buffer (pH 2.6) is easy to prepare, inexpensive and inactivates serotype A and O FMDV in epithelial tissue within 2hours, while maintaining RNA integrity for downstream diagnostic processes and virus characterisation.

Fibroblast growth factor 11 inhibits foot-and-mouth disease virus gene expression and replication in vitro

Foot-and-mouth disease virus (FMDV) causes highly contagious disease of cloven-hoofed animals such as cattle, swine, and sheep. Although FMD vaccine is the traditional way to protect against the disease, the use of FMD vaccines to protect early infection is limited. The alternative strategy of applying antiviral agents is required to control the spread of FMDV in outbreak situations. Fibroblast growth factor 11 (FGF11) is a member of the intracellular FGF. Here, we identified the inhibitory effect of FGF11 on FMDV gene expression through the transcriptional and translational regulation. For the quantitative analysis of FMDV transcription/translation level, we firstly constructed a plasmid reporter system (FMDV five prime untranslated region (5′ UTR) -luci) conjugating luciferase encoding gene with FMDV 5′ UTR region, which is a non-coding region to control FMDV transcription/translation and includes cis-acting replication element (CRE) and internal ribosome entry site (IRES). FGF11 decreased the gene expression of FMDV 5′ UTR-luci reporter in a dose-dependent manner. We further confirmed the inhibitory function of FGF11 on FMDV gene expression a replication in the FMDV-infected pig cells. FGF11 expression inhibited RNA production of FMDV RNA polymerase 3D gene in the FMDV-infected cells. In addition, while FMDV cell infection induced cytopathic effect (CPE) within 24 hr, FGF11 expression dramatically repressed CPE at the basal level. These results indicate that FGF11 inhibits FMDV gene expression and replication in vitro, implicating to provide intervention strategy for FMDV pathogenesis and transmission.

Development and Validation of a Competitive ELISA Based on Bovine Monoclonal Antibodies for the Detection of Neutralizing Antibodies against Foot-and-Mouth Disease Virus Serotype A

The level of neutralizing antibodies in vaccinated animals is directly related to their level of protection against a virus challenge. The virus neutralization test (VNT) is a "gold standard" method for detecting neutralizing antibodies against foot-and-mouth disease virus (FMDV). However, VNT requires high-containment facilities that can handle live viruses and is not suitable for large-scale serological surveillance. In this study, a bovine broadly neutralizing monoclonal antibody (W145) against FMDV serotype A was successfully produced using fluorescence-based single-B-cell antibody technology. Using biotinylated W145 as a detector antibody and another bovine cross-reactive monoclonal antibody, E32, which was produced previously as a capture antibody, a competitive enzyme-linked immunosorbent assay for the detection of neutralizing antibodies (NAC-ELISA) against FMDV serotype A was developed. The specificity and sensitivity of the assay were evaluated to be 99.04% and 100%, respectively. A statistically significant correlation (r = 0.9334, P < 0.0001) was observed between the NAC-ELISA titers and the VNT titers, suggesting that the NAC-ELISA could detect neutralizing antibodies against FMDV serotype A and could be used to evaluate protective immunity.

Highly Specific Loop-Mediated Isothermal Amplification Using Graphene Oxide-Gold Nanoparticles Nanocomposite for Foot-and-Mouth Disease Virus Detection

Loop-mediated isothermal amplification (LAMP) is a molecular diagnosis technology with the advantages of rapid results, isothermal reaction conditions, and high sensitivity. However, this diagnostic system often produces false positive results due to a high rate of non-specific reactions caused by formation of hairpin structures, self-dimers, and mismatched hybridization. The non-specific signals can be due to primers used in the methods because the utilization of multiple LAMP primers increases the possibility of self-annealing of primers or mismatches between primers and templates. In this study, we report a nanomaterial-assisted LAMP method that uses a graphene oxide-gold nanoparticles (AuNPs@GO) nanocomposite to enable the detection of foot-and-mouth disease virus (FMDV) with high sensitivity and specificity. Foot-and-mouth disease (FMD) is a highly contagious and deadly disease in cloven-hoofed animals; hence, a rapid, sensitive, and specific detection method is necessary. The proposed approach exhibited high sensitivity and successful reduction of non-specific signals compared to the traditionally established LAMP assays. Additionally, a mechanism study revealed that these results arose from the adsorption of single-stranded DNA on AuNPs@GO nanocomposite. Thus, AuNPs@GO nanocomposite is demonstrated to be a promising additive in the LAMP system to achieve highly sensitive and specific detection of diverse diseases, including FMD.

