Antigenic sites of foot-and-mouth disease virus (FMDV): an analysis of the specificities of anti-FMDV antibodies after vaccination of naturally susceptible host species

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

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

Phage Display Screening of Bovine Antibodies to Foot-and-Mouth Disease Virus and Their Application in a Competitive ELISA for Serodiagnosis

For serodiagnosis of foot-and-mouth disease virus (FMDV), monoclonal antibody (MAb)-based competitive ELISA (cELISA) is commonly used since it allows simple and reproducible detection of antibody response to FMDV. However, the use of mouse-origin MAb as a detection reagent is questionable, as antibody responses to FMDV in mice may differ in epitope structure and preference from those in natural hosts such as cattle and pigs. To take advantage of natural host-derived antibodies, a phage-displayed scFv library was constructed from FMDV-immune cattle and subjected to two separate pannings against inactivated FMDV type O and A. Subsequent ELISA screening revealed high-affinity scFv antibodies specific to a serotype (O or A) as well as those with pan-serotype specificity. When BvO17, an scFv antibody specific to FMDV type O, was tested as a detection reagent in cELISA, it successfully detected FMDV type O antibodies for both serum samples from vaccinated cattle and virus-challenged pigs with even higher sensitivity than a mouse MAb-based commercial FMDV type O antibody detection kit. These results demonstrate the feasibility of using natural host-derived antibodies such as bovine scFv instead of mouse MAb in cELISA for serological detection of antibody response to FMDV in the susceptible animals.

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

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

Unravelling Selection Shifts among Foot-and-Mouth Disease virus (FMDV) Serotypes

FMDV virus has been increasingly recognised as the most economically severe animal virus with a remarkable degree of antigenic diversity. Using an integrative evolutionary and computational approach we have compelling evidence for heterogeneity in the selection forces shaping the evolution of the seven different FMDV serotypes. Our results show that positive Darwinian selection has governed the evolution of the major antigenic regions of serotypes A, Asia1, O, SAT1 and SAT2, but not C or SAT3. Co-evolution between sites from antigenic regions under positive selection pinpoints their functional communication to generate immune-escape mutants while maintaining their ability to recognise the host-cell receptors. Neural network and functional divergence analyses strongly point to selection shifts between the different serotypes. Our results suggest that, unlike African FMDV serotypes, serotypes with wide geographical distribution have accumulated compensatory mutations as a strategy to ameliorate the effect of slightly deleterious mutations fixed by genetic drift. This strategy may have provided the virus by a flexibility to generate immune-escape mutants and yet recognise host-cell receptors. African serotypes presented no evidence for compensatory mutations. Our results support heterogeneous selective constraints affecting the different serotypes. This points to the possible accelerated rates of evolution diverging serotypes sharing geographical locations as to ameliorate the competition for the host.

How foot-and-mouth disease virus receptor mediates foot-and-mouth disease virus infection

This study reviews the FMDV receptor-binding domain, integrin receptors, and heparan sulfate receptors to provide references for studies regarding the mechanisms underlying FMDV infection.

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

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

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.

Challenges for Serology-Based Characterization of Foot-and-Mouth Disease Outbreaks in Endemic Areas; Identification of Two Separate Lineages of Serotype O FMDV in Uganda in 2011

