Microneutralization tests for serological typing and subtyping of foot-and-mouth disease virus strains

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.

Compared to Aluminum Hydroxide Adjuvant, Montanide ISA 206 VG Induces a Higher and More Durable Neutralizing Antibody Response against FMDV in Goats

Foot-and-mouth disease (FMD) has a high prevalence in cloven-hoofed animals. It is also highly contagious and remains a serious threat to livestock worldwide. Despite the widespread vaccination program in Iran, outbreaks of FMD continue to occur. Vaccination is one of the most effective methods of preventing FMD. The vaccines used in Iran are of the inactivated type and contain several serotypes. Since inactivated vaccines without adjuvants do not induce a high and durable antibody response, it is necessary to use adjuvants. Montanide ISA 206 VG is a mineral oil-based adjuvant that produces a water-in-oil-in-water (w:o:w) emulsion in vaccine preparations. However, a large number of manufacturers in Iran and around the world still use alum adjuvant (with or without saponin) to produce the FMD vaccine. This study used Montanide ISA 206 and alum adjuvants to administer the O2010 serotype of the FMD virus to goats. A total of six goats were divided randomly into three groups. Vaccines were administered subcutaneously twice, at a one-month interval. Blood sampling was done at different times, and the micro-neutralization method was used to measure the neutralizing antibody titer in each serum. Seven days after the second vaccination, the alum group's antibody titer was higher but not statistically significant. However, from the 28th day after the second injection until the end of the study, the Montanide ISA 206 group's antibody titer was significantly higher than that of the alum group. Six months after the second injection, the antibody titer in the ISA 206 group remained at the peak level, while in the alum group, it decreased and reached the minimum protective level. Nine months after the second injection, the antibody titer remained at its peak level in the ISA 206 group, whereas it dropped significantly in the alum group. Based on the findings, ISA 206 VG is capable of generating long-term humoral immunity in goats against the FMD serotype O2010 and could replace aluminum hydroxide adjuvants in FMD vaccine preparations.

Emergence of a novel genetic lineage 'A/ASIA/G-18/2019' of foot and mouth disease virus serotype A in India: A challenge to reckon with

Foot and mouth disease (FMD) has engendered large scale socioeconomic crises on numerous occasions owing to its extreme contagiousness, transboundary nature, complicated epidemiology, negative impact on productivity, trade embargo, and need for intensive surveillance and expensive control measures. Emerging FMD virus variants have been predicted to have originated and spread from endemic Pool 2, native to South Asia, to other parts of the globe. In this study, 26 Indian serotype A isolates sampled between the year 2015 and 2022 were sequenced for the VP1 region. BLAST and maximum likelihood phylogeny suggest emergence of a novel genetic group within genotype 18, named here as 'A/ASIA/G-18/2019' lineage, that is restricted so far only to India and its eastern neighbour, Bangladesh. The lineage subsequent to its first appearance in 2019 seems to have displaced all other prevalent strains, in support of the phenomenon of 'genotype/lineage turnover'. It has diversified into two distinct sub-clusters, reflecting a phase of active evolution. The rate of evolution of the VP1 region for the Indian serotype A dataset was estimated to be 6.747 × 10-3 substitutions/site/year. India is implementing a vaccination centric FMD control programme. The novel lineage showed good antigenic match with the proposed vaccine candidate A IND 27/2011 when tested in virus neutralization test, while the existing vaccine strain A IND 40/2000 showed homology with only 31% of the isolates. Therefore, in order to combat this challenge of antigenic divergence, A IND 27/2011 could be the preferred strain in the Indian vaccine formulations.

Foot-and-Mouth Disease Virus Serotype O Exhibits Phenomenal Genetic Lineage Diversity in India during 2018-2022

In India, widespread foot-and-mouth disease (FMD) outbreaks occurred in 2021. The objective of this study was to identify genetic lineages and evaluate the antigenic relationships of FMD virus (FMDV) isolates gathered from outbreaks reported between 2019 and 2022. Our study shows that the lineages O/ME-SA/Ind2001e and the O/ME-SA/Cluster-2018 were both responsible for the FMD outbreaks on an epidemic scale during 2021. This observation is in contrast to earlier findings that suggested epidemic-scale FMD outbreaks in India are often connected to a single genetic lineage. Additionally, we report here the identification of the O/ME-SA/PanAsia-2/ANT10 sub-lineage in India for the first time, which was connected to two intermittent outbreaks in Jammu and Kashmir. The current study demonstrates that the O/ME-SA/ind2001e lineage has a strong presence outside of the Indian subcontinent. Furthermore, the O/ME-SA/Cluster-2018 was observed to have a wider geographic distribution than previously, and like the O/ME-SA/Ind2001d and O/ME-SA/Ind2001e lineages in the past, it may eventually spread outside of its geographic niche. For O/ME-SA/Ind2001e and O/ME-SA/Cluster-2018, the predicted substitution rate for the VP1 region was 6.737 × 10^-3 and 8.257 × 10^-3 nt substitutions per site per year, respectively. The time of the most recent common ancestor of the O/ME-SA/Ind2001e and O/ME-SA/Cluster-2018 strains suggests that the viruses possibly emerged during 2003-2011 and 2009-2017, respectively. Recent sightings of the O/ME-SA/PanAsia2/ANT10 virus in India and the O/ME-SA/Ind2001e virus in Pakistan point to possible cross-border transit of the viruses. The results of a two-dimensional viral neutralization test revealed that all of the field isolates were antigenically matched to the currently used Indian vaccine strain O INDR2/1975. These results suggest that the serotype O vaccine strain can protect against outbreaks brought on by all three circulating lineages.

High antigenic diversity of serotype 1 infectious bursal disease virus revealed by antigenic cartography

The antigenic characterization of IBDV, a virus that causes an immunosuppressive disease in young chickens, has been historically addressed using cross virus neutralization (VN) assay and antigen-capture enzyme-linked immunosorbent (AC-ELISA). However, VN assay has been usually carried out either in specific antibody negative embryonated eggs, for non-cell culture adapted strains, which is tedious, or on chicken embryo fibroblasts (CEF), which requires virus adaptation to cell culture. AC-ELISA has provided crucial information about IBDV antigenicity, but this information is limited to the epitopes included in the tested panel with a lack of information of overall antigenic view. The present work aimed at overcoming those technical limitations and providing an extensive antigenic landscape based on original cross VN assays employing primary chicken B cells, where no previous IBDV adaptation is required. Sixteen serotype 1 IBDV viruses, comprising both reference strains and documented antigenic variants were tested against eleven chicken post-infectious sera. The VN data were analysed by antigenic cartography, a method which enables reliable high-resolution quantitative and visual interpretation of large binding assay datasets. The resulting antigenic cartography revealed i) the existence of several antigenic clusters of IBDV, ii) high antigenic relatedness between some genetically unrelated viruses, iii) a highly variable contribution to global antigenicity of previously identified individual epitopes and iv) broad reactivity of chicken sera raised against antigenic variants. This study provides an overall view of IBDV antigenic diversity. Implementing this approach will be instrumental to follow the evolution of IBDV antigenicity and control the disease.

