Development of tests for antibodies against foot-and-mouth disease virus in cattle milk.

The liquid-phase blocking ELISA (LPBE) and a specific isotype assay (SIA) for bovine IgG1 were modified to detect antibodies against FMDV isolate O1 Manisa in cattle milk. Samples from vaccinated animals were mostly indistinguishable from negative control cattle in the LPBE but 90% of milks from convalescent animals (which had also been vaccinated several times previously) gave positive results. The SIA was able to detect 95% of cattle vaccinated up to 12 months previously, and 100% of the recovered animals examined. Both tests could, therefore, be used for surveillance purposes following an outbreak of FMD to identify herds of cattle which had been infected, but the SIA would be required to show the presence of vaccinated animals. Samples from convalescent cattle showed the highest correlation between antibody levels in milk and in sera. Agreement was also high among recently vaccinated animals, but declined with increasing time since immunisation, though there was still a strong correlation of IgG1 levels after 6 months.