A Vaccine Based on the A/ASIA/G-VII Lineage of Foot-and-Mouth Disease Virus Offers Low Levels of Protection against Circulating Viruses from the A/ASIA/Iran-05 lineage

The recent emergence and circulation of the A/ASIA/G-VII (A/G-VII) lineage of foot-and-mouth disease virus (FMDV) in the Middle East has resulted in the development of homologous vaccines to ensure susceptible animals are sufficiently protected against clinical disease. However, a second serotype A lineage called A/ASIA/Iran-05 (A/IRN/05) continues to circulate in the region and it is therefore imperative to ensure vaccine strains used will protect against both lineages. In addition, for FMDV vaccine banks that usually hold a limited number of strains, it is necessary to include strains with a broad antigenic coverage. To assess the cross protective ability of an A/G-VII emergency vaccine (formulated at 43 (95% CI 8-230) PD50/dose as determined during homologous challenge), we performed a heterologous potency test according to the European Pharmacopoeia design using a field isolate from the A/IRN/05 lineage as the challenge virus. The estimated heterologous potency in this study was 2.0 (95% CI 0.4-6.0) PD50/dose, which is below the minimum potency recommended by the World Organisation for Animal Health (OIE). Furthermore, the cross-reactive antibody titres against the heterologous challenge virus were poor (≤log10 0.9), even in those cattle that had received the full dose of vaccine. The geometric mean r1-value was 0.2 (95% CI 0.03-0.8), similar to the potency ratio of 0.04 (95% CI 0.004-0.3). Vaccination decreased viraemia and virus excretion compared to the unvaccinated controls. Our results indicate that this A/G-VII vaccine does not provide sufficient protection against viruses belonging to the A/IRN/05 lineage and therefore the A/G-VII vaccine strain cannot replace the A/IRN/05 vaccine strain but could be considered an additional strain for use in vaccines and antigen banks.

Interleukin-10-Mediated Lymphopenia Caused by Acute Infection with Foot-and-Mouth Disease Virus in Mice

Foot-and-mouth disease (FMD) is characterized by a pronounced lymphopenia that is associated with immune suppression. However, the mechanisms leading to lymphopenia remain unclear. In this study, the number of total CD4⁺, CD8⁺ T cells, B cells, and NK cells in the peripheral blood were dramatically reduced in C57BL/6 mice infected with foot-and-mouth disease virus (FMDV) serotype O, and it was noted that mice with severe clinical symptoms had expressively lower lymphocyte counts than mice with mild or without clinical symptoms, indicating that lymphopenia was associated with disease severity. A further analysis revealed that lymphocyte apoptosis and trafficking occurred after FMDV infection. In addition, coinhibitory molecules were upregulated in the expression of CD4⁺ and CD8⁺ T cells from FMDV-infected mice, including CTLA-4, LAG-3, 2B4, and TIGIT. Interestingly, the elevated IL-10 in the serum was correlated with the appearance of lymphopenia during FMDV infection but not IL-6, IL-2, IL-17, IL-18, IL-1β, TNF-α, IFN-α/β, TGF-β, and CXCL1. Knocking out IL-10 (IL-10^-/-) mice or blocking IL-10/IL-10R signaling in vivo was able to prevent lymphopenia via downregulating apoptosis, trafficking, and the coinhibitory expression of lymphocytes in the peripheral blood, which contribute to enhance the survival of mice infected with FMDV. Our findings support that blocking IL-10/IL-10R signaling may represent a novel therapeutic approach for FMD.

