Identification of foot-and-mouth disease virus-specific linear B-cell epitopes to differentiate between infected and vaccinated cattle

Epidemiological and genetic characteristics of foot-and-mouth disease virus in China from 2010 to 2022

Foot-and-mouth disease virus (FMDV) is a highly contagious picornavirus that can infect cloven-hoofed animals of significant agricultural importance. In China, foot-and-mouth disease (FMD) epidemics occur annually, resulting in localized outbreaks or sporadic epidemics that cause significant economic losses. This study summarized 123 cases of FMD reported in China between 2010 and 2022, using data from the official website of the Chinese Center for Animal Disease Control and Prevention. The epidemic situation and genetic characteristics of FMDV in China were studied through phylogenetic analysis, amino acid variation analysis of antigenic epitopes, and genetic recombination analysis. The findings provide important references for predicting the FMDV epidemic situation in China, developing vaccines, and effectively preventing and controlling FMD.

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.

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 Vaccine Development and Challenges in Inducing Long-Lasting Immunity: Trends and Current Perspectives

Foot and mouth disease (FMD) is an extremely contagious viral disease of livestock caused by foot and mouse disease virus genus: Aphthovirus, which causes a serious economic impact on both individual farmers and the national economy. Many attempts to advance a vaccine for FMD have failed to induce sterile immunity. The classical methods of vaccine production were due to selective accumulation of mutations around antigenic and binding sites. Reversion of the agent by positive selection and quasi-species swarm, use of this method is inapplicable for use in non-endemic areas. Chemical attenuation using binary ethyleneimine (BEI) protected the capsid integrity and produced a pronounced immunity against the challenge strain. Viral antigens which have been chemically synthesized or expressed in viruses, plasmid, or plants were tried in the vaccination of animals. DNA vaccines expressing either structural or nonstructural protein antigens have been tried to immunize animals. Using interleukins as a genetic adjuvant for DNA vaccines have a promising effect. While the challenges of inducing sterile immunity lies on non-structural (NS) proteins of FMDV which are responsible for apoptosis of dendritic cells and have negative effects on lympho-proliferative responses which lead to transient immunosuppression. Furthermore, destruction of host protein trafficking by nonstructural proteins suppressed CD₈⁺ T-cell proliferation. In this review, it tried to address multiple approaches for vaccine development trials and bottle necks of producing sterile immunity.

Development and Validation of Confirmatory Foot-and-Mouth Disease Virus Antibody ELISAs to Identify Infected Animals in Vaccinated Populations

In foot-and-mouth disease (FMD)-endemic countries, vaccination is commonly used to control the disease, whilst in FMD-free countries, vaccination is considered as an option, in addition to culling the infected and in contact animals. FMD vaccines are mainly comprised of inactivated virions and stimulate protective antibodies to virus structural proteins. In contrast, infection with FMD virus leads to virus replication and additional antibody responses to viral nonstructural proteins (NSP). Therefore, antibodies against NSPs are used to differentiate infection in vaccinated animals (DIVA), in order to estimate the prevalence of infection or its absence. Another advantage of NSP antibody tests is that they detect FMD infection in the field, irrespective of the serotypes of virus in circulation. In cattle, the NSP tests that target the 3ABC polyprotein provides the highest sensitivity, detecting up to 90% of vaccinated animals that become carriers after exposure to infection, with a specificity of around 99%. Due to insufficient diagnostic sensitivity and specificity, detection of a low level of infection is difficult at the population level with a high degree of confidence. The low level of non-specific responses can be overcome by retesting samples scored positive using a second confirmatory test, which should have at least comparable sensitivity to the first test. In this study, six in-house tests were developed incorporating different NSP antigens, and validated using bovine sera from naïve animals, field cases and experimentally vaccinated and/or infected animals. In addition, two (short and long incubation) new commercial NSP tests based on 3ABC competitive blocking ELISAs (ID Screen^® FMD NSP Competition, IDvet, France) were validated in this study. The two commercial ELISAs had very similar sensitivities and specificities that were not improved by lengthening the incubation period. Several of the new in-house tests had performance characteristics that were nearly as good as the commercial ELISAs. Finally, the in-house tests were evaluated for use as confirmatory tests following screening with the PrioCHECK^® and ID Screen^® FMDV NS commercial kits, to assess the diagnostic performance produced by a multiple testing strategy. The in-house tests could be used in series (to confirm) or in parallel (to augment) with the PrioCHECK^® and IDvet^® FMDV NS commercial kits, in order to improve either the specificity or sensitivity of the overall test system, although this comes at the cost of a reduction in the counterpart (sensitivity/specificity) parameter.

Are Epitopic Sites of 3AB and 3D Nonstructural Proteins Sufficient for Detection of Foot and Mouth Disease?

An efficient method for detection of foot and mouth disease (FMD) and, particularly, differentiation of vaccinated from infected animals is the use of nonstructural (NS) proteins as antigens in Enzyme-Linked Immunosorbent Assay (ELISA) Kits. In this study, only epitopic regions of 3AB and 3D NS proteins were used for recombinant protein production, as a cost-effective method instead of peptide synthesis, for application in in-house ELISA diagnostic kits. Specific primers were designed according to the antigenic regions of 3AB (C-terminus of 3A and the whole 3B) and 3D (N-terminus) proteins, and the polymerase chain reaction (PCR) amplification was performed. Purified amplicons were cloned into pET21a (+) vectors and then transformed into Escherichia coli (BL21). Thereafter, bacteria were induced with 1 mM isopropyl β-d-1-thiogalactopyranoside (IPTG) for expression of antigenic proteins. Antigenic 3AB protein was expressed in soluble form, but 3D protein was extracted from the bacterial lysate. Protein expression was confirmed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analyses. An indirect ELISA was developed for each protein, and the diagnostic sensitivity and specificity were determined. The 3AB-ELISA showed higher sensitivity and specificity than 3D-ELISA (95.24% and 100%, compared with 90.48% and 88.71%, respectively). The epitopic 3AB-ELISA developed here can be used for detection and differentiation of FMD infected from vaccinated animals, but the epitopic 3D-ELISA showed lower efficiency in screening for FMD status.

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.

Multiplexed DIVA tests for rapid detection of FMDV infection/circulation in endemic countries

Foot-and-mouth disease (FMD) is an important transboundary disease affecting domestic and wild ruminants. Due to FMD outbreaks, the annual economic losses in endemic countries range from USD 6.1 billion to 200 billion. It also restricts the export of animals/animal by-products to FMD-free countries. FMD-free countries can experience a more severe economic loss due to the culling of infected animals as experienced by the UK in 2001 outbreaks. In endemic countries outbreaks occur mainly due to unrestricted animal movements. This creates a difficult situation in an endemic setting for controlling FMD spread to nearby areas. During post-vaccination surveillance, testing of serum samples using single test may not be able to substantiate complete freedom from infection. Thus, there is a requirement of more sensitive, robust, and accurate diagnostic tests to detect the FMDV infection/virus circulation in the vaccinated population with more accuracy than the available diagnostic tests. This can be achieved by using multiple antigens and setting the criteria for the positivity/negativity of the samples. Thus, this review emphasizes the comparison and the practical utility of the available diagnostic tests which detect antibodies against single antigen with those which detect antibodies against multiple antigens in single testing. It also emphasizes the utility of these tests in PCP-FMD (Progressive Control Pathway for Foot-and-Mouth Disease) going on in endemic countries.

