Preparation and application of porcine broadly neutralizing monoclonal antibodies in an immunoassay for efficiently detecting neutralizing antibodies against foot-and-mouth disease virus serotype O

Neutralizing antibodies provide vital protection against foot-and-mouth disease virus (FMDV). The virus neutralization test (VNT) is a gold standard method for the detection of neutralizing antibodies. However, its application is limited due to the requirement for live virus and unsuitability for large-scale serological surveillance. In this study, a porcine broadly neutralizing monoclonal antibody (PO18-10) against FMDV was obtained from the heterologous sequentially vaccinated pig using single-B-cell antibody technology. A competitive enzyme-linked immunosorbent assay (C-ELISA) for detecting neutralizing antibodies against FMDV serotype O was developed using biotinylated PO18-10 as a detector antibody. The sensitivity and specificity of the assay were 100% and 99.55%, respectively, and the positive/negative coincidence rate with VNT was 94%, suggesting that C-ELISA based on natural host-derived monoclonal antibody (mAb) could be a promising tool to detect neutralizing antibodies against FMDV serotype O and evaluate the vaccine efficacy.IMPORTANCEFoot-and-mouth disease virus (FMDV) serotype O is one of the most prevalent serotypes in the world. The neutralizing antibody titers in primo-vaccinated animals are directly related to their level of protection against a virus challenge. The development of a safe, rapid, and accurate method for the detection of the neutralizing antibody is essential for the control and eradication of FMD. In this study, an inter-serotype broadly neutralizing monoclonal antibody PO18-10 was successfully produced using single-B-cell antibody technology from sequentially vaccinated pigs. A competitive ELISA based on this natural host-derived mAb for the detection of neutralizing antibodies against FMDV serotype O was developed and validated. The assay demonstrates high sensitivity, specificity, and coincidence rate with VNT, making it an alternative tool for confirming FMDV infection and evaluating the vaccine efficacy.

Mapping novel antigenic determinants on foot-and-mouth disease virus serotype Asia 1 using neutralising monoclonal antibody resistant mutants

Foot-and-mouth disease (FMD) is a severe and, highly contagious viral disease caused by FMD virus (FMDV) that primarily targets ungulates. Identifying neutralising antigenic sites on the virus is crucial for understanding the virus's antigenic characteristics. Numerous studies have pinpointed the critical residues of the neutralising antigenic sites in FMDV serotypes O, A, and C. However, information on serotype Asia 1 is very limited. This study reports the generation and characterization of forty-one monoclonal antibodies (mAbs) against FMDV serotype Asia 1 (current Indian vaccine strain). Of these, a panel of 23 neutralising mAbs was utilized to generate mAb resistant (MAR) mutants for mapping the virus's antigenic sites. New critical residues defining sites 1, 2, and 4 in FMDV serotype Asia 1 were identified. These findings significantly enhance our understanding of the antigenic nature of FMDV serotype Asia 1, and provide insights to designing broadly acting vaccines against FMD.

Complete coding region sequence analyses and antigenic characterization of emerging lineage G-IX of foot- and-mouth disease virus serotype Asia1

Foot-and-mouth disease Virus (FMDV) serotype Asia1 is prevalent in the Indian subcontinent, with only G-III and G-VIII reported in India until 2020. However, in 2019, a novel genetic group within serotype Asia1, designated as G-IX, emerged in Bangladesh, followed by its detection in India in 2020. This report presents analyses of the complete coding region sequences of the G-IX lineage isolates. The length of the open reading frame (ORF) of the two G-IX isolates was 6990 nucleotides without any deletion or insertion. The G-IX isolates showed the highest sequence similarity with an isolate of G-III at the ORF, L, P2, and P3 regions, and with an isolate of G-VIII at the P1 region. Phylogenetic analysis based on the capsid region (P1) supports the hypothesis that G-VIII and G-IX originated from a common ancestor, as speculated earlier. Further, VP1 region-based phylogenetic analyses revealed the re-emergence of G-VIII after a gap of 3 years. One isolate of G-VIII collected during 2023 revealed a codon insertion in the G-H loop of VP1. The vaccine matching studies support the suitability of the currently used Indian vaccine strain IND63/1972 to contain outbreaks due to viruses belonging to G-IX.

Epidemiological and Genetic Insights of the Circulating Foot-and-Mouth Disease Virus Serotypes in Egypt

Foot-and-mouth disease virus (FMDV) remains a major threat to livestock in Egypt, with ongoing outbreaks involving serotypes A, O, and SAT2. This study aimed to improve the understanding of these circulating FMDV strains to improve control measures. Between 2022 and 2023, 134 cattle samples from across Egypt were analyzed, revealing a 67.9% positivity rate for Pan FMDV. Of these positive samples, 64 were identified as serotype A and 27 as serotype O. Genetic analysis indicated that serotype O strains clustered within the EA-3 topotype, suggesting endemic persistence and potential vaccine evasion, while serotype A strains were associated with the African topotype and linked to regions such as Ethiopia, Kenya, and Sudan. Notable amino acid mutations in the VP1 protein of both serotypes highlighted potential challenges to vaccine effectiveness. These findings underscore the need for enhanced surveillance, timely vaccine updates, and regional cooperation to effectively manage FMD outbreaks in Egypt and neighboring countries.

Diagnostic and prophylactic potential of a stabilized foot-and-mouth disease serotype Asia1 virus like particles designed through a structure guided approach

Intact capsids of foot-and-mouth disease virus (FMDV) play a vital role in eliciting a protective immune response. Any change in the physico-chemical environment of the capsids results in dissociation and poor immunogenicity. Structural bioinfomatics studies have been carried out to predict the amino acids at the interpentameric region that resulted in the identification of mutant virus-like particles(VLPs) of FMDV serotype Asia1/IND/63/1972. The insect cell expressed VLPs were evaluated for their stability by sandwich ELISA. Among 10 mutants, S93H showed maximum retention of antigenicity at different temperatures, indicating its higher thermal stability as revealed by the in-silico analysis and retained the antigenic sites of the virus demonstrated by Sandwich ELISA. The concordant results of the liquid phase blocking ELISA for estimation of antibody titre of known sera with stable mutant VLP as antigen in place of virus antigen demonstrate its diagnostic potential. The stable mutant VLP elicited a robust immune response with 85.6 % protection in guinea pigs against virus challenge. The stabilized VLP based antigen requires minimum biosafety and cold storage for production and transit besides, complying with differentiation of infected from vaccinated animals. It can effectively replace the conventional virus handling during antigen production for prophylactic and diagnostic use.

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.

