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Volume 95, Number 1 >
Pp. 1-2
The Priest's House, Sissinghurst Castle, Cranbrook TN17 2AB, UK
Now that the disastrous epizootic of foot and mouth disease is over, thoughts can turn to the best method of control in future. From the perspective of the mathematical modellers, expressed at a meeting of the RSM's Section of Comparative Medicine on 17 October, the only criticism of the management of the outbreak is that the slaughter policy was implemented too slowly. In particular, the modellers see no advantage from supplementing slaughter with vaccination, because of the delay before vaccination becomes effective. (In fact, protection in cattle begins in as little as four days.) Among the audience there was some feeling that computer models need to be complemented by the modern day version of shoe-leather epidemiology—namely, the application of molecular biology to tracing the origin of the strain, ascertaining its mode of entry into the country and tracking the route of spread.
According to the committee of inquiry into the 1967-1968 epizootic1, the dozen years from 1954 had seen 179 primary outbreaks of foot and mouth disease, of which 98 were confined to the first infected farm and only 3 caused more than 50 secondary outbreaks. The measures introduced in 1968 to control imports of meat and meat products from infected areas, aided in no small part by the increasing control of the disease in Continental Europe by vaccination, were strikingly effective. Thus between 1968 and 2001 there was only one outbreak, confined to the Isle of Wight, before the latest episode. Import controls, together with prompt diagnosis and action, did a good job. But will they be as effective in future? For three reasons this is unlikely. First, the import controls across Europe have to be 100% effective, and in view of the increased movement of people and animals this is asking the impossible; ascertainment of the route of entry in 2001 (or earlier) might help in devising a preventive strategy. Second, travel from infected areas into the UK and Europe is also increasing and the carriage of food as personal baggage adds to the likelihood of a breach of the defences. Third, there is now a real hazard of agricultural bioterrorism, especially threatening to countries and areas where a slaughter policy prevails.
Another factor to take into account is the likelihood that an importation will trigger an epizootic. This hazard may have increased. Although in the period 1954-1967 most importations were confined to the farm of origin, virological confirmation was not the rule and some of the outbreaks were probably not foot and mouth; nowadays all incidents are checked virologically. As pointed out in a previous commentary2, good management would be much helped by a sensitive diagnostic test that can be used on the farm. Even with such methods, however, I think that most importations would result in secondary spread, because of the increasing movement of animals from place to place. This trend will be hard to reverse, driven as it is by the concentration of markets and the policy for bigger abattoirs. Moreover, the general public seems to have little stomach for another round of massive slaughter.
If this analysis is accepted, then the logical way to control the disease is by routine prophylactic immunization. This is not a simple matter, but fortunately there is a long favourable experience of using vaccines in this way—for example, in Continental Europe until 1991, and in South America. The first consideration is what strain to use. In Europe it would probably be sufficient at present to use the current OManisa vaccine strain. Prevalent strains in different areas are monitored by the World Reference Centre at Pirbright, and the strains in vaccines can be adjusted accordingly—much as happens with influenza vaccines. The threat of bioterrorism is a different matter. The most prudent course, probably, is to immunize routinely against the strains picked up by the surveillance system, since these will be the easiest for a terrorist to acquire, but to have stocks of other types available for an emergency.
The implementation of a vaccine policy should not pose great difficulty; farmers are accustomed to immunizing their animals against various diseases. To be successful, it would have to be compulsory and a subsidy for farmers would be reasonable since vaccination would represent a form of insurance for the country as a whole. The tourist industry in particular would benefit if foot and mouth outbreaks became a thing of the past. This vaccination policy would, of course, have to be adopted throughout the European Union; and it might even become part of a global exercise on the pattern of the Expanded Programme on Immunization. Such a programme would demand methods of serological surveillance that distinguish between vaccinated and infected animals as well as rapid diagnostic tests for use on the farm2. Although there is no real prospect of eradication, because of the reservoir in wild animals, the disease might be confined to those areas where farm livestock have contact with naturally infected cloven-hoofed wild animals. This leaves the question of bioterrorism; but at least we have highly effective vaccines at our disposal.
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