Thermostable negative-marker foot-and-mouth disease virus serotype O induces protective immunity in guinea pigs

Foot-and-mouth disease (FMD) is a contagious viral disease of high economic importance, caused by FMD virus (FMDV), a positive-sense single-stranded RNA virus, affecting cloven-hoofed animals. Preventive vaccination using inactivated virus is in practice to control the disease in many endemic countries. While the vaccination induces antibodies mainly to structural proteins, the presence of antibodies to the non-structural proteins (NSP) is suggestive of infection, a criterion for differentiation of infected from vaccinated animals (DIVA). Also, there is a growing demand for enhancing the stability of the FMD vaccine virus capsid antigen as the strength of the immune response is proportional to the amount of intact 146S particles in the vaccine. Considering the need for a DIVA compliant stable vaccine, here we report generation and rescue of a thermostable and negative marker virus FMDV serotype O (IND/R2/1975) containing a partial deletion in non-structural protein 3A, generated by reverse genetics approach. Immunization of guinea pigs with the inactivated thermostable-negative marker virus antigen induced 91% protective immune response. Additionally, a companion competitive ELISA (cELISA) targeting the deleted 3A region was developed, which showed 92.3% sensitivity and 97% specificity, at cut-off value of 36% percent inhibition. The novel thermostable-negative marker FMDV serotype O vaccine strain and the companion cELISA could be useful in FMDV serotype O enzootic countries to benefit the FMD control program. KEY POINTS: • Thermostable foot-and-mouth disease virus serotype O with partial deletion in 3A. • Inactivated thermostable marker vaccine induced 91% protection in guinea pigs. • Companion cELISA based on deleted region in 3A could potentially facilitate DIVA.

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.

Diversity of SAT2 foot-and-mouth disease virus in Sudan: implication for diagnosis and control

Like other East African countries, Sudan experienced circulation of more than one topotype of SAT2 foot-and-mouth disease virus (FMDV). In Sudan, topotype XIII of SAT2 virus was recorded in 1977 and 2008 and topotype VII in 2007, 2010, 2013, 2014 and 2017. This work evaluated the impact of such diversity on diagnosis and control. After one or three doses of a vaccine derived from a Sudanese SAT2 virus of topotype VII originated in 2010, heterologous neutralizing antibody titres with Sudanese SAT2 viruses in 2008 were ≤ 1.2 log 10, not consistent with likely protection. Simultaneously, homologous titres were 1.65 (after one dose) or 1.95 and 2.55 log10 (after 3 doses). When r1 values between the vaccine virus and the SAT2 viruses isolated in 2008, whilst topotype XIII was circulating, were derived, values (≈ 0.00) suggested similarly poor antigenic relationship and unlikely cross protection. Concurrently, SAT2 positive field sera from Sudan in 2016 were not unvaryingly identified by virus neutralization tests (VNT) employing SAT2 viruses from 2010 and 2008. Proportions of positive sera by SAT2 virus from 2010 were always higher than those by viruses from 2008; consistent with the more frequent and recent circulation of topotype VII prior to 2016. Proportions by SAT2 virus from 2010 were 0.68 (± 0.1) in one location (n = 72), 0.39 (± 0.1) in another one (n = 94) and 0.52 (± 0.1) in the whole test group (n = 166). Corresponding values by viruses of 2008 were 0.53 (± 0.1), 0.27 (± 0.1) and 0.38 (± 0.1). In the whole test group, differences were statistically significant (p = .02339). Like post-vaccination sera, field sera (natural immunity) showed no considerable cross neutralization between topotype VII and presumably XIII; almost 45% (43/96) of SAT2 positive field sera were positive to one topotype but not to the other. Experimental and surveillance findings emphasized the implication of SAT2 diversity in Sudan. It is concluded that it is difficult to control SAT2 infection in Sudan using a monovalent vaccine. Beside a prophylactic vaccine from topotype VII, stockpiling of antigens from topotype XIII and enhanced virological surveillance with rapid genotyping and matching studies are necessary approaches. When more frequent circulation of more than one SAT2 topotype occurs, retrospective diagnosis by serological surveys could be problematic or imprecise.

A Five-Year Retrospective Study of Foot-and-Mouth Disease Outbreaks in Southern Africa, 2014 to 2018

Foot-and-mouth disease (FMD) virus (FMDv), like other ribonucleic acid (RNA) genome viruses, has a tendency to mutate rapidly. As such, available vaccines may not confer enough cross-protection against incursion of new lineages and sublineages. This paper is a retrospective study to determine the topotypes/lineages that caused previous FMD outbreaks in 6 southern African countries and the efficacy of the current vaccines to protect cattle against them. A total of 453 bovine epithelial tissue samples from 33 FMD outbreaks that occurred in these countries from 2014 to 2018 were investigated for the presence of FMDv. The genetic diversity of the identified Southern African Type (SAT)-FMD viruses was determined by comparing sequences from outbreaks and historical prototype sequences. Of the 453 samples investigated, 176 were positive for four FMDv serotypes. Out of the 176 FMD positive cases there were 105 SAT2 samples, 32 SAT1 samples, 21 SAT3 samples, and 18 serotype O samples. Phylogenetic analysis grouped the SATs VP1 gene sequences into previously observed topotypes in southern Africa. SAT1 viruses were from topotypes I and III, SAT2 viruses belonged to topotypes I, II, III, and IV, and SAT3 viruses were of topotypes I and II. Vaccine matching studies on the field FMDv isolates produced r 1-values greater than or equal to 0.3 for the three SAT serotypes. This suggests that there is no significant antigenic difference between current SAT FMD vaccine strains and the circulating SAT serotypes. Therefore, the vaccines are still fit-purpose for the control FMD in the region. The study did not identify incursion of any new lineages/topotypes of FMD into the sampled southern African countries.

Infection and protection responses of deletion mutants of non-structural proteins of foot-and-mouth disease virus serotype Asia1 in guinea pigs

The development of a negative marker vaccine against the foot-and-mouth disease virus (FMDV) will enhance the capabilities to differentiate vaccinated from infected animals and move forward in the progressive control pathway for the control of FMD. Here, we report the development of mutant FMDV of Asia1 with partial deletion of non-structural proteins 3A and 3B and characterization of their infectivity and protection response in the guinea pig model. The deleted FMDV Asia1/IND/63/1972 mutants, pAsia^Δ3A and pAsia^Δ3A3B1 were constructed from the full-length infectious clone pAsia^WT, the viable virus was rescued, and the genetic stability of the mutants was confirmed by 20 monolayer passages in BHK21 cells. The mutant Asia1 viruses showed comparable growth pattern and infectivity with that of Asia^WT in the cell culture. However, the Asia^Δ3A3B1 virus showed smaller plaque and lower virus titer with reduced infectivity in the suckling mice. In guinea pigs, the Asia^Δ3A3B1 virus failed to induce the disease, whereas the Asia^Δ3A virus induced typical secondary lesions of FMD. Vaccination with inactivated Asia1 mutant viruses induced neutralizing antibody response that was significantly lower than that of the parent virus on day 28 post-vaccination (dpv) in guinea pigs (P < 0.05). Furthermore, challenging the vaccinated guinea pigs with the homologous vaccine strain of FMDV Asia1 conferred complete protection. It is concluded that the mutant Asia^Δ3A3B1 virus has the potential to replace the wild-type virus for use as a negative marker vaccine after assessing the vaccine worth attributes in suspension cell and protective efficacy study in cattle.Key points• Deletion mutant viruses of FMDV Asia1, developed by PCR-mediated mutagenesis of NSP 3A and 3B1, were genetically stable.• The growth kinetics and antigenic relatedness of the mutant viruses were comparable with that of the wild-type virus.• Vaccination of guinea pigs with the deletion mutant viruses conferred complete protection upon challenge with the homologous virus.

