Submitted to: Veterinary Immunology and Immunopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/29/1994
Publication Date: N/A
Citation: Interpretive Summary: Ovine progressive pneumonia (OPP) is an important and widespread sheep viral disease. Currently available serum diagnostic tests to detect OPP infection use expensive and impure viral test antigens which can result in inaccurate test results. In this study, the performance of three new immunoassay tests, using an inexpensive and highly purified antigen produced by genetic engineering (recombinant) methods, was compared with two currently available tests which use conventional test antigens. The new recombinant protein assays were more accurate and sensitive than the available conventional assays to detect OPP infection.
Technical Abstract: Recombinant transmembrane protein (TM) gp40, major-core protein p25, and minor-core (matrix) protein p16 of ovine lentivirus (OLV) were used as solid-phase antigens in enzyme-linked immunosorbent assays (ELISAs) for the detection of specific antibodies against OLV in sheep sera. Sensitivity, specificity, and agreement of these three recombinant assays were compared with each other and with the two currently available conventional OLV sero-assays, the agar gel immunodiffusion (AGID) test and a whole-virus (WV) ELISA. Field sera from a total of 412 Midwestern United States sheep were tested and compared by the five OLV detection methods, including visibly healthy sheep selected for public sale (Group A, n = 171), samples from a breeding flock of Finnsheep and Finn-cross ewes (Group B, n = 184) and moribund sheep with clinical signs associated with OLV (Group C, n = 57). The rTM ELISA was the most sensitive OLV detection assay, both overall and in each group. Sera from 48.1% (198/412) were rTM ELISA reactive. By contrast, positive rates for the rP25, rP16, and WV ELISAs and AGID test were 34.2, 32.3, 36.9, and 26.9% respectively. The rTM ELISA reactivity was 36.8% for Group A sera, 50.0% for Group B sera, and 75.4% for Group C sera. Among the 21 Group C sheep possessing OLV lung lesions at necropsy, 20 (95.2%) were rTM ELISA positive. The greatest test agreement occurred between the rP25 and the rP16 ELISAs. The data suggest that the recombinant transmembrane immunoassay is the most accurate and sensitive of the five methods evaluated for the detection of OLV in sheep, both early and late in the disease course.