Maedi

Maedi is a chronic, progressive, and debilitating disease affecting sheep and goats. It is caused by a retrovirus known as the Maedi-Visna virus (MVV). The virus targets the immune system, particularly macrophages, and can lead to a variety of clinical signs affecting different organ systems. The disease is widespread globally, with a higher prevalence in certain regions.

The transmission of MVV primarily occurs through direct contact between infected and susceptible animals, especially via respiratory secretions and colostrum from infected mothers to their offspring. The virus has a long incubation period, meaning animals can be infected for months or even years before showing symptoms.

Clinical manifestations of Maedi are diverse and can include neurological signs such as ataxia (staggering gait), tremors, and paralysis, leading to the "osis" form (older term for neurological signs). Respiratory signs, including pneumonia and difficult breathing, characterize the "itis" form (older term for lung involvement). Goats may also develop mastitis (inflammation of the udder), referred to as caprine arthritis-encephalitis (CAE) when it affects goats, though MVV is the causative agent for both sheep and goats. Arthritis, leading to lameness and joint swelling, is another common symptom.

Diagnosis is typically made through serological tests that detect antibodies against MVV in the blood. There is no cure for Maedi, and treatment focuses on supportive care and managing symptoms. Prevention strategies involve testing and culling infected animals, implementing biosecurity measures, and raising uninfected offspring separately from their mothers. Genetic resistance to MVV is being studied as a long-term control measure.