Cattle, sheep and pigs vaccinated against foot and mouth disease: does trade in these animals and their products present a risk of transmitting the disease?

The foot and mouth disease (FMD) status of a country or region has a profound bearing on access to export markets for live animals and animal products. In countries without FMD-free status, and in accordance with the international standards of the World Organisation for Animal Health (OIE), restrictions may be applied to trade in both vaccinated and unvaccinated animals and their products. Available information suggests that, provided there is compliance with essential criteria concerning vaccines, vaccination and other zoosanitary measures (especially quarantine and ante- and post-mortem inspection), the risk of spreading FMD through the importation of vaccinated cattle, sheep and pigs is extremely small. The risk from products derived from vaccinated animals is even smaller, provided that appropriate risk mitigation measures are applied. Knowledge of the zoosanitary status of the exporting country is critical for risk assessment, but can be difficult to verify. Although empirical evidence and practical experience strongly indicate low risk, it is not possible to assert that the risk is zero for vaccinated animals or their products. In the absence of key factual data, risk analysis is only practicable on a qualitative or semi-quantitative basis. However, a very low level of risk is both unavoidable and acceptable if such trade is to be conducted.

The pathogenesis and diagnosis of foot-and-mouth disease.

The pathogenesis of foot-and-mouth disease (FMD) is reviewed, taking account of knowledge gained from field and experimental studies and embracing investigations at the level of the virus, the cell, the organ, the whole animal and the herd or flock. The review also addresses the immune response and the carrier state in FMD. Progress made in understanding the pathogenesis of the disease is highlighted in relation to developments in diagnosis and methods of control.

Investigation of the possible spread of foot-and-mouth disease virus by the burning of animal carcases on open pyres.

An atmospheric dispersion model was used to predict the airborne spread and concentrations of foot-and-mouth disease virus within the plumes generated by 11 pyres built to burn infected carcases during the epidemic of 2001 in the UK. On the basis of assumptions about the quantity of virus emitted during the three hours after the pyres were built and the threshold concentration of virus required to cause an infection in cattle, it was concluded that none of the disease breakdowns which occurred under the plumes was due to the spread of virus from the pyres.

Aspects of emergency vaccination against foot-and-mouth disease.

Emergency vaccination is one of several measures which may be deployed to control outbreaks of foot-and-mouth disease. It can be a valuable adjunct to the application of the essential zoosanitary controls which must include rapid diagnosis, tracing, movement control and disinfection and which may also include slaughter of infected and in-contact animals and their safe disposal. Criteria which determine the successful application of emergency vaccination include access to vaccine(s) that (i) contain virus strain(s) of sufficient antigenic relatedness to the outbreak strain(s) (ii) are of the required type of vaccine formulation (iii) have acceptable innocuity and potency (iv) have appropriate availability, including quantity and immediacy of supply and (v) meet considerations of cost. Contingency planning should include provision for emergency vaccination and must address the complex decisions of not only when, where, and how to apply vaccine but also its economic consequences. Computer modelling may be a useful aid to cost benefit and decision support systems in this context. Planning must be detailed and regularly reviewed and should ensure, (i) that the legal and financial aspects are catered for (ii) that any contractual supply agreements are in place (iii) that information is collected and its currency maintained on the species, numbers and whereabouts of susceptible livestock (iv) that vaccination teams are formed and trained (v) that the vaccine cold chain is established and maintained (vi) that supplies of vaccination equipment are held in readiness and (vii) that briefing materials are available to inform the various stakeholders on relevant aspects of emergency vaccination. Knowledge concerning the characteristics and performance of emergency vaccines is summarised and areas identified for further research.

Foot and mouth disease: the future of vaccine banks.

The authors briefly review the history of vaccine banks for foot and mouth disease, their current location and their constituent serotypes and strains, together with the occasions on which they have been activated. Experimental studies on emergency vaccines are summarised and areas identified for further investigation. The future of such banks is considered, including the principal strengths and weaknesses of existing banks, and suggestions are made for potential improvements. The fact that the banks have been activated on relatively few occasions over the 25 years of their existence testifies in part to the relatively rare calls which have been made upon them, but also reflects the difficulty in deciding when and how to utilise emergency vaccination. Nevertheless, in an era of increasing global risks of the spread of foot and mouth disease, banks will most certainly continue to have strategic and tactical importance in the control of this most readily communicable of animal diseases.