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.

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.

Selection of Vaccine Candidate for Foot-and-Mouth Disease Virus Serotype O Using a Blocking Enzyme-Linked Immunosorbent Assay

Foot-and-mouth disease (FMD) is a highly contagious disease and one of the most economically important diseases of livestock. Vaccination is an important measure to control FMD and selection of appropriate vaccine strains is crucial. The objective of this study was to select a vaccine candidate and to evaluate the potential of a blocking ELISA for detecting neutralizing antibodies (NA-ELISA) in vaccine strain selection. Binary ethylenimine inactivated vaccines, prepared from four representative circulating strains (FMDV O/Mya/98, SCGH/CHA/2016, O/Tibet/99, and O/XJ/CHA/2017) belonging to four lineages within three different topotypes of FMD virus (FMDV) serotype O in China, were used to vaccinate cattle (12-13 animals for each strain), sheep (12-13 animals for each strain), and pigs (10 animals for each strain). The results of immunogenicity comparison showed that O/XJ/CHA/2017 exhibited the highest immunogenicity among the four strains in pigs, cattle, and sheep both by NA-ELISA and virus neutralizing test (VNT). Cross-neutralization analysis indicated that O/XJ/CHA/2017 displayed broad antigen spectrum and was antigenically matched with other three representative strains both by NA-ELISA and VNT. In addition, A significant correlation (p < 0.0001) was observed between the NA-ELISA titers and the VNT titers for four representative strains. The results showed that O/XJ/CHA/2017 was a promising vaccine strain candidate and NA-ELISA was comparable to VNT in neutralizing antibodies detection and could be used as the reference test system for vaccine strain selection.

Predicting the Antigenic Relationship of Foot-and-Mouth Disease Virus for Vaccine Selection Through a Computational Model

Foot-and-mouth disease virus (FMDV) is an antigenic-variable RNA virus that is responsible for the recurrence of foot-and-mouth disease in livestock and can be prevented and controlled using a vaccine with broad-spectrum protection. Current anti-genicity evaluation methods, which involve animal immunity experiments and serum preparation, are unable to fulfill the needs of high-throughput antigenicity measurements. This study designed an antigenicity scoring model to rapidly predict the antigenicity of FMDV. Antigenic-dominant sites were initially determined on the VP1 protein, a position-specific scoring matrix and physical chemical indexes were integrated to generate antigenicity descriptors. Independent tests showed a high accuracy of 0.848 and an AUC value of 0.889, indicating the good performance of the model in antigenicity measurement. When applying this model to historical data, annual antigenicity coverage of widely used vaccine strains was successfully evaluated, this was also supported by previous experiments. Furthermore, the utility of this model was extended to select potential broad-spectrum vaccines among 1,201 historical non-redundant strains to recommend potential univalent, bivalent and trivalent vaccine candidates. The results suggested that the computational model designed in this study could be used for the high-throughput antigenicity measurement of FMDV and could aid in vaccine development for preventing FMDV epidemics.

Genetic variation and evolution of foot-and-mouth disease virus serotype A in relation to vaccine matching

Foot-and-mouth disease (FMD) is a severe, highly contagious viral disease that affects a wide variety of domestic and wild cloven-hoofed animals. FMD vaccines can play a vital role in disease control and are very widely used globally each year. However, due to the diversity of FMDV, the choice of FMD vaccine is still a huge challenge. In this study, 45 FMDV/A isolates were phylogenetically categorized into three topotypes: ASIA (n = 31), AFRICA (n = 10), and EURO-SA (n = 4). Three sera collected from vaccinated cattle with FMDV A22/IRQ/24/64, A/IRN/05, and A/ARG/01 were used to evaluate their antigenic relationship (r₁) with the field isolates. The IRQ/24/64 serum demonstrated a 39% (17/44) match (r₁ ≥ 0.3) to the field isolates, whereas IRN/05 serum and ARG/01serum showed an 18% (8/44) and a 2% (1/44) match (r₁ ≥ 0.3) to the field isolates, respectively. The A22/IRQ/24/64 matched with isolates mainly from topotype ASIA, with limited cross-topotype match with isolates from topotypes AFRICA and EURO-SA. However, the A/IRN/05 did not show a cross-topotype match with topotype AFRICA isolates and A/ARG/01 failed to match any isolates from topotypes ASIA and AFRICA. After analyzing the amino acid variation of the known antigenic sites of 45 strains of FMDV/A, it was found that together antigenic sites 1 and 3 contributed about 71% of the amino acid changes to the vaccine evaluated. Based on the capsid sequences, the FMDV/A evolved unequally among topotypes. The topotypes of ASIA and AFRICA evolves faster than that of EURO-SA. The FMDV/A continues to show a high level of genetic diversity driven by a high substitution rate, purifying selection, and positive selection concentrated on antigenic sites or near antigenic sites. The current research shows the challenges of the FMDV/A vaccine selection and emphasizes the importance of continuous monitoring of antigenic evolution for the selection of effective vaccines.

Genetic characterization of foot-and-mouth disease virus serotype O isolates collected during 2014-2018 revealed dominance of O/ME-SA/Ind2001e and the emergence of a novel lineage in India

Foot-and-mouth disease (FMD) is endemic in India with a preponderance of outbreaks caused by FMD virus (FMDV) serotype O. Out of the 11 global topotypes of serotype O, only ME-SA topotype has been reported in the country so far. Lineage O/ME-SA/Ind2001 and O/ME-SA/PanAsia are documented as the most dominant ones in terms of the number of outbreaks caused by them. To understand the distribution of topotype/lineages in India and their antigenic behaviour during the year 2014-2018, a total of 286 FMDV serotype O viral isolates were sequence determined at the VP1 region, and 109 isolates were characterized antigenically. All the isolates grouped in the ME-SA topotype, being distributed in lineage O/ME-SA/Ind2001 (within sub-lineages O/ME-SA/Ind2001d and O/ME-SA/Ind2001e), and a new group designated here as O/ME-SA/2018 cluster. The sub-lineage O/ME-SA/Ind2001e reported for the first time in India during the year 2015, replaced sub-lineage O/ME-SA/Ind2001d gradually, which was dominating since 2008. During the years 2014-2018, the sub-lineage O/ME-SA/Ind2001e was found to be the most predominant one whose mean evolutionary rate was observed to be faster than that of the sub-lineage O/ME-SA/Ind2001d. The codon sites 45 and 85 of VP1 were found to be under diversifying selection in a large proportion of trees. The common ancestor predicted for sub-lineages O/ME-SA/Ind2001e and O/ME-SA/2018 dates back to 2012 and 2016, respectively. The sustenance and spread of the new O/ME-SA/2018 cluster need to be assessed by continued surveillance. The Indian vaccine strain O/INDR2/1975 was found to provide adequate antigenic coverage to the emerging and prevalent serotype O lineages. The trait association tests showed frequent virus exchange among different states, which could be an important confounder in the region-specific assessment of effectiveness of FMD control programme.