Identification of three linear B cell epitopes against non-structural protein 3ABC of FMDV using monoclonal antibodies

Foot-and-mouth disease virus (FMDV) has led to serious losses in the farming industry worldwide, particularly in cattle and swine. In developing countries, the control and eradication of FMD rely upon vaccination, in which the inactivated vaccine is predominant. In the preparation of inactivated vaccine, a series of purification methods were used to remove non-structural proteins (NSPs). It is necessary to develop a quantitative detection method of residual NSP and confirm a threshold value for the evaluation of the vaccine. Meanwhile, it is also important to develop a sensitive and rapid diagnostic method to distinguish infected animals from vaccinated animals (DIVA). In this study, three monoclonal antibodies (MAbs) against NSP 3ABC, designated 2G5, 9E2, and 1E10, were used. Subsequently, a series of overlapping peptides were expressed using a prokaryotic expression system to determine the minimal epitopes identified by the MAbs. Three linear B cell epitopes (BCEs), "⁹²EYIEKA⁹⁷" "²³EGPYAGPLE³¹" and "²⁰⁹EPHH²¹²", were identified by MAbs 2G5, 9E2, and 1E10, respectively. Alanine-scanning mutagenesis analysis confirmed the critical amino acid in these epitopes. The epitope "⁹²EYIEKA⁹⁷" is located in 3A, which is deleted in some natural deletion mutants that result in a change in virus tropism. MAb 9E2 that identified the epitope "²³EGPYAGPLE³¹" reacted with 3B1 and 3B2, but did not react with 3B3. In combination with sequence alignment analysis, the epitope "²³EGPYAGPLE³¹" is highly conserved among different FMDV isolates. Preliminary screening using the known positive and negative sera indicated the MAb 9E2 has the potential for the development of a diagnostic method for DIVA. The residual NSP in inactivated vaccines can be detected using 9E2-HRP, which indicated the MAb 9E2 is able to evaluate inactivated vaccines. The four-amino acid epitope is the first reported to date that is recognized by 1E10. These results provide valuable insight into the diagnosis of DIVA and the NSP residual evaluation in inactivated vaccines.

Identification of a conserved linear epitope using monoclonal antibody against non-structural protein 3A of foot-and-mouth disease virus with potential for differentiation between infected and vaccinated animals

Foot-and-mouth disease (FMD) is a highly contagious and economically devastating viral disease of cloven-hoofed animals. Vaccination is a key element in the control of FMD among countries where the disease is enzootic. Differentiating infected from vaccinated animals in herds after immunization is an important component of effective eradication strategies. Non-structural protein (NSP) 3A of FMDV is as part of a larger detected antigen that is used for this differential diagnosis. Here, we generated a specific monoclonal antibody (MAb) against FMDV non-structural protein called 3A10, and further defined the linear epitopes recognized by the MAb 3A10 using a series of peptides that expressed GST-fused protein. Using Western blot, it was showed that the 5-aa peptide ¹²⁶ERTLP¹³⁰ of 3A was the minimal epitope reactive to MAb 3A10. Alanine-scanning mutagenesis analysis revealed that Arg127 and Leu129 were crucial for MAb 3A10 binding to ¹²⁶ERTLP¹³⁰. Furthermore, sequence alignment analysis, indicated that the epitope ¹²⁶ERTLP¹³⁰ recognized by 3A10 was shown to be conserved among seven serotypes of FMDV strains. The synthetic peptide Elisa demonstrated that this epitope peptide could be recognized by sera from FMDV-infected pigs and cattle, but negative reactivity to unvaccinated and vaccinated healthy animal sera. Thus, the MAb reagents and the linear epitopes defined herein provide theoretical and technical support for the development of diagnostic tools for infection differentiating FMDV infected from vaccinated animals.

Recombinant occlusion bodies of baculovirus as carriers of a non-structural protein of foot-and-mouth disease virus

Here, we developed a diagnostic ELISA for foot-and-mouth disease using recombinant occlusion bodies (rOBs) of baculovirus. We fused Δ3AB_1-3, a polypeptide derived from non-structural proteins of foot-and-mouth disease virus, to polyhedrin (POLH), the major constituent of OBs, under polh promoter. To further assess the most convenient strategy to improve yields, we designed two recombinant baculoviruses, vPOLH and vPOLH_E44G. These carried the sequence of the fusion protein POLH-Δ3AB_1-3 with an additional copy in cis of polh or polh _E44G , respectively, under p10 promoter. Our results show that both viruses expressed POLH-Δ3AB_1-3, which was detected by western blot in purified rOBs with anti-POLH and anti-3AB1 antibodies. We also found that vPOLH_E44G produced larger polyhedra and a significant increase of antigen yield (p < 0.01). Furthermore, the chimeric protein POLH-Δ3AB_1-3 was recognized by sera from experimentally infected animals, showing that translational fusion to POLH does not alter the antigenicity of Δ3AB_1-3. Finally, the rOBs were successfully used in an ELISA test to differentiate infected from vaccinated animals. Taken together, these results demonstrate the great potential of rOBs to develop diagnostic schemes adaptable to animal infectious diseases.

An improved, rapid competitive ELISA using a novel conserved 3B epitope for the detection of serum antibodies to foot-and-mouth disease virus

The highly contagious foot-and-mouth disease virus (FMDV) afflicts cloven-hoofed animals, resulting in significant costs because of loss of trade and recovery from disease. We developed a sensitive, specific, and rapid competitive ELISA (cELISA) to detect serum antibodies to FMDV. The cELISA utilized a monoclonal blocking antibody specific for a highly conserved FMDV nonstructural 3B epitope, a recombinant mutant FMDV 3ABC coating protein, and optimized format variables including serum incubation for 90 min at 20-25°C. Samples from 16 animals experimentally infected with one FMDV serotype (A, O, Asia, or SAT-1) demonstrated early detection capacity beginning 7 d post-inoculation. All samples from 55 vesicular stomatitis virus antibody-positive cattle and 44 samples from cloven-hoofed animals affected by non-FMD vesicular diseases were negative in the cELISA, demonstrating 100% analytical specificity. The diagnostic sensitivity was 100% against sera from 128 cattle infected with isolates of all FMDV serotypes, emphasizing serotype-agnostic results. Diagnostic specificities of U.S. cattle ( n = 1135) and swine ( n = 207) sera were 99.4% and 100%, respectively. High repeatability and reproducibility were demonstrated with 3.1% coefficient of variation in percent inhibition data and 100% agreement using 2 kit lots and 400 negative control serum samples, with no difference between bench and biosafety cabinet operation. Negative results from vaccinated, uninfected cattle, pig, and sheep sera confirmed the DIVA (differentiate infected from vaccinated animals) capability. This rapid (<3 h), select agent-free assay with high sensitivity and specificity, DIVA capability, and room temperature processing capability will serve as a useful tool in FMDV surveillance, emergency preparedness, response, and outbreak recovery programs.