Mapping of foot-and-mouth disease virus antigenic sites recognized by single-domain antibodies reveals different 146S particle specific sites and particle flexibility

Vaccination with intact (146S) foot-and-mouth disease virus (FMDV) particles is used to control FMD. However, 146S particles easily dissociate into stable pentameric 12S particles which are less immunogenic. We earlier isolated several single-domain antibody fragments (VHHs) that specifically bind either 146S or 12S particles. These particle-specific VHHs are excellent tools for vaccine quality control. In this study we mapped the antigenic sites recognized by these VHHs by competition ELISAs, virus neutralization, and trypsin sensitivity of epitopes. We included two previously described monoclonal antibodies (mAbs) that are either 12S specific (mAb 13A6) or 146S specific (mAb 9). Although both are 12S specific, the VHH M3F and mAb 13A6 were found to bind independent antigenic sites. M3F recognized a non-neutralizing and trypsin insensitive site whereas mAb 13A6 recognized the trypsin sensitive VP2 N-terminus. The Asia1 146S-specific site was trypsin sensitive, neutralizing and also recognized by the VHH M8F, suggesting it involves the VP1 GH-loop. The type A 146S-specific VHHs recognized two independent antigenic sites that are both also neutralizing but trypsin insensitive. The major site was further mapped by cross-linking mass spectrometry (XL-MS) of two broadly strain reactive 146S-specific VHHs complexed to FMDV. The epitopes were located close to the 2-fold and 3-fold symmetry axes of the icosahedral virus 3D structure, mainly on VP2 and VP3, overlapping the earlier identified mAb 9 site. Since the epitopes were located on a single 12S pentamer, the 146S specificity cannot be explained by the epitope being split due to 12S pentamer dissociation. In an earlier study the cryo-EM structure of the 146S-specific VHH M170 complexed to type O FMDV was resolved. The 146S specificity was reported to be caused by an altered conformation of this epitope in 12S and 146S particles. This mechanism probably also explains the 146S-specific binding by the two type A VHHs mapped by XL-MS since their epitopes overlapped with the epitope recognized by M170. Surprisingly, residues internal in the 146S quaternary structure were also cross-linked to VHH. This probably reflects particle flexibility in solution. Molecular studies of virus-antibody interactions help to further optimize vaccines and improve their quality control.

Relationship between neutralizing and opsonizing monoclonal antibodies against foot-and-mouth disease virus

Previous studies demonstrated that polyclonal antibodies against foot-and-mouth disease virus (FMDV) generated by vaccination can mediate immune functions not only through virus neutralization but also through promoting virus uptake by macrophages and dendritic cells that are otherwise resistant to FMDV infection. This causes abortive infections resulting in activation, enhanced antigen presentation but also cell death. Here we report the use of RAW264.7 cells representing a murine macrophage cells line to characterize opsonizing functions of a collection of monoclonal antibodies (mAbs) against FMDV O and A serotypes. We demonstrate that all neutralizing immunoglobulin G isotype mAbs are able to opsonize FMDV resulting in increased cell death of RAW264.7 cells. In contrast, neutralizing IgM antibodies did not possess this activity. Opsonization was observed with broader reactivity within the serotype when compared to neutralization. Importantly, the anti-O serotype D9 mAb reacting with the continuous epitope within the G-H loop of VP1 that contains the RGD binding site of FMDV, opsonized several FMDV serotypes despite its restricted neutralizing activity within the O serotype. Furthermore, by generating RAW264.7 cells expressing bovine CD32, an easy-to-use cell-based assay system to test for bovine antibody-dependent enhanced infection of FMDV was generated and tested with a collection of sera. The data indicate that opsonizing titers correlated better with vaccine dose when compared to neutralizing titers. On the other hand, neutralization and opsonization titers were similar predictive of protection. We conclude that low avidity interactions are sufficient to mediate Fcγ receptor-mediated immune functions that could contribute to protective immune responses against FMDV.

Characterization of the O/ME-SA/Ind-2001d foot-and-mouth disease virus epidemic recorded in the Maghreb during 2014-2015

The O/ME-SA/Ind-2001d has been the main foot-and-mouth disease virus (FMDV) lineage responsible for FMD epidemics outside the Indian subcontinent from 2013 to 2017. In 2014, outbreaks caused by this FMDV lineage were reported in Maghreb, where it was initially detected in Algeria and Tunisia and later in Morocco. This was the first incursion of an FMDV type O of exotic origin in the Maghreb region after 14 years of absence. In this study, we report analyses of both VP1 and whole-genome sequences (WGSs) generated from 22 isolates collected in Algeria and Tunisia between 2014 and 2015. All the WGSs analysed showed a minimum pairwise identity of 98.9% at the nucleotide level and 99% at the amino acid level (FMDV coding region). All Tunisian sequences shared a single putative common ancestor closely related to FMDV strains circulating in Libya during 2013. Whereas sequences from Algeria suggest the country experienced two virus introductions. The first introduction is represented by strains circulating in 2014 which are closely related to those from Tunisia, the second one, of which the origin is more uncertain, includes strains collected in Algeria in 2015 that gave origin to the 2015 outbreak reported in Morocco. Overall, our results demonstrated that a unique introduction of O/Ind-2001d FMDV occurred in Maghreb through Tunisia presumably in 2014, and from then the virus spread into Algeria and later into Morocco.

Evolutionary Dynamics of Foot and Mouth Disease Virus Serotype A and Its Endemic Sub-Lineage A/ASIA/Iran-05/SIS-13 in Pakistan

Foot and mouth disease (FMD) causes severe economic losses to the livestock industry of endemic countries, including Pakistan. Pakistan is part of the endemic pool 3 for foot and mouth disease viruses (FMDV), characterized by co-circulating O, A, and Asia 1 serotypes, as designated by the world reference laboratory for FMD (WRL-FMD). FMDV serotype A lineage ASIA/Iran-05 is widespread in buffalos and cattle populations and was first reported in Pakistan in 2006. This lineage has a high turnover, with as many as 10 sub-lineages reported from Pakistan over the years. In this study, we reconstructed the evolutionary, demographic, and spatial history of serotype A and one of its sub-lineages, A/ASIA/Iran-05/SIS-13, prevalent in Pakistan. We sequenced nearly complete genomes of three isolates belonging to sub-lineage A/ASIA/Iran-05/SIS-13. We estimated recombination patterns and natural selection acting on the serotype A genomes. Source and transmission routes in Pakistan were inferred, and the clustering pattern of isolates of the SIS-13 sub-lineage were mapped on a tree. We hereby report nearly complete genome sequences of isolates belonging to sub-lineage A/ASIA/Iran-05/SIS-13, along with purported recombinant genomes, and highlight that complete coding sequences can better elucidate the endemic history and evolutionary pressures acting on long-term co-circulating FMDV strains.

