Differentiation of convalescent animals from those vaccinated against foot-and-mouth disease by a peptide ELISA

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.

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 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.

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.

Novel Purification Method for Recombinant 3AB1 Nonstructural Protein of Foot-and-Mouth Disease Virus for Use in Differentiation between Infected and Vaccinated Animals

An indirect enzyme-linked immunosorbent assay (ELISA) was developed for differentiation of animals infected with foot-and-mouth disease virus (FMDV) from vaccinated animals. The test was based on a highly pure and concentrated preparation of recombinant 3AB1 protein obtained by expression in a prokaryotic system, protein separation by sodium dodecyl sulfate–polyacrylamide gel electrophoresis, and electro elution. Experimental- and field-serum samples from naive, vaccinated, and infected cattle were tested for anti3AB1 antibody using the ELISA. A cutoff level was set at 35% of the maximum absorbance obtained with a positive control serum (FMDV-infected animal, 21 days postinfection [dpi]). This assay could detect antibodies from sera of animals experimentally infected by contact ( n = 118) with a sensitivity of 97.5%. The specificity was 100%, based on negative test results obtained on 109 sera from naive animals. Remarkably, all sera from animals vaccinated either once ( n = 102) or twice ( n = 30) were negative. In addition, this 3AB1-ELISA could detect seroconversion at 7 dpi in animals inoculated intradermolingually. This assay constitutes an important tool for the rapid detection of FMDV outbreaks in a vaccinated population. In addition, it presents a reliable, economical, and simple method for testing large numbers of serum samples.

Development and Evaluation of an Indirect Enzyme-Linked Immunosorbent Assay for Detection of Foot-and-Mouth Disease Virus Nonstructural Protein Antibody using a Chemically Synthesized 2B Peptide as Antigen

Forty peptides were synthesized corresponding to hydrophilic clusters of amino acids within the sequences of foot-and-mouth disease virus (FMDV) nonstructural proteins (NSP). Six peptides were studied in more detail and the most promising, a 2B peptide, was evaluated in enzyme-linked immunosorbent assay (ELISA) using sera from naïve, vaccinated, and vaccinated-and-challenged cattle as well as bovine sera from field outbreaks. The performance of the new NSP peptide ELISA was compared to that of 4 commercial NSP ELISA kits. Antibody to 2B was detectable from the end of the first week to the second week after infection in most of the nonvaccinated animals and by the second to third week in vaccinated-and-challenged animals. The sensitivity of the 2B peptide ELISA was comparable to the 3ABC Ceditest ( Ceditest® FMDV-NS, Cedi Diagnostics B.V.; Chung et al., 2002). With some modification and further validation, this 2B test could be useful as a screening or conformational NSP test in postvaccination surveillance for FMD.

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 multiplex Luminex assay for detecting swine antibodies to structural and nonstructural proteins of foot-and-mouth disease virus in Taiwan

BACKGROUND/PURPOSE(S)

Foot-and-mouth disease (FMD) and swine vesicular disease (SVD) are serious vesicular diseases that have devastated swine populations throughout the world. The aim of this study was to develop a multianalyte profiling (xMAP) Luminex assay for the differential detection of antibodies to the FMD virus of structural proteins (SP) and nonstructural proteins (NSP).

METHODS

After the xMAP was optimized, it detected antibodies to SP-VP1 and NSP-3ABC of the FMD virus in a single serum sample. These tests were also compared with 3ABC polypeptide blocking enzyme-linked immunosorbent assay (ELISA) and virus neutralization test (VNT) methods for the differential diagnosis and assessment of immune status, respectively.

RESULTS

To detect SP antibodies in 661 sera from infected naïve pigs and vaccinated pigs, the diagnostic sensitivity (DSn) and diagnostic specificity (DSp) of the xMAP were 90.0-98.7% and 93.0-96.5%, respectively. To detect NSP antibodies, the DSn was 90% and the DSp ranged from 93.3% to 99.1%. The xMAP can detect the immune response to SP and NSP as early as 4 days postinfection and 8 days postinfection, respectively. Furthermore, the SP and NSP antibodies in all 15 vaccinated but unprotected pigs were detected by xMAP. A comparison of SP and NSP antibodies detected in the sera of the infected samples indicated that the results from the xMAP had a high positive correlation with results from the VNT and a 3ABC polypeptide blocking ELISA assay. However, simultaneous quantitation detected that xMAP had no relationship with the VNT. Furthermore, the specificity was 93.3-94.9% with 3ABC polypeptide blocking ELISA for the FMDV-NSP antibody.