Development of a chemiluminescence immunoassay using recombinant non-structural epitope-based proteins to accurately differentiate foot-and-mouth disease virus-infected and vaccinated bovines

The contamination of inactivated vaccine with non-structural proteins (NSPs) leads to a high false-positive rate, which is a substantial barrier to accurately differentiate foot-and-mouth disease virus (FMDV)-infected animals from vaccinated animals. To address this problem, a new chemiluminescence immunoassay (CLIA) method was developed to detect antibodies targeting the two recombinant epitope-based proteins located in 3A and 3B. The 3Aepitp-3Bepitp CLIA exhibited a diagnostic sensitivity of 94.0% and a diagnostic specificity of 97.5% for the detection of serum samples (naïve bovines, n = 52, vaccinated bovines, n = 422, infected bovines, n = 116) from animals with known status. The CLIA method also had a concordance rate of 88.1% with the PrioCHECK FMDV NSP ELISA based on the detection of 270 serum samples from the field. Importantly, the 3Aepitp-3Bepitp CLIA produced no false-positives when used to detect FMDV in samples from bovines that had been vaccinated up to five times, and it was demonstrated a low false-positive rate when the bovines had been vaccinated up to ten (2.15%) and fifteen times (5.93%). Therefore, the 3Aepitp-3Bepitp CLIA detects FMDV in samples from frequently vaccinated bovines with high accuracy and represents an alternative method to differentiate FMDV-infected and vaccinated bovines.

Development of a Blocking ELISA Using a Monoclonal Antibody to a Dominant Epitope in Non-Structural Protein 3A of Foot-and-Mouth Disease Virus, as a Matching Test for a Negative-Marker Vaccine

Foot-and-mouth disease (FMD) is a devastating animal disease. Strategies for differentiation of infected from vaccinated animals (DIVA) remain very important for controlling disease. Development of an epitope-deleted marker vaccine and accompanying diagnostic method will improve the efficiency of DIVA. Here, a monoclonal antibody (Mab) was found to recognize a conserved “AEKNPLE” epitope spanning amino acids 109–115 of non-structural protein (NSP) 3A of foot-and-mouth disease virus (FMDV; O/Tibet/CHA/99 strain), which could be deleted by a reverse-genetic procedure. In addition, a blocking ELISA was developed based on this Mab against NSP 3A, which could serve as a matching test for a negative-marker vaccine. The criterion of this blocking ELISA was determined by detecting panels of sera from different origins. The serum samples with a percentage inhibition (PI) equal or greater than 50% were considered to be from infected animals, and those with <50% PI were considered to be from non-infected animals. This test showed similar performance when compared with other 2 blocking ELISAs based on an anti-NSP 3B Mab. This is the first report of the DIVA test for an NSP antibody based on an Mab against the conserved and predominant “AEKNPLE” epitope in NSP 3A of FMDV.

The carboxy-terminal half of nonstructural protein 3A is not essential for foot-and-mouth disease virus replication in cultured cell lines

In foot-and-mouth disease (FMD)-endemic parts of the globe, control is mainly implemented by preventive vaccination with an inactivated purified vaccine. ELISAs detecting antibodies to the viral nonstructural proteins (NSP) distinguish FMD virus (FMDV)-infected animals in the vaccinated population (DIVA). However, residual NSPs present in the vaccines are suspected to be a cause of occasional false positive results, and therefore, an epitope-deleted negative marker vaccine strategy is considered a more logical option. In this study, employing a serotype Asia 1 FMDV infectious cDNA clone, it is demonstrated that while large deletions differing in size and location in the carboxy-terminal half of 3A downstream of the putative hydrophobic membrane-binding domain (deletion of residues 86-110, 101-149, 81-149 and 81-153) are tolerated by the virus without affecting its infectivity in cultured cell lines, deletions in the amino-terminal half (residues 5-54, 21-50, 21-80, 55-80 and 5-149) containing the dimerization and the transmembrane domains are deleterious to its multiplication. Most importantly, the virus could dispense with the entire carboxy-terminal half of 3A (residues 81-153) including the residues involved in the formation of the 3A-3B1 cleavage junction. The rescue of a replication-competent FMDV variant carrying the largest deletion ever in 3A (residues 81-153) and the fact that the deleted region contains a series of linear B-cell epitopes inspired us to devise an indirect ELISA based on a recombinant 3A carboxy-terminal fragment and to evaluate its potential to serve as a companion diagnostic assay for differential serosurveillance if the 3A-truncated virus is used as a marker vaccine.

Identification of a conserved linear epitope using a monoclonal antibody against non-structural protein 3B of foot-and-mouth disease virus

Foot-and-mouth disease virus (FMDV) is a member of the family Picornaviridae that has caused severe economic losses in many countries of the world. Regular vaccinations have been effectively used to control foot-and-mouth disease (FMD) in countries where the disease is enzootic. Distinguishing between infected and vaccinated animals in herds after immunization is an important component of effective eradication strategies. Nonstructural protein (NSP) 3B of FMDV is part of a larger antigen that is used for this differential diagnosis. In this study, an FMDV serotype-independent monoclonal antibody (MAb) against NSP 3B, 5D12, was generated. Using western blot, it was revealed that MAb 5D12 binds to three fragments of 3B displaying the motifs G(1)PYAGPLERQKPLK(14), K(18)LPQQEGPYAGPMER(32) and V(45)KEGPYEGPVKKPVA(59). The motif G(1)PYAGPLERQKPLK(14) was chosen for further mapping. Different truncated motifs derived from the motif G(1)PYAGPLERQKPLK(14) were expressed as GST-fusion constructs for western blot analysis. The results showed that the 5-aa peptide P(2)YAGP(6) was the minimal epitope reactive to MAb 5D12. Subsequent alanine-scanning mutagenesis analysis revealed that Pro(2), Gly(5) and Pro(6) were crucial for MAb 5D12 binding to P(2)YAGP(6). Furthermore, through sequence alignment analysis, the epitope PxxGP recognized by 5D12 was found to be present not only in 3B-1 but also in 3B2 and 3B3 and was highly conserved in seven serotypes of FMDV strains. Western blot analysis also revealed that the peptide epitope could be recognized by sera from FMDV-infected pigs and cattle. Thus, the 5D12-recognized 3B epitope identified here provides theoretical support for the development of MAb 5D12 as a differential diagnosis reagent for FMDV infection.

