[Continuation of the observation and serological investigation of a Maedi-Visna virus infected sheep flock from January 1990 to June 1996]. / Fortsetzung der Beobachtung und der serologischen Untersuchung einer Maedi-Visna-Virus-infizierten Schafherde von Jänner 1990 bis Juni 1996.

ABSTRACT

This paper describes the second part of a longtime-study, started in 1987. Serologic investigations for detecting antibodies against Maedi Visna-virus (MVV) were performed, involving an institute own sheep flock. The method used was the immunodiffusiontest. The flock consisted of different breeds and their offsprings. So far, the virus seems to persist in the herd. This work also shows the importance of the central role of the does for spreading the virus. Seroconversion was detected in a sheep at the age of 32 months. The mother of this sheep was a thoroughbred and MVV-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 high ab-titers anymore. Since 1990 only offsprings increased the size of the herd. The health status of the flock was clinically inconspicuous. It can be concluded that in spite of good food quality, good hygiene, without culling positive animals and just giving away accidentally some sheep, no elimination of MVV was registered in the flock over a period of more than six years. There was only seen a reduction of seropositive animals. Single results of serological tests, without knowing the sheep and the serological status of the herd, could pretend a false negative status.