Simultaneous and Staggered Foot-and-Mouth Disease Virus Coinfection of Cattle

Foot-and-mouth disease (FMD) field studies have suggested the occurrence of simultaneous infection of individual hosts by multiple virus strains; however, the pathogenesis of foot-and-mouth disease virus (FMDV) coinfections is largely unknown. In the current study, cattle were experimentally exposed to two FMDV strains of different serotypes (O and A). One cohort was simultaneously infected with both viruses, while additional cohorts were initially infected with FMDV A and subsequently superinfected with FMDV O after 21 or 35 days. Coinfections were confirmed during acute infection, with both viruses concurrently detected in blood, lesions, and secretions. Staggered exposures resulted in overlapping infections as convalescent animals with persistent subclinical FMDV infection were superinfected with a heterologous virus. Staggering virus exposure by 21 days conferred clinical protection in six of eight cattle, which were subclinically infected following the heterologous virus exposure. This effect was transient, as all animals superinfected at 35 days post-initial infection developed fulminant FMD. The majority of cattle maintained persistent infection with one of the two viruses while clearing the other. Analysis of viral genomes confirmed interserotypic recombination events within 10 days in the upper respiratory tract of five superinfected animals from which the dominant genomes contained the capsid coding regions of the O virus and nonstructural coding regions of the A virus. In contrast, there were no dominant recombinant genomes detected in samples from simultaneously coinfected cattle. These findings inculpate persistently infected carriers as potential FMDV mixing vessels in which novel strains may rapidly emerge through superinfection and recombination. IMPORTANCE Foot-and-mouth disease (FMD) is a viral infection of livestock of critical socioeconomic importance. Field studies from areas of endemic FMD suggest that animals can be simultaneously infected by more than one distinct variant of FMD virus (FMDV), potentially resulting in emergence of novel viral strains through recombination. However, there has been limited investigation of the mechanisms of in vivo FMDV coinfections under controlled experimental conditions. Our findings confirmed that cattle could be simultaneously infected by two distinct serotypes of FMDV, with different outcomes associated with the timing of exposure to the two different viruses. Additionally, dominant interserotypic recombinant FMDVs were discovered in multiple samples from the upper respiratory tracts of five superinfected animals, emphasizing the potential importance of persistently infected FMDV carriers as sources of novel FMDV strains.

Identification of the O/ME-SA/Ind-2001e Sublineage of Foot-and-Mouth Disease Virus in Cambodia

Foot-and-mouth (FMD) is endemic in Cambodia with numerous outbreaks in cattle, pigs and other susceptible animal species reported every year. Historically, these outbreaks were caused by the FMD virus (FMDV) of serotype O PanAsia and Mya-98 lineages and serotype A Sea-97 lineage. However, the trans-pool movement of FMDV between inter-pool regions or countries throughout FMD endemic regions has raised concerns regarding infection with the new genotype or serotype of FMDV in Cambodia. In this study, 19 sequences of VP1 coding region obtained from 33 clinical samples collected from FMDV-affected cattle farms in Cambodia during January to March 2019 were genetically characterized to identify the genotypes/lineages of FMDV. Phylogenetic analysis of VP1 coding sequences revealed that recent field viruses belonged to O/ME-SA/Ind-2001e (15.8%), O/ME-SA/PanAsia (52.7%), and A/ASIA/Sea-97 (31.5%). Besides, the field viruses of O/ME-SA/Ind-2001e in Cambodia showed 93.5-96.8% identity with the VP1 coding sequences of the same sublineage viruses from pool 1 and 2 surrounding Cambodia. This is the first report of O/ME-SA/Ind-2001e infection in Cambodia, suggesting that the trans-pool movement of the new genotype should be closely monitored for efficient control of FMD.

Foot-and-Mouth Disease Virus VP3 Protein Acts as a Critical Proinflammatory Factor by Promoting Toll-Like Receptor 4-Mediated Signaling

Foot-and-mouth disease virus (FMDV) infection in cloven-hoofed animals causes severe inflammatory symptoms, including blisters on the oral mucosa, hoof, and breast; however, the molecular mechanism underlying the inflammatory response is unclear. In this study, we provide the first evidence that the FMDV protein VP3 activates lipopolysaccharide-triggered Toll-like receptor 4 (TLR4) signaling. FMDV VP3 increased the expression of TLR4 by downregulating the expression of the lysozyme-related protein Rab7b. Additionally, Rab7b can interact with VP3 to promote the replication of FMDV. Our findings suggested that VP3 regulates the Rab7b-TLR4 axis to mediate the inflammatory response to FMDV.

IMPORTANCE Foot-and-mouth disease virus (FMDV) infection causes a severe inflammatory response in cloven-hoofed animals, such as pigs, cattle, and sheep, with typical clinical manifestations of high fever, numerous blisters on the oral mucosa, hoof, and breast, as well as myocarditis (tigroid heart). However, the mechanism underlying the inflammatory response caused by FMDV is enigmatic. In this study, we identified the VP3 protein of FMDV as an important proinflammatory factor. Mechanistically, VP3 interacted with TLR4 to promote TLR4 expression by inhibiting the expression of the lysozyme-related protein Rab7b. Our findings suggest that FMDV VP3 is a major proinflammatory factor in FMDV-infected hosts.

