Ovine Progressive Pneumonia in Sheep: Symptoms, Testing and Control

Quick Answer
  • Ovine progressive pneumonia, or OPP, is a chronic viral disease of sheep caused by a small ruminant lentivirus.
  • Most sheep do not show signs until adulthood, often after 2 years of age, and many are over 4 years old when breathing trouble and weight loss become obvious.
  • Common signs include gradual weight loss, exercise intolerance, faster breathing, poor thrift, and sometimes secondary bacterial pneumonia.
  • There is no practical curative treatment or vaccine. Flock control usually focuses on blood testing, biosecurity, and removing or separating positive animals based on your vet's plan.
  • Typical U.S. testing costs are about $7-$11 per sheep for ELISA blood testing, with PCR often around $50-$52 per sample, plus farm call, exam, and shipping or lab fees.
Estimated cost: $7–$52

What Is Ovine Progressive Pneumonia in Sheep?

Ovine progressive pneumonia, often called OPP or maedi-visna, is a long-term viral disease of sheep caused by a small ruminant lentivirus. It most often affects the lungs, where it causes a slowly worsening interstitial pneumonia. Some sheep can also develop wasting, reduced production, or less common nervous system signs.

A challenging part of OPP is that infected sheep may look normal for months or years. Clinical disease is uncommon in sheep under 2 years old, and obvious signs are seen more often in mature animals. By the time a sheep is breathing harder or losing condition, the infection has usually been present for a long time.

There is no practical cure and no vaccine currently available. That does not mean there are no options. Your vet can help you choose a flock plan that fits your goals, whether that means confirming infection, limiting spread, improving comfort for affected sheep, or building a longer-term control program.

Symptoms of Ovine Progressive Pneumonia in Sheep

  • Gradual weight loss or poor body condition
  • Progressively faster or harder breathing, especially with handling or exercise
  • Exercise intolerance or lagging behind the flock
  • Chronic unthriftiness or reduced productivity
  • Chronic cough or abnormal lung sounds
  • Fever or obvious nasal discharge when a secondary bacterial pneumonia is also present
  • Arthritis or stiffness in some infected sheep
  • Neurologic signs such as head tilt, circling, weakness, or paralysis in rare visna cases

Many sheep with OPP look normal early on, so a flock can carry infection before anyone notices a problem. Worry more when an adult sheep has slow, unexplained weight loss plus increasing breathing effort, or when several mature sheep seem less thrifty over time. See your vet promptly if a sheep is open-mouth breathing, cannot keep up with the flock, has neurologic signs, or seems to have a secondary pneumonia.

What Causes Ovine Progressive Pneumonia in Sheep?

OPP is caused by a lentivirus in the retrovirus family. In sheep and goats, these viruses are grouped under the term small ruminant lentiviruses, or SRLVs. Once a sheep is infected, the virus can persist for life because it hides within immune cells and is not cleared well by the body.

Transmission happens mainly through infected colostrum or milk and through respiratory secretions or aerosol spread during close contact. Crowding, frequent mixing of animals, and bringing in untested replacements can make flock spread more likely. Cross-species transmission between sheep and goats can also occur.

Not every infected sheep becomes obviously sick right away. Some remain carriers for long periods, which is why OPP can move quietly through a flock. That is also why prevention focuses so heavily on testing, quarantine, and careful sourcing of new animals.

How Is Ovine Progressive Pneumonia in Sheep Diagnosed?

Your vet usually starts with the flock history, age of affected sheep, body condition trends, and breathing signs. OPP can look like other chronic sheep lung problems, including ovine pulmonary adenocarcinoma, abscesses, caseous lymphadenitis involving the chest, parasitic disease, or chronic bacterial pneumonia. Because of that, diagnosis should not rely on signs alone.

The most common live-animal tests are blood-based serology, especially ELISA and sometimes AGID. ELISA is widely used for flock screening because it is sensitive and practical. A recently infected sheep can still test negative early on, so your vet may recommend repeat testing over time, especially after exposure or when building a control program.

In some cases, your vet may also use PCR to look for viral genetic material, especially when clarifying uncertain cases. Ultrasound can help rule out other chest diseases in live sheep, and necropsy with histopathology may be the clearest way to confirm the cause in a sheep that dies or is euthanized. For many flocks, the most useful answer comes from combining clinical findings, lab testing, and a practical flock-level plan.

