Introduction: Maedi-visna virus and caprine arthritis encephalitis virus are two closely related lentiviruses which causemultisystemic, progressive and persistent infection in goats and sheep. Because these viruses frequently cross the species barrier,they are considered to be one genetic group called small-ruminant lentiviruses (SRLV). They have in vivo tropism mainly formonocytes and macrophages and organ tropism with unknown mechanisms. Typical clinical signs are pneumonia in sheep,arthritis in goats, and mastitis in both species. Infection with SRLV cannot currently be treated or prevented, and controlprogrammes are the only approaches to avoiding its spread. These programmes rely mainly on annual serological testing andelimination of positive animals. However, the high genetic and antigenic variability of SRLV complicate their early anddefinitive diagnosis. The objective of this review is to summarise the current knowledge of SRLV genetic variation and itsimplications for tropism, the development of diagnostic tests and vaccines and the effectiveness of control and eradicationprogrammes. Material and Methods: Subject literature was selected from the PubMed and the Google Scholar databases.Results: The high genetic diversity of SRLV affects the performance of diagnostic tools and therefore control programmes. Forthe early and definitive diagnosis of SRLV infection, a combination of serological and molecular tests is suggested. Testing byPCR can also be considered for sub-yearling animals. There are still significant gaps in our knowledge of the epidemiology,immunology and biology of SRLV and their impact on animal production and welfare. Conclusion: This information may aidselection of the most effective SRLV spread reduction measures.