CONCLUSION

The results indicated that xMAP has the potential to detect antibodies to FMDV-SP-VP1 and NSP-3ABC and to distinguish FMDV-infected pigs from pigs infected with the swine vesicular disease virus.

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.

Foot-and-mouth disease: past, present and future

Foot-and-mouth disease (FMD) is a highly contagious disease of cloven-hoofed animals including cattle, pigs, sheep and many wildlife species. It can cause enormous economic losses when incursions occur into countries which are normally disease free. In addition, it has long-term effects within countries where the disease is endemic due to reduced animal productivity and the restrictions on international trade in animal products. The disease is caused by infection with foot-and-mouth disease virus (FMDV), a picornavirus. Seven different serotypes (and numerous variants) of FMDV have been identified. Some serotypes have a restricted geographical distribution, e.g. Asia-1, whereas others, notably serotype O, occur in many different regions. There is no cross-protection between serotypes and sometimes protection conferred by vaccines even of the same serotype can be limited. Thus it is important to characterize the viruses that are circulating if vaccination is being used for disease control. This review describes current methods for the detection and characterization of FMDVs. Sequence information is increasingly being used for identifying the source of outbreaks. In addition such information can be used to understand antigenic change within virus strains. The challenges and opportunities for improving the control of the disease within endemic settings, with a focus on Eurasia, are discussed, including the role of the FAO/EuFMD/OIE Progressive Control Pathway. Better control of the disease in endemic areas reduces the risk of incursions into disease-free regions.

Evaluation of cross-protection against three topotypes of serotype O foot-and-mouth disease virus in pigs vaccinated with multi-epitope protein vaccine incorporated with poly(I:C)

Epitope-based vaccines are always questioned for their cross-protection against the antigenically variable foot-and-mouth disease virus (FMDV). In this study, we proved the cross-protection effect of a multi-epitope vaccine incorporated with poly(I:C) against three topotypes of O type FMDV. A total of 45 naïve pigs were vaccinated with different doses of multi-epitope protein vaccine incorporated with poly(I:C). At 28 days post-vaccination, 45 vaccinated and 6 unvaccinated control pigs (two pigs for each group) were challenged with three topotypes of virulent O type FMDV, namely, O/Mya/98 (Southeast Asia topotype), O/HN/CHA/93 (Cathay topotype) and O/Tibet/CHA/99 (PanAsia topotype) strains. All unvaccinated pigs developed generalised FMD clinical signs. Results showed that all pigs (n=15) conferred complete protection against the O/Mya/98 and O/HN/CHA/93 FMDV strains, 11 of which were protected against the O/Tibet/CHA/99 FMDV strain. The 50% protective dose values of the vaccine against the O/Mya/98, O/HN/CHA/93 and O/Tibet/CHA/99 FMDV strains were 15.59, 15.59 and 7.05, respectively. Contact challenge experiment showed that transmission occurred from the donors to the unvaccinated but not to vaccinated pigs. These results showed that vaccination with multi-epitope protein vaccine incorporated with poly(I:C) can efficiently prevent FMD in pigs.

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.

Development of a Luminex assay for the detection of swine antibodies to non-structural proteins of foot-and-mouth disease virus

Foot-and mouth disease (FMD), swine vesicular disease (SVD), and vesicular stomatitis (VS) are highly contagious vesicular diseases of swine but are not easy to differentiate clinically. For the purpose of instant detecting of FMD and differentiating it from the other vesicular diseases, a Luminex assay was developed. Sera from 64 infected, 307 vaccinated, and 280 naïve pigs were tested by the Luminex assay. Diagnostic sensitivity of the assay was 100%. Diagnostic specificity of the assay was 98.7% in vaccinated pigs and 97.5% to 100% in naïve pigs. Agreement between the results from the Luminex assay and those from a 3ABC polypeptide blocking ELISA was 96.3% with kappa statistics of 0.92. The Luminex assay can detect the immune response to NSP-3ABC in swine as early as eight days post-infection. Moreover, all of the 15 vaccinated but unprotected pigs were all detected by the Luminex assay. The results indicated that the Luminex assay has potential with specificity in detecting antibodies to FMDV 3ABC NSP and in distinguishing FMDV-infected pigs from with either SVDV or VSV.