Pan-Serotype Diagnostic for Foot-and-Mouth Disease Using the Consensus Antigen of Nonstructural Protein 3B

An amino acid consensus sequence for the seven serotypes of foot-and-mouth disease virus (FMDV) nonstructural protein 3B, including all three contiguous repeats, and its use in the development of a pan-serotype diagnostic test for all seven FMDV serotypes are described. The amino acid consensus sequence of the 3B protein was determined from a multiple-sequence alignment of 125 sequences of 3B. The consensus 3B (c3B) protein was expressed as a soluble recombinant fusion protein with maltose-binding protein (MBP) using a bacterial expression system and was affinity purified using amylose resin. The MBP-c3B protein was used as the antigen in the development of a competition enzyme-linked immunosorbent assay (cELISA) for detection of anti-3B antibodies in bovine sera. The comparative diagnostic sensitivity and specificity at 47% inhibition were estimated to be 87.22% and 93.15%, respectively. Reactivity of c3B with bovine sera representing the seven FMDV serotypes demonstrated the pan-serotype diagnostic capability of this bioreagent. The consensus antigen and competition ELISA are described here as candidates for a pan-serotype diagnostic test for FMDV infection.

Development of a competitive enzyme-linked immunosorbent assay for detection of antibodies against the 3B protein of foot-and-mouth disease virus

Foot-and-mouth disease (FMD) is one of the most highly contagious and economically devastating diseases, and it severely constrains the international trade of animals. Vaccination against FMD is a key element in the control of FMD. However, vaccination of susceptible animals raises critical issues, such as the differentiation of infected animals from vaccinated animals. The current study developed a reliable and rapid test to detect antibodies against the conserved, nonstructural proteins (NSPs) of the FMD virus (FMDV) to distinguish infected animals from vaccinated animals. A monoclonal antibody (MAb) against the FMDV NSP 3B was produced. A competitive enzyme-linked immunosorbent assay (cELISA) for FMDV/NSP antibody detection was developed using a recombinant 3ABC protein as the antigen and the 3B-specific MAb. Sera collected from naive, FMDV experimentally infected, vaccinated carrier, and noncarrier animals were tested using the 3B cELISA. The diagnostic specificity was 99.4% for naive animals (cattle, pigs, and sheep) and 99.7% for vaccinated noncarrier animals. The diagnostic sensitivity was 100% for experimentally inoculated animals and 64% for vaccinated carrier animals. The performance of this 3B cELISA was compared to that of four commercial ELISA kits using a panel of serum samples established by the World Reference Laboratory for FMD at The Pirbright Institute, Pirbright, United Kingdom. The diagnostic sensitivity of the 3B cELISA for the panel of FMDV/NSP-positive bovine serum samples was 94%, which was comparable to or better than that of the commercially available NSP antibody detection kits. This 3B cELISA is a simple, reliable test to detect antibodies against FMDV nonstructural proteins.

Development of a blocking ELISA based on a monoclonal antibody against a predominant epitope in non-structural protein 3B2 of foot-and-mouth disease virus for differentiating infected from vaccinated animals

A monoclonal antibody (McAb) against non-structural protein (NSP) 3B of foot-mouth-disease virus (FMDV) (3B4B1) was generated and shown to recognize a conserved epitope spanning amino acids 24-32 of 3B (GPYAGPMER) by peptide screening ELISA. This epitope was further shown to be a unique and predominant B cell epitope in 3B2, as sera from animals infected with different serotypes of FMDV blocked the ability of McAb 3B4B1 to bind to NSP 2C3AB. Also, a polyclonal antibody against NSP 2C was produced in a rabbit vaccinated with 2C epitope regions expressed in E. coli. Using McAb 3B4B1 and the 2C polyclonal antibody, a solid-phase blocking ELISA (SPB-ELISA) was developed for the detection of antibodies against NSP 2C3AB to distinguish FMDV-infected from vaccinated animals (DIVA test). The parameters for this SPB-ELISA were established by screening panels of sera of different origins. Serum samples with a percent inhibition (PI) greater than or equal to 46% were considered to be from infected animals, and a PI lower than 46% was considered to indicate a non-infected animal. This test showed a similar performance as the commercially available PrioCHECK NS ELISA. This is the first description of the conserved and predominant GPYAGPMER epitope of 3B and also the first report of a DIVA test for FMDV NSP 3B based on a McAb against this epitope.

Production and characterization of single-chain antibody (scFv) against 3ABC non-structural protein in Escherichia coli for sero-diagnosis of Foot and Mouth Disease virus

Differentiation of Foot-and-Mouth Disease infected from vaccinated animals is essential for effective implementation of vaccination based control programme. Detection of antibodies against 3ABC non-structural protein of FMD virus by immunodiagnostic assays provides reliable indication of FMD infection. Sero-monitoring of FMD in the large country like India is a big task where thousands of serum samples are annually screened. Currently, monoclonal or polyclonal antibodies are widely used in these immunodiagnostic assays. Considering the large population of livestock in the country, an economical and replenishable alternative of these antibodies was required. In this study, specific short chain variable fragment (scFv) antibody against 3B region of 3ABC poly-protein was developed. High level of scFv expression in Escherichia coli system was obtained by careful optimization in four different strains. Two formats of enzyme immunoassays (sandwich and competitive ELISAs) were optimized using scFv with objective to differentiate FMD infected among the vaccinated population. The assays were statistically validated by testing 2150 serum samples. Diagnostic sensitivity/specificity of sandwich and competitive ELISAs were determined by ROC method as 92.2%/95.5% and 89.5%/93.5%, respectively. This study demonstrated that scFv is a suitable alternate for immunodiagnosis of FMD on large scale.

Characterization of monoclonal antibodies against foot-and-mouth disease virus serotype O and application in identification of antigenic variation in relation to vaccine strain selection

BACKGROUND

Foot-and-mouth disease (FMD) has severe implications for animal farming which leads to considerable financial losses because of its rapid spread, high morbidity and loss of productivity. For these reasons, the use of vaccine is often favoured to prevent and control FMD. Selection of the proper vaccine is extremely difficult because of the antigenic variation within FMDV serotypes. The aim of the current study was to produce a panel of mAbs and use it for the characterization of new isolates of FMDV serotype O.

RESULTS

A panel of FMDV/O specific mAb was produced. The generated mAbs were then characterized using the peptide array and mAb resistant mutant selection. Seven out of the nine mAbs reacted with five known antigenic sites, thus the other two mAbs against non-neutralizing sites were identified. The mAbs were then evaluated by antigenic ELISA for the detection of forty-six FMDV serotype O isolates representing seven of ten known topotypes. Isolates ECU/4/10 and HKN/2/11 demonstrated the highest antigenic variation compared to the others. Furthermore, the panel of mAbs was used in vaccine matching by antigenic profiling ELISA with O1/Manisa as the reference strain. However, there was no correlation between vaccine matching by antigenic ELISA and the gold standard method, virus neutralisation test (VNT), for the forty-six FMDV/O isolates. Nine isolates had particularly poor correlation with the reference vaccine strain as revealed by the low r1 values in VNT. The amino acid sequences of the outer capsid proteins for these nine isolates were analyzed and compared with the vaccine strain O1/Manisa. The isolate ECU/4/10 displayed three unique amino acid substitutions around the antigenic sites 1, 3 and 4.

CONCLUSIONS

The panel of mAbs is useful to monitor the emergence of antigenically different strains and determination of relevant antigenic site differences. However, for vaccine matching VNT remains the preferred method but a combination of VNT, antigenic profiling with a panel of mAbs and genetic sequencing would probably be more ideal for full characterization of any new outbreak isolates as well as for selection of vaccine strains from FMDV antigen banks.

