Maedi-Visna in Sheep: Chronic Respiratory Disease Explained
- Maedi-visna, also called ovine progressive pneumonia or OPP, is a lifelong viral infection of sheep caused by a small ruminant lentivirus.
- Most affected sheep show a slow decline over months, with weight loss and increasing breathing effort; signs are most common in adults older than 2 years and often over 4 years.
- There is no curative treatment or vaccine. Flock control usually relies on blood testing, separating or removing positive sheep, and preventing lamb exposure to infected milk or close-contact spread.
- Typical U.S. costs in 2025-2026 include about $6-$10 per sheep for ELISA screening, roughly $50 for some PCR tests, plus exam, farm-call, and sample-handling fees.
What Is Maedi-Visna in Sheep?
Maedi-visna is a chronic viral disease of sheep caused by a small ruminant lentivirus. You may also hear your vet call it ovine progressive pneumonia (OPP). The virus stays in the body for life, and infected sheep can carry and spread it long before obvious illness appears.
The name describes two classic disease patterns. Maedi refers to the lung form, where sheep develop slowly worsening breathing trouble. Visna refers to the less common neurologic form, which can cause weakness, incoordination, or paralysis. In many U.S. flocks, the respiratory form is the main concern.
This disease usually affects adult sheep, not young lambs. Signs often develop gradually, so pet parents and producers may first notice a ewe that is thinner than expected, tires more easily, or breathes harder after handling. Over time, the infection can reduce productivity, shorten useful lifespan, and create ongoing flock health losses.
Because maedi-visna is incurable and progressive, the goal is not to cure one sheep with medication. Instead, your vet helps you confirm the diagnosis, assess how much of the flock may be affected, and choose a practical control plan that fits your goals and budget.
Symptoms of Maedi-Visna in Sheep
- Progressive weight loss despite a fair appetite
- Exercise intolerance or lagging behind the flock
- Increased breathing effort or labored breathing
- Chronic dry cough, especially with handling or movement
- Poor body condition and reduced thriftiness in adult sheep
- Hard udder or reduced milk production in some ewes
- Lameness or chronic arthritis in some cases
- Head tilt, circling, weakness, or hindlimb paralysis in the neurologic form
Maedi-visna usually causes a slow, chronic decline rather than a sudden crash. Many sheep show no signs for years, then gradually develop weight loss and worsening respiratory effort. Fever is not typical unless there is a secondary bacterial infection, so a sheep can look chronically unwell without acting acutely sick.
See your vet promptly if an adult sheep has ongoing weight loss, chronic breathing changes, poor milk production, or neurologic signs. See your vet immediately if breathing becomes markedly labored, the sheep cannot rise, or you are seeing multiple thin, coughing adults in the flock, because other serious diseases can look similar and need to be ruled out.
What Causes Maedi-Visna in Sheep?
Maedi-visna is caused by a small ruminant lentivirus, a type of retrovirus that infects immune cells and persists for life. Once a sheep is infected, the immune system does not clear the virus. That is why infected animals remain carriers even if they look normal for a long time.
Transmission most often happens through colostrum or milk from infected ewes and through close-contact respiratory spread from infected aerosol droplets. Intrauterine spread appears to be less common. Crowding, close confinement, and management systems that increase prolonged contact can make spread within a flock more likely.
Not every infected sheep becomes obviously ill right away. In fact, the incubation period is long, and some sheep may carry the virus for years before clinical signs appear. This delay is one reason the disease can move quietly through a flock before anyone realizes there is a problem.
Genetics may also influence susceptibility. USDA research has identified TMEM154 gene variants associated with higher or lower risk of infection, so some breeding programs use genetic selection as one part of long-term flock control. That said, genetics do not replace testing and biosecurity.
How Is Maedi-Visna in Sheep Diagnosed?
Diagnosis starts with the history, age of the sheep, and pattern in the flock. Your vet will consider maedi-visna when adult sheep have chronic weight loss, progressive breathing difficulty, reduced productivity, or occasional neurologic signs. Because several other diseases can look similar, testing matters.
In live sheep, the most common screening tools are blood tests such as ELISA or AGID. ELISA is widely used for flock screening, and some U.S. veterinary diagnostic laboratories list OPP/maedi-visna ELISA fees around $6-$10 per sample. PCR may also be used in some situations, but it is usually less available and more costly, with some labs listing fees around $50 per sample.
Your vet may also recommend additional work to rule out other causes of chronic respiratory disease, such as pulmonary adenocarcinoma, abscesses, caseous lymphadenitis, or bacterial pneumonia. In some sheep, ultrasound or necropsy findings help clarify the diagnosis. Definitive flock understanding often comes from combining serology, clinical signs, and postmortem findings rather than relying on one test alone.
A negative test does not always completely rule out early infection, especially soon after exposure. That is why your vet may suggest repeat testing once or twice yearly in at-risk flocks and careful interpretation of results in the context of the whole flock.
Treatment Options for Maedi-Visna in Sheep
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Physical exam and practical flock history review
- Basic supportive care for body condition, housing comfort, and reduced stress
- Isolation of clinically affected sheep from lambing and nursery groups
- Targeted blood testing of high-risk adults only
- Necropsy of deceased animals when feasible to confirm flock disease pattern
Recommended Standard Treatment
- Veterinary flock consultation and biosecurity plan
- Whole-group or strategic ELISA screening of adult sheep
- Retesting on a scheduled interval, often yearly or every 6 months in active control programs
- Segregation or culling of positive sheep
- Lamb-rearing changes to reduce exposure to infected colostrum, milk, and close-contact spread
Advanced / Critical Care
- Comprehensive flock mapping with repeated whole-flock testing
- PCR or additional diagnostics in selected cases
- Strict segregation groups, closed-flock biosecurity, and replacement strategy redesign
- Artificial rearing or highly controlled lamb management from low-risk lines
- Genetic selection planning, including discussion of TMEM154 susceptibility data where appropriate
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Maedi-Visna in Sheep
Bring these questions to your vet appointment to get the most out of your visit.
- Based on this sheep's age and signs, how likely is maedi-visna compared with other chronic lung diseases?
- Which test do you recommend first in this flock, ELISA, AGID, PCR, or necropsy confirmation?
- If this sheep tests negative today, when should we retest to catch early infection?
- Should we test the whole flock now or start with high-risk adults and close contacts?
- How should we manage lambing, colostrum, and milk exposure if positive ewes are present?
- Which sheep should be separated or culled first to reduce spread most effectively?
- Are there local laboratory options and what total cost range should I expect after farm-call and submission fees?
- Would genetic selection, including TMEM154 testing, make sense in our breeding program?
How to Prevent Maedi-Visna in Sheep
Prevention focuses on keeping the virus out of the flock or reducing spread if it is already present. The most important steps are to test incoming sheep, avoid bringing in animals of unknown status, and work with your vet on a written biosecurity plan. Closed flocks generally have lower risk than flocks that frequently purchase replacements.
If maedi-visna is already in the flock, prevention becomes a control program. That usually means regular serologic testing, separating or removing positive sheep, and reducing lamb exposure to infected dams, especially through colostrum, milk, and close contact. Because sheep may test negative early after infection, repeat testing is often part of the plan.
Management details matter. Avoid unnecessary crowding, keep air quality as good as possible in barns, and maintain clear records for testing, lambing groups, and replacements. These steps do not eliminate the virus on their own, but they can reduce opportunities for spread.
Long-term prevention may also include genetic selection for lower-susceptibility lines, though this should be viewed as one tool rather than a stand-alone fix. Your vet can help you choose a prevention strategy that matches your flock size, breeding goals, and budget.