Control of foot-and-mouth disease (FMD) in Uganda by ring vaccination largely depends on costly trivalent vaccines, and use of monovalent vaccines could improve the cost effectiveness. This, however, requires application of highly specific diagnostic tests. This study investigated outbreaks of FMD in seven Ugandan districts, during 2011, using the PrioCHECK® FMDV NS ELISA, solid-phase blocking ELISAs (SPBEs) and virus neutralization tests (VNTs), together with virological analyses for characterization of the responsible viruses. Two hundred and eighteen (218) cattle and 23 goat sera as well as 82 oropharyngeal fluid/epithelial tissue samples were collected. Some 50% of the cattle and 17% of the goat sera were positive by the PrioCHECK® FMDV NS ELISA, while SPBEs identified titres ≥80 for antibodies against serotype O FMD virus (FMDV) in 51% of the anti-NSP positive cattle sera. However, 35% of the anti-NSP positive cattle sera had SPBE titres ≥80 against multiple serotypes, primarily against serotypes O, SAT 1 and SAT 3. Comparison of SPBEs and VNTs for the detection of antibodies against serotypes O, SAT 1 and SAT 3 in 72 NSP positive cattle sera showed comparable results against serotype O (P = 0.181), while VNTs detected significantly fewer samples positive for antibodies against SAT 1 and SAT 3 than the SPBEs (P < 0.001). Detection of antibodies against serotype O was consistent with the isolation of serotype O FMDVs from 13 samples. Four of these viruses were sequenced and belonged to two distinct lineages within the East Africa-2 (EA-2) topotype, each differing from the currently used vaccine strain (EA-1 topotype). The relationships of these lineages to other serotype O viruses in the Eastern Africa region are discussed. To enhance the control of FMD in Uganda, there is need to improve the specificity of the SAT-SPBEs, perform vaccine matching and implement improved regional FMD control.

Rescue of infective virus from a genome-length cDNA clone of the FMDV serotype O (IND-R2/75) vaccine strain and its characterization

We report here the construction and characterization of an infectious cDNA clone of the Indian vaccine strain of foot and mouth disease virus (FMDV) serotype O, IND-R2/75. Viral genome was amplified by reverse transcription-polymerase chain reaction (RT-PCR) in five fragments and subsequently assembled sequentially in a plasmid vector to generate a complete cDNA clone, flanked by the T7 RNA polymerase promoter and poly (A) tail at 5' and 3' ends, respectively. Transfection of BHK-21 cells with the RNA transcribed from this genome-length cDNA construct allowed the recovery of infectious recombinant FMDV particles as evidenced by cytopathic effect in BHK-21 cells. Characterization of the recombinant virus revealed its similarity to the parental strain. Recombinant virus could be distinguished from the parental virus based on the presence of a unique marker sequence in the former, which was incorporated in the cDNA using a silent mutation. The virus showed no significant amino acid changes in the capsid-coding region when serially passaged up to ten times in BHK-21 cells, while retaining the marker sequence.

Improved neutralising antibody response against foot-and-mouth-disease virus in mice inoculated with a multi-epitope peptide vaccine using polyinosinic and poly-cytidylic acid as an adjuvant

A peptide-based vaccine for foot-and-mouth disease (FMD) was designed. The peptide immunogen had a G-H loop domain optimised for immunogenicity and broad-spectrum antigenicity to different lineages of serotype-O FMD viruses (FMDVs). Polyinosinic and poly-cytidylic acid [poly (I:C)] was used as the adjuvant to overcome the low humoral antibody levels often observed in association with peptide-based vaccines. The multi-epitope peptide alone induced the secretion of a certain level of neutralising antibodies in mice. In contrast, co-administration of the multi-epitope peptide with poly (I:C) induced the secretion of a significantly higher level of neutralising antibodies (P<0.005). Indeed, the resultant level was slightly higher even than that induced by the inactivated vaccine (P>0.05). These initial results indicate that poly (I:C) is highly effective as an adjuvant for use with the FMDV multi-epitope peptide vaccine. This combination could yield a promising vaccine for the prevention and control of FMD. Further study is needed to evaluate the efficiency of this combination on animals susceptible naturally to FMDV.

Foot-and-mouth disease virus epitope dominance in the antibody response of vaccinated animals

Five neutralizing antigenic sites have been identified on the surface of serotype O foot-and-mouth disease virus (FMDV). A set of mAb neutralization-escape mutant viruses was used for the first time to evaluate the relative use of known binding sites by polyclonal antibodies from three target species: cattle, sheep and pigs. Antibodies to all five neutralizing antigenic sites were detected in all three species, with most antibodies directed against antigenic site 2, followed by antigenic site 1. In 76 % of cattle, 65 % of sheep and 58 % of pigs, most antibodies were directed against site 2. Antibodies specific to antigenic sites 3, 4 and 5 were found to be minor constituents in the sera of each of the target species. This implies that antigenic site 2 is a dominant neutralization immunogenic site in serotype O FMDV and may therefore be a good candidate for designing novel vaccines.

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.

