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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.

PROCEEDINGSdeveloped, particularly for detecting the circulation of FMD virus in a subclinical form in FMD-vaccinated populations.When adapted for use in sheep, the 3ABC MAt-ELISA showed similar specificity, giving negative results with sera from vaccinated animals and positive in experimentally infected sheep that developed antibodies to FMDV structural proteins. In field conditions, the test was able to detect silent infections in asymptomatic sheep. However, there was more variation in antibody levels in naturally exposed animals than in experimental animals and not all sheep suspected to have been exposed to infection scored positive to 3ABC, (in spite of the detection of antibodies to sructural proteins) The failure to detect 3ABC induced antibodies in such animals could reflect a possible, individual immuno-tolerance to 3ABC, a poor sensitivity of the test, or the occurrence of a previous, unknown vaccination. Alternatively, the delayed onset and the shorter half-life of anti-3ABC antibodies with respect to antibodies against structural proteins should be considered.In conclusion, the demonstration of antibodies to 3ABC is conclusive evidence of FMD infection. Following extensive validation, the 3ABC MAt-ELISA is indicated to detect viral circulation in FMD-vaccinated populations, representing a valuable diagnostic tool for FMD eradication campaigns and control programs. For the application on a single animal further research is required, mainly in two directions: i) the correlation between 3ABC antibodies and the carrier status, ii) the immune response to both structural and non-structural FMDV proteins in sheep and other species following infection. ACKNOWLEDGEMENTS

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To estimate the presence of, and the risk factors for HTLV-I and HTLV-II infections among HIV-1 infected subjects in Sao Paulo, Brazil, a serosurvey was performed in 471 HIV-1 infected patients, including 216 intravenous drug addicts (IVDA), 229 homosexual/bisexual men, and 26 with other risk factors. Serum samples were screened for HTLV seroreactivity by ELISA; reactive samples were analyzed by Western Blot (WB), using whole HTLV-I lysate as antigen. To confirm and discriminate HTLV-I and HTLV-II infections, sera presenting any bands on WB were further analyzed by a WB containing recombinant HTLV-I and HTLV-II proteins (WB 2.3), and by enzyme immunoassays using synthetic peptides specific for envelope proteins (Synth-EIA). In 22 cases, cell samples were available for polymerase chain reaction (PCR) studies. On WB, 114 sera were reactive and, of these, 37 and 25 were concordantly positive on both WB 2.3 and Synth-EIA procedures for HTLV-I and HTLV-II specific antibodies, respectively; 37 specimens were negative on both assays, and 15 gave discordant or indeterminate results. PCR findings confirmed concordant results obtained in the discriminatory serological assays. The prevalence rates of HTLV-I and HTLV-II infections were 15.3% and 11.1% in IVDA, and 0.9% and 0.4% in homosexual/bisexual men, respectively. No case of HTLV-I/HTLV-II co-infection was found.