visna

Visna is a chronic, progressive, and debilitating disease affecting sheep, caused by the small ruminant lentivirus (SRLV). This virus is also known as ovine lentivirus. Visna is characterized by neurological and respiratory signs, though it can also affect other organs. The neurological form, often referred to as visna-encephalomyelitis, typically involves progressive hindlimb weakness and incoordination, leading to paralysis and eventual death. Respiratory involvement, known as ovine pulmonary adenomatosis or jaagsiekte, can cause progressive labored breathing and fluid accumulation in the lungs.

The transmission of SRLV primarily occurs through direct contact with infected animals, especially via respiratory secretions and milk. Infected ewes can also transmit the virus to their lambs during pregnancy or nursing. The incubation period for visna is long, often spanning months or even years, making clinical diagnosis challenging. Diagnosis relies on serological testing to detect antibodies against the virus and molecular methods to detect viral RNA or DNA.

There is no cure or vaccine for visna. Control strategies focus on preventing the introduction and spread of the virus within flocks. This includes testing and removing infected animals, implementing biosecurity measures, and managing breeding programs to avoid transmission. Visna poses a significant economic threat to sheep farming due to reduced productivity, increased mortality, and the costs associated with disease management. Global efforts are ongoing to understand the pathogenesis of SRLV and develop effective control strategies.