Novel Foot-and-Mouth Disease Vaccine Platform: Formulations for Safe and DIVA-Compatible FMD Vaccines With Improved Potency

Inactivated, wild-type foot-and-mouth disease virus (FMDV) vaccines are currently used to control FMD around the world. These traditional FMD vaccines are produced using large quantities of infectious, virulent, wild-type FMD viruses, with the associated risk of virus escape from manufacturing facilities or incomplete inactivation during the vaccine formulation process. While higher quality vaccines produced from wild-type FMDV are processed to reduce non-structural antigens, there is still a risk that small amounts of non-structural proteins may be present in the final product. A novel, antigenically marked FMD-LL3B3D vaccine platform under development by Zoetis, Inc. and the USDA-ARS, consists of a highly attenuated virus platform containing negative antigenic markers in the conserved non-structural proteins 3D^pol and 3B that render resultant vaccines fully DIVA compatible. This vaccine platform allows for the easy exchange of capsid coding sequences to create serotype-specific vaccines. Here we demonstrate the efficacy of the inactivated FMD-LL3B3D-A₂₄ Cruzeiro vaccine in cattle against wild-type challenge with A₂₄ Cruzerio. A proprietary adjuvant system was used to formulate the vaccines that conferred effective protection at low doses while maintaining the DIVA compatibility. In contrast to wild-type FMDV, the recombinant FMD-LL3B3D mutant viruses have been shown to induce no clinical signs of FMD and no shedding of virus in cattle or pigs when inoculated as a live virus. The FMD-LL3B3D vaccine platform, currently undergoing development in the US, provides opportunities for safer vaccine production with full DIVA compatibility in support of global FMDV control and eradication initiatives.

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.

Foot-and-Mouth Disease Virus 3A Protein Causes Upregulation of Autophagy-Related Protein LRRC25 To Inhibit the G3BP1-Mediated RIG-Like Helicase-Signaling Pathway

We show that foot-and-mouth disease virus (FMDV) 3A inhibits retinoic acid-inducible gene I (RIG-I)-like helicase signaling by degrading G3BP1 protein. Furthermore, FMDV 3A reduces G3BP1 by upregulating the expression of autophagy-related protein LRRC25. Additionally, other picornavirus 3A proteins, such as Seneca Valley virus (SVV) 3A, enterovirus 71 (EV71) 3A, and encephalomyocarditis virus (EMCV) 3A, also degrade G3BP1 by upregulating LRRC25 expression. This study will help us improve the design of current vaccines and aid the development of novel control strategies to combat FMD.

Foot-and-mouth disease virus (FMDV) is one of the most notorious pathogens in the global livestock industry. To establish an infection, FMDV needs to counteract host antiviral responses. Several studies have shown how FMDV suppresses the type I interferon (IFN) response; however, whether FMDV modulates the integrated autophagy and innate immunity remains largely unknown. Here, the porcine Ras-GAP SH3-binding protein 1 (G3BP1) was shown to promote the retinoic acid-inducible gene I (RIG-I)-like helicase (RLH) signaling by upregulating the expression of RIG-I and melanoma differentiation-associated gene 5 (MDA5). FMDV nonstructural protein 3A interacted with G3BP1 to inhibit G3BP1 expression and G3BP1-mediated RLH signaling by upregulating the expression of autophagy-related protein LRRC25. In addition, 3A proteins of other picornaviruses, including Seneca Valley virus (SVV) 3A, enterovirus 71 (EV71) 3A, and encephalomyocarditis virus (EMCV) 3A, also showed similar actions. Taking the data together, we elucidated, for the first time, a novel mechanism by which FMDV has evolved to inhibit IFN signaling and counteract host innate antiviral responses by autophagy.

IMPORTANCE We show that foot-and-mouth disease virus (FMDV) 3A inhibits retinoic acid-inducible gene I (RIG-I)-like helicase signaling by degrading G3BP1 protein. Furthermore, FMDV 3A reduces G3BP1 by upregulating the expression of autophagy-related protein LRRC25. Additionally, other picornavirus 3A proteins, such as Seneca Valley virus (SVV) 3A, enterovirus 71 (EV71) 3A, and encephalomyocarditis virus (EMCV) 3A, also degrade G3BP1 by upregulating LRRC25 expression. This study will help us improve the design of current vaccines and aid the development of novel control strategies to combat FMD.

Immunogenicity and protective efficacy of 3A truncated negative marker foot-and-mouth disease virus serotype A vaccine

Foot-and-mouth disease (FMD) is a highly contagious, economically significant disease of cloven-hoofed animals caused by FMD virus (FMDV) of the Picornaviridae family. Vaccination of susceptible animals with inactivated virus vaccine is the standard practice for disease control. The prophylactic use of the inactivated vaccines has reduced the disease burden in many countries endemic to FMD. In the process of implementation of the mass vaccination program and disease eradication, it is essential to differentiate infected from vaccinated animals (DIVA) where a large proportion of the animal population is vaccinated, and disease-free zones are being established, to help in sero-surveillance of the disease. In such a scenario, the use of a negative marker vaccine is beneficial to rule out false-positive results in a disease-free zone. Here we report the construction and rescue of an infectious cDNA clone for FMDV serotype A Indian vaccine strain lacking 58 amino acid residues (87-144 amino acid position) in the carboxy-terminal region of the viral 3A protein. The recombinant deletion mutant virus showed similarity in the antigenic relationship with the parental strain. Immunization of guinea pigs with the inactivated vaccine formulated using the deletion mutant virus induced potent immune response with 100% protective efficacy upon challenge with homologous virus. Further, we show that sera from the guinea pigs infected with the deletion mutant virus did not show reactivity in an indirect ELISA test targeting the deleted portion of 3A protein. We conclude that the recombinant deletion mutant virus vaccine along with the newly developed companion indirect ELISA targeting portion of FMDV 3A protein could be useful in the implementation of a precise DIVA policy in our country when we reach FMD free status with vaccination.

