Maedi-Visna in Sheep: Slow Virus Welfare Management
Maedi-visna virus causes progressive respiratory disease and neurological wasting in sheep over years, with welfare management focused on identification, segregation, and prevention.
Key Facts
- A lentivirus causing slow progressive pneumonia (maedi) and encephalitis (visna) in sheep
- Most infected sheep remain subclinically infected for years before clinical disease develops
- Respiratory form causes progressive weight loss, dyspnoea, and eventually death
- Neurological form causes progressive ataxia and paresis in a minority of infected animals
- No treatment exists; control relies on testing, segregation, and culling infected animals
Welfare Considerations
Maedi-visna welfare impact develops over years as infected sheep progress from asymptomatic to clinically affected. The respiratory form creates chronic welfare compromise through progressive breathing difficulty and weight loss over months to years. Affected sheep experience increasing exercise intolerance and eventually inability to maintain adequate nutrition through grazing. The neurological form causes progressive weakness and paralysis. Welfare management requires regular clinical assessment of known positive animals and prompt euthanasia when welfare becomes unacceptable. Accredited maedi-visna-free flock status prevents the ongoing welfare burden through elimination of the virus.
What You Can Do
- Test your flock for maedi-visna and pursue accreditation for MVA-free status
- Segregate positive animals and manage them as a separate closed group
- Monitor positive animals regularly for clinical signs and euthanize when welfare is compromised
- Do not feed pooled colostrum that could spread infection to lambs
- Purchase replacement stock only from MVA-accredited flocks