A Review of OIE Country Status Recovery Using Vaccinate-to-Live Versus Vaccinate-to-Die Foot-and-Mouth Disease Response Policies I: Benefits of Higher Potency Vaccines and Associated NSP DIVA Test Systems in Post-Outbreak Surveillance

To rapidly return to trade, countries with OIE status, FMD-free country where vaccination is not practised, have destroyed emergency vaccinated animals, raising ethical concerns with respect to social values, the environment, animal welfare and global food security. This two-part review explores whether science could support eligibility to return to previous OIE status in 3 months irrespective of vaccinate-to-live or vaccinate-to-die policies. Here, we examine the benefits of higher potency (≥ 6 PD50 ), high-purity vaccines formulated from antigen banks for emergency use, their efficacy and performance in differentiating infected from vaccinated animals (DIVA) assays for post-outbreak surveillance. From an intensive programme of research, we conclude that high-quality, higher potency vaccines are proven to reduce FMD virus (FMDV) subclinical circulation and the risk of carriers. Broader coverage than predicted by serology suggests the potential to hold a few 'key' vaccine strains improving logistics and reducing the financial burden of antigen banks. The OIE should adopt formal definitions for emergency vaccination and emergency vaccines. In terms of supportive tools, we consider that the lack of OIE recognition of DIVA tests other than those of PANAFTOSA in cattle is a shortcoming. There is need for research on maternal antibody interference with DIVA tests and on the use of such tests to establish whether greater purification of vaccines improves performance. We consider that alignment of waiting periods for vaccinate-to-live and vaccinate-to-die in OIE Code Article 8.5.9 1 b. and c. is feasible until an acceptable level of statistical certainty for surveillance or target probability of freedom is established to substantiate the absence of FMDV infection or circulation. It is surveillance intensity rather than waiting periods that establishes the risk of residual FMDV. EU Directive 2003/85/EC implicitly recognizes this, permitting derogation of the OIE waiting periods.

Poly(I:C) combined with multi-epitope protein vaccine completely protects against virulent foot-and-mouth disease virus challenge in pigs

We designed a series of epitope proteins containing the G-H loops of three topotypes of foot-and-mouth disease virus (FMDV) serotype O and promiscuous artificial Th sites and selected one epitope protein (designated as B4) with optimal immunogenicity and cross-reactivity. Three out of five pigs immunized intramuscularly with this B4 were protected against virulent FMDV challenge after a single inoculation, while all pigs co-immunized with B4 and polyinosinic-cytidylic acid [poly(I:C)] conferred complete protection following FMDV challenge. Additionally, we demonstrated that all pigs co-immunized with B4 and poly(I:C) elicited FMDV-specific neutralizing antibodies, total IgG antibodies, type I interferon (IFN-α/β) and cytokines IFN-γ. In contrast, some pigs immunized with B4 alone produced parameters mentioned above, while some not, suggesting that poly(I:C) reduced animal-to-animal variations in both cellular and humoral responses often observed in association with epitope-based vaccines and up-regulated T-cell immunity often poorly observed in protein-based vaccines. We propose that poly(I:C) is an effective adjuvant for this epitope-based vaccine of FMDV. This combination could yield an effective and safe candidate vaccine for the control and eradication of FMD in pigs.