Near-Complete Genome Sequence of a Potential Foot-and-Mouth Disease Virus Serotype A Vaccine Strain Isolated from Bangladesh

The near-complete genome sequence of foot-and-mouth disease virus (FMDV) serotype A potential vaccine strain BAN/CH/Sa-304/2016 is reported here. Its genome revealed antigenic heterogeneity with the current Indian vaccine strain IND40/00, with four amino acid substitutions in antigenically critical sites of the VP1 protein.

The near-complete genome sequence of foot-and-mouth disease virus (FMDV) serotype A potential vaccine strain BAN/CH/Sa-304/2016 is reported here. Its genome revealed antigenic heterogeneity with the current Indian vaccine strain IND40/00, with four amino acid substitutions in antigenically critical sites of the VP1 protein.

Foot-and-Mouth Disease Virus: Immunobiology, Advances in Vaccines and Vaccination Strategies Addressing Vaccine Failures-An Indian Perspective

A mass vaccination campaign in India seeks to control and eventually eradicate foot-and-mouth disease (FMD). Biosanitary measures along with FMD monitoring are being conducted along with vaccination. The implementation of the FMD control program has drastically reduced the incidence of FMD. However, cases are still reported, even in regions where vaccination is carried out regularly. Control of FMD outbreaks is difficult when the virus remains in circulation in the vaccinated population. Various FMD risk factors have been identified that are responsible for FMD in vaccinated areas. The factors are discussed along with strategies to address these challenges. The current chemically inactivated trivalent vaccine formulation containing strains of serotype O, A, and Asia 1 has limitations including thermolability and induction of only short-term immunity. Advantages and disadvantages of several new-generation alternate vaccine formulations are discussed. It is unfeasible to study every incidence of FMD in vaccinated animals/areas in such a big country as India with its huge livestock population. However, at the same time, it is absolutely necessary to identify the precise reason for vaccination failure. Failure to vaccinate is one reason for the occurrence of FMD in vaccinated areas. FMD epidemiology, emerging and re-emerging virus strains, and serological status over the past 10 years are discussed to understand the impact of vaccination and incidences of vaccination failure in India. Other factors that are important in vaccination failure that we discuss include disrupted herd immunity, health status of animals, FMD carrier status, and FMD prevalence in other species. Recommendations to boost the search of alternate vaccine formulation, strengthen the veterinary infrastructure, bolster the real-time monitoring of FMD, as well as a detailed investigation and documentation of every case of vaccination failure are provided with the goal of refining the control program.

A novel method for performing antigenic vaccine matching for foot-and-mouth disease in absence of the homologous virus

Foot-and-mouth-disease (FMD) is a highly contagious transboundary animal disease that has negative consequences on regional and international trade. Vaccination is an important approach for FMD control and an essential consideration is the degree of cross-protection conferred by the vaccine against currently circulating field viruses. The objective of this study was to evaluate a new vaccine matching technique that does not require knowledge concerning the homologous vaccine virus. As a proof of concept, the vaccine-match was assessed for 41 FMD field viruses isolated from southern Africa over a 25-year period. A diverse group of 20 SAT1 and 21 SAT2 FMDV isolates collected from cattle and wildlife during 1991-2015 were selected for this study. Virus neutralization tests were performed against two sets of pooled sera for each serotype: vaccinated cattle sera (4-16 weeks post-vaccination) and convalescent cattle sera (3 weeks post-experimental challenge). Novel r₁-values were calculated as the ratio of the titre of the vaccinated sera to the titre for convalescent cattle sera. A validation r₁-value was calculated based on an assumption concerning the true homologous vaccine virus. There was a strong positive correlation between r₁-values for the novel and the validation methods for SAT1 viruses (Spearman's rho = 0.84, P < 0.01) and a very strong correlation for SAT2 viruses (Spearman's rho = 0.90, P < 0.01). In addition, there was moderate to good agreement between the novel and validation methods for both serotypes based on a r₁-value cut-off of 0.3, which is presumed to represent a good vaccine-match. The agreement between methods using prevalence-adjusted and bias-adjusted kappa (PABAK) was 0.67 and 0.84 for SAT1 and SAT2 viruses, respectively. The new r₁-value method provides a feasible, alternative vaccine matching approach that could benefit FMD control in southern Africa.

Genetic and antigenic variation of foot-and-mouth disease virus during persistent infection in naturally infected cattle and Asian buffalo in India

The role of foot-and-mouth disease virus (FMDV) persistently infected ruminants in initiating new outbreaks remains controversial, and the perceived threat posed by such animals hinders international trade in FMD-endemic countries. In this study we report longitudinal analyses of genetic and antigenic variations of FMDV serotype O/ME-SA/Ind2001d sublineage during naturally occurring, persistent infection in cattle and buffalo at an organised dairy farm in India. The proportion of animals from which FMDV RNA was recovered was not significantly different between convalescent (post-clinical) and sub-clinically infected animals or between cattle and buffalo across the sampling period. However, infectious virus was isolated from a higher proportion of buffalo samples and for a longer duration compared to cattle. Analysis of the P1 sequences from recovered viruses indicated fixation of mutations at the rate of 1.816 x 10-2substitution/site/year (s/s/y) (95% CI 1.362-2.31 x 10-2 s/s/y). However, the majority of point mutations were transitional substitutions. Within individual animals, the mean dN/dS (ω) value for the P1 region varied from 0.076 to 0.357, suggesting the selection pressure acting on viral genomes differed substantially across individual animals. Statistical parsimony analysis indicated that all of the virus isolates from carrier animals originated from the outbreak virus. The antigenic relationship value as determined by 2D-VNT assay revealed fluctuation of antigenic variants within and between carrier animals during the carrier state which suggested that some carrier viruses had diverged substantially from the protection provided by the vaccine strain. This study contributes to understanding the extent of within-host and within-herd evolution that occurs during the carrier state of FMDV.

Generation and characterisation of recombinant FMDV antibodies: Applications for advancing diagnostic and laboratory assays

Foot-and-mouth disease (FMD) affects economically important livestock and is one of the most contagious viral diseases. The most commonly used FMD diagnostic assay is a sandwich ELISA. However, the main disadvantage of this ELISA is that it requires anti-FMD virus (FMDV) serotype-specific antibodies raised in small animals. This problem can be, in part, overcome by using anti-FMDV monoclonal antibodies (MAbs) as detecting reagents. However, the long-term use of MAbs may be problematic and they may need to be replaced. Here we have constructed chimeric antibodies (mouse/rabbit D9) and Fabs (fragment antigen-binding) (mouse/cattle D9) using the Fv (fragment variable) regions of a mouse MAb, D9 (MAb D9), which recognises type O FMDV. The mouse/rabbit D9 chimeric antibody retained the FMDV serotype-specificity of MAb D9 and performed well in a FMDV detection ELISA as well as in routine laboratory assays. Cryo-electron microscopy analysis confirmed engagement with antigenic site 1 and peptide competition studies identified the aspartic acid at residue VP1 147 as a novel component of the D9 epitope. This chimeric expression approach is a simple but effective way to preserve valuable FMDV antibodies, and has the potential for unlimited generation of antibodies and antibody fragments in recombinant systems with the concomitant positive impacts on the 3Rs (Replacement, Reduction and Refinement) principles.

