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Four groups of six cattle were vaccinated from two to five times at 6 month intervals with two different trivalent FMD vaccines licensed in the given year. The FMDV type A strains in the vaccines designated A5F and A5B were closely related. Three months after the last vaccination the cattle were challenged by contact with animals inoculated with the original field strain A5B. The inoculated animals developed typical FMD symptoms with vesicles in the mouth and on the feet. Those cattle which had received vaccines that did not contain strain A5B also became severely sick, even after five vaccinations. Animals vaccinated twice with type B containing vaccine were also not completely protected. A safe protection can obviously only be achieved for fairly short periods of time if vaccine and challenge strain are homologous. It is proposed to change the rules of licensing, to speed up the procedure to vaccinate in cases of outbreaks. The need for further research, especially into improving vaccines, is stressed.

A method for extracting RNA from animal-derived materials that provides foot-and-mouth disease viral template suitable for Tth polymerase-dependent synthesis of cDNA and subsequent PCR is described. Viral genomes were detected in less than 24 h. Nasal swabs that can be easily and repeatedly collected, proved suitable for virus detection by PCR, even during the asymptomatic stages of infection.

Antibodies raised in cattle against foot-and-mouth disease virus by vaccination or by experimental infection were distinguished. Vaccination elicited only antibodies to virus capsid proteins and the polymerase 3D. Virus replication in cattle elicited additional antibodies directed against the non-structural proteins 2B, 2C, 3AB1, and/or 3C irrespective of prior vaccination or whether the cattle exhibited symptoms of disease. Non-permissive mice inoculated with virus responded in the same way, indicating that antibodies raised due to the transient presence of antigen are safely recognized by the method applied which was radioimmunoprecipitation. All kinds of infections were thus detected and it was possible to differentiate between cattle exposed or not exposed to challenge in the field, and further between protected animals and possible virus carriers.

Following an outbreak of FMD caused by an A5 strain in the spring of 1984, ten cattle were vaccinated with samples of the five commercial vaccines used for the vaccination campaign in that year, i.e. two animals per vaccine. Six weeks later the cattle were challenged by contact with animals inoculated with the virus strain isolated from the field outbreak. Seven of the ten cattle became severely ill, exhibiting the typical symptoms of FMD, one animal did not show any clinical symptoms, the remaining two weak ones that might have escaped recognition by the cattlemen. Virus could be recovered from the vaccinated animals from days 2 to 10 following contact with the non-vaccinated infected cattle. It was concluded that a single vaccination does not protect cattle against the isolate.