Preparation and characterization of neutralizing monoclonal antibodies against FMDV serotype O with synthetic peptide antigen

A short linear peptide was designed according to the antigenic site analysis of VP1 protein of foot-and-mouth virus (FMDV) serotype O and synthesized as the peptide immunogen. The peptide, which covers the region from amino acid 133 to 160 of VP1 of FMDV, was linked to the N-terminal cysteine and conjugated with the carrier protein of keyhole limpet hemocyanin (KLH). Normal 6- to 8-week-old BALB/c mice were immunized with the 20 μg dose conjugated peptide antigen four times. The splenocytes from the immunized mice were fused with SP2/0 mouse myeloma cells, and positive hybridomas were selected by indirect enzyme-linked immunosorbent assay (ELISA) and subcloned four times with limiting dilution. Five stable hybridoma cell lines, designated as 4F9, 1B11, 1E10, 1D4, and 4B8, were obtained. Isotyping of all obtained MAbs indicated that the MAbs of 4F9, 1E10, and 4B8 belonged to IgG2b; the 1B11 and 1D4 belonged to IgG1 and IgM, respectively. The micro-neutralization test indicated that the MAbs of 4F9, 4B8, and 1B11 were capable of neutralizing FMDV serotype O with neutralization indices ranging from 1.81 to 2.11. These results suggest that linear synthetic peptide conjugate can elicit antibodies against native FMDV virus and can be used as an alternative immunogen for production of MAbs with exact epitope.

Marker vaccine potential of a foot-and-mouth disease virus with a partial VP1 G-H loop deletion

Previous work in cattle and pigs demonstrated that protection against foot-and-mouth disease (FMD) could be achieved following vaccination with chimeric foot-and-mouth disease virus (FMDV) vaccines, in which the VP1 G-H loop had been substituted with that from another serotype. This indicated that the VP1 G-H loop may not be essential for the protection of natural hosts against FMDV. If this could be substantiated there would be potential to develop FMD marker vaccines, characterised by the absence of this region. Here, we investigate the serological responses to vaccination with a virus with a partial VP1 G-H loop deletion in order to determine the likelihood of achieving protection and the potential of this virus as a marker vaccine. Inactivated, oil adjuvanted, vaccines, consisting of chemically inactivated virus with or without a partially deleted VP1 G-H loop, were used to immunise cattle. Serum was collected on days 0, 7, 14 and 21 and antibody titres calculated using the virus neutralisation test (VNT) to estimate the likelihood of protection. We predict a good likelihood that cattle vaccinated with a vaccine characterised by a partial VP1 G-H loop would be protected against challenge with the same virus containing the VP1 G-H loop. We also present evidence on the potential of such a construct to act as a marker vaccine, when used in conjunction with a novel serological test.

Viren mit einzelsträngigem RNA-Genom in Plusstrangorientierung

Heute sind acht Virusfamilien bekannt, deren Vertreter eine einzelsträngige RNA in Plusstrangorientierung besitzen: Die Picornaviridae, Caliciviridae, Astroviridae und Hepeviren verfügen über Capside, die keine Hüllmembran aufweisen, wohingegen die Flaviviridae, Togaviridae, Arteriviridae und Coronaviridae durch membranumhüllte Partikel gekennzeichnet sind. Allen gemeinsam ist, dass sie ihre Genome als mRNA verwenden und davon ein oder mehrere Polyproteine synthetisieren, die im weiteren Verlauf durch virale oder auch zelluläre Proteasen in Einzelkomponenten gespalten werden. Die Viren verfügen über eine RNA-abhängige RNA-Polymerase, welche die Plusstrang-RNA sowie die als Zwischenprodukte der Replikation auftretenden Negativstränge übersetzt; dabei gehen die neuen genomischen RNA-Moleküle aus dem zweiten Transkriptionsschritt hervor. Die Einteilung in die unterschiedlichen Familien richtet sich nach Zahl, Größe, Lage und Orientierung der Virusgene auf der RNA, nach der Anzahl der unterschiedlichen Polyproteine, die während der Infektion synthetisiert werden, und nach dem Vorhandensein einer Hüllmembran als Teil der Virionen.