Two Cross-Protective Antigen Sites on Foot-and-Mouth Disease Virus Serotype O Structurally Revealed by Broadly Neutralizing Antibodies from Cattle

Foot-and-mouth disease virus (FMDV) is a highly contagious virus that infects cloven-hoofed animals. Neutralizing antibodies play critical roles in antiviral infection. Although five known antigen sites that induce neutralizing antibodies have been defined, studies on cross-protective antigen sites are still scarce. We mapped two cross-protective antigen sites using 13 bovine-derived broadly neutralizing monoclonal antibodies (bnAbs) capable of neutralizing 4 lineages within 3 topotypes of FMDV serotype O. One antigen site was formed by a novel cluster of VP3-focused epitopes recognized by bnAb C4 and C4-like antibodies. The cryo-electron microscopy (cryo-EM) structure of the FMDV-OTi (O/Tibet/99)-C4 complex showed close contact with VP3 and a novel interprotomer antigen epitope around the icosahedral 3-fold axis of the FMDV particle, which is far beyond the known antigen site 4. The key determinants of the neutralizing function of C4 and C4-like antibodies on the capsid were βB (T65), the B-C loop (T68), the E-F loop (E131 and K134), and the H-I loop (G196), revealing a novel antigen site on VP3. The other antigen site comprised two group epitopes on VP2 recognized by 9 bnAbs (B57, B73, B77, B82, F28, F145, F150, E46, and E54), which belong to the known antigen site 2 of FMDV serotype O. Notably, bnAb C4 potently promoted FMDV RNA release in response to damage to viral particles, suggesting that the targeted epitope contains a trigger mechanism for particle disassembly. This study revealed two cross-protective antigen sites that can elicit cross-reactive neutralizing antibodies in cattle and provided new structural information for the design of a broad-spectrum molecular vaccine against FMDV serotype O. IMPORTANCE FMDV is the causative agent of foot-and-mouth disease (FMD), which is one of the most contagious and economically devastating diseases of domestic animals. The antigenic structure of FMDV serotype O is rather complicated, especially for those sites that can elicit a cross-protective neutralizing antibody response. Monoclonal neutralization antibodies provide both crucial defense components against FMDV infection and valuable tools for fine analysis of the antigenic structure. In this study, we found a cluster of novel VP3-focused epitopes using 13 bnAbs against FMDV serotype O from natural host cattle, which revealed two cross-protective antigen sites on VP2 and VP3. Antibody C4 targeting this novel epitope potently promoted viral particle disassembly and RNA release before infection, which may indicate a vulnerable region of FMDV. This study reveals new structural information about cross-protective antigen sites of FMDV serotype O, providing valuable and strong support for future research on broad-spectrum vaccines against FMD.

Emergency FMD Serotype O Vaccines Protect Cattle against Heterologous Challenge with a Variant Foot-and-Mouth Disease Virus from the O/ME-SA/Ind2001 Lineage

Vaccination is one of the best approaches to control and eradicate foot-and-mouth disease (FMD). To achieve this goal, vaccines with inactivated FMD virus antigen in suitable adjuvants are being used in addition to other control measures. However, only a limited number of vaccine strains are commercially available, which often have a restricted spectrum of activity against the different FMD virus strains in circulation. As a result, when new strains emerge, it is important to measure the efficacy of the current vaccine strains against these new variants. This is important for countries where FMD is endemic but also for countries that hold an FMD vaccine bank, to ensure they are prepared for emergency vaccination. The emergence and spread of the O/ME-SA/Ind-2001 lineage of viruses posed a serious threat to countries with OIE-endorsed FMD control plans who had not reported FMD for many years. In vitro vaccine-matching results showed a poor match (r₁-value < 0.3) with the more widely used vaccine strain O₁ Manisa and less protection in a challenge test. This paper describes the use of the O3039 vaccine strain as an alternative, either alone or in combination with the O₁ Manisa vaccine strain with virulent challenge by a O/ME-SA/Ind-2001d sub-lineage virus from Algeria (O/ALG/3/2014). The experiment included challenge at 7 days post-vaccination (to study protection and emergency use) and 21 days post-vaccination (as in standard potency studies). The results indicated that the O3039 vaccine strain alone, as well as the combination with O₁ Manisa, is effective against this strain of the O/ME-SA/Ind/2001d lineage, offering protection from clinical disease even after 7 days post-vaccination with a reduction in viraemia and virus excretion.