Expression of Foot-and-Mouth Disease Virus Non-Structural Protein, 3D in Insect Cells and its Application in Detection of Anti-FMDV Antibodies

Non-structural proteins (NSPs) based diagnostics are useful for large-scale sero-surveillance of foot-and-mouth disease (FMD) and to monitor viral activity as a follow up to the vaccination campaign in FMD endemic countries like India which aim at disease control through vaccination. These diagnostics are also handy in the serology of import/export of cloven-footed animals. In the present study, non-structural protein RNA polymerase (3D gene) of FMD virus (FMDV) was expressed using baculovirus expression system. Protein expression was analyzed by SDS-PAGE and confirmed by its immuno-reactivity with serum from a FMDV infected bovine, in the western blot. Recombinant 3D protein was purified and evaluated in the indirect ELISA with 1072 cattle serum samples. Diagnostic sensitivity and specificity of the assay were found to be 92 and 100 %, respectively, when tested with cattle sera of known FMD status. The 3D based ELISA developed here is useful for screening the animals as an adjunct to other NSP based diagnostics available for routine serosurveillance of FMD.

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.

Immunodiagnosis of foot-and-mouth disease using mutated recombinant 3ABC polyprotein in a competitive ELISA

Differentiation of infected from vaccinated animals (DIVA) is essential for effective control of foot-and-mouth disease (FMD) by vaccination. The antibody response against FMD viral non-structural proteins (NSPs) has been used widely for this purpose. Among all the NSPs, the 3ABC polyprotein has been recognized as the most appropriate indicator for DIVA. In this study, mutated full-length 3ABC polyprotein was expressed in a prokaryotic system and monoclonal antibody against the recombinant protein was developed. A competitive ELISA (C-ELISA) for DIVA was standardized for different species of livestock animals using recombinant 3ABC and monoclonal antibodies. The diagnostic sensitivity and specificity of the assay were estimated by testing a panel of known serum samples consisting of sera from naive, vaccinated and infected animals as 86.9% with 66.4-97.2 (95%) confidence interval and 97% with 89.6-99.6 (95%) confidence interval respectively at 40% inhibition cut-off. The assay was validated further by testing sera from different livestock species collected at random from different parts of the country. The assay will provide a common method for testing sera from different species of livestock and wild animals. The C-ELISA is a sensitive and specific DIVA assay for FMD and can be used as a method for FMD control programme with vaccination.

Development of a Listeria monocytogenes-based vaccine against hepatocellular carcinoma

Live attenuated Listeria monocytogenes (LM) is a promising bacterial vector able to induce a T-cell response to tumor-associated antigens and demonstrates great potential for use in vaccine development. A novel recombinant LM-based vaccine (Lmdd (LM ΔdalΔdat)-MPFG (multiple peptide fusing genes)) was developed with the ability to express and secrete hepatocellular carcinoma (HCC)-related tumor-associated antigens fragments due to the insertion of hepatitis B virus (HBV)-X protein (HBx)-derived epitopes HBx(52-60) and HBx(140-148), the universal T-helper epitope, alpha-fetoprotein (AFP) epitope AFP(158-166), and melanoma antigen gene (MAGE)-3(271-279) into the HBV core protein. Following immunization with the Lmdd-MPFG vaccine, macrophages exhibited uptake of the bacteria; the vaccine was then nearly cleared 3 days after the first administration. It disappeared even more quickly following subsequent vaccinations. However, recombinant Lmdd-MPFG allowed for the full development of an antitumor response towards the human leukocyte antigen (HLA)-A0201 epitopes of MPFG. Each epitope stimulated an augmented T-cell proliferation and enhanced the supernatant level of interferon (IFN)-γ in vitro. In addition, IFN-γ-producing CD8(+) T cells as well as in vivo cytolytic activity were significantly increased in HLA-A2 transgenic mice. Additionally, the Lmdd-MPFG developed a strong antitumor response, as indicated by the significant resistance of immunized mice to MPFG-positive Hepa1-6 cell challenge in both a prophylactic and therapeutic setting. Tumor regression was accompanied by an enhanced cytotoxic T lymphocyte response and a decrease of regulatory T cells in the tumor. Collectively, these results suggest that utilizing attenuated LM as a vaccine vector, able to carry the MPFG gene, presents a potentially feasible strategy for prevention of HCC.

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.