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.

Preparation of the Secretory Recombinant ALV-J gp85 Protein Using Pichia pastoris and Its Immunoprotection as Vaccine Antigen Combining with CpG-ODN Adjuvant

This study focuses on preparing the secretory recombinant J subgroup of avian leukosis virus (ALV-J) gp85 protein using Pichia pastoris and evaluating its immunoprotection as vaccine antigen combining with CpG-ODN adjuvant. The secretory recombinant plasmid pPIC9-gp85 containing ALV-J gp85 gene was designed and was transfected into the genome of P. pastoris (GS115) cells. The recombinant plasmid was expressed under the induction of methanol. The expressed products in the medium of the cells were purified and identified with endoglycosidase digestion assay and western blot mediated with monoclonal antibody (MAb) JE9. The purified product combining with CpG-ODN adjuvant was inoculated intramuscularly into 7-day-old chickens and three booster inoculations were performed on 21 days post first inoculation (dpfi), 42, and 56 dpfi. The antibody responses and cellular immune responses were detected, and the protective effects were analyzed after challenge with ALV-J. The results showed that the secretory pPIC9-gp85 plasmid was successfully constructed and could be stably expressed in GS115 cells. The expressed products were N-acetylglucosylated and could specifically combine with MAb (JE9). The secreted gp85 protein combining with CpG-ODN adjuvant could induce higher antibody response and spleen lymphocyte proliferation response and IFN-γ-inducing response, and could protect all the inoculated chickens against the viremia and the immunosuppressive lesions caused by ALV-J challenge. The results of neutralizing test in vitro suggested that the antisera with some ALV-J antibody titers could neutralize ALV-J strain and inhibit the growth of virus in vitro. The result of IFA showed that IgG antibody in the antisera could specifically combine with ALV-J strain in cells. It can be concluded that the secretory recombinant gp85 protein, as a new acetylglucosylated gp85 protein, was successfully prepared and combining with CpG-ODN adjuvant could protect the inoculated chickens against ALV-J infection. This study first reported the methods on preparing the secretory recombinant ALV-J gp85 protein using P. pastoris and evaluated its immunoprotection.

Selection of vaccine strains for serotype O foot-and-mouth disease viruses (2007-2012) circulating in Southeast Asia, East Asia and Far East

Foot-and-mouth disease (FMD) is endemic in Southeast Asia (SEA) and East Asia with circulation of multiple serotypes and multiple genotypes within each serotype of the virus. Although countries like Japan and South Korea in the Far East were free of FMD, in 2010 FMD serotype O (O/Mya-98) outbreaks were recorded and since then South Korea has experienced several FMD outbreaks despite regular vaccination. In this study a total of 85 serotype O FMD viruses (FMDV) isolated from 2007 to 2012 from SEA, East Asia and Far East were characterized by virus neutralisation tests using antisera to four existing (O/HKN/6/83, O/IND/R2/75, O/SKR/2010 and O/PanAsia-2) and one putative (O/MYA/2009) vaccine strains, and by full capsid sequencing. Serological studies revealed broad cross-reactivity with the vaccine strains; O/PanAsia-2 exhibited a good match with 95.3%, O/HKN/6/83 with 91.8%, O/IND/R2/75 with 80%, and the putative strain O/MYA/2009 with 89.4% isolates employed in this study. Similarly O/PanAsia-2 and O/IND/R2/75 vaccines showed a good match with all eight viruses belonging to O-Ind-2001d sublineage whereas the vaccines of O/Mya-98 lineage, O/MYA/2009 and O/SKR/2010 exhibited the lowest match indicating their unsuitability to protect infections from O-Ind-2001d viruses. A Bayesian analysis of the capsid sequence data indicated these circulating viruses (n = 85) to be of either SEA or Middle East-South Asian (ME-SA) topotype. The ME-SA topotype viruses were mainly detected in Lao PDR, Vietnam, Myanmar and Thailand reflecting the trade links with the Indian subcontinent, and also within the SEA countries. Implications of these results in the context of FMD control in SEA and East Asian countries are discussed.

Genetic and antigenic characterization of serotype O FMD viruses from East Africa for the selection of suitable vaccine strain

Foot-and-mouth disease (FMD) is endemic in Eastern Africa with circulation of multiple serotypes of the virus in the region. Most of the outbreaks are caused by serotype O followed by serotype A. The lack of concerted FMD control programmes in Africa has provided little incentive for vaccine producers to select vaccines that are tailored to circulating regional isolates creating further negative feedback to deter the introduction of vaccine-based control schemes. In this study a total of 80 serotype O FMD viruses (FMDV) isolated from 1993 to 2012 from East and North Africa were characterized by virus neutralisation tests using bovine antisera to three existing (O/KEN/77/78, O/Manisa and O/PanAsia-2) and three putative (O/EA/2002, O/EA/2009 and O/EA/2010) vaccine strains and by capsid sequencing. Genetically, these viruses were grouped as either of East African origin with subdivision into four topotypes (EA-1, 2, 3 and 4) or of Middle-East South Asian (ME-SA) topotype. The ME-SA topotype viruses were mainly detected in Egypt and Libya reflecting the trade links with the Middle East countries. There was good serological cross-reactivity between the vaccine strains and most of the field isolates analysed, indicating that vaccine selection should not be a major constraint for control of serotype O FMD by vaccination, and that both local and internationally available commercial vaccines could be used. The O/KEN/77/78 vaccine, commonly used in the region, exhibited comparatively lower percent in vitro match against the predominant topotypes (EA-2 and EA-3) circulating in the region whereas O/PanAsia-2 and O/Manisa vaccines revealed broader protection against East African serotype O viruses, even though they genetically belong to the ME-SA topotype.

Uncleaved 2A-peptide of foot-and-mouth disease virus can display foreign epitope-tag at the virion surface

Foot-and-mouth disease virus (FMDV) capsid precursor protein P1-2A is cleaved by viral-encoded 3C protease (3Cpro) to generate VP0, VP3, VP1 and 2A proteins. It was reported earlier that substitution of a single amino acid residue within the 2A peptide sequence (L2P) blocked the 3Cpro mediated VP1/2A cleavage and produced 'self-tagged' FMDV particles containing uncleaved 2A-peptide. To determine whether the uncleaved 2A-peptide can function as a target structure to harbour and display exogenous epitope on FMDV particles, a full-length FMDV cDNA clone containing a HA-tag within the uncleaved 2A-peptide sequence was constructed. Subsequently, chimeric marker FMDV, displaying a HA-tag on the viral surface was rescued through reverse genetics approach. The 2A-HA epitope tag-inserted recombinant chimeric FMDV serotype O was genetically stable through up to ten serial passages in cell culture and exhibited growth properties similar to the parental virus. Furthermore the surface displayed HA-epitope tag was able to react with anti-HA antibodies as determined by various immuno-assays. The results from our study suggest that the uncleaved 2A-peptide of FMDV is suitable to present foreign antigenic epitopes on the surface of FMD virion.

