CONTINUATION OF THE OBSERVATION AND SEROL OGICAL INVESTIGATION OF A MEADI-VISNA-VIRUS-INFECTED SHEEP FLOCK FROM JANUARY-1990 TO JUNE-1996

This paper describes the second part of a longtime-study, started in 1 987. Serologic investigations for detecting antibodies against Maedi V isna-virus (MVV) were performed, involving an institute own sheep floc k. The method used was the immunodiffusiontest. The flock consisted of different breeds and their offsprings. So far, the virus seems to per sist in the herd. This work also shows the importance of the central r ole of the does for spreading the virus. Seroconversion was detected i n a sheep at the age of 32 months. The mother of this sheep was a thor oughbred and MW-negative mountain sheep. After removal of the animals with high antibody (ab)-titers, until the end of 1991, the percentage of seronegative sheep increased. Then seropositive sheep didn't show h igh ab-titers anymore. Since 1990 only offsprings increased the size o f the herd. The health status of the flock was clinically inconspicuou s. It can be concluded that in spite of good food quality, good hygien e, without culling positive animals and just giving away accidentally some sheep, no elimination of MW was registrated in the flock over a p eriod of more than six years. There was only seen a reduction of serop ositive animals. Single results of serological tests, without knowing the sheep and the serological status of the herd, could pretend a fals e negative status.