Treatment Options for Ovine Progressive Pneumonia in Sheep

Spectrum of Care means you have options. Here are treatment tiers at different price points.

Budget-Conscious Care

$0–$75
Best for: Small flocks, limited budgets, or situations where the goal is comfort and practical risk reduction rather than rapid flock eradication.
  • Isolation from the main flock if respiratory signs are present
  • Supportive care such as easy access to feed, water, shelter, and reduced handling stress
  • Monitoring body condition, breathing effort, and flock mates for similar signs
  • Targeted testing of the sick sheep or highest-risk group instead of whole-flock screening
  • Cull planning for sheep with poor thrift or worsening respiratory disease
Expected outcome: Clinical OPP is progressive. Supportive care may improve comfort for a time, but infected sheep usually do not recover fully.
Consider: Lowest immediate cost, but infection can remain in the flock and spread silently. This approach may not protect long-term flock status.
Most Common

Recommended Standard Treatment

$7–$11
Best for: Most flocks trying to control spread, reduce losses, and make decisions based on evidence rather than guesswork.
  • Veterinary exam and flock risk assessment
  • Serologic screening with ELISA, with repeat testing once or twice yearly when indicated
  • Testing all new additions before entry and quarantining them for at least 3 weeks
  • Removal, segregation, or strategic culling of positive animals based on flock goals
  • Biosecurity changes such as maintaining a closed flock and avoiding pooled colostrum from unknown-status animals
Expected outcome: Good for improving flock control over time when testing and biosecurity are followed consistently. Individual infected sheep still carry a guarded to poor long-term outlook.
Consider: Requires repeat testing, recordkeeping, and management discipline. Up-front costs are higher than supportive care alone.

Advanced / Critical Care

$50–$52
Best for: Seedstock flocks, higher-value breeding programs, mixed sheep-goat operations, or flocks pursuing tighter disease control.
  • PCR testing for selected animals when serology and clinical findings do not fully match
  • Ultrasound or additional diagnostics to separate OPP from lung tumors, abscesses, or other chronic chest disease
  • Necropsy and histopathology on losses to confirm the flock diagnosis
  • Aggressive flock restructuring with separate positive and negative groups or replacement from low-risk sources
  • Use of heat-treated or negative-source colostrum and milk replacer in selected control programs
Expected outcome: Best chance of improving flock-level disease status, but it still does not cure infected sheep.
Consider: More labor, more testing, and more management complexity. It can be worthwhile for some flocks, but it is not necessary for every situation.

Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.

Questions to Ask Your Vet About Ovine Progressive Pneumonia in Sheep

Bring these questions to your vet appointment to get the most out of your visit.

  1. Do this sheep's signs fit OPP, or do we need to rule out lung tumors, abscesses, parasites, or chronic bacterial pneumonia?
  2. Which test makes the most sense for my flock right now: ELISA, AGID, PCR, or necropsy on a loss?
  3. If this sheep tests negative today, when should we retest to catch a recent infection?
  4. Should we test the whole flock, only adults, or only high-risk groups first?
  5. Is culling, segregation, or monitoring the best fit for my flock goals and budget?
  6. How should I quarantine and test new sheep before they join the flock?
  7. Do I need to change how I handle colostrum, milk feeding, or lamb rearing in this flock?
  8. What biosecurity steps will give me the biggest reduction in spread for the cost?

How to Prevent Ovine Progressive Pneumonia in Sheep

Prevention starts with not bringing the virus onto the farm. The most practical steps are to maintain a closed flock when possible, buy replacements only from lower-risk sources, and test new animals before entry. Quarantine new arrivals away from the main flock for at least a few weeks while results are pending and while your vet reviews the risk.

Because OPP can spread through colostrum, milk, and close contact, lambing and nursery management matter. Some flocks use colostrum only from test-negative ewes, heat-treated colostrum, or milk replacer as part of a control plan. Your vet can help decide whether that level of management is worthwhile for your operation.

There is no vaccine, so prevention depends on testing and biosecurity. Many flocks benefit from repeat whole-flock or targeted testing over time, especially before breeding or lambing seasons. Clean equipment, avoid unnecessary mixing with outside sheep or goats, and keep good records so positive animals and their offspring can be tracked clearly.

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