Maedi-visna in Pomeranian Coarsewool sheep in Germany: Seroprevalence, environmental and genetic risk factors

Small ruminant lentiviruses (SRLV) cause maedi-visna (MV), an incurable, wasting disease affecting sheep worldwide. This study evaluated the seroprevalence of the maedi-visna virus (MVV) in the endangered German Pomeranian Coarsewool Sheep (RPL) and identified environmental and genetic risk factors for individual and flock-level seropositivity. A total of 849 samples from 35 farms across 9 German states were analyzed for MVV antibodies. Individual seroprevalence and clinical incidence were 3.5% and 13.3%, respectively. Seropositive sheep were detected in 6 flocks, with prevalences between 5.3% and 37.5%. Eastern German flocks and sheep older than 3 years showed the highest seroprevalence. Purchasing positive ewes was identified as the main risk factor for seropositivity. Serotyping of SRLV in the MVV-positive sheep identified besides genotype A for the first time in Germany genotypes B and E, suggesting multiple routes of virus introduction into this breed. Furthermore, 530 sheep from 54 flocks were genotyped for position 35 of the ovine transmembrane protein 154 (TMEM154) coding region. The putative protective TMEM154 genotype KK and allele K were present in 28% and 53%, respectively. Association analysis between TMEM154 genotypes and MVV seropositivity showed only a tendency towards significance, potentially confounded by the low number of positive sheep and/or different SRLV genotypes. Despite a low MVV seroprevalence in the RPL breed in Germany, regular monitoring is strongly recommended to avoid its spread. Selection of sheep for the less susceptible TMEM154 genotype KK may help to eradicate the disease in affected flocks but requires further investigation.