A pilot project to eradicate Maedi-Visna in the Swiss breed "Walliser Schwarznasenschafe"

Maedi-Visna is a lentiviral disease of sheep with a worldwide distribution. The transmission of the virus occurs primarily via colostrum and milk from the infected ewe to its newborn lamb but also horizontally between sheep. The most obvious clinical symptoms are progressive dyspnoe and emaciation. In this prospective study an eradication based on serological testing and r emoving of seropositive animals was performed in 24 flocks of sheep of the breed "Walliser Schwarznasenschafe" leading to a reduction of the seropreva lence from 35% to 1% within two years. The control group consisted of 21 fl ocks of sheep. Lambs of seropositive ewes had a 7.6 times higher risk to se roconvert within their first two years of life compared to those of seroneg ative ewes. The dynamics of the spread of the infection were studied in bir th cohort groups. Cohort animals of seropositive ewes showed an obvious tre nd to seroconvert slowly. Seropositive ewes had a significantly lower repro duction rate and their lambs suffered from significantly higher death and l ower growth rates, probably due to a reduced milk production, resulting in economic losses.