Diagnostic potential of recombinant nonstructural protein 3B to detect antibodies induced by foot-and-mouth disease virus infection in bovines

Detection of antibodies to nonstructural proteins (NSP) of foot-and-mouth disease virus is the preferred diagnostic method to differentiate infected from vaccinated animals. In India, an endemic region practising preventive biannual vaccination, 3AB3 indirect ELISA (r3AB3 I-ELISA) has been employed as the primary screening test for serosurveillance. However, because of the variability observed in the immune response to the NSPs, the likelihood of detecting or confirming an infected animal is increased if an antibody profile against multiple NSPs is considered for diagnosis. In this study, all three copies of NSP 3B were expressed in a prokaryotic system to develop an indirect ELISA (r3B I-ELISA). At the decided cutoff of 40 percent positivity, the diagnostic sensitivity and specificity of the r3B I-ELISA were estimated to be 92.1% (95% CI: 89.0-94.5) and 98.1% (95% CI: 96.9-98.8), respectively, as compared to 97.04% and 95.04% for r3AB3 I-ELISA. Although r3B I-ELISA displayed lower sensitivity compared to the screening assay, which could possibly be attributed to additional relevant B-cell epitopes in the carboxy-terminal half of the 3A protein, the former achieved considerably higher specificity on repeatedly vaccinated animals. NSP antibodies could be detected from 10 to as late as 998 days postinfection in experimental calves. Substantial agreement in the test results (90.6%) was found between the two ELISAs. The r3B I-ELISA, when used in conjunction with the r3AB3 I-ELISA as an integrated system, can potentially augment the efficiency and confidence of detection of infected herds against the backdrop of intensive vaccination.

Detection of antibodies specific for foot-and-mouth disease virus infection using indirect ELISA based on recombinant nonstructural protein 2B

Foot-and-mouth disease (FMD) is a highly contagious viral disease of transboundary importance. In India, since the launch of the FMD control programme, there has been a substantial increase in the vaccinated bovine population. In this scenario, there is a need for additional locally developed non-structural protein (NSP)-based immnoassays for efficient identification of FMD virus (FMDV)-infected animals in the vaccinated population. The 2B NSP of FMDV, lacking the transmembrane domain (Δ2B), was expressed successfully in a prokaryotic system, and an indirect ELISA (I-ELISA) was developed and validated in this study. The diagnostic sensitivity and specificity of the Δ2B I-ELISA were found to be 95.3 % and 94.6 %, respectively. In experimentally infected cattle, the assay could consistently detect Δ2B-NSP-specific antibodies from 10 to approximately 400 days postinfection. The assay was further validated with bovine serum samples collected randomly from different parts of the country. The performance of the Δ2B I-ELISA was compared with the in-house r3AB3 I-ELISA, and the overall concordance in test results was found to be 86.49 %. The Δ2B I-ELISA could be useful as a screening or confirmatory assay in the surveillance of FMD irrespective of vaccination.

Truncated recombinant non-structural protein 2C-based indirect ELISA for FMD sero-surveillance

Foot-and-mouth disease (FMD) is a transboundary animal disease caused by foot-and-mouth disease virus. In India, systematic preventive vaccination using inactivated trivalent (O, A and Asia 1) vaccine is the strategy being adopted to control FMD. The use of non-structural protein (NSP)-contaminated inactivated vaccine raises concerns over differentiation of infected and vaccinated animals (DIVA) by NSP based immunoassays. However, 2C being a membrane associated protein usually remain absent in vaccine formulations and thus, anti-2C response is one of the most reliable indicator of the FMDV infection. In this study, 34 amino acids from N-terminus of 2C protein were removed to eliminate membrane-binding amphipathic helicase activity for the expression of recombinant protein in soluble form. Truncated 2C (2Ct) was utilized for development of an indirect ELISA (I-ELISA) for bovine and the developed 2Ct I-ELISA was validated using a panel constituting of serum of naïve, vaccinated and infected animals. The assay was compared with the in-house r3AB3 I-ELISA and the overall concordance was 85.31%. The diagnostic sensitivity and specificity of the 2Ct I-ELISA were 92.9% and 94.0%, respectively. The apparent prevalence of anti-2C antibodies for random bovine samples tested by the developed assay was 23.7%. The developed ELISA will help in augmenting the sensitivity of detection if used in combination with r3AB3 I-ELISA for sero-surveillance.

Antigenic heterogeneity of capsid protein VP1 in foot-and-mouth disease virus (FMDV) serotype Asia 1

Foot and mouth disease virus (FMDV), with its seven serotypes, is a highly contagious virus infecting mainly cloven-hoofed animals. The serotype Asia1 occurs mainly in Asian regions. An in-silico approach was taken to reveal the antigenic heterogeneities within the capsid protein VP1 of Asia1. A total of 47 VP1 sequences of Asia1 isolates from different countries of South Asian regions were selected, retrieved from database, and were aligned. The structure of VP1 protein was modeled using a homology modeling approach. Several antigenic sites were identified and mapped onto the three-dimensional protein structure. Variations at these antigenic sites were analyzed by calculating the protein variability index and finding mutation combinations. The data suggested that vaccine escape mutants have derived from only few mutations at several antigenic sites. Five antigenic peptides have been identified as the least variable epitopes, with just fewer amino acid substitutions. Only a limited number of serotype Asia1 antigenic variants were found to be circulated within the South Asian region. This emphasizes a possibility of formulating synthetic vaccines for controlling foot-and-mouth disease by Asia1 serotypes.

A safe foot-and-mouth disease vaccine platform with two negative markers for differentiating infected from vaccinated animals

Vaccination of domestic animals with chemically inactivated foot-and-mouth disease virus (FMDV) is widely practiced to control FMD. Currently, FMD vaccine manufacturing requires the growth of large volumes of virulent FMDV in biocontainment-level facilities. Here, two marker FMDV vaccine candidates (A(24)LL3D(YR) and A(24)LL3B(PVKV)3D(YR)) featuring the deletion of the leader coding region (L(pro)) and one of the 3B proteins were constructed and evaluated. These vaccine candidates also contain either one or two sets of mutations to create negative antigenic markers in the 3D polymerase (3D(pol)) and 3B nonstructural proteins. Two mutations in 3D(pol), H(27)Y and N(31)R, as well as RQKP(9-12)→PVKV substitutions, in 3B(2) abolish reactivity with monoclonal antibodies targeting the respective sequences in 3D(pol) and 3B. Infectious cDNA clones encoding the marker viruses also contain unique restriction endonuclease sites flanking the capsid-coding region that allow for easy derivation of custom designed vaccine candidates. In contrast to the parental A(24)WT virus, single A(24)LL3D(YR) and double A(24)LL3B(PVKV)3D(YR) mutant viruses were markedly attenuated upon inoculation of cattle using the natural aerosol or direct tongue inoculation. Likewise, pigs inoculated with live A(24)LL3D(YR) virus in the heel bulbs showed no clinical signs of disease, no fever, and no FMD transmission to in-contact animals. Immunization of cattle with chemically inactivated A(24)LL3D(YR) and A(24)LL3B(PVKV)3D(YR) vaccines provided 100% protection from challenge with parental wild-type virus. These attenuated, antigenically marked viruses provide a safe alternative to virulent strains for FMD vaccine manufacturing. In addition, a competitive enzyme-linked immunosorbent assay targeted to the negative markers provides a suitable companion test for differentiating infected from vaccinated animals.

