Review Lecture: Foot-And-Mouth Disease -- One of the Remaining Great Plagues

Foot-and-mouth disease has been known for at least four centuries. The earliest reports of its occurrence are from Italy; it did not reach England until 1839. Its occurrence in South America was first described in 1871 and is probably linked to the movement of infected cattle from Europe to that part of the world. The earliest reports of the disease in Asia and Africa date from 1842 and 1892 respectively. The causal agent of the disease, a virus belonging to the family Picornaviridae, was discovered by Loeffler & Frosch in 1897; its antigenic diversity was described in the early 1920s. Seven serologically distinct types of the virus are now recognized, thus rendering the task of vaccination more complex, particularly as there is also considerable antigenic diversity within the serotypes. Nevertheless, good inactivated vaccines are available and, as demonstrated in western Europe over the last 30 years, these have proved to be extremely effective when applied prophylactically in efficiently organized programmes. The failure to control the disease adequately in Africa, Asia and South America can be partly explained by the more difficult local conditions and less-efficient veterinary services, together with the problems associated with maintaining the potency of a wet vaccine which is relatively unstable and requires storage at refrigerator temperatures. The potency of a vaccine is related to the mass of intact virus particles that it contains, and it is generally accepted that about 5 μ g, as a single injection, will confer immunity against the severe challenge test which most national authorities demand. Studies of the structure of the virus have identified those parts of the particle which confer immunity when injected into susceptible host animals. Although the fine details have still to be determined, it appears that the major immunogenic site is contained within a sequence of 20 amino acids of one of the four structural proteins. At present, better methods for presenting the peptide so that it is more immunogenic are being sought; the ultimate solution may depend on obtaining the three-dimensional structure of the immunogenic site by X-ray crystallography. The prospect of an indefinitely stable vaccine, which can be synthesized chemically and which could confer long-lasting immunity by a delayed-release mechanism, provides the impetus for further research in this field.