Avidity of Polyclonal Antibodies to Foot-and-Mouth Disease Virus in Bovine Serum Measured Using Bio-Layer Interferometry

Foot-and-mouth disease (FMD) is a disease of cloven-hoofed livestock caused by FMD virus (FMDV). FMD can be controlled through the use of inactivated vaccines, and it is well established that the protection afforded by FMD vaccines correlates strongly with neutralising antibody titres. However, the overall strength of binding, referred to as avidity, is also an important parameter with respect to the ability of antibodies to neutralise virus infection, and there is evidence that avidity can affect the level of protection afforded by FMDV vaccines. Here, as an alternative to modified enzyme-linked immunosorbent assays (avidity ELISAs) incorporating a chaotropic wash step, we used bio-layer interferometry (BLI) to measure the avidity of bovine polyclonal antibodies against FMDV capsids. We conducted preliminary experiments using recombinant FMDV capsids, as well as peptides representing antigenic loops, to demonstrate that the binding of monoclonal antibodies targeting specific antigenic sites could be detected using BLI. Subsequent experiments using polyclonal sera derived from FMD vaccinated cattle provided evidence of a positive correlation between the neutralising titre of the serum and the avidity as measured by BLI. Furthermore, we observed an increase in BLI avidity, as well as in the titre, in vaccinated animals upon challenge with the live virus.

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.

Evolutionary and Ecological Drivers Shape the Emergence and Extinction of Foot-and-Mouth Disease Virus Lineages

Livestock farming across the world is constantly threatened by the evolutionary turnover of foot-and-mouth disease virus (FMDV) strains in endemic systems, the underlying dynamics of which remain to be elucidated. Here, we map the eco-evolutionary landscape of cocirculating FMDV lineages within an important endemic virus pool encompassing Western, Central, and parts of Southern Asia, reconstructing the evolutionary history and spatial dynamics over the last 20 years that shape the current epidemiological situation. We demonstrate that new FMDV variants periodically emerge from Southern Asia, precipitating waves of virus incursions that systematically travel in a westerly direction. We evidence how metapopulation dynamics drive the emergence and extinction of spatially structured virus populations, and how transmission in different host species regulates the evolutionary space of virus serotypes. Our work provides the first integrative framework that defines coevolutionary signatures of FMDV in regional contexts to help understand the complex interplay between virus phenotypes, host characteristics, and key epidemiological determinants of transmission that drive FMDV evolution in endemic settings.

Molecular Basis of Antigenic Drift in Serotype O Foot-and-Mouth Disease Viruses (2013-2018) from Southeast Asia

Foot and mouth disease (FMD) is a highly contagious disease of cloven-hoofed animals with serious economic consequences. FMD is endemic in Southeast Asia (SEA) and East Asia (EA) with the circulation of multiple serotypes, posing a threat to Australia and other FMD-free countries. Although vaccination is one of the most important control measures to prevent FMD outbreaks, the available vaccines may not be able to provide enough cross-protection against the FMD viruses (FMDVs) circulating in these countries due to the incursion of new lineages and sub-lineages as experienced in South Korea during 2010, a FMD-free country, when a new lineage of serotype O FMDV (Mya-98) spread to the country, resulting in devastating economic consequences. In this study, a total of 62 serotype O (2013-2018) viruses selected from SEA and EA countries were antigenically characterized by virus neutralization tests using three existing (O/HKN/6/83, O/IND/R2/75 and O/PanAsia-2) and one putative (O/MYA/2009) vaccine strains and full capsid sequencing. The Capsid sequence analysis revealed three topotypes, Cathay, SEA and Middle East-South Asia (ME-SA) of FMDVs circulating in the region. The vaccines used in this study showed a good match with the SEA and ME-SA viruses. However, none of the recently circulating Cathay topotype viruses were protected by any of the vaccine strains, including the existing Cathay topotype vaccine (O/HKN/6/83), indicating an antigenic drift and, also the urgency to monitor this topotype in the region and develop a new vaccine strain if necessary, although currently the presence of this topotype is mainly restricted to China, Hong Kong, Taiwan and Vietnam. Further, the capsid sequences of these viruses were analyzed that identified several capsid amino acid substitutions involving neutralizing antigenic sites 1, 2 and 5, which either individually or together could underpin the observed antigenic drift.

Development of an Indirect Chemiluminescence Immunoassay Using a Multiepitope Recombinant Protein To Specifically Detect Antibodies against Foot-and-Mouth Disease Virus Serotype O in Swine

Foot-and-mouth disease virus (FMDV) has led to serious losses in animal husbandry worldwide. Seromonitoring of FMDV postvaccination is important for the control and eradication of foot-and-mouth disease (FMD) in regions and countries where vaccination is widespread. However, many commercial kits present high false-positive rates. In this study, a multiepitope-based indirect chemiluminescence immunoassay (ME-CLIA) was developed for specifically detecting antibodies against FMDV serotype O in swine sera. The developed method presented high diagnostic sensitivity and excellent diagnostic specificity, and it could detect a broad spectrum of antibodies against FMDV serotype O. The diagnostic performance, accuracy rate, and analytical sensitivity of ME-CLIA were compared with those of three commercial kits. The immune protection value of multiple-epitope recombinant vaccine detected using ME-CLIA was preliminarily determined by observation of clinical symptoms postimmunization challenge, the results of which indicated that the ME-CLIA can be employed as a matching detection method for evaluating multiple-epitope recombinant vaccine. The percent positive values of ME-CLIA determined using swine vaccinated with inactivated vaccine were significantly positively correlated with the titers of liquid-phase-blocking enzyme-linked immunosorbent assay (ELISA) (LBPE) (r = 0.8361; P < 0.0001). These results indicated that ME-CLIA is suitable for detection of antibodies against FMDV serotype O in swine and for potency evaluation of multiple-epitope and inactivated vaccines.

The history of foot-and-mouth disease virus serotype C: the first known extinct serotype?