Genetic analysis of foot-and-mouth disease virus serotype A of Indian origin and detection of positive selection and recombination in leader protease-and capsid-coding regions

The leader protease (L pro) and capsid-coding sequences (P1) constitute approximately 3 kb of the foot-and-mouth disease virus (FMDV). We studied the phylogenetic relationship of 46 FMDV serotype A isolates of Indian origin collected during the period 1968-2005 and also eight vaccine strains using the neighbour-joining tree and Bayesian tree methods. The viruses were categorized under three major groups -Asian, Euro-South American and European. The Indian isolates formed a distinct genetic group among the Asian isolates. The Indian isolates were further classi?ed into different genetic subgroups (<5% divergence).Post-1995 isolates were divided into two subgroups while a few isolates which originated in the year 2005 from Andhra Pradesh formed a separate group. These isolates were closely related to the isolates of the 1970s. The FMDV isolates seem to undergo reverse mutation or convergent evolution wherein sequences identical to the ancestors are present in the isolates in circulation. The eight vaccine strains included in the study were not related to each other and belonged to different genetic groups. Recombination was detected in the L pro region in one isolate (A IND 20/82) and in the VP1 coding 1D region in another isolate (A RAJ 21/96). Positive selection was identi?ed at aa positions 23 in the L pro (P < 0.05; 0.046*) and at aa 171 in the capsid protein VP1 (P < 0.01; 0.003**).

Passive immunization with llama single-domain antibody fragments reduces foot-and-mouth disease transmission between pigs

We aim to develop a method that confers rapid protection against foot-and-mouth disease (FMD) by passive immunization with recombinant llama single-domain antibody fragments (VHHs). Previously constructed genetic fusions of two VHHs (VHH2s) that either neutralizes FMDV or binds to porcine immunoglobulin to increase the serum half-life, conferred only limited protection to pigs. We therefore now generated VHH3s containing an additional FMDV binding VHH. Two VHH3s neutralized FMDV more potently than single VHHs and were highly produced by yeast cells. Injection of a mixture of these two VHH3s 24h before FMD challenge infection of pigs reduced and delayed the development of clinical disease, viraemia and viral shedding. Furthermore, it significantly (P=0.023) delayed FMD transmission. Thus, we have shown a proof of concept of passive FMD immunoprophylaxis using VHHs.

Synthesis of empty capsid-like particles of Asia I foot-and-mouth disease virus in insect cells and their immunogenicity in guinea pigs

The assembly of foot-and-mouth disease virus (FMDV) requires the cleavage of the P12A polyprotein into individual structural proteins by protease 3C. In this study, we constructed a recombinant baculovirus that simultaneously expressed the genes for the P12A and 3C proteins of Asia I FMDV from individual promoters. The capsid proteins expressed in High Five™ insect cells were processed by viral 3C protease, as shown by Western blotting, and were antigenic, as revealed by their reactivity in an indirect sandwich-ELISA, and by immunofluorescent assay. The empty capsid-like particles were similar to authentic 75S empty capsids from FMDV in terms of their shape, size and sedimentation velocity, as demonstrated by sucrose gradient centrifugation. Both empty capsid-like particles and some small-sized particles (about 10 nm in diameter) were also observed using immunoelectron microscopy. Furthermore, the empty capsid-like particles or intermediates induced high levels of FMDV-specific antibodies in guinea pigs following immunization, and neutralizing antibodies were induced in the second week after vaccination. These recombinant, non-infectious, FMDV empty capsids are potentially useful for the development of new diagnostic techniques and vaccines.

Genetic variation of foot-and-mouth disease virus isolates recovered from persistently infected water buffalo (Bubalus bubalis)

