Item 6 Diagnostics – antibody detection

scale – just to control an outbreak – both methods of eradication must be considered.

Dr Chris Griot presented a paper on the evaluation of eradication strategies including the acceptance of any future vaccination of livestock in case of an FMD outbreak in Switzerland (Appendix 16). The evaluation involved a roundtable discussion with the livestock producers, state veterinary services, consumer organisations, animal rights activists and food retailers. The aim was to inform all participants about the basic aspects of FMD, current eradication strategies and the alternative possibilities. The main conclusions drawn from these discussions were a) stamping out of infected herds is accepted to be the basic tool for eradication; b) mass prophylactic vaccination is not conceived to be an option for the protection of animals; c) suppressive vaccination is rejected; and, d) protective vaccination is accepted by all stakeholders. The consumer organisations as well as the food retailers seemed to be willing to accept the marketing of products from vaccinated animals although there was some hesitation expressed by food retailers to sell products from FMDV vaccinated animals.

Dr Alex Donaldson informed the meeting that the “minimum conditions for the importation into Europe of live animals fresh meat and offal of the bovine species” are under revision.

Conclusions

• Models can be a valuable tool to aid the decision-making processes but in the absence of strong data they should not be used to drive control policy.

• Policy discussions on disease eradication strategies with stakeholders and consumer organisations should be initiated before any FMD “crisis” arises.

• The use of highly sensitive fully validated NSP tests would allow veterinary services to establish whether virus was still circulating following a vaccination campaign and compensate for the reduced effıciency of clinical surveillance resulting from vaccination.

• The devastating consequences of the UK 2001 epidemic have stimulated consideratıons of disease control strategies less reliant on extensive cullıng.

Recommendations

• The possibility of applying increased biosecurity to farms, transport of carcasses and rendering plants during FMD emergencies using containment principles from biosecure laboratories should be investigated.

• Refine existing models and apply them as a decision support process after peer review.

• It is recommended to investigate whether principles applied in the high-containment laboratory can – in addition to existing procedures – also be applied on suspicious and outbreak farms. The development of a completely closed system for transporting carcasses which, on arrival at rendering plants enter air locks, should be investigated.

• It is recommended that the development and full validation of improved tests for serological surveillance, in particular the NSP tests, is supported.

Item 3: Pathogenicity and transmission

This item started with a presentation by Dr Soren Alexandersen about quantitative parameters of virus excretion and transmission (Appendix 17). The purpose of this study was to provide quantitative disease parameters that could improve models predicting the spread of FMD virus. Transmission of FMD virus within a group of cattle resulted in more severe lesions in the contact infected animals than in the inoculated animals. Airborne virus excretion starts with the occurrence of clinical signs and fall within the viraemic period. Clinical disease appears approximately 3-4 days later in the contact cattle under the conditions used. In pigs, the time of development of clinical disease in contact pigs seems to be related to the number of pigs kept together and that virus transmission is more efficient when more animals are kept together. Dr Alexandersen concluded that real time RT-PCR on nasal swabs is a promising tool for the detection of FMD. Based on the estimated half-life of virus RNA excreted it may take up to 30 days before the concentration falls below 1 RNA copy per ml of sample.

Dr Zhidong Zhang studied the temporal patterns of viral load in esopharyngeal fluid (OPfluid) in FMDV infected cattle (Appendix 18). The experiments showed no correlation between virus growth rate, doubling time or virus peak levels and whether cattle became carriers or non-carriers. In contrast, the viral load clearance rate (half-life) early after peak levels was significantly slower in carriers than in non-carriers indicating that an early event determines whether or not a carrier state is established. Albeit that the clearance in OP-fluid was faster in non-carriers than in carriers, the clearance was slower than observed in the blood or in nasal or mouth swabs.

Dr Melvyn Quan described efforts to develop a mathematical model of FMD virus infection in pigs (Appendix 19). In the two infection experiments performed, including groups given a high, medium and low dose of virus, he found statistical significant differences between the first time active vireamia was detected in the groups. He was able to fit a model partly explaining the results, but more research has to be performed on the validity of the model.

Dr Ciara Murphy described studies of inflammatory and antiviral cytokines in pigs experimentally infected with FMD virus (Appendix 20). After a short introduction on the role of the different cytokines she showed results of two infection experiments and both experiments showed a complicated pattern of activation and degradation of mRNAs isolated from PBMCs. More research is needed to clarify the results and to define the role of the different cytokines in the innate immune response to FMD virus.

Dr Aldo Dekker presented a paper evaluating transmission of FMDV between individually housed calves (Appendix 21). The study used FMDV type O from the 2001 outbreaks in the Netherlands. In experiments 1-4 a single calf were inoculated intranasally and were housed at a 1 metre distance from a naïve calf and in experiments 5-6 a single intranasally inoculated calf housed between two naïve calves. Although the calves were housed side by side in experiment 5-6, the calves could only with difficulty get in direct contact. All inoculated calves became infected but none of the other calves showed any signs of infection, i.e. no rise in temperature, no vesicular lesions and serologically negative.

Conclusions

• The number of animals kept together in direct contact may influence the incubation period and the efficiency of spread.

• Real time RT-PCR on nasal swabs is a promising tool for the detection of FMD.

• A difference in the viral load in OP-fluid samples of carrier and non-carrier cattle was observed already early in infection, i.e. shortly after peak levels.

• It was possible to fit a preliminary mathematical model to experimental data of viraemia levels in pigs but more work is needed to optimise the model and to test several interesting hypotheses.

• Preliminary work of cytokine mRNA levels and activation of innate immunity in FMDV infected pigs is interesting but future work is needed to clarify and extend the findings.

• Transmission of FMDV between calves may be limited when separated physically.

Recommendations

• Efficiency and speed of transmission of FMDV is variable and highly dependant on direct or indirect contact intensity and on housing conditions. More studies under varying conditions and using several different strains of virus will provide a better understanding of the epidemiology of FMD and such data are urgently required for development of realistic simulation models of disease spread. Also modelling of virus infection in the animals and studies of pathogenesis can help in refining epidemiological models.

• More research aimed at understanding the mechanisms of the carrier state should be encouraged.

Item 4: Virus characterisation

Dr. Soren Alexandersen presented the paper by Mason et al (Appendix 22) on behalf of Nick Knowles on the sequence analysis of 5FMDV type O PanAsia strains from separate geographical regions based on the comparisons of complete genomes. These analyses revealed a remarkable conservation of all portions of the genomes among the PanAsia virus isolates and provided confirmation of the close relationship between the viruses responsible for South African and UK outbreaks. The complete genome analysis indicated that only minor changes in the genome of FMDV can dramatically alter virulence in animals.

Dr. Neeraj Aggarwal presented a paper on the characterisation of five monoclonal antibodies against FMDV vaccine strain C1 Oberbayern (Appendix 23). Based on their reactivity with five field isolates of type C viruses it was concluded that the MAbs represented 4 different epitopes 2 of which were neutralising. Due to the limited number of MAbs and unknown correlation between antigenic sites and in vivo protection, it was not possible to assess the suitability of the vaccine strain against the field isolates. It was concluded that a much larger panel of well characterised MAbs are needed to eventually replace the current characterisation based on establishment of r values using polyclonal antisera.