Small Ruminant Lentiviruses: Maedi-Visna & Caprine Arthritis and Encephalitis
Maedi-visna and caprine arthritis and encephalitis are economically important viral diseases that affect sheep and goats. These diseases are caused by a group of lentiviruses called the small ruminant lentiviruses (SRLVs). SRLVs include maedivisna virus (MVV), which mainly occurs in sheep, and caprine arthritis encephalitis virus (CAEV), mainly found in goats, as well as other SRLV variants and recombinant viruses. The causative viruses infect their hosts for life, most often subclinically; however, some animals develop one of several progressive, untreatable disease syndromes. The major syndromes in sheep are dyspnea (maedi) or neurological signs (visna), which are both eventually fatal. Adult goats generally develop chronic progressive arthritis, while encephalomyelitis is seen in kids. Other syndromes (e.g., outbreaks of arthritis in sheep) are also reported occasionally, and mastitis occurs in both species. Additional economic losses may occur due to marketing and export restrictions, premature culling and/or poor milk production. Economic losses can vary considerably between flocks.