Maedi-Visna in Sheep: Managing a Progressive Lentivirus Infection

Maedi-visna causes chronic progressive lung and nervous system disease in sheep, with no treatment and management focused on reducing transmission and culling affected animals.

Key Facts

Maedi-visna virus (MVV) is a lentivirus causing progressive pneumonia and neurological disease
Maedi refers to the pulmonary form causing chronic progressive respiratory failure
Visna refers to the neurological form causing progressive hindlimb ataxia and paralysis
Transmission occurs through colostrum and milk from infected ewes to lambs
Horizontal transmission between adult sheep is less efficient but occurs over prolonged contact
No vaccine or treatment exists - control relies on testing, segregation, and culling
Nordic countries have achieved MVV-free status through systematic testing and culling programs

Welfare Considerations

Maedi-visna causes prolonged, progressive suffering. Ewes with the pulmonary form experience gradually worsening breathlessness over months to years before dying of respiratory failure. The neurological form causes progressive paralysis that is equally distressing. There is no treatment, so welfare management focuses on preventing new infections through colostrum management, and identifying and removing infected animals before disease reaches advanced stages. Operations that test systematically and cull infected animals in early disease reduce the total suffering burden compared to allowing natural disease progression.

What You Can Do

Test your flock for MVV if purchasing status is unknown or you have introduced animals from unknown status flocks
Implement colostrum management (pasteurization or replacement) to prevent lamb infection in infected flocks
Segregate MVV-positive animals from negative animals to reduce horizontal transmission
Cull animals showing clinical signs of maedi or visna before disease reaches terminal stages
Consider joining MVV accreditation programs to achieve disease-free status over time
Purchase rams and ewes only from MVV-free accredited flocks when possible
Discuss MVV management strategy with your vet based on your flock's current prevalence