Antigenic variability of foot-and-mouth disease virus serotype O during serial cytolytic passage

The emergence and disappearance of antigenic variants of foot-and-mouth disease virus (FMDV) during a field outbreak occurs periodically due to the volatile nature of its genome. In the present analysis, change in antigenic behavior of serotype O FMDV during the serial cytolytic passage in the absence of immune pressure was observed. Initially, the isolate showed a poor antigenic match (relationship value <0.3) with the serotype O vaccine strain and upon serial passage increase in relationship value was observed. Comparison of capsid sequence revealed substitution at four positions (VP3:K₅₈ → E and P₁₅₈ → S, VP1:E₈₃ → K and R₁₇₂ → Q) acquired during the serial passage. Examination of passage level and amino acid substitution revealed the critical role of position VP3-58 that was identified earlier as crucial for antigenic site IV, in the observed antigenic variability. The role of position VP3-58 was further confirmed using reverse genetics approach.

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.

Emergence of antigenic variants within serotype A FMDV in the Middle East with antigenically critical amino acid substitutions

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The recent A-Iran-05 viruses circulating in the Middle East do not match with the existing vaccines.

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Full capsid sequence of 13 SIS-10 and SIS-12 viruses was generated.

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The r₁-values generated using antisera raised against two existing vaccines and a new vaccine.

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Amino acid changes in neutralizing antigenic sites 1, 2 and 4 were observed.

A new immunologically distinct strain (A-Iran-05) of foot-and-mouth disease virus serotype A emerged in the Middle East in 2003 that replaced the previously circulating strains (A-Iran-96 and A-Iran-99) in the region. This resulted in introduction of a new vaccine of this strain (A/TUR/2006) in 2006. Though this vaccine strain has been predominantly used to control FMD in the region, recent viruses isolated in 2012 and 2013 have shown antigenic drift and a poor match with it. In this study, we report the antigenic matching results and capsid sequence data of currently circulating viruses belonging to the SIS-10 and SIS-12 sub-lineages of A-Iran-05 (isolated in 2012 and 2013), highlighting the inadequacy of the currently used serotype A vaccines. Implications of these results in the context of FMD control in the Middle East are discussed.

Evaluation of the efficacy of a new oil-based adjuvant ISA 61 VG FMD vaccine as a potential vaccine for cattle

Foot-and-mouth disease is an important viral disease of cloven-hoofed animals. Inactivated whole particle virus vaccines are still widely used in prophylactic vaccination campaigns. The choice of adjuvant is a very important factor in enhancing immune responses and the efficacy of inactivated vaccines. Montanide ISA 61 VG is a new ready-to-use mineral oil-based adjuvant developed by SEPPIC Inc. (SEPPIC, France) with high-potential immune responses needed for clinical protection against FMD infection. In this study, we compared the efficacy of two FMD vaccines either formulated with the new oil-based adjuvant ISA 61 VG and saponin, or with aluminum hydroxide gel and saponin. Both vaccines contained the same antigen payloads of O2010/IR. Two groups of 15 naive cattle received a single vaccination with different doses (full dose, 1/3 dose and 1/9 dose) to calculate their PD50 (50% protective dose) after being challenged with the homologous virulent virus. The mean neutralizing antibody titer was determined at 0, 7, 14 and 21 days after vaccination, measured by a micro neutralization test. The new vaccine improved humoral immune responses by 19%, while inducing a higher geometric mean. The titer for neutralizing antibodies was 2.91 log10 compared to the alum-gel based adjuvant vaccine which was 2.44 log10 (P-value=0.1782). The new vaccine showed a PD50 value of 10.05 as compared to a PD50 value of 4.171, respectively. According to the results, the FMD vaccine formulated with the new oil adjuvant, ISA 61 VG, shows potential as an alternative vaccine for routine and emergency vaccinations in the FMD enzootic region.

Megaprimer-mediated capsid swapping for the construction of custom-engineered chimeric foot-and-mouth disease virus

Foot-and-mouth disease (FMD) is a highly contagious, economically important disease of transboundary importance. Regular vaccination with chemically inactivated FMD vaccine is the major means of controlling the disease in endemic countries like India. However, the selection of appropriate candidate vaccine strain and its adaptation in cell culture to yield high titer of virus is a cumbersome process. An attractive approach to circumvent this tedious process is to replace the capsid coding sequence of an infectious full-genome length cDNA clone of a good vaccine strain with those of appropriate field strain, to produce custom-made chimeric FMD virus (FMDV). Nevertheless, the construction of chimeric virus can be difficult if the necessary endonuclease restriction sites are unavailable or unsuitable for swapping of the capsid sequence. Here we described an efficient method based on megaprimer-mediated capsid swapping for the construction of chimeric FMDV cDNA clones. Using FMDV vaccine strain A IND 40/2000 infectious clone (pA(40/2000)) as a donor plasmid, we exchanged the capsid sequence of pA(40/2000) with that of the viruses belonging to serotypes O (n = 5), A (n = 2), and Asia 1 (n = 2), and subsequently generated infectious FMDV from their respective chimeric cDNA clones. The chimeric viruses exhibited comparable infection kinetics, plaque phenotypes, antigenic profiles, and virion stability to the parental viruses. The results from this study suggest that megaprimer-based reverse genetics technology is useful for engineering chimeric vaccine strains for use in the control and prevention of FMD in endemic countries.

Cross-protective efficacy of engineering serotype A foot-and-mouth disease virus vaccine against the two pandemic strains in swine

Foot-and-mouth disease (FMD) is a highly contagious vesicular disease that affects domestic and wild cloven-hoofed animals worldwide. Recently, a series of outbreaks of type A FMDV occurred in Southeast Asian countries, China, the Russia Federation, Mongolia, Kazakhstan and South Korea. The FMD virus (A/GDMM/CHA/2013) from China's Guangdong province (2013) is representative of those responsible for the latest epidemic, and has low amino acid identity (93.9%) in VP1 protein with the epidemic strain A/WH/CHA/09 from Wuhan, China in 2009. Both of isolates belong to the Sea-97 genotype of ASIA topotype. Therefore, the application of a new vaccine strain with cross-protective efficacy is of fundamental importance to control the spread of the two described pandemic strains. A chimeric strain rA/P1-FMDV constructed by our lab previously through replacing the P1 gene in the vaccine strain O/CHA/99 with that from the epidemic stain A/WH/CHA/09, has been demonstrated to exhibit good growth characteristics in culture, and the rA/P1-FMDV inactivated vaccine can provide protection against epidemic strain A/WH/CHA/09 in cattle. However, it is still unclear whether the vaccine produces efficient protection against the new pandemic strain (A/GDMM/CHA/2013). Here, vaccine matching and pig 50% protective dose (PD50) tests were performed to assess the vaccine potency. The vaccine matching test showed cross-reactivity of sera from full dose vaccine vaccinated pigs with A/WH/CHA/09 and A/GDMM/CHA/2013 isolates, with average r1 values of 0.94±0.12 and 0.68±0.06 (r1≥0.3), which indicates that the rA/P1-FMDV vaccine is likely to confer good cross-protection against the two isolates. When challenged with two pandemic isolates A/WH/CHA/09 and A/GDMM/CHA/2013 strain, the vaccine achieved 12.51 PD50 and 10.05 PD50 per dose (2.8μg), respectively. The results indicated that the rA/P1-FMDV inactivated vaccine could protect pigs against both A/WH/CHA/09 and A/GDMM/CHA/2013 pandemic isolates.