Differentiation of foot-and-mouth disease-infected pigs from vaccinated pigs using antibody-detecting sandwich ELISA

The presence of serum antibodies for nonstructural proteins of the foot-and-mouth disease virus (FMDV) can differentiate FMDV-infected animals from vaccinated animals. In this study, a sandwich ELISA was developed for rapid detection of the foot-and-mouth disease (FMD) antibodies; it was based on an Escherichia coli-expressed, highly conserved region of the 3ABC nonstructural protein of the FMDV O/TW/99 strain and a monoclonal antibody derived from the expressed protein. The diagnostic sensitivity of the assay was 98.4%, and the diagnostic specificity was 100% for naïve and vaccinated pigs; the detection ability of the assay was comparable those of the PrioCHECK and UBI kits. There was 97.5, 93.4 and 66.6% agreement between the results obtained from our ELISA and those obtained from the PrioCHECK, UBI and CHEKIT kits, respectively. The kappa statistics were 0.95, 0.87 and 0.37, respectively. Moreover, antibodies for nonstructural proteins of the serotypes A, C, Asia 1, SAT 1, SAT 2 and SAT 3 were also detected in bovine sera. Furthermore, the absence of cross-reactions generated by different antibody titers against the swine vesicular disease virus and vesicular stomatitis virus (VSV) was also highlighted in this assay's specificity.

Strategies for differentiating infection in vaccinated animals (DIVA) for foot-and-mouth disease, classical swine fever and avian influenza

The prophylactic use of vaccines against exotic viral infections in production animals is undertaken exclusively in regions where the disease concerned is endemic. In such areas, the infection pressure is very high and so, to assure optimal protection, the most efficient vaccines are used. However, in areas considered to be free from these diseases and in which there is the possibility of only limited outbreaks, the use of Differentiation of Infected from Vaccinated Animals (DIVA) or marker vaccines allows for vaccination while still retaining the possibility of serological surveillance for the presence of infection. This literature review describes the current knowledge on the use of DIVA diagnostic strategies for three important transboundary animal diseases: foot-and-mouth disease in cloven-hoofed animals, classical swine fever in pigs and avian influenza in poultry.

Development of a chromatographic strip assay for detection of porcine antibodies to 3ABC non-structural protein of foot-and-mouth disease virus serotype O

A chromatographic strip assay was developed for rapid detection of serum antibodies to non-structural protein of foot-and-mouth disease virus. The assay was based on Escherichia coli-expressed 3ABC non-structural protein and an immunochromatographic technique, which shortened the detection time to about one hour. The sensitivity of the assay was determined to be 96.8% for infected pigs; its specificity was 100% for naïve pigs and 98.8% for vaccinated pigs. In the experimentally infected pigs, anti-3ABC antibodies were detectable from eight days post-infection until the end of the study, 34 days post-infection. The performance of this assay was comparable to that of two commercial ELISA kits, Ceditest FMDV-NS and UBI FMDV NS EIA, and was better than that of CHEKIT FMD-3ABC po. Given its advantages of instant testing and quantitative measurement, this assay has potential as a useful tool for rapid on-farm diagnosis of foot-and-mouth disease.

Discriminating foot-and-mouth disease virus-infected and vaccinated animals by use of beta-galactosidase allosteric biosensors

Recombinant beta-galactosidases accommodating one or two different peptides from the foot-and-mouth disease virus (FMDV) nonstructural protein 3B per enzyme monomer showed a drastic enzymatic activity reduction, which mainly affected proteins with double insertions. Recombinant beta-galactosidases were enzymatically reactivated by 3B-specific murine monoclonal and rabbit polyclonal antibodies. Interestingly, these recombinant beta-galactosidases, particularly those including one copy of each of the two 3B sequences, were efficiently reactivated by sera from infected pigs. We found reaction conditions that allowed differentiation between sera of FMDV-infected pigs, cattle, and sheep and those of naïve and conventionally vaccinated animals. These FMDV infection-specific biosensors can provide an effective and versatile alternative for the serological distinction of FMDV-infected animals.

