Current Perspectives on the Immunopathogenesis and Pathology of Small Ruminant Lentivirus Infections

Small ruminant lentiviruses (SRVLs), including ovine maedi-visna virus and caprine arthritis-encephalitis virus, are considered genetically a single pathogen that causes a progressive multisystemic inflammatory disease. Continuous interspecies transmission in areas where these species come into contact, along with dual infection in individual animals, results in recombination between variants. The main routes of infection are ingestion of infected colostrum and/or milk and inhalation of respiratory secretions. SRLVs primarily target monocytes/macrophages and dendritic cells. Following infection, chronic lymphocytic inflammatory infiltrates are observed in the main target organs: lungs, brain, joints, and mammary gland. Infection with the virus causes lifelong infection in its host, characterized by slow progression until overt disease, which is observed in approximately one-third of the infected animals, occurs. The affected system appears to depend on SRLV strain tropism, the species affected, and the genetic background of each breed or animal. This review examines the immunopathogenesis and pathology of small ruminant lentiviruses.