Foot-and-mouth disease (FMD) is a highly contagious animal disease caused by an RNA virus subdivided into seven serotypes that are unevenly distributed in Asia, Africa, and South America. Despite the challenges of controlling FMD, since 1996 there have been only two outbreaks attributed to serotype C, in Brazil and in Kenya, in 2004. This article describes the historical distribution and origins of serotype C and its disappearance. The serotype was first described in Europe in the 1920s, where it mainly affected pigs and cattle but as a less common cause of outbreaks than serotypes O and A. No serotype C outbreaks have been reported in Europe since vaccination stopped in 1990. FMD virus is presumed to have been introduced into South America from Europe in the nineteenth century, although whether serotype C evolved there or in Europe is not known. As in Europe, this serotype was less widely distributed and caused fewer outbreaks than serotypes O and A. Since 1994, serotype C had not been reported from South America until four small outbreaks were detected in the Amazon region in 2004. Elsewhere, serotype C was introduced to Asia, in the 1950s to the 1970s, persisting and evolving for several decades in the Indian subcontinent and for eighteen years in the Philippines. Serotype C virus also circulated in East Africa between 1957 and 2004. Many serotype C viruses from European and Kenyan outbreaks were closely related to vaccine strains, including the most recently recovered Kenyan isolate from 2004. International surveillance has not confirmed any serotype C cases, worldwide, for over 15 years, despite more than 2,000 clinical submissions per year to reference laboratories. Serology provides limited evidence for absence of this serotype, as unequivocal interpretation is hampered by incomplete intra-serotype specificity of immunoassays and the continued use of this serotype in vaccines. It is recommended to continue strengthening surveillance in regions of FMD endemicity, to stop vaccination against serotype C and to reduce working with the virus in laboratories, since inadvertent escape of virus during such activities is now the biggest risk for its reappearance in the field.

Targeted Modification of the Foot-And-Mouth Disease Virus Genome for Quick Cell Culture Adaptation

Foot-and-mouth disease virus (FMDV) causes the highly contagious foot-and-mouth disease, which is characterized by the appearance of vesicles in and around the mouth and feet of cloven-hoofed animals. BHK-21 cells are the cell line of choice for the propagation of FMDV for vaccine production worldwide but vary in their susceptibility for different FMDV strains. Previous studies showed that the FMDV resistance of a certain BHK cell line can be overcome by using a closely related but permissive cell line for the pre-adaptation of the virus, but the adapted strains were found to harbor several capsid mutations. In this study, these adaptive mutations were introduced into the original Asia-1 Shamir isolate individually or in combination to create a panel of 17 Asia-1 mutants by reverse genetics and examine the effects of the mutations on receptor usage, viral growth, immunogenicity and stability. A single amino acid exchange from glutamic acid to lysine at position 202 in VP1 turned out to be of major importance for productive infection of the suspension cell line BHK-2P. In consequence, two traditionally passage-derived strains and two recombinant viruses with a minimum set of mutations were tested in vivo. While the passaged-derived viruses showed a reduced particle stability, the genetically modified viruses were more stable but did not confer a protective immune response against the original virus isolate.

Emergence of foot-and-mouth disease virus serotype Asia1 group IX in India

Foot-and-mouth disease virus (FMDV) serotype Asia1 is prevalent in India and is responsible for a minor proportion of FMD outbreaks. Globally, serotype Asia1 is grouped into nine different groups (GI-IX) based on genetic analysis. In India, only Asia1/G-III and Asia1/G-VIII have been documented so far. Phylogenetic analysis of recent serotype Asia1 isolates from India revealed the emergence of Asia1/G-IX. The Asia1/G-IX lineage shares recent common ancestry with Asia1/G-VIII dating to 2016. The root state posterior probabilities of Asia1/G-VIII are inclusive and there may have been either an incursion of the virus from Bangladesh, where it was first identified, or in situ evolution of the virus within India, which is an intriguing possibility.

Monitoring the performance of foot-and-mouth disease vaccines prepared against local strains in the face of antigenic evolution in the field

National programs for foot-and-mouth disease (FMD) eradication includes the use of vaccination; Turkey which is endemic to FMD virus (FMDV) (except for the Thrace region) and there is a risk of incursion of exotic strains from eastern borders. In 2015, a devastating outbreak was caused by the A/ASIA/G-VII (G-VII) lineage, which led to the inclusion of a new vaccine strain (A/TUR/15) derived from this lineage in 3 months. Although most of the cattle population in Turkey was then immunized with A/TUR/15 (vaccine coverage: 92.8%), the G-VII lineage continued to cause outbreaks in the field despite the evidence of protection observed with A/TUR/15 in in vivo and in vitro tests. When G-VII field strains were examined, changes in their genomes were detected. As the lineage appeared to be evolving, an unconventional vaccination strategy was adapted which changed the vaccine strain with new variants of G-VII according to antigenic evolution. To assess the suitability of candidate vaccine strains derived from the variants of the G-VII lineage, three viral candidates were assessed (A/TUR/15, A/TUR/16 and A/TUR/17) by in vitro virus neutralization tests for r₁ vaccine matching and in vivo heterologous challenge tests. Although all three vaccine strains were antigenically well matched with each other and other G-VII field viruses, due to continues outbreaks the vaccine strain was changed three times in 20 months from A/TUR/15 (Dec 2015) to A/TUR/16 (Dec 2016) and then to A/TUR/17 (Aug 2017). With this strategy serotype A has not been observed in the field since January 2018. This study highlights the importance of adapting the vaccine strains according to antigenic evolution as this could be a valuable combat strategy in endemic countries, rather than using well-known vaccine strain and relying only on the relationship coefficient (r₁ ) value.

Development and validation of a simplified serotyping ELISA based on monoclonal antibodies for the diagnosis of foot-and-mouth disease virus serotypes O, A, C and Asia 1

This study describes the development and validation of a simplified enzyme-linked immunosorbent assay (ELISA) for the detection and discrimination of foot-and-mouth disease virus (FMDV) serotypes O, A, C and Asia 1. The multiplex ELISA was designed using selected, type-specific monoclonal antibodies (MAbs) coated onto ELISA plates as catching antibodies and a unique pan-FMDV MAb (1F10) as detector conjugate. Capture MAbs with the broadest intratypic reactivity were selected for each of the four FMDV serotypes by screening large panels of candidate MAbs with a wide spectrum of representative FMDV isolates. An additional pan-FMDV ELISA using 1F10 MAb for both capture and detection was used to complement the specific typing ELISAs to detect virus isolates, which might escape binding to the selected serotype-specific MAbs. This multiplex ELISA was prepared in a stabilized format, with immunoplates pre-coated with six MAbs and positive antigen controls already trapped by the relevant MAb, with the view to make available a diagnostic kit. Diagnostic performance of the MAbs-multiplex ELISA was analysed using 299 FMDV-positive epithelial suspensions representative of the antigenic and genomic variability within each serotype. Overall, the results provided evidence that the diagnostic performance of this assay platform is improved compared to the more complex polyclonal-based antigen detection ELISA; combining data from different serotypes and referring to the gold standard tests (i.e. virus isolation and/or RT-PCR), the MAbs-multiplex ELISA showed a sensitivity of 79% for the serotype-specific ELISA, compared to 72% for the polyclonal ELISA. The absence of reactivity of a minority of FMDV strains using the MAbs-multiplex ELISA can largely be attributed to deteriorated or low antigen concentration in the sample. This multiplex ELISA is simple, rapid and stable. FMDV antigenic diversity was adequately covered by the selected MAbs. Therefore, it can be used to replace existing polyclonal ELISAs for FMDV detection and serotyping.

