Early detection of maedi-visna (ovine progressive pneumonia) virus seroconversion in field sheep samples

The aim of this work was to investigate whether an enzyme-linked immunosorb ent assay (ELISA) was useful for early detection of maedi-visna virus (MVV) infection in sheep under field conditions. An ELISA based on p25 recombina nt protein and a gp46 synthetic peptide was used. Sequentially obtained ser um samples (n = 1,941) were studied for 4 years. ELISA results were compare d with those of the agar gel immunodiffusion (AGID) test, and results of bo th tests were compared with a reference result established using consensus scores for at least 2 of 3 serologic techniques (AGID, ELISA, and western b lotting, which was used to resolve result discrepancies between the other 2 techniques). A total of 247 discrepancies were observed between ELISA and AGID. Of these, 131 were due to an earlier detection of 120 sera by the ELI SA and 11 sera by AGID. The remaining discrepancies (116) were due to the p resence of false reactions in both tests. Fewer false-negative results were found by ELISA than with AGID (6 vs. 69 sera, respectively), whereas the n umber of false-positive results was virtually the same for ELISA and AGID ( 21 vs. 20, respectively). In relation to the reference result, ELISA sensit ivity and specificity were 97.8% and 98.2%, respectively, whereas values fo r AGID were 76.3% and 98.3%, respectively. The agreement between ELISA and the reference result was higher than that between AGID and the reference re sult (kappa value: 0.96 and 0.77, respectively). A variation in the ELISA s ignal (based on optical density) was observed during the study period, sugg esting different antibody levels throughout the animal's life. The ELISA wa s useful for detecting MVV-infected sheep in field conditions and has poten tial for use in control and eradication programs.