The Potential Adjuvanticity of CAvant®SOE for Foot-and-Mouth Disease Vaccine

Foot-and-mouth disease (FMD) is a notifiable contagious disease of cloven-hoofed mammals. A high potency vaccine that stimulates the host immune response is the foremost strategy used to prevent disease persistence in endemic regions. FMD vaccines comprise inactivated virus antigens whose immunogenicity is potentiated by immunogenic adjuvants. Oil-based adjuvants have clear advantages over traditional adjuvant vaccines; however, there is potential to develop novel adjuvants to increase the potency of FMD vaccines. Thus, we aimed to evaluate the efficacy of a novel water-in-oil emulsion, called CAvant^®SOE, as a novel vaccine adjuvant for use with inactivated FMD vaccines. In this study, we found that inactivated A22 Iraq virus plus CAvant^®SOE (iA22 Iraq-CAvant^®SOE) induced effective antigen-specific humoral (IgG, IgG1, and IgG2a) and cell-mediated immune responses (IFN-γ and IL-4) in mice. Immunization of pigs with a single dose of iA22 Iraq-CAvant^®SOE also elicited effective protection, with no detectable clinical symptoms against challenge with heterologous A/SKR/GP/2018 FMDV. Levels of protection are strongly in line with vaccine-induced neutralizing antibody titers. Collectively, these results indicate that CAvant^®SOE-adjuvanted vaccine is a promising candidate for control of FMD in pigs.

The Insufficient Activation of RIG-I-Like Signaling Pathway Contributes to Highly Efficient Replication of Porcine Picornaviruses in IBRS-2 Cells

Seneca Valley virus (SVV) or commonly known as senecavirus A, is one of the picornavirus that is associated with vesicular disease and neonatal mortality in swine herds. Our previous study found that SVV replicates extremely faster in porcine Instituto Biologico-Rim Suino-2 (IBRS-2) cells than that in porcine kidney-15 (PK-15) cells. However, the underlying mechanism remains unknown. In this study, we comprehensively compared the expression features between IBRS-2 cells and PK-15 cells in response to SVV infection by an unbiased high-throughput quantitative proteomic analysis. We found that the innate immune response–related pathways were efficiently activated in PK-15 cells but not in IBRS-2 cells during SVV infection. A large amount of interferon (IFN)-stimulated genes were induced in PK-15 cells. In contrast, no IFN-stimulated genes were induced in IBRS-2 cells. Besides, we determined similar results in the two cell lines infected by another porcine picornavirus foot-and-mouth disease virus. Further study demonstrated that the Janus kinase signal transducer and activator of transcription signaling pathway was functioning properly in both IBRS-2 and PK-15 cells. A systematic screening study revealed that the aberrant signal transduction from TANK-binding kinase 1 to IFN regulatory factor 3 in the retinoic acid–inducible gene I–like receptor signaling pathway in IBRS-2 cells was the fundamental cause of the different innate immune response manifestation and different viral replication rate in the two cell lines. Together, our findings determined the different features of IBRS-2 and PK-15 cell lines, which will help for clarification of the pathogenesis of SVV. Besides, identification of the underlying mechanisms will provide new targets and an insight for decreasing the viral clearance rate and probably improve the oncolytic effect by SVV in cancer cells.

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Divergent innate immune responses were triggered by SVV in IBRS-2 and PK-15 cells.

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SVV induced higher levels of type I IFN in PK-15 cells than in IBRS-2 cells.

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IBRS-2 cell line has an aberrant RLR pathway but an intact type I IFN pathway.

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TBK1-mediated antiviral signal transduction was dysfunctional in IBRS-2 cells.

Efficacy of SAT2 Foot-and-Mouth Disease Vaccines Formulated with Montanide ISA 206B and Quil-A Saponin Adjuvants

