Comparison of a maedi-visna virus CA-TM fusion protein ELISA with other assays for detecting sheep infected with North American ovine lentivirus strains

A maedi-visna virus CA-TM fusion protein ELISA (MW ELISA) was evaluated for the detection of antibody in sheep infected with North American ovine lent ivirus (OvLV). The results of the MW ELISA were compared with other assays for OvLV antibody and with viral infection in an intensively studied group of 38 sheep with a high prevalence of OvLV infection and disease. The sensi tivity, specificity, and concordance of assays for OvLV antibody (MVV ELISA , indirect ELISA, Western blot, and AGID), virus (virus isolation, PCR, ant igen ELISA), and OvLV-induced disease in each animal were compared with OvL V infection status as defined by a positive result in two or more of the as says. Five sheep met the criteria for absence of OvLV infection. The sensit ivity of the MVV ELISA in detecting OvLV infected sheep was 64%, whereas th e sensitivity of the other three tests for antibody ranged from 85 to 94%. All the antibody assays were 100% specific in this group of animals. Of the assays for virus, the PCR test had the highest sensitivity and the best co ncordance with OvLV infection, but it also had the lowest specificity of an y of the virus or antibody assays. Among the antibody tests, the concordanc e of the MVV ELISA compared most favorably with the AGID test for detecting OvLV-infected sheep. Analysis of serum samples from 28 lambs experimentall y-infected with one of three North American strains of OvLV suggested that there were no significant strain differences detectable by antibody assay. Twenty virus-inoculated lambs were positive by both the MW ELISA and the AG ID test, five lambs were MVV ELISA negative and AGID test positive, and thr ee lambs were MVV ELISA positive and AGID test negative. No pre-inoculation samples were positive by either assay. In a longitudinal study involving s even lambs, antibodies to OvLV were detected by AGID 3-5 weeks post-inocula tion, but were not detected by MVV ELISA until 5-10 weeks post-inoculation. Among 128 naturally and experimentally-infected sheep that were seropositi ve in the AGID test, the overall sensitivity of the MVV ELISA was higher in the naturally infected sheep (84%) than in the experimentally infected she ep (69%). The data indicated that the MVV ELISA represents a less sensitive , but specific alternative for the detection of OvLV antibodies. (C) 1999 E lsevier Science B.V. All rights reserved.