Foot-and-mouth disease (FMD) recombinant non-capsideal viral antigens 3A, 3B, 2C, 3D and 3ABC were assessed individually
in an indirect enzyme-linked immunosorbent assay (I-ELISA) for their ability to screen for persistent infection-specific antibodies
in cattle, regardless of vaccination condition. Results of sequential serum samples from non-vaccinated animals with experimentally
induced persistent infection, and their correlation with virus isolation, indicated that the polypeptides 3A, 3B and 3ABC
showed the most adequate characteristics for further field studies.
Reliable performance of the I-ELISA with the selected antigen 3ABC was indicated by the distinct patterns observed for the
frequency distribution values of naive and true positive samples. For regularly vaccinated livestock, a clear negative profile
was proved in samples from regions without recent history of FMD. In contrast, at 90 and 900 days post-outbreak, coexistence
of a positive and a negative population was established. These findings indicated that, irrespective of vaccination, the test
allowed a classification of the herd-disease status.
A high degree of agreement was observed between I-ELISA-3ABC and EITB results for clearly reactive and non-reactive sera.
For samples with reactivity values close to that of the cut-off, the EITB profiles upheld the definition of the infection
condition. On this basis, screening by I-ELISA-3ABC, together with confirmation of suspect or positive samples by EITB is
proposed as an adequate and accurate approach for large-scale epidemiological surveillance.
Accepted October 24, 1999