Genetic variation of foot-and-mouth disease virus (FMDV) isolates, serotype O, recovered serially over a 1-year period from persistently infected buffalos was assessed. The persistent state was established experimentally with plaque-purified FMDV, strain O(1)Campos, in five buffalos (Bubalus bubalis). Viral isolates collected from esophageal-pharyngeal (EP) fluids for up to 71 weeks after infection were analyzed at different times by nucleotide sequencing and T(1) RNase oligonucleotide fingerprinting to assess variability in the VP1-coding region and in the complete genome, respectively. Genetic variation increased, although irregularly, with time after infection. The highest values observed for the VP1-coding region and for the whole genome were 2.5% and 1.8%, respectively. High rates of fixation of mutations were observed using both methodologies, reaching values of 0.65 substitutions per nucleotide per year (s/nt/y) and 0.44s/nt/y for nucleotide sequencing and oligonucleotide fingerprinting, respectively, when selected samples recovered at close time periods were analyzed. The data herein indicate that complex mixtures of genotypes may arise during FMDV type O persistent infection in water buffalos, which can act as viral reservoirs and also represent a potential source of viral variants. These results fit within the quasi-species dynamics described for FMDV, in which viral populations are constituted by related, non-identical genomes that evolve independently from each other, and may predominate at a given time.

Study on the porcinophilic foot-and-mouth disease virus I. production and characterization of monoclonal antibodies against VP1

Monoclonal antibodies (MAbs) reported here were produced against the porcinophilic foot-and-mouth disease virus (FMDV) that caused the devastating swine disease on 1997 in Taiwan. A panel (25) of MAbs were found to react with VP1 of O/Taiwan/97 (O/97) by ELISA with various potencies. The biological identities of these VP1 reacting MAbs, such as neutralization activity, isotype and capability to distinguish between two serotype O FMDVs, O/97 and O/Taiwan/KM1/99 (O/99), were further analyzed. Eleven out of the total eighteen O/97 neutralizing MAbs were able to neutralize heterologous O/99. Eight O/97 neutralizing and five non-neutralizing MAbs could differentiate two serotype O FMDVs by immunofluorescence assay (IFA) implied that these thirteen MAbs recognized O/97 specific epitope(s). Furthermore, reactivities of the VP1 reacting MAbs with a 29 amino acids synthetic peptide (P29) representing the betaG-betaH loop of VP1 were analyzed by ELISA and fourteen were found positive. MAb clone Q10E-3 reacting strongest with VP1 and P29, neutralizing both but not differentiating two serotype O viruses suggested that the antibody binding site might involve the RGD motif and its C terminal conserved region on betaG-betaH loop. MAbs with diverse characters presented in this study were the first raised against porcinophilic FMDV. The complete set of MAbs may be used for further studies of vaccine, diagnostic methods, prophylaxis, etiological and immunological researches on FMDV.

Application of DIVA vaccines and their companion diagnostic tests to foreign animal disease eradication

The risk of foreign animal disease introduction continues to exist despite Canada's strict regulations concerning the importation of animals and animal products. Given the rapidity with which these diseases can spread, especially in areas with dense livestock populations, eradication efforts which rely solely on quarantine and stamping-out measures can present a formidable undertaking. This, combined with growing economic and ethical considerations, has led to renewed interest in the use of vaccination as a tool in controlling foreign animal disease outbreaks. Vaccination has effects at the individual and population levels. Efficacious vaccines reduce or prevent clinical signs without necessarily preventing virus replication. They may also increase the dose of virus needed to establish an infection and/or reduce the level and duration of virus shedding following infection. Vaccine effectiveness within a population is a function of its ability to reduce virus transmission. Transmission is best described by the reproductive ratio, R, which is defined as the average number of new infections caused by one infectious individual. By helping to reduce the R-value below 1, vaccination can be an effective adjunct in abbreviating an outbreak. Nevertheless, vaccination can also complicate serological surveillance activities that follow eradication, if the antibody response induced by vaccination is indistinguishable from that which follows infection. This disadvantage can be overcome by the use of DIVA vaccines and their companion diagnostic tests. The term DIVA (differentiating infected from vaccinated individuals) was coined in 1999 by J. T. van Oirschot of the Central Veterinary Institute, in The Netherlands. It is now generally used as an acronym for 'differentiating infected from vaccinated animals'. The term was originally applied to the use of marker vaccines, which are based on deletion mutants of wild-type microbes, in conjunction with a differentiating diagnostic test. The DIVA strategy has been extended to include subunit and killed whole-virus vaccines. This system makes possible the mass vaccination of a susceptible animal population without compromising the serological identification of convalescent individuals. The DIVA approach has been applied successfully to pseudorabies and avian influenza eradication, and has been proposed for use in foot-and-mouth disease and classical swine fever eradication campaigns. This paper will survey current vaccine technology, the host immune response, and companion diagnostic tests that are available for pseudorabies, foot-and-mouth disease, classical swine fever and avian influenza.