Detection of Bovine Antibodies against a Conserved Capsid Epitope as the Basis of a Novel Universal Serological Test for Foot-and-Mouth Disease

Diagnostic tests for foot-and-mouth disease (FMD) include the detection of antibodies against either the viral nonstructural proteins or the capsid. The detection of antibodies against the structural proteins (SP) of the capsid can be used to monitor seroconversion in both infected and vaccinated animals. However, SP tests need to be tailored to the individual FMD virus (FMDV) serotype and their sensitivity may be affected by antigenic variability within each serotype and mismatching between test reagents. As a consequence, FMD reference laboratories are required to maintain multiple type-specific SP assays and reagents. A universal SP test would simplify frontline diagnostics and facilitate large-scale serological surveillance and postvaccination monitoring. In this study, a highly conserved region in the N terminus of FMDV capsid protein VP2 (VP2N) was characterized using a panel of intertype-reactive monoclonal antibodies. This revealed a universal epitope in VP2N which could be used as a peptide antigen to detect FMDV-specific antibodies against all types of the virus. A VP2-peptide enzyme-linked immunosorbent assay (VP2-ELISA) was optimized using experimental and reference antisera from immunized, convalescent, and naïve animals (n = 172). The VP2-ELISA is universal and simple and provided sensitive (99%) and specific (93%) detection of antibodies to all FMDV strains used in this study. We anticipate that this SP test could have utility for serosurveillance during virus incursions in FMD-free countries and as an additional screening tool to assess FMD virus circulation in countries where the disease is endemic.

Towards improvements in foot-and-mouth disease vaccine performance

Foot-and-mouth disease (FMD) remains one of the most economically important infectious diseases of production animals. Six (out of 7 that have been identified) different serotypes of the FMD virus continue to circulate in different parts of the world. Within each serotype there is also extensive diversity as the virus constantly changes. Vaccines need to be “matched” to the outbreak strain, not just to the serotype, to confer protection. Vaccination has been used successfully to assist in the eradication of the disease from Europe but is no longer employed there unless outbreaks occur. Thus the animal population in Europe, as in North America, is fully susceptible to the virus if it is accidentally (or deliberately) introduced. Almost 3 billion doses of the vaccine are made each year to control the disease elsewhere. Current vaccines are produced from chemically inactivated virus that has to be grown, on a large scale, under high containment conditions. The vaccine efficiently prevents disease but the duration of immunity is rather limited (about 6 months) and vaccination does not provide sterile immunity or block the development of carriers. Furthermore, the vaccine is quite unstable and a cold chain needs to be maintained to preserve the efficacy of the vaccine. This can be a challenge in the parts of the world where the disease is endemic. There is a significant interest in developing improved vaccines and significant progress in this direction has been made using a variety of approaches. However, no alternative vaccines are yet available commercially. Improved disease control globally is clearly beneficial to all countries as it reduces the risk of virus incursions into disease free areas.

Implication of Broadly Neutralizing Bovine Monoclonal Antibodies in the Development of an Enzyme-Linked Immunosorbent Assay for Detecting Neutralizing Antibodies against Foot-and-Mouth Disease Virus Serotype O

Vaccination with inactivated vaccines is still the main measure to control foot-and-mouth disease (FMD) in areas where the disease is endemic, and the level of neutralizing antibody in vaccinated animals is directly related to their protection against virus challenge. Currently, neutralizing antibody is mainly detected using the virus neutralization test (VNT) based on cell culture, which is laborious and time-consuming and requires restrictive biocontainment facilities. In this study, two broadly neutralizing antibodies (bnAbs), E46 and F128, were successfully produced using techniques for the isolation of single B cells from peripheral blood mononuclear cells (PBMCs) from bovines sequentially immunized with three topotypes of foot-and-mouth disease virus (FMDV) serotype O. Based on these bnAbs, a blocking enzyme-linked immunosorbent assay (ELISA) for detecting neutralizing antibodies (NA-ELISA) against FMDV serotype O was developed. The specificity and sensitivity of the test were estimated to be 99.21% and 100%, respectively. A significant correlation (P < 0.01) was observed between the NA-ELISA titers and the VNT titers for all sera from vaccinated animals and for all tested strains, suggesting that the NA-ELISA could detect neutralizing antibodies against FMDV serotype O strains of wide antigenic and molecular diversity and could be used for the evaluation of protective immunity.

Review on Outbreak Dynamics, the Endemic Serotypes, and Diversified Topotypic Profiles of Foot and Mouth Disease Virus Isolates in Ethiopia from 2008 to 2018

Foot and mouth disease (FMD) endemicity in Ethiopia's livestock remains an ongoing cause for economic concern, with new topotypes still arising even in previously unaffected areas. FMD outbreaks occur every year almost throughout the country. Understanding the outbreak dynamics, endemic serotypes, and lineage profiles of FMD in this country is very critical in designing control and prevention programs. For this, detailed information on outbreak dynamics in Ethiopia needs to be understood clearly. In this article, therefore, we review the spatial and temporal patterns and dynamics of FMD outbreaks from 2008 to 2018. The circulating serotypes and the topotypic profiles of the virus are also discussed. FMD outbreak data were obtained from; reports of MoARD (Ministry of Agriculture and Rural Development)/MoLF (Ministry of livestock and Fishery, NVI (National Veterinary Institute), and NAHDIC (National Animal Health Diagnostic and Investigation Center); published articles; MSc works; PhD theses; and documents from international organizations. To effectively control and prevent FMD outbreaks, animal health agencies should focus on building surveillance systems that can quickly identify and control ongoing outbreaks and implement efficient preventive measures.

