Risk factors for the infection of Swiss goat herds with small ruminant lentivirus: a case-control study

In the mid-1980s, Switzerland started a programme to eradicate caprine arthritis-encephalitis - an infectious disease of goats caused by the small ruminant lentivirus (srlv). Since 1996, progress towards eradication has slowed down, owing to infections occurring on farms from which the infection had previously been eliminated. To investigate specific risk factors for these new infections and to improve the eradication programme, a case-control study was conducted. Cases consisted of farms that had been officially free of srlv for at least three consecutive years but on which at least one srlv-seropositive animal had been detected during the annual serological surveys of 2001 and 2002. On all the case and control farms where sheep were housed together with goats, a subset of sheep was screened for antibodies to srlv. Potential risk factors were analysed in a logistic regression model; the results indicated that close contact with srlv-seropositive sheep was highly correlated with seroconversion in srlv-seronegative goat herds (odds ratio=26.9), supporting the hypothesis that srlv can be transmitted between sheep and goats, and suggesting that the measures taken so far will not lead to the complete eradication of srlv from Switzerland within the next few years.