Comparison of immune responses against foot-and-mouth disease virus induced by fusion proteins using the swine IgG heavy chain constant region or beta-galactosidase as a carrier of immunogenic epitopes

Previously, we demonstrated that a fusion protein (Gal-FMDV) consisting of beta-galactosidase and an immunogenic peptide, amino acids (141-160)-(21-40)-(141-160), of foot-and-mouth disease virus (FMDV) VP1 protein induced protective immune responses in guinea pigs and swine. We now designed a new potential recombinant protein vaccine against FMDV in swine. The immunogenic peptide, amino acids (141-160)-(21-40)-(141-160) from the VP1 protein of serotype O FMDV, was fused to the carboxy terminus of a swine immunoglobulin G single heavy chain constant region and expressed in Escherichia coli. The expressed fusion protein (IgG-FMDV) was purified and emulsified with oil adjuvant. Vaccination twice at an interval of 3 weeks with the emulsified IgG-FMDV fusion protein induced an FMDV-specific spleen proliferative T-cell response in guinea pigs and elicited high levels of neutralizing antibody in guinea pigs and swine. All of the immunized animals were efficiently protected against FMDV challenge. There was no significant difference between IgG-FMDV and Gal-FMDV in eliciting immunity after vaccination twice in swine. However, when evaluating the efficacy of a single inoculation of the fusion proteins, we found that IgG-FMDV could elicit a protective immune response in swine, while Gal-FMDV only elicited a weak neutralizing activity and could not protect the swine against FMDV challenge. Our results suggest that the IgG-FMDV fusion protein is a promising vaccine candidate for FMD in swine.

Isolation of foot-and-mouth disease virus specific bovine antibody fragments from phage display libraries

Foot-and-mouth disease virus (FMDV) is an important veterinary pathogen which can cause widespread epidemics. Due to the high antigenic variability of FMDV, it is important to undertake mutation analysis under immunological pressure. To study the bovine antibody response at a molecular level, phage display technology was used to produce bovine anti-FMDV Fabs. CH1-VH chains with FMDV specific binding could be isolated after selection from a library made from vaccinated cattle. Though their involvement in the bovine immune response remains to be ascertained, it is planned to express the five different selected VH domains in bacterial or insect systems as sequence homologies with integrin beta6 chain could shed light on the basis of FMDV type receptor specificities.

Evaluation of genetically engineered derivatives of a Chinese strain of foot-and-mouth disease virus reveals a novel cell-binding site which functions in cell culture and in animals

Adaptation of field isolates of foot-and-mouth disease virus (FMDV) to grow in cells in culture can result in changes in viral properties that include acquisition of the ability to bind to cell surface heparan sulfate (HS). After 13 passages on BHK cells to produce a vaccine, a Cathay topotype isolate of FMDV serotype O from China (O/CHA/90) extended its cell culture host range and bound to heparin-Sepharose, although it did not require cell surface HS as a receptor molecule. To understand these phenomena, we constructed chimeric viruses by using a type A(12) infectious cDNA and the capsid protein-coding regions of O/CHA/90 and its cell culture-adapted derivative (vac-O/CHA/90). Using a set of viruses derived from these chimeras by exchanging portions of the capsid-coding regions, we discovered that a group of amino acid residues that surround the fivefold axis of the icosahedral virion determine host range in cell culture and influence pathogenicity in pigs. These residues included aromatic amino acids at positions 108 and 174 and positively charged residues at positions 83 and 172 in protein 1D. To test if these residues participated in non-integrin-dependent cell binding, the integrin-binding RGD sequence in protein 1D was changed to KGE in two different chimeras. Evaluation of these KGE viruses indicated that growth in cell culture was not dependent on HS. One of these viruses was tested in pigs, where it produced a mild disease and maintained its KGE sequence. These results are discussed in terms of receptor utilization and pathogenesis of this important pathogen.