Differential antibody responses to the major antigenic sites of FMD virus serotype O after primo-vaccination, multiply-vaccination and after natural exposure

Foot and mouth disease (FMD) virus serotype O is the predominant cause of FMD outbreaks in several regions of the world including India. Five independent neutralizing antigenic sites have been identified on the capsid surface of FMD virus serotype O. The relative importance of these neutralizing sites in eliciting antibody responses in the polyclonal sera collected from un-infected vaccinated (both primo and multiply-vaccinated) and naturally infected cattle populations were determined through a combination of reverse genetics and serology. The known critical amino acid residues present on the five antigenic sites of FMD virus serotype O Indian vaccine strain O IND R2/1975 were mutated through site-directed mutagenesis. The mutant viruses were rescued in cell-culture and analyzed through virus-neutralization assays along with parent virus using the polyclonal sera collected from three groups of cattle. In the polyclonal sera from primo-vaccinated cattle, significantly higher level of antibodies were directed towards antigenic site 2. In contrast, in polyclonal sera from multiply vaccinated animals, both antigenic sites 1 and 2 were equally important. In case of naturally infected animals, antibody responses were elicited against all the five antigenic sites. Although a drop in neutralization titres was observed for all the mutants, in one instance, increase in titre was noticed for a site 3 mutant. The findings from this study extend our knowledge on the antibody immunodominace following FMDV vaccination and infection, and may improve our strategies for vaccine strain selection and rational vaccine design.

Identification of novel epitopes in serotype O foot-and-mouth disease virus by in vitro immune selection

Foot-and-mouth disease virus (FMDV) displays various epitopes on the capsid outer surface. In addition to the five neutralizing antigenic sites, there is evidence of the existence of other, yet unidentified, epitopes that are believed to play a role in antibody-mediated protection. Previous attempts to identify these epitopes revealed two additional substitutions at positions VP2-74 and -191 (5M2/5 virus) to be of antigenic significance. However, complete resistance to neutralization was not obtained in the neutralization assay, indicating the existence of other, undisclosed epitopes. Results from this study provides evidence of at least two new neutralizing epitopes involving residues VP3-116 and -195 around the threefold axis that have significant impact on the antigenic nature of the virus. These findings extend our knowledge of the surface features of the FMDV capsid known to elicit neutralizing antibodies, and should help with rational vaccine design.

Foot-and-mouth disease outbreaks due to an exotic virus serotype A lineage (A/AFRICA/G-IV) in Algeria in 2017

This study describes the genetic characterization of serotype A viruses collected during outbreaks of foot-and-mouth disease (FMD) that occurred in Algeria in 2017. These are the first reports of clinical cases due to this serotype in the country since 1977. One complete genomic sequence (comprising 8,119 nucleotides) and three additional near-complete genomic sequences were generated. Phylogenetic analyses demonstrated that these viruses were classified within the A/AFRICA/G-IV lineage, most closely related to viruses circulating in Nigeria between 2009 and 2015. These unexpected results motivate further studies to define the precise pathways by which this viral lineage has been introduced into North Africa in order to understand risks of future disease incursions into the region.

Recombinant mutagenic 3ABC protein and monoclonal antibody for quality-control testing in foot-and-mouth disease vaccines

To achieve the goal of performing quality control on vaccines for foot-and-mouth disease several steps were performed in this study. First, the gene that encodes the 3ABC region of the A24 Cruzeiro strain (which is used in vaccine production) was amplified. Second, to improve protein stability, the 3ABC protein was mutated at the 3C^pro catalytic site and cloned the amplification products in the pET-SUMO expression vector. In the third step, the resulting recombinant protein was tested, which the polyclonal antibody recognized, with the semi-purified viral 3ABC protein using an immunoassay test. Fourth, the muted recombinant protein was used to produce a monoclonal antibody. Of the 217 clones obtained, two of them that were particularly stable (mAb2D3 and mAb3D12) were selected to work with. One showed better results, as characterized by immunoassay (ELISA), Western blotting, spot synthesis, and sequencing methodologies; it also showed high reactivity against the 3ABC protein. This kind of monoclonal antibodies, which was considered as immunochemical inputs, have been used in industrial processes as part of quality-control procedures, to evaluate the elimination of the 3ABC protein so as to ensure regulatory approval of the vaccine. They have also been used in immunological tests to distinguish infected from vaccinated animals.

Foot and mouth disease vaccine strain selection: current approaches and future perspectives

INTRODUCTION

Lack of cross protection between foot and mouth disease (FMD) virus (FMDV) serotypes as well as incomplete protection between some subtypes of FMDV affect the application of vaccine in the field. Further, the emergence of new variant FMD viruses periodically makes the existing vaccine inefficient. Consequently, periodical vaccine strain selection either by in vivo methods or in vitro methods become an essential requirement to enable utilization of appropriate and efficient vaccines.

AREAS COVERED

Here we describe the cross reactivity of the existing vaccines with the global pool of circulating viruses and the putative selected vaccine strains for targeting protection against the two major circulating serotype O and A FMD viruses for East Africa, the Middle East, South Asia and South East Asia.

EXPERT COMMENTARY

Although in vivo cross protection studies are more appropriate methods for vaccine matching and selection than in vitro neutralization test or ELISA, in the face of an outbreak both in vivo and in vitro methods of vaccine matching are not easy, and time consuming. The FMDV capsid contains all the immunogenic epitopes, and therefore vaccine strain prediction models using both capsid sequence and serology data will likely replace existing tools in the future.

Single-cell analysis reveals the relevance of foot-and-mouth disease virus persistence to emopamil-binding protein gene expression in host cells

Foot-and-mouth disease virus (FMDV) infects host cells in either an acute or persistent manner. In this study, we examined the relevance of the establishment of FMDV persistence to the expression of the emopamil-binding protein (EBP) gene in 231 individual persistently infected baby hamster kidney (BHK-21) cells after passages 28, 38, and 68 (PI28, PI38, and PI68). At PI28, the stage at which persistent infection of FDMV becomes unstable, the percentage of cells carrying FMDV was 66.7%, while 80.2% of cells were EBP positive. Additionally, in 55.6% of the EBP-positive cells at PI28, EBP expression was upregulated approximately 149.9% compared to uninfected BHK-21 cells. This was the highest expression level among all cell passages measured. Interestingly, in a parallel experiment, the average EBP expression level in the whole cell population at PI28 was only slightly higher (108.2%) than that in uninfected BHK-21 cells. At PI38, 98.7% of the cells were positive for FMDV 3D (an RNA-dependent RNA polymerase enzyme gene), and its maximum expression level observed at this passage. The expression level of EBP in 78.2% of the total cells, however, was reduced significantly. At PI68, 95.8% of the cells were 3D positive, and the expression of both the EBP and 3D genes were at the lowest levels of all the passages. Our studies using single cells yielded data that are otherwise inaccessible a using whole cell population. These results suggest that the establishment of persistent infection by FMDV is a dynamic process that results from the continuous adaptation and coevolution of viruses and cells to reach an equilibrium.