An overview on ELISA techniques for FMD

Background

FMD is one of the major causes of economic loss of cloven-hoofed animals in the world today. The assessment of dominant genotype/lineage and prevalent trends and confirmation the presence of infection or vaccination not only provides scientific basis and first-hand information for appropriate control measure but also for disease eradication and regaining FMD free status following an outbreak. Although different biological and serological approaches are still applied to study this disease, ELISA test based on the distinct format, antigen type and specific antibody reinforce its predominance in different research areas of FMD, and this may replace the traditional methods in the near future. This review gives comprehensive insight on ELISA currently available for typing, antigenic analysis, vaccination status differentiation and surveillance vaccine purity and content at all stages of manufacture in FMDV. Besides, some viewpoint about the recent advances and trends of ELISA reagent for FMD are described here.

Methods

More than 100 studies regarding ELISA method available for FMD diagnosis, antigenic analysis and monitor were thoroughly reviewed. We investigated previous sagacious results of these tests on their sensitivity, specificity.

Results

We found that in all ELISA formats for FMD, antibody-trapping and competitive ELISAs have high specificity and RT-PCR (oligoprobing) ELISA has extra sensitivity. A panel of monoclonal antibodies to different sites or monoclonal antibody in combination of antiserum is the most suitable combination of antibodies in ELISA for FMD. Even though from its beginning, 3ABC is proven to be best performance in many studies, no single NSP can differentiate infected from vaccinated animals with complete confidence. Meanwhile, recombinant antigens and peptide derived from FMDV NPs, and NSPs have been developed for use as an alternative to the inactivated virus antigen for security.

Conclusions

There is a need of target protein, which accurately determines the susceptible animal status based on the simple, fast and reliable routine laboratory test. A further alternative based on virus-like particle (VLP, also called empty capsids) in combination of high throughput antibody technique (Phage antibody library/antibody microarray) may be the powerful ELISA diagnostic reagents in future.

Comparative complete genome analysis of Indian type A foot-and-mouth disease virus field isolates

Comparative complete genome analysis of 17 serotype A Indian field isolates representing different genotypes and sub-lineages is presented in this report. Overall 79% of amino acids were invariant in the coding region. Chunk deletion of nucleotide was observed in S and L fragment of 5'-UTR. More variability which is comparable to that of capsid coding region was found in L and 3A region. Functional motifs and residues critical for virus biology were conserved most. Polyprotein cleavage sites accepted few changes. Many sites were detected to be under positive selection in L, P1, 2C, 3A, 3C, and 3D region and of which some are functionally important and antigenically critical. Genotype/lineage specific signature residues could be identified which implies evolution under different selection pressure. Transmembrane domain could be predicted in 2B, 2C, 3A, and 3C proteins in agreement with their membrane binding properties. Phylogenetic analysis at complete coding region placed the isolates in genotype IV, VI, and VII and two broad clusters comprising VP3(59)-deletion and non-deletion group within genotypes VII. The VP3(59)-deletion group has diversified genetically with time giving rise to three lineages. Incongruence in tree topology observed for different non structural protein coding region and UTRs-based phylogeny indicate suspected recombination.

Development and validation of a prokaryotically expressed foot-and-mouth disease virus non-structural protein 2C'3AB-based immunochromatographic strip to differentiate between infected and vaccinated animals

Background

Foot-and-mouth disease (FMD) is an extremely contagious viral disease of cattle, pigs, sheep, goats, and many cloven-hoofed wild animals. FMDV serotypes O and Asia 1 have circulated separately in China during the last fifty years, and eliminating infected animals and vaccination are the main policies to prevent and control FMD. Antibodies to NSPs exist in infected animals, and were utilized to differentiate between infected and vaccinated animals. The reliability of detection of 3AB or 3ABC antibodies is higher than that of other NSPs. The test of 3AB is still credible because 3C protein's immunogenicity is the weakest. The 2C protein, immediately N-terminal of 3AB, was used to differentiate between infected and vaccinated animals. The use of the immunochromatographic strip is facile for clinical laboratories lacking specialized equipment and for rapid field diagnosis.

Results

In this study, an immunochromatographic strip with non-structural protein (NSP) 2C'3AB was developed and validated to differentiate foot-and-mouth disease infected from vaccinated animals. A part of N-terminal of 2C protein gene and whole 3AB gene were connected and prokaryotically expressed as the antigens labeled with colloidal gold was used as the detector, the 2C'3AB protein and rabbits anti-2C'3AB antibodies were blotted on the nitrocellulose(NC) membrane for the test and control lines, respectively. 387 serum samples were collected to evaluate the characteristics of the strip in comparison with existing commercial 3ABC antibody ELISA kit. The coincidence rate of pigs negative serum, pigs vaccinated serum, pigs infected serum was 100%, 97.2%, 95.0%, respectively. The coincidence rate of cattle negative serum, cattle vaccinated serum, cattle infected serum was 100%, 96.7%, 98.0%, respectively. The coincidence rate of sheep negative serum, sheep infected serum was 97.6%, 96.3%, respectively. The strip was shown to be of high specificity and sensitivity, good repeatability and stability.

Conclusion

These data suggest that the immunochromatographic strip is a useful tool for rapid on-site diagnosing animals infected foot-and-mouth disease virus.

A mutant of Asia 1 serotype of Foot-and-mouth disease virus with the deletion of an important antigenic epitope in the 3A protein

Foot-and-mouth disease is a highly contagious viral disease of cloven-hoofed animals. The availability of a vaccine for differentiating infected from vaccinated animals (DIVA) is crucial for the control and eradication of Foot-and-mouth disease virus (FMDV). Because traditional inactivated vaccines may contain trace nonstructural proteins interfering with the DIVA, we hypothesized that mutant FMDV with deletion of immunodominant epitopes may be valuable. Our previous study has generated a full-length cDNA clone (pBSAs) of FMDV serotype Asia 1 isolated in China. In this study, a B-cell epitope was identified in the 3A region of a nonstructural protein (NSP) by anti-FMDV cattle sera. Furthermore, we generated recombinant FMDV (rvAs-3A14D) by selectively deleting 14 amino acids (position 91–104) in the 3A region of the NSP. Following in vitro transcription and transfection in BHK-21 cells, we successfully rescued the rvAs-3A14D from BHK-21 cells. Characterization of the rvAs-3A14D revealed that the infectivity, antigenicity, and replication kinetics in BHK-21 cells and virulence in mice of the rvAs-3A14D were similar to that of its parent virus. Notably, the mutant rvAs-3A14D only replicated well in BHK-21 but did poorly in primary calf kidney cells. These data suggest that the recombinant FMDV with deletion of this epitope in the NSP may be potentially used as a candidate inactivated vaccine. Therefore, the application of the marker vaccine and differential diagnostic tests may open a promising new avenue for the development of a vaccine for DIVA.

