Phylogenetic analysis of small-ruminant lentivirus subtype B1 in mixed flocks: evidence for natural transmission from goats to sheep.

Small-ruminant lentiviruses (SRLV), consisting of the caprine arthritis-encephalitis virus (CAEV) and the maedi-visna virus (MVV), cause chronic multisystemic infections in goats and sheep. The SRLV subtype B1, characterized by the prototypic strain CAEV-CO, has a worldwide distribution and, remarkably, has been isolated exclusively from goats, suggesting potential host specificity. To test this hypothesis, SRLV pol sequences were obtained by PCR amplification from blood samples of seropositive dairy goats and sheep living in mixed flocks. Phylogenetic analysis of these sequences demonstrates that SRLV subtype B1 does cross the species barrier under field conditions through direct contact between adult animals. This implies that SRLV control programs targeting only sheep or goats can no longer be proposed (based on a putative species specificity of the SRLV subtype B1).