Isolation of Single-Domain Antibody Fragments That Preferentially Detect Intact (146S) Particles of Foot-and-Mouth Disease Virus for Use in Vaccine Quality Control

Intact (146S) foot-and-mouth disease virus (FMDVs) can dissociate into specific (12S) viral capsid degradation products. FMD vaccines normally consist of inactivated virions. Vaccine quality is dependent on 146S virus particles rather than 12S particles. We earlier isolated two llama single-domain antibody fragments (VHHs) that specifically recognize 146S particles of FMDV strain O₁ Manisa and shown their potential use in quality control of FMD vaccines during manufacturing. These 146S-specific VHHs were specific for particular O serotype strains and did not bind strains from other FMDV serotypes. Here, we describe the isolation of 146S-specific VHHs against FMDV SAT2 and Asia 1 strains by phage display selection from llama immune libraries. VHHs that bind both 12S and 146S particles were readily isolated but VHHs that bind specifically to 146S particles could only be isolated by phage display selection using prior depletion for 12S particles. We obtained one 146S-specific VHH-M332F-that binds to strain Asia 1 Shamir and several VHHs that preferentially bind 146S particles of SAT2 strain SAU/2/00, from which we selected VHH M379F for further characterization. Both M332F and M379F did not bind FMDV strains from other serotypes. In a sandwich enzyme-linked immunosorbent assay (ELISA) employing unlabeled and biotinylated versions of the same VHH M332F showed high specificity for 146S particles but M379F showed lower 146S-specificity with some cross-reaction with 12S particles. These ELISAs could detect 146S particle concentrations as low as 2.3-4.6 µg/l. They can be used for FMD vaccine quality control and research and development, for example, to identify virion stabilizing excipients.

Tracking the Antigenic Evolution of Foot-and-Mouth Disease Virus

Quantifying and predicting the antigenic characteristics of a virus is something of a holy grail for infectious disease research because of its central importance to the emergence of new strains, the severity of outbreaks, and vaccine selection. However, these characteristics are defined by a complex interplay of viral and host factors so that phylogenetic measures of viral similarity are often poorly correlated to antigenic relationships. Here, we generate antigenic phylogenies that track the phenotypic evolution of two serotypes of foot-and-mouth disease virus by combining host serology and viral sequence data to identify sites that are critical to their antigenic evolution. For serotype SAT1, we validate our antigenic phylogeny against monoclonal antibody escape mutants, which match all of the predicted antigenic sites. For serotype O, we validate it against known sites where available, and otherwise directly evaluate the impact on antigenic phenotype of substitutions in predicted sites using reverse genetics and serology. We also highlight a critical and poorly understood problem for vaccine selection by revealing qualitative differences between assays that are often used interchangeably to determine antigenic match between field viruses and vaccine strains. Our approach provides a tool to identify naturally occurring antigenic substitutions, allowing us to track the genetic diversification and associated antigenic evolution of the virus. Despite the hugely important role vaccines have played in enhancing human and animal health, vaccinology remains a conspicuously empirical science. This study advances the field by providing guidance for tuning vaccine strains via site-directed mutagenesis through this high-resolution tracking of antigenic evolution of the virus between rare major shifts in phenotype.

Prediction and characterization of novel epitopes of serotype A foot-and-mouth disease viruses circulating in East Africa using site-directed mutagenesis

Epitopes on the surface of the foot-and-mouth disease virus (FMDV) capsid have been identified by monoclonal antibody (mAb) escape mutant studies leading to the designation of four antigenic sites in serotype A FMDV. Previous work focused on viruses isolated mainly from Asia, Europe and Latin America. In this study we report on the prediction of epitopes in African serotype A FMDVs and testing of selected epitopes using reverse genetics. Twenty-four capsid amino acid residues were predicted to be of antigenic significance by analysing the capsid sequences (n = 56) using in silico methods, and six residues by correlating capsid sequence with serum-virus neutralization data. The predicted residues were distributed on the surface-exposed capsid regions, VP1-VP3. The significance of residue changes at eight of the predicted epitopes was tested by site-directed mutagenesis using a cDNA clone resulting in the generation of 12 mutant viruses involving seven sites. The effect of the amino acid substitutions on the antigenic nature of the virus was assessed by virus neutralization (VN) test. Mutations at four different positions, namely VP1-43, VP1-45, VP2-191 and VP3-132, led to significant reduction in VN titre (P value = 0.05, 0.05, 0.001 and 0.05, respectively). This is the first time, to our knowledge, that the antigenic regions encompassing amino acids VP1-43 to -45 (equivalent to antigenic site 3 in serotype O), VP2-191 and VP3-132 have been predicted as epitopes and evaluated serologically for serotype A FMDVs. This identifies novel capsid epitopes of recently circulating serotype A FMDVs in East Africa.

Antigenic and genetic comparison of foot-and-mouth disease virus serotype O Indian vaccine strain, O/IND/R2/75 against currently circulating viruses

Foot-and-mouth disease (FMD) virus serotype O is the most common cause of FMD outbreaks in India and three of the six lineages that have been described are most frequently detected, namely Ind2001, PanAsia and PanAsia 2. We report the full capsid sequence of 21 serotype O viruses isolated from India between 2002 and 2012. All these viruses belong to the Middle East-South Asia (ME-SA) topotype. The serological cross-reactivity of a bovine post-vaccination serum pool raised against the current Indian vaccine strain, O/IND/R2/75,was tested by virus neutralisation test with the 23 Indian field isolates, revealing a good match between the vaccine and the field isolates. The cross reactivity of the O/IND/R2/75 vaccine with 19 field isolates from other countries (mainly from Asia and Africa) revealed a good match to 79% of the viruses indicating that the vaccine strain is broadly cross-reactive and could be used to control FMD in other countries. Comparison of the capsid sequences of the serologically non-matching isolates with the vaccine strain sequence identified substitutions in neutralising antigenic sites 1 and 2, which could explain the observed serological differences.