Genetic characterization of Indian type O FMD virus 3A region in context with host cell preference

The 3A region of foot-and-mouth disease virus has been implicated in host range and virulence. For example, amino acid deletions in the porcinophilic strain (O/TAW/97) at 93-102aa of the 153 codons long 3A protein have been recognized as the determinant of species specificity. In the present study, 18 type O FMDV isolates from India were adapted in different cell culture systems and the 3A sequence was analyzed. These isolates had complete 3A coding sequence (153aa) and did not exhibit growth restriction in cells based on species of origin. The 3A region was found to be highly conserved at N-terminal half (1-75aa) but exhibited variability or substitutions towards C-terminal region (80-153). Moreover the amino acid substitutions were more frequent in recent Indian buffalo isolates but none of the Indian isolates showed deletion in 3A protein, which may be the reason for the absence of host specificity in vitro. Further inclusive analysis of 3A region will reveal interesting facts about the variability of FMD virus 3A region in an endemic environment.

Identification of major histocompatibility complex restriction and anchor residues of foot-and-mouth disease virus-derived bovine T-cell epitopes

Despite intensive research on the identification of T-cell epitopes in cattle after foot-and-mouth disease virus (FMDV) infection during the last 20 years, knowledge of major histocompatibility complex (MHC) restriction and anchor residues of such epitopes is still sparse. Therefore, as a first step, we tested lymphocytes from two experimentally FMDV serotype A24-vaccinated and -challenged cattle for recognition of FMDV-derived pentadecapeptides in proliferation assays. Two epitopes were identified: amino acid residues 66 to 80 within the structural protein 1D and amino acid residues 22 to 36 within the structural protein 1A. The latter epitope was recognized by lymphocytes from both cattle. Peptide-specific proliferation was caused by a response of CD4(+) T helper cells as identified by carboxyfluorescein diacetate succinimidyl ester proliferation assays. Having identified one epitope that was recognized by two cattle, we hypothesized that these animals should have common MHC class II alleles. Cloning and sequencing of DRB3, DQA, and DQB alleles revealed that both animals possessed DQA allele 22021 and DQB allele 1301 but had no common DRB3 allele. A parallel analysis of amino acid residues involved in MHC presentation by peptides with alanine substitutions showed that the amino acid residues in positions 5 and 9 within the pentadecapeptide representing the 1A epitope were important for MHC binding in both cattle. These data indicate that the epitope located on FMDV protein 1A can be presented by MHC class II DQ molecules encoded by DQA allele 22021 and DQB allele 1301 and present the first evidence of the binding motif of this particular DQ molecule.

Development of an epitope-blocking-enzyme-linked immunosorbent assay to differentiate between animals infected with and vaccinated against foot-and-mouth disease virus

An epitope-blocking ELISA (EB-ELISA) was developed to distinguish animals infected with foot-and-mouth-disease (FMDV) from those immunized with commercial vaccines. The assay used monoclonal antibodies to target the 3B core repeat motif (QKPLK) and purified recombinant 3AB proteins from the major B cell line epitopes of FMDV. Sera from uninfected and regularly vaccinated cattle, pigs, goats, and sheep (raised in FMDV free areas) were screened to evaluate the specificity of the EB-ELISA. The specificity scores of the assays were 99.8-100% and 100%, respectively. Reference sera from cattle, pigs, goats, and sheep experimentally infected with FMDV tested positive, with only a single exception. Antibodies formed in response to FMDV 3B appeared 1 week after infection and persisted at high levels for more than 8 weeks within the sera collected from serial bleeding of animals infected with FMDV O/SKR/2000. The EB-ELISA was used to differentiate between farms vaccinated against and those infected with FMDV (FMDV Asia serotype) during the 2005 epidemic in Mongolia by detecting antibodies against the FMDV Asia serotype in outbreak farms. This EB-ELISA method shows promise as an effective tool for FMDV control and eradication.

Chimeric tymovirus-like particles displaying foot-and-mouth disease virus non-structural protein epitopes and its use for detection of FMDV-NSP antibodies

Expression of Physalis mottle tymovirus (PhMV) coat protein (CP) in Escherichia coli (E. coli) was earlier shown to self-assemble into empty capsids that are nearly identical to the capsids formed in vivo. Aminoacid substitutions were made at the N-terminus of wild-type PhMV CP with single or tandem repeats of infection related B-cell epitopes of foot-and-mouth disease virus (FMDV) non-structural proteins (NSPs) 3B1, 3B2, 3AB, 3D and 3ABD of lengths 48, 66, 49, 51 and 55, respectively to produce chimeras pR-Ph-3B1, pR-Ph-3B2, pR-Ph- 3AB, pR-Ph-3D and pR-Ph-3ABD. Expression of these constructs in E. coli resulted in chimeric proteins which self-assembled into chimeric tymovirus-like particles (TVLPs), Ph-3B1, Ph-3B2, Ph-3AB, Ph-3D and Ph-3ABD as determined by ultracentrifugation and electron microscopy. Ph-3B1, Ph-3B2, Ph-3AB and Ph-3ABD reacted with polyclonal anti-3AB antibodies in ELISA and electroblot immunoassay, while wild-type PhMV TVLP and Ph-3D antigens did not react. An indirect ELISA (I-ELISA) was developed using Ph-3AB to detect FMDV-NSP antibodies in sera of animals that showed clinical signs of FMD. Field serum samples from cattle, buffalos, sheep, goats and pigs were examined by using these chimeric TVLPs for the differentiation of FMDV infected animals from vaccinated animals (DIVA). The assay was demonstrated to be highly specific (100%) and reproducible with sensitivity levels (94%) comparable to the Ceditest kit (P>0.05).

Production and application of recombinant antibodies to foot-and-mouth disease virus non-structural protein 3ABC

The stamping out of animals to control a foot-and-mouth disease (FMD) outbreak results in enormous livestock losses. The implementation of vaccination strategies can reduce these losses; however it complicates the process of establishing freedom from disease following an outbreak. The availability of quality diagnostic tests to differentiate infected from vaccinated animals (DIVA) is crucial to prove freedom from disease and allow for the resumption of trade in livestock products. All current foot-and-mouth disease virus (FMDV) DIVA tests rely on polyclonal or monoclonal hybridoma derived antibody reagents, which can be difficult to prepare and maintain in a quality-assured manner and in the quantities required for post-outbreak surveillance. Recombinant antibodies can be produced in large quantities at low cost in bacteria to guarantee the supply of a consistent and well-characterised reagent. The production of recombinant antibodies does not rely on animal immunisation and does not require the maintenance of viable hybridoma cell lines. In this study, phage display libraries of recombinant antibody single chain variable fragments (scFv) against FMDV were generated from chickens immunised with recombinant non-structural protein (NSP) 3ABC. A total of 32 positive clones were obtained that represented three distinctive genetic sequences, Chicken Recombinant Antibody-Foot-and-Mouth disease (CRAb-FM) 26, -FM27 and -FM29. Each was shown to bind the 3B region of the 3ABC protein. When evaluated in a C-ELISA format using sera derived from cattle, sheep and pigs representing naïve, FMDV-vaccinated or FMDV-infected animals, CRAb-FM27 gave the best performance when paired with an E. coli-derived recombinant 3ABC, demonstrating the potential to be used as a species- and serotype-independent FMDV DIVA test. To our knowledge, this is the first FMDV DIVA test that uses both recombinant antibody and antigen derived from bacterial expression systems.