An MHC-restricted CD8+ T-cell response is induced in cattle by foot-and-mouth disease virus (FMDV) infection and also following vaccination with inactivated FMDV

Foot-and-mouth disease virus (FMDV) causes a highly contagious disease of cloven-hooved animals that carries enormous economic consequences. CD8(+) cytotoxic T lymphocytes play an important role in protection and disease outcome in viral infections but, to date, the role of the CD8(+) T-cell immune response to FMDV remains unclear. This study aimed to investigate major histocompatibility complex (MHC) class I-restricted CD8(+) T-cell responses to FMDV in vaccinated and in infected cattle. An in vitro assay was used to detect antigen-specific gamma interferon release by CD8(+) T cells in FMDV-infected cattle of known MHC class I genotypes. A significant MHC class I-restricted CD8(+) T-cell response was detected to both FMDV strain O1 BFS and a recombinant fowlpox virus expressing the structural proteins of FMDV. Antigen-specific MHC class I-restricted CD8(+) T-cell responses were also detected in cattle vaccinated with inactivated FMDV. These responses were shown to be directed, at least in part, to epitopes within the structural proteins (P12A region) of the virus. By using mouse cells expressing single cattle MHC class I alleles, it was possible to identify the restriction elements in each case. Identification of these epitopes will facilitate the quantitative and qualitative analysis of FMDV-specific memory CD8(+) T cells in cattle and help to ensure that potential vaccines induce a qualitatively appropriate CD8(+) T-cell response.

Development and validation of a 3ABC indirect ELISA for differentiation of foot-and-mouth disease virus infected from vaccinated animals

Non-structural protein (NSP) 3ABC antibody is considered to be the most reliable indicator of present or past infection with foot-and-mouth disease virus (FMDV) in vaccinated animals. An indirect ELISA was established, using purified His-tagged 3ABC fusion protein as antigen, for detection of the antibody response to FMDV NSP 3ABC in different animal species. The method was validated by simultaneous detection of the early antibody responses to NSP and structural protein (SP) in FMDV Asia 1 infected animals. The performance of the method was also validated by detection of antibody in reference sera from the FMD World Reference Laboratory (WRL) in Pirbright, UK, and comparison with two commercial NSP ELISA kits. The results showed that the antibody response to SP developed more quickly than that to NSP 3ABC in FMDV infected animals. In contact-infected cattle, the antibody response to NSP 3ABC was significantly delayed compared with that to SP antibody. The early antibody responses to SP and NSP 3ABC in FMDV inoculated cattle and contact-infected or inoculated sheep and pigs were generally consistent. In pigs, 3ABC antibody was linked to the presence of clinical signs; however, in sheep, subclinical infection was detected by the development of 3ABC antibodies. Therefore, the antibody responses to 3ABC varied between host species. Eight out of 10 positive serum samples from FMD WRL were tested to be positive at cutoff value of 0.2. The rate of agreement with the ceditest FMDV-NS and the UBI NSP ELISA were 98.05% (302/308) and 93.2% (287/308), respectively. The prevalence of 3ABC antibodies reached 71.4% in some diseased cattle herds. The further work is required to evaluation the performance of this method in different animal species and different field situations.

Use of a standardized bovine serum panel to evaluate a multiplexed nonstructural protein antibody assay for serological surveillance of foot-and-mouth disease

Liquid array technology has previously been used to show proof of principle of a multiplexed nonstructural protein serological assay to differentiate foot-and-mouth disease virus-infected and vaccinated animals. The current multiplexed assay consists of synthetically produced peptide signatures 3A, 3B, and 3D and the recombinant protein signature 3ABC in combination with four controls. To determine the diagnostic specificity of each signature in the multiplex, the assay was evaluated against a naive population (n = 104) and a vaccinated population (n = 94). Subsequently, the multiplexed assay was assessed by using a panel of bovine sera generated by the World Reference Laboratory for foot-and-mouth disease in Pirbright, United Kingdom. This serum panel has been used to assess the performance of other singleplex enzyme-linked immunosorbent assay (ELISA)-based nonstructural protein antibody assays. The 3ABC signature in the multiplexed assay showed performance comparable to that of a commercially available nonstructural protein 3ABC ELISA (Cedi test), and additional information pertaining to the relative diagnostic sensitivity of each signature in the multiplex was acquired in one experiment. The encouraging results of the evaluation of the multiplexed assay against a panel of diagnostically relevant samples promote further assay development and optimization to generate an assay for routine use in foot-and-mouth disease serological surveillance.

