Item 7 FMD vaccines and vaccination

Dr. Emiliana Brocchi reported on the characterisation of 24 Mabs raised against FMDV type Asia 1 (Appendix 24). Ten type specific MAbs identified at least 3 different sites involved in neutralisation, while 14 non-neutralising MAbs showed different features of reactivity with also heterologous FMDV types. MAbs against 2 of the 3 neutralising sites, as well as all nonneutralising MAbs, broadly reacted with 11 field isolates tested, suggesting the target sites are well conserved and stable, whilst one neutralising site seemed specific for the homologous strain. One isolate (Cambodia 3/93) appeared considerably changed being not recognised by any of the neutralising MAbs. Carefully selected MAbs proved to have high potential as diagnostic reagents. Sandwich ELISAs for antigen detection have been developed, specific for Asia 1 type or universal for all types tested (Asia, O, A, C) depending on the combination of Mabs selected as catching and conjugated antibody. A SPCE using a neutralising MAb as competitor proved to work in principle. It detected the candidate reference sera (Phase XVII) correctly, although improvements of sensitivity and specificity may be achieved through further studies.

Following the presentation of papers a panel discussion was held for Items 3 and 4. Dr. Soren Alexandersen raised the following points: the need for more full length sequence data in addition to the partial sequence data of VP1; the need for more work on excretion, transmission and virulence studies for emerging FMD strains, so that it would be possible to predict the outcome of an infection if the disease entered the country.

Dr. Aldo Dekker mentioned that the selection of vaccine strains should be done by determination of r values and epidemiological studies by sequencing. He stressed that more work is necessary on r values and the selection of reference sera.

Dr. Emiliana Brocchi stated that sequencing is important mainly for epidemiological studies. Antigenic characterisation can be better achieved using a well-characterised panel of MAbs directed against known sites. MAbs profiling can also be a valuable tool, helping in the appropriate selection of vaccine strains. To this purpose MAbs to neutralising sites are appropriate considering that virus neutralisation is a potent, well known mechanism of protection in FMD.

Dr. Sinan Aktas stated that the r values are important but the actual titres of antibodies induced by vaccine strains against field viruses is also very important for decision making. He also supported Dr. Brocchi for the usefulness of monoclonal antibody profiling.

Dr. David Paton stressed the importance of standardised determination of r-values and pointed out the limited supply of post-vaccine sera. In this respect close cooperation between WRL and vaccine manufacturers is important.

Conclusions

• Sequencing studies conducted on FMD PanAsia virus isolates from distant geographical regions confirmed the suitability of this method for analysing relationships between isolates and for establishing links to previous outbreaks.

• Partial sequence analysis provides useful information for most epidemiological studies.

The comparison of full genome sequences of isolates may provide additional information to be used for virus characterisation.

• Although sequence data are useful for establishing genetic relationships, they do not provide sufficient information on antigenicity.

• Antigenic characterisation of viruses using polyclonal sera (r values) and monoclonal antibody profiling provides essential data which complements genetic analysis.

Recommendations

• New field isolates should continuously be characterised antigenically (ELISA and VNT) for the determination of r values against existing vaccine strains.

• A panel of reference sera for antigenic characterisation should be prepared, updated as necessary and be made available.

• Given the large number of MAbs produced against FMDV in various laboratories efforts should be directed for establishing common panels of MAbs that can be used for the antigenic characterisation of field isolates in addition to the determination of r values. One or more Institutes should be designated to coordinate information on MAbs produced in various laboratories and to produce MAbs against other strains in order to complete the panels, when necessary.

• More complete genome sequences should be obtained for better characterisation of FMD viruses.

Item 5: Diagnostics - virus detection

Mr Scott Reid presented a paper on the diagnosis of FMD by real-time, automated RT-PCR (Appendix 25). The main objective of his work was to accelerate laboratory diagnosis in order to avoid situations where herds have to be stamped out on the basis of clinical suspicion alone. Improvements were made on the nucleic acid extraction from test samples in order to increase the speed, flexibility and capacity and of RT and PCR procedures without harming the assay sensitivity. PCR results can now be achieved on a 96-well plate by 2 people within a day. Definitive diagnostic results can be achieved on first passage cell culture supernatant fluids.

Mr Scott Reid presented another paper (Appendix 26) on the comparison of RT-PCR procedures for diagnosis of clinical samples of FMD virus (serotypes O, A, C and Asia 1) under the European Union Concerted Action Group Project PL 98-4032. RT-PCR results from the 7 participating laboratories using locally-employed procedures were presented. Each laboratory had been supplied with 40 unlabelled epithelial suspensions (10 each of the serotypes O, A,C and Asia1) and five laboratories had also received cell culture grown virus preparations. A variety of procedures were used including conventional RT-PCRs with universal and serotype-specific primer sets, nested PCR, a novel PCR with restriction enzyme digestion and quantitative methods (not automated). Some primer sets were used in more than one laboratory.