[Comparative studies of maedi-visna diagnosis: immunodiffusion test, enzyme immunoassay, immunoblot]

The agar gel immunodiffusion test (AGIDT) is applied worldwide for the serological field diagnosis of ovine/caprine lentivirus infections (Maedi-Visna and Caprine Arthritis-Encephalitis). To a lesser extent, enzyme-linked immunosorbent assay (ELISA) systems are in use. The sensitivity and specificity of available ELISA systems is strongly influenced by technical details. We present here an MVV-ELISA of high sensitivity, which is based on an antigen preparation containing a high amount of the major antigenic surface protein gp 135. This result was achieved by a simple and gentle purification method of antigen from whole virus. The test was applied to evaluate the seroprevalence of MVV-antibodies in herds derived from eleven farms located in the North-East of Germany. Furthermore, the antibody kinetics in experimentally infected sheep was investigated. The results were confirmed by internal controls and by immunoblot analysis of antibodies against p 28. The ELISA displayed significant differences between positive and negative results and identified up to 25% more seropositive samples than the AGIDT. Therefore, a final diagnosis of questionable AGIDT results was obtained. The specificity of results was confirmed by immunoblots with selected sera. We recommend to use the ELISA especially for screening of herds and for population controls. In addition, immunoblots are a valuable tool to test individual sera from specified cases.