In this study the sensitivity and specificity of an immunoperoxidase technique for the detection of lentiviral protein in formalin-fixed lung tissues of sheep were assessed. Formalin-fixed specimens of lungs of 52 sheep originating from two different infected flocks and formalin-fixed lung specimens of 20 sheep from a third, non-infected flock were selected. Multiple sections from each animal were stained with a monoclonal antibody against Maedi-Visna Virus (MVV) antigen. Control sections were stained with an irrelevant antibody, and without antibody, respectively in both the positive and negative groups. Histologic lesions of Maedi were graded according to severity and the number of sections staining positive. The average count of infected cells was determined for all animals which exhibited positive staining against viral protein. It was determined that the IMP technique had a sensitivity of 51,9% and a specificity of 100% if three sections of each animal were examined in both infected flocks. The sensitivity was greatly influenced by the presence or absence of typical histological lesions and the average cell counts seem to be correlated with the severity of the histological lesions. Animals without histological lesions were mostly negative with the IMP technique. The sensitivity was also influenced by the number of sections examined per animal and decreased if fewer sections were examined. Statistical analysis confirmed that the proportions of sections which were positive by means of IMP staining differed significantly between the four histological categories of normal, mild, moderate and severe. The more severe the lesions, the higher the proportion of sections were that could be diagnosed as infected by means of the IMP technique. It also confirmed that the ability to detect MVV infection in sections decreases significantly with a smaller sample size. In conclusion it would seem that this technique may be used in confirming infection in individual animals selected on the presence of typical pulmonary lesions. It is, however, not suitable as a routine screening test for the infection.
Dissertation (MMedVet (Pathology))--University of Pretoria, 2006.