Reduction of foot-and-mouth disease (FMD) virus load in nasal excretions, saliva and exhaled air of vaccinated pigs following direct contact challenge

In future, a policy of "vaccinate-to-live" may be included in the repertoire of foot-and-mouth disease (FMD) control measures and in support of this approach, we have investigated the hypothesis that vaccine-induced reduction in virus replication and excretion from pigs can be correlated to the severity of clinical signs of FMD by measuring excretion of virus in natural secretions and aerosols. The other aims of this study were to verify the existence of sub-clinical infection in vaccinated pigs, to evaluate the correlation between this and seroconversion to foot-and-mouth disease virus (FMDV) non-structural protein antibodies and to re-examine the occurrence of FMDV persistence in the oro-pharynx of pigs. Therefore, pigs were vaccinated (O1 Manisa) and challenged (O1 UKG) in a manner calculated to produce a broad range of clinical outcomes and were monitored for a minimum of another 33 days post-challenge. Eighty-one percent of the early (10 days vaccinated) challenged pigs and 25% of the late (29 days vaccinated) challenged pigs were clinically infected and all other vaccinated pigs were sub-clinically infected. Although vaccination could not provide complete clinical or virological protection, it reduced the severity of the disease, virus excretion and production of non-structural FMDV antibodies in vaccinated and subsequently infected pigs. As hypothesised, vaccine-induced reduction of virus replication and excretion was found to be correlated to the severity of clinical disease. RNA copies, but no live virus was detected from the pharyngeal and soft palate tissues of a minority of vaccinated and infected pigs beyond the acute stage of the infection.

Foot-and-mouth disease non-structural protein serology in cattle: use of a Bayesian framework to estimate diagnostic sensitivity and specificity of six ELISA tests and true prevalence in the field

The diagnostic performance of six foot-and-mouth disease (FMD) assays for detection of antibodies to the non-structural proteins (NSP) of the FMD virus (FMDV) was estimated using a Bayesian analysis on field sera from cattle of unknown infection status originating from post-FMDV outbreak situations in Israel and Zimbabwe. Estimations of the disease prevalence in both populations were also obtained. The diagnostic sensitivity estimates did not differ between both field studies, although overall Bayesian estimates were markedly higher than those previously reported based on sera from comparable experimentally infected (vaccinated) cattle populations. All NSP-based assays demonstrated a lower diagnostic specificity when applied to the Zimbabwean sera compared to both published specificities and similar Bayesian specificity estimates derived for the Israeli dataset. In Israel, the disease prevalence was estimated at 23.9% (95% credibility interval: 19.5-28.8%), whereas 65.4% (59.0-72.5%) was found in Zimbabwe. The need for reliable diagnostic test performance estimates and the benefits of Bayesian analysis in obtaining them are also addressed.

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).

Immune responses of pigs to commercialized emulsion FMD vaccines and live virus challenge

The immune response to structural and non-structural proteins (NSPs) was studied on sequential serum samples in swine from O/Taiwan/97 FMDV challenge studies, outbreaks and after vaccination. The results showed that pigs vaccinated with a commercial vaccine prior to or after infection maintained high neutralizing antibody titers with gradual decline from peak titers over the duration of this study. However, neutralizing antibody titers in non-vaccinated pigs only reached moderate levels 2-4 weeks post infection and remained low thereafter. For the 3B and 3ABC NSP antibody ELISA responses, there were gradually decreasing levels of NSP antibody over time. In multiple vaccinations, all pigs showed significant increases in neutralizing antibodies after booster vaccination. For the 3B NSP antibody ELISA after vaccination, the mean S/P ratios for pigs vaccinated with all three FMD vaccines were all below the 0.23 cut-off value set by the manufacture, but some sera from individual vaccinated pigs gave results above this cut-off after primary or secondary vaccination. However, with the 3ABC NSP antibody ELISA, all sera from vaccinated pigs had negative results for NSP antibody for all time points.