Identification of a major antibody binding epitope in the non-structural protein 3D of foot-and-mouth disease virus in cattle and the development of a monoclonal antibody with diagnostic applications

Detection of FMDV non-structural protein 3D antibodies has been used as a complementary method for sero-epidemiological studies as an indirect indicator of FMDV infection. In order to develop a sensitive cELISA to detect FMDV antibodies, immune dominant epitopes in FMDV-3D protein were identified by peptide array analysis. Monoclonal antibodies were then raised to a selected epitope and used in cELISA. Ninety two peptides corresponding to the complete amino acid sequence of FMDV-3D were synthesized. The sera from 15 FMDV infected cows were tested for binding to the peptides in an indirect ELISA. One major peptide (3D-4) was recognized by antisera in 12 of the 15 infected cows (80%). The sequence was formed by amino acid residues 16-30 of FMDV-3D. The mAbs produced from the mice immunized with native 3D showed neither reactivity to this epitope nor competition with sera from FMDV infected cattle. However, the mAbs produced from the mice immunized with native 3D and boosted with the peptide 3D-4 showed reactivity with native 3D, recombinant 3D as well as competition with sera of FMDV infected cattle and sheep in ELISA assays. Immune response to FMDV-3D was determined using a cELISA. All cattle and sheep tested were positive at 9 dpi and remained positive until the end of the experiment on days 28-31 (>50% inhibition). This demonstrated that mAbs directed to the peptide 3D-4 were effective competitors to the polyclonal antibodies against 3D in infected sera. The approach described here provides a useful tool for specific mAb production in the development of new diagnostic tests.

Serologic marker candidates identified among B-cell linear epitopes of Nsp2 and structural proteins of a North American strain of porcine reproductive and respiratory syndrome virus

We describe B-cell linear epitopes detected by Pepscan in the Nsp2 and all of the structural proteins of a US PRRSV strain, using sera of 15 experimentally infected pigs. The Nsp2 was found to contain the highest frequency of immunodominant epitopes (n = 18) when compared to structural proteins. Ten of these 18 Nsp2 peptides were reactive with 80 to 100% of the examined sera. In the structural proteins, epitopes consistently recognized by immune sera were located at gp2 (n = 2), gp3 (n = 4), gp5 (n = 3), M (n = 2) and N (n = 2). Overall, the highest degree of immunogenicity and conservation was exhibited by two epitopes identified in the C-terminal end of the M protein (ORF6). The antibodies recognizing the immunodominant epitopes of each protein were detected as early as days 7 to 15 pi and remained detectable until the end of the experiment (day 90 pi). These findings have direct implications for PRRSV differential diagnostics and eventual eradication as the identified epitopes may represent serologic marker candidates for differential (DIVA) PRRSV vaccines, derived from infectious cDNA clones.

Multiplexed Detection of Antibodies to Nonstructural Proteins of Foot-and-Mouth Disease Virus

Liquid array technology was used to develop a multiplexed assay for the detection of antibodies to viral nonstructural proteins (NSPs), raised in cattle in response to infection with foot-and-mouth disease (FMD) virus. Two assays, one based on recombinant NSPs and the other on synthetically produced peptides, were developed and compared side-by-side. Serum samples from serial bleeds of cattle, each experimentally infected with one of the seven serotypes (C, A, O, Asia, SAT1, SAT2, SAT3) of FMD virus were analyzed. A distinct pattern in the detection of NSP antibodies and a close correlation of the recombinant protein and peptide-based assays were observed. The detection of antibodies to NSPs is a method to differentiate FMD-infected and FMD-vaccinated animals, and a high-throughput assay would be an invaluable tool in the case of an outbreak of FMD in North America, when emergency vaccination may be utilized to spare vaccinated, noninfected animals from slaughter and subsequent disposal.

Virus-coated layer-by-layer colloids as a multiplex suspension array for the detection and quantification of virus-specific antibodies

BACKGROUND

Suspension array technology has surpassed ELISA for automated, simultaneous detection and quantification of soluble biomarkers such as virus-specific antibodies. We describe assays in which antigens are attached to a lipid bilayer surrounding color-coded particles.

METHODS

We used layer-by-layer technology to establish a multiplex suspension array with distinguishable microbeads coated with authentic viral surfaces to catch and quantify virus-specific antibodies in a flow cytometric analysis. Antigenic surfaces were generated by chimeric and wild-type baculoviruses plus 2 different influenza A virus subtypes fused to a lipid bilayer surrounding distinctly colored particles. Specificity of binding of chosen antibodies and sera was detected by immunofluorescence. Results of multiplex analysis were compared with results of ELISA.

RESULTS

Titrations of virus-specific antibodies in the multiplex suspension array demonstrated specific binding to the viral surface proteins. The multiplex suspension array gave positive results for up to log 5-diluted primary antibodies with an approximately 5- to 10-fold reduced dynamic range compared with the respective ELISA.

CONCLUSIONS

The bead-based multiplex suspension array is customizable and easy to establish. By displaying native influenza A virus surfaces and recombinant HIV-1 epitopes, the new assay provides a tool for the detection of major viral infections in humans.

Several recombinant capsid proteins of equine rhinitis a virus show potential as diagnostic antigens

Equine rhinitis A virus (ERAV) is a significant pathogen of horses and is also closely related to Foot-and-mouth disease virus (FMDV). Despite these facts, knowledge of the prevalence and importance of ERAV infections remains limited, largely due to the absence of a simple, robust diagnostic assay. In this study, we compared the antigenicities of recombinant full-length and fragmented ERAV capsid proteins expressed in Escherichia coli by using sera from experimentally infected and naturally exposed horses. We found that, from the range of antigens tested, recombinant proteins encompassing the C-terminal region of VP1, full-length VP2, and the N-terminal region of VP2 reacted specifically with antibodies present in sera from each of the five experimentally infected horses examined. Antibodies to epitopes on VP2 (both native and recombinant forms) persisted longer postinfection (>105 days) than antibodies specific for epitopes on other fragments. Our data also suggest that B-cell epitopes within the C terminus of VP1 and N terminus of VP2 contribute to a large proportion of the total reactivity of recombinant VP1 and VP2, respectively. Importantly, the reactivity of these VP1 and VP2 recombinant proteins in enzyme-linked immunosorbent assays (ELISAs) correlated well with the results from a range of native antigen-based serological assays using sera from 12 field horses. This study provides promising candidates for development of a diagnostic ERAV ELISA.