The effective control of foot-and-mouth disease (FMD) relies strongly on the separation of susceptible and infected livestock or susceptible livestock and persistently infected wildlife, vaccination, and veterinary sanitary measures. Vaccines affording protection against multiple serotypes for longer than six months and that are less reliant on the cold chain during handling are urgently needed for the effective control of FMD in endemic regions. Although much effort has been devoted to improving the immune responses elicited through the use of modern adjuvants, their efficacy is dependent on the formulation recipe, target species and administration route. Here we compared and evaluated the efficacy of two adjuvant formulations in combination with a structurally stabilized SAT2 vaccine antigen, designed to have improved thermostability, antigen shelf-life and longevity of antibody response. Protection mediated by the Montanide ISA 206B-adjuvanted or Quil-A Saponin-adjuvanted SAT2 vaccines were comparable. The Montanide ISA 206B-adjuvanted vaccine elicited a higher SAT2 neutralizing antibody response and three times higher levels of systemic IFN-γ responses at 14- and 28-days post-vaccination (dpv) were observed compared to the Quil-A Saponin-adjuvanted vaccine group. Interestingly, serum antibodies from the immunized animals reacted similarly to the parental vaccine virus and viruses containing mutations in the VP2 protein that simulate antigenic drift in nature.

DDX21, a Host Restriction Factor of FMDV IRES-Dependent Translation and Replication

In cells, the contributions of DEAD-box helicases (DDXs), without which cellular life is impossible, are of utmost importance. The extremely diverse roles of the nucleolar helicase DDX21, ranging from fundamental cellular processes such as cell growth, ribosome biogenesis, protein translation, protein–protein interaction, mediating and sensing transcription, and gene regulation to viral manipulation, drew our attention. We designed this project to study virus–host interactions and viral pathogenesis. A pulldown assay was used to investigate the association between foot-and-mouth disease virus (FMDV) and DDX21. Further insight into the DDX21–FMDV interaction was obtained through dual-luciferase, knockdown, overexpression, qPCR, and confocal microscopy assays. Our results highlight the antagonistic feature of DDX21 against FMDV, as it progressively inhibited FMDV internal ribosome entry site (IRES) -dependent translation through association with FMDV IRES domains 2, 3, and 4. To subvert this host helicase antagonism, FMDV degraded DDX21 through its non-structural proteins 2B, 2C, and 3C protease (3C^pro). Our results suggest that DDX21 is degraded during 2B and 2C overexpression and FMDV infection through the caspase pathway; however, DDX21 is degraded through the lysosomal pathway during 3C^pro overexpression. Further investigation showed that DDX21 enhanced interferon-beta and interleukin-8 production to restrict viral replication. Together, our results demonstrate that DDX21 is a novel FMDV IRES trans-acting factor, which negatively regulates FMDV IRES-dependent translation and replication.

Post-vaccination Monitoring to Assess Foot-and-Mouth Disease Immunity at Population Level in Korea

In South Korea, domestic cattle, pigs, and goats were subjected to mandatory foot-and-mouth disease (FMD) vaccination and year-round serosurveillance since 2011. In 2020, approximately USD 95 million was spent solely for FMD vaccine purchase for 59 million livestock, and 1.25 million samples were tested to estimate the population immunity and demonstrate the absence of virus circulation. As the FMD vaccination program was revised in 2018, the post-vaccination monitoring (PVM) was designed to evaluate the effectiveness of the vaccine program of three vaccines approved for routine use. To this end, monitoring post-vaccination immunity has been conducted by collecting 35,626 serum samples at 28 days post-vaccination following regular national vaccinations, which were carried out in April and in October in 2020. The design of the serological test for PVM was specially targeted at particular livestock groups, including dairy cattle, goats, and beef cattle aged 6–12 months, which were generally estimated to have a low expected seroprevalence. The risk factors had also been identified, considering the increased likelihood of infection in a particular location, herd size, and husbandry system applied in a targeted sample collection. Serum sample collection and SP-O and NSP antibody tests were performed by local veterinary laboratories using commercially available ELISAs. The current FMD vaccination program, which was performed twice a year following the regimen of primary vaccination and boost, resulted in over 80% population immunity. The seroprevalence monitored after the vaccination in fall was higher than the one studied in spring except in pigs. It was demonstrated that the seroprevalence of risk-based targeted samples ranged from 93.8 to 100% in cattle, 63.2 to 100% in pigs, and 20.0 to 100% in goats. Of note is the area near the North Korean borders which showed a relatively low seroprevalence among the targeted regions, and no NSP sero-positive reactor was detected in this region. When subpopulation immunity at the individual level was assessed, the seroprevalence in young cattle stock was slightly lower (95.8%) than that of adults (98.4%). In conclusion, the FMD vaccination campaign has been successfully implemented in Korea, and the PVM can be a supplementary program for massive routine surveillance in terms of providing timely information needed both to estimate population immunity and to properly target “risk-based surveillance.”