Comparison of sensitivity and specificity in three commercial foot-and-mouth disease virus non-structural protein ELISA kits with swine sera in Taiwan

Three commercialized ELISA kits for the detection of antibodies to the non-structural proteins (NSPs) of FMD virus were compared, using sera from uninfected, vaccinated, challenged and naturally infected pigs. The kinetics of the antibody response to NSPs was compared on sequential serum samples in swine from challenge studies and outbreaks. The results showed that ELISA A (UBI) and ELISA B (CEDI) had better sensitivity than that of the 3ABC recombinant protein-based ELISA C (Chekit). The peak for detection of antibodies to NSPs in ELISA C was significantly delayed in sera from natural infection and challenged swine as compared to the ELISA A and B. The sensitivity of the three ELISAs gradually declined during the 6-month post-infection as antibodies to NSP decline. ELISA kits A and B detected NSP antibody in 50% of challenged pigs by the 9-10th-day and 7-8th-day post-challenge, respectively. ELISA B and C had better specificity than ELISA A on sequential serum samples obtained from swine immunized with a type O FMD vaccine commercially available in Taiwan. Antibody to NSPs before vaccination was not detected in swine not exposed to FMD virus, however, antibody to NSPs was found in sera of some pigs after vaccination. All assays had significantly lower specificity when testing sera from repeatedly vaccinated sows and finishers in 1997 that were tested after the 1997 FMD outbreak. However, when testing sera from repeatedly vaccinated sows or finishers in 2003-2004, the specificity for ELISAs A, B and C were significantly better than those in 1997. This effect was less marked for ELISA A. The ELISA B was the best test in terms of the highest sensitivity and specificity and the lowest reactivity with residual NSP in vaccinates.

Serological differentiation of FIV-infected cats from dual-subtype feline immunodeficiency virus vaccine (Fel-O-Vax FIV) inoculated cats

Feline immunodeficiency virus (FIV) vaccine, Fel-O-Vax FIV, was released for sale in the US in 2002. The antibodies of vaccinated cats interfere with serological assays by currently available FIV diagnostic kits. In this study, we investigated whether it is possible to distinguish serologically cats vaccinated with Fel-O-Vax FIV from cats experimentally or naturally infected with FIV. A total of 153 sera taken from 97 cats were used as serum samples. Enzyme linked immunosorbent assay (ELISA) was performed using whole FIV antigen and formalin treated whole FIV antigen, recombinant-gag (r-gag) antigen, and transmembrane (TM) peptide. Statistical analysis was performed using ELISA optical density (O.D.) values obtained with each antigen as variables. Except for the ELISA O.D. values obtained with r-gag antigen, a significant difference in ELISA O.D. values was observed between the vaccinated and the infected groups. However, it was not possible to distinguish both groups unequivocally. Using discriminant analysis, it was possible to distinguish the two groups with an accuracy of 97.1% with two discriminating variables (ELISA O.D. values obtained with formalin treated whole FIV antigen, and TM peptide), 97.8% with three discriminating variables (ELISA O.D. values obtained with whole FIV antigen, formalin treated whole FIV antigen, and TM peptide). Therefore, it was considered possible to distinguish cats vaccinated with Fel-O-Vax FIV from FIV-infected cats by ELISA using two types of antigens including formalin treated whole FIV antigen and TM peptide, or three types of antigens including formalin treated whole FIV antigen, TM peptide and whole FIV antigen.

Comparative evaluation of six ELISAs for the detection of antibodies to the non-structural proteins of foot-and-mouth disease virus

To validate the use of serology in substantiating freedom from infection after foot-and-mouth disease (FMD) outbreaks have been controlled by measures that include vaccination, 3551 sera were tested with six assays that detect antibodies to the non-structural proteins of FMD virus. The sera came from naïve, vaccinated, infected and vaccinated-and-infected animals; two-thirds from cattle, the remainder from sheep and pigs. The assays were covariant for sensitivity, but not necessarily for specificity. A commercial kit from Cedi-diagnostics and an in-house assay from IZS-Brescia were comparable to the NCPanaftosa-screening index method described in the Diagnostic Manual of the World Animal Health Organisation. Using these three tests the specificity and sensitivity for the detection of carriers in vaccinated cattle approaches or exceeds 99% and 90%, respectively.

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.