Genetic and antigenic characterisation of serotype A FMD viruses from East Africa to select new vaccine strains

Vaccine strain selection for emerging foot-and-mouth disease virus (FMDV) outbreaks in enzootic countries can be addressed through antigenic and genetic characterisation of recently circulating viruses. A total of 56 serotype A FMDVs isolated between 1998 and 2012, from Central, East and North African countries were characterised antigenically by virus neutralisation test using antisera to three existing and four candidate vaccine strains and, genetically by characterising the full capsid sequence data. A Bayesian analysis of the capsid sequence data revealed the viruses to be of either African or Asian topotypes with subdivision of the African topotype viruses into four genotypes (Genotypes I, II, IV and VII). The existing vaccine strains were found to be least cross-reactive (good matches observed for only 5.4-46.4% of the sampled viruses). Three bovine antisera, raised against A-EA-2007, A-EA-1981 and A-EA-1984 viruses, exhibited broad cross-neutralisation, towards more than 85% of the circulating viruses. Of the three vaccines, A-EA-2007 was the best showing more than 90% in-vitro cross-protection, as well as being the most recent amongst the vaccine strains used in this study. It therefore appears antigenically suitable as a vaccine strain to be used in the region in FMD control programmes.

Challenges and prospects for the control of foot-and-mouth disease: an African perspective

The epidemiology of foot-and-mouth disease (FMD) in Africa is unique in the sense that six of the seven serotypes of FMD viruses (Southern African Territories [SAT] 1, SAT2, SAT3, A, O, and C), with the exception of Asia-1, have occurred in the last decade. Due to underreporting of FMD, the current strains circulating throughout sub-Saharan Africa are in many cases unknown. For SAT1, SAT2, and serotype A viruses, the genetic diversity is reflected in antigenic variation, and indications are that vaccine strains may be needed for each topotype. This has serious implications for control using vaccines and for choice of strains to include in regional antigen banks. The epidemiology is further complicated by the fact that SAT1, SAT2, and SAT3 viruses are maintained and spread by wildlife, persistently infecting African buffalo in particular. Although the precise mechanism of transmission of FMD from buffalo to cattle is not well understood, it is facilitated by direct contact between these two species. Once cattle are infected they may maintain SAT infections without the further involvement of buffalo. No single strategy for control of FMD in Africa is applicable. Decision on the most effective regional control strategy should focus on an ecosystem approach, identification of primary endemic areas, animal husbandry practices, climate, and animal movement. Within each ecosystem, human behavior could be integrated in disease control planning. Different regions in sub-Saharan Africa are at different developmental stages and are thus facing unique challenges and priorities in terms of veterinary disease control. Many science-based options targeting improved vaccinology, diagnostics, and other control measures have been described. This review therefore aims to emphasize, on one hand, the progress that has been achieved in the development of new technologies, including research towards improved tailored vaccines, appropriate vaccine strain selection, vaccine potency, and diagnostics, and how it relates to the conditions in Africa. On the other hand, we focus on the unique epidemiological, ecological, livestock farming and marketing, socioeconomic, and governance issues that constrain effective FMD control. Any such new technologies should have the availability of safe livestock products for trade as the ultimate goal.

Determining the epitope dominance on the capsid of a serotype SAT2 foot-and-mouth disease virus by mutational analyses

Monoclonal-antibody (MAb)-resistant mutants were used to map antigenic sites on foot-and-mouth disease virus (FMDV), which resulted in the identification of neutralizing epitopes in the flexible βG-βH loop in VP1. For FMDV SAT2 viruses, studies have shown that at least two antigenic sites exist. By use of an infectious SAT2 cDNA clone, 10 structurally exposed and highly variable loops were identified as putative antigenic sites on the VP1, VP2, and VP3 capsid proteins of SAT2/Zimbabwe (ZIM)/7/83 (topotype II) and replaced with the corresponding regions of SAT2/Kruger National Park (KNP)/19/89 (topotype I). Virus neutralization assays using convalescent-phase antisera raised against the parental virus, SAT2/ZIM/7/83, indicated that the mutant virus containing the TQQS-to-ETPV mutation in the N-terminal part of the βG-βH loop of VP1 showed not only a significant increase in the neutralization titer but also an increase in the index of avidity to the convalescent-phase antisera. Furthermore, antigenic profiling of the epitope-replaced and parental viruses with nonneutralizing SAT2-specific MAbs led to the identification of two nonneutralizing antigenic regions. Both regions were mapped to incorporate residues 71 to 72 of VP2 as the major contact point. The binding footprint of one of the antigenic regions encompasses residues 71 to 72 and 133 to 134 of VP2 and residues 48 to 50 of VP1, and the second antigenic region encompasses residues 71 to 72 and 133 to 134 of VP2 and residues 84 to 86 and 109 to 11 of VP1. This is the first time that antigenic regions encompassing residues 71 to 72 of VP2 have been identified on the capsid of a SAT2 FMDV.

IMPORTANCE

Monoclonal-antibody-resistant mutants have traditionally been used to map antigenic sites on foot-and-mouth disease virus (FMDV). However, for SAT2-type viruses, which are responsible for most of the FMD outbreaks in Africa and are the most varied of all seven serotypes, only two antigenic sites have been identified. We have followed a unique approach using an infectious SAT2 cDNA genome-length clone. Ten structurally surface-exposed, highly varied loops were identified as putative antigenic sites on the VP1, VP2, and VP3 capsid proteins of the SAT2/ZIM/7/83 virus. These regions were replaced with the corresponding regions of an antigenically disparate virus, SAT2/KNP/19/89. Antigenic profiling of the epitope-replaced and parental viruses with SAT2-specific MAbs led to the identification of two unique antibody-binding footprints on the SAT2 capsid. In this report, evidence for the structural engineering of antigenic sites of a SAT2 capsid to broaden cross-reactivity with antisera is provided.

Genetic basis of antigenic variation in foot-and-mouth disease serotype A viruses from the Middle East

Foot-and-mouth disease viruses (FMDV) from serotype A exhibit high antigenic diversity. Within the Middle East, a strain called A-Iran-05 emerged in 2003, and subsequently replaced the A-Iran-96 and A-Iran-99 strains that were previously circulating in the region. Viruses from this strain did not serologically match with the established A/Iran/96 vaccine, although most early samples matched with the older A22/Iraq vaccine. However, many viruses from this strain collected after 2006 had poor serological match with the A22/Iraq vaccine necessitating the development of a new vaccine strain (A/TUR/2006). More recently, viruses from the region now exhibit lower cross-reactivity with the A/TUR/2006 antisera highlighting the inadequacy of the serotype A vaccines used in the region. In order to understand the genetic basis of these antigenic phenotypes, we have determined the full capsid sequence for 57 Middle Eastern viruses isolated between 1996 and 2011 and analysed these data in context of antigenic relationship (r1) values that were generated using antisera to A22/Iraq and A/TUR/2006. Comparisons of capsid sequences identified substitutions in neutralising antigenic sites (1, 2 and 4), which either individually or together underpin these observed antigenic phenotypes.