Quantitative Proteomic Analysis of BHK-21 Cells Infected with Foot-and-Mouth Disease Virus Serotype Asia 1

Stable isotope labeling with amino acids in cell culture (SILAC) was used to quantitatively study the host cell gene expression profile, in order to achieve an unbiased overview of the protein expression changes in BHK-21 cells infected with FMDV serotype Asia 1. The SILAC-based approach identified overall 2,141 proteins, 153 of which showed significant alteration in the expression level 6 h post FMDV infection (57 up-regulated and 96 down-regulated). Among these proteins, six cellular proteins, including three down-regulated (VPS28, PKR, EVI5) and three up-regulated (LYPLA1, SEC62 and DARs), were selected according to the significance of the changes and/or the relationship with PKR. The expression level and pattern of the selected proteins were validated by immunoblotting and confocal microscopy. Furthermore, the functions of these cellular proteins were assessed by small interfering RNA-mediated depletion, and their functional importance in the replication of FMDV was demonstrated by western blot, reverse transcript PCR (RT-PCR) and 50% Tissue Culture Infective Dose (TCID50). The results suggest that FMDV infection may have effects on the expression of specific cellular proteins to create more favorable conditions for FMDV infection. This study provides novel data that can be utilized to understand the interactions between FMDV and the host cell.

Evolutionary dynamics of foot-and-mouth disease virus O/ME-SA/Ind2001 lineage

Foot-and-mouth disease (FMD) virus serotype O Ind2001 lineage within the Middle East-South Asia topotype is the major cause of recent FMD incidences in India. A sub-lineage of Ind2001 caused severe outbreaks in the southern region of the country during 2013 and also reported for the first time from Libya. In this study, we conducted a detailed evolutionary analysis of Ind2001 lineage. Phylogenetic analysis of Ind2001 lineage based on maximum likelihood method revealed two major splits and three sub-lineages. The mean nucleotide substitution rate for this lineage was calculated to be 6.338×10(-3)substitutions/site/year (s/s/y), which is similar to those of PanAsian sub-lineages. Evolutionary time scale analysis indicated that the Ind2001 lineage might have originated in 1989. The sub-lineage Ind2001d that caused 2013 outbreaks seems to be relatively more divergent genetically from other Ind2001 sub-lineages. Seven codons in the VP1 region of Ind2001 were found to be under positive selection. Four out of 24 recent Ind2001 strains tested in 2D-MNT had antigenic relationship value of <0.3 with the serotype O vaccine strain indicating intra-epidemic antigenic diversity. Amino acid substitutions found in these minor variants with reference to antigenic diversity have been discussed. The dominance of antigenically homologous strains indicates absence of vaccine immunity in the majority of the affected hosts. Taken together, the evolution of Ind2001 lineage deviates from the strict molecular clock and a typical lineage evolutionary dynamics characterized by periodic emergence and re-emergence of Ind2001 and PanAsia lineage have been observed in respect of serotype O.

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.

Antibody responses induced by recombinant ALV-A gp85 protein vaccine combining with CpG-ODN adjuvant in breeder hens and the protection for their offspring against early infection

To observe the antibody responses induced by recombinant A subgroup avian leukosis virus (ALV-A) gp85 protein vaccine plus CpG-ODN adjuvant and the protection of maternal antibodies (MAbs) for the hatched chickens against early infection, the gp85 gene was amplified from the proviral cDNA of ALV-A-SDAU09C1 strain using PCR and the recombinant plasmid containing target gene was constructed and expressed in EscherichiaColi. The expressed product was confirmed using SDS-PAGE and western blot that it is about 46KD of recombinant protein. The purified recombinant proteins combining with CpG-ODN adjuvant or Freund's adjuvant were inoculated into the breeder hens, the ALV-A antibodies in serum and in egg-yolk were detected; the fertilized eggs from the vaccinated hens with different titers of egg-yolk antibody were hatched and then challenged with 10(4.2)/0.1mL TCID50 of ALV-A-SDAU09C1 strain, all the hatched chickens were weekly detected for the viremias and the cloacal swab P27 antigen and pathological lesions; the neutralizing test of antisera in vitro was conducted. The results showed that the recombinant gp85 proteins combining with CpG-ODN adjuvant could induce the breeder hens to produce better antibody responses than gp85 protein with Freund's adjuvant or without adjuvant; the MAbs with higher titers induced by CpG-ODN+gp85 proteins could obviously decrease the ratios of viremias (13% vs 33%), cloacal detoxification (20% vs 67%) and death (0% vs 22%) caused by ALV-A infection than those by gp85 protein without adjuvant. The results of the neutralizing test indicated that the antisera from the hatched chickens could neutralize the ALV-A-SDAU09C1 strain in vitro, but which depends on the antibody titers. The results of IFA confirmed that the serum antibody could combine with the ALV in DF1 cells. It can be concluded that the prepared ALV-A gp85 subunit vaccine combining with CpG-ODN adjuvant could induce the breeder hens to produce better neutralizing antibody responses and protect 80% of their offspring chickens against early infection.

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.

A positively charged lysine residue at VP2 131 position allows for the enhanced adaptability of foot-and-mouth disease virus serotype A in BHK-21 cells

Field outbreak strains of foot-and-mouth disease virus (FMDV) infect host cells through certain Arg-Gly-Asp (RGD) dependent integrin family of cellular receptors. In contrast, FMDV adapted in non-host cell cultures are reported to acquire the ability to infect cells via heparin sulphate (HS) or other unidentified cell surface molecules. It has been reported that during the serial passage of FMDV serotype A in BHK-21 cell culture, VP2 E131K (E2131K) substitution was fixed within the heparin sulphate binding site. The fixation of positively charged residue at position VP2 131 of serotype A is considered to associate with the ability to utilise alternative receptor. In this study, an infectious full-length cDNA clone for Indian FMDV vaccine strain A IND 40/2000 was constructed. Through site-directed mutagenesis on the cDNA clone, recombinant virus containing positive charged amino acid residue at position VP2 131 was rescued. The recombinant mutated virus was shown to have specific and strong affinity for HS and demonstrated an enhanced infectivity in BHK-21 cell line. The introduction of lysine residue at VP2 131 position that allows cell culture adaptation of FMDV serotype A could be exploited for the generation of vaccine seed stocks with improved growth properties in BHK-21 cell line.

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.