DIFFERENTIATING FOOT-AND-MOUTH-DISEASE VIRUS-INFECTED FROM VACCINATEDANIMALS WITH BACULOVIRUS-EXPRESSED SPECIFIC PROTEINS

We had shown in preliminary studies with a small number of animals tha t antibodies against 2C could be detected in cattle and pigs which had been infected with FMDV but not in animals which had been vaccinated against the disease. To determine whether this test was generally appl icable, sera from several hundred animals which had been vaccinated wi th different products in many countries have been tested in an ELISA u sing baculovirus expressed 2C, Our results show that only 1-2% of the sera gave a positive reaction by this method. In contrast, 100% of ser a from convalescent animals gave a positive reaction. To be useful in differentiating between convalescent and vaccinated animals it is nece ssary to know how long these antibodies can be detected by our ELISA, We have determined the levels of antibodies against 2C and also other virus-specific proteins which are present in cattle and pigs following infection with FMDV, Our results show that levels of anti-3ABC antibo dies could be detected by ELISA with baculovirus-expressed protein up to one year after infection. In contrast, the levels of anti-2C antibo dies fell more rapidly than those against 3ABC indicating that the lat ter protein may be preferable for detecting convalescent animals. Neve rtheless, we envisage that the final test format should include severa l virus-specific proteins to determine accurately the immune status of an animal.