Maedi-Visna in Sheep: Chronic Viral Disease of the Lungs and Nervous System
- Maedi-visna, also called ovine progressive pneumonia or OPP in the US, is a lifelong lentiviral infection of sheep that most often causes slowly worsening breathing trouble and weight loss.
- Some sheep also develop hard udders with poor milk production, exercise intolerance, or less commonly neurologic signs such as weakness and incoordination.
- There is no curative antiviral treatment or vaccine. Management focuses on testing, separating or removing positive sheep, supportive flock care, and preventing spread to lambs.
- See your vet promptly if a sheep has chronic cough, labored breathing, progressive weight loss, poor thrift, or neurologic changes, especially in an adult animal.
What Is Maedi-Visna in Sheep?
Maedi-visna is a chronic viral disease of sheep caused by a small ruminant lentivirus. In the United States, your vet may call it ovine progressive pneumonia (OPP). The virus causes lifelong infection and tends to progress slowly over months to years rather than causing sudden illness.
The classic form affects the lungs, leading to a gradual, nonresponsive pneumonia with increasing effort to breathe and loss of body condition. Some sheep also develop inflammation in the udder, joints, or nervous system. The neurologic form is less common, but it can cause weakness, incoordination, and wasting.
Many infected sheep look normal for a long time. That makes flock control challenging. A sheep can carry and spread the virus before obvious signs appear, so testing and flock-level planning with your vet are central parts of care.
Symptoms of Maedi-Visna in Sheep
- Progressive weight loss or poor body condition
- Exercise intolerance
- Chronic increased breathing effort
- Chronic cough
- Hard udder with reduced milk production
- Poor thrift in adult sheep
- Weakness, incoordination, or hindlimb deficits
- Secondary bacterial pneumonia signs
Maedi-visna usually causes a slow, progressive illness rather than a sudden crash. Chronic weight loss, reduced stamina, and gradually worsening breathing in an adult sheep are common red flags. Because many other diseases can look similar, your vet will need to sort out viral pneumonia from lungworms, bacterial pneumonia, ovine pulmonary adenocarcinoma, and other causes.
See your vet immediately if breathing becomes labored at rest, the sheep stops eating, cannot keep up with the flock, or shows neurologic signs like stumbling, weakness, or trouble rising. Those signs need prompt veterinary attention even if maedi-visna is only one possibility.
What Causes Maedi-Visna in Sheep?
Maedi-visna is caused by a lentivirus in the Retroviridae family. Once a sheep is infected, the infection is considered lifelong. The virus targets cells involved in the immune system and can lead to chronic inflammation in the lungs, mammary gland, joints, and central nervous system.
Transmission most often happens through infected colostrum or milk and through respiratory secretions or aerosol spread during close contact. Crowding, prolonged indoor housing, and keeping infected and uninfected sheep together can increase the chance of spread. Because infected sheep may appear healthy for long periods, the virus can move quietly through a flock.
This is not a disease caused by poor care. It is a contagious flock health problem that often requires long-term management decisions. Your vet can help you build a plan that fits your goals, whether that means surveillance in a commercial flock, protecting replacement lambs, or working toward a lower-prevalence or test-negative flock.
How Is Maedi-Visna in Sheep Diagnosed?
Diagnosis starts with history and exam findings. Your vet will look at age, body condition, breathing pattern, milk production, flock history, and whether signs are chronic and progressive. Because several sheep diseases can mimic OPP, diagnosis usually combines clinical suspicion with laboratory testing.
The most common flock-level tests are serologic antibody tests, especially ELISA-based screening. Positive results support exposure or infection, but timing matters because recently infected sheep may test negative early on. In some cases, your vet may recommend repeat testing, PCR on selected samples, or postmortem examination of lung tissue to confirm the diagnosis and rule out look-alike conditions.
Chest imaging is not routine in most field sheep cases, but necropsy and histopathology can be very helpful when a diagnosis is uncertain. Your vet may also recommend fecal testing for lungworms, bacterial workup, or other flock disease testing depending on the signs present. A flock diagnosis is often more useful than focusing on one sheep alone.
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
- Veterinary exam or herd-health consultation focused on quality of life and likely differentials
- Isolation from lambing groups and high-contact areas if feasible
- Body condition support with easy feed access, low-stress handling, and monitoring
- Culling or humane euthanasia planning for sheep with progressive disease
- Targeted testing of the sick sheep or a small number of flockmates when budget is limited
Recommended Standard Treatment
- Veterinary-confirmed diagnosis plan with serologic testing such as OPP ELISA
- Testing of exposed flockmates and identification of positive animals
- Segregation or removal of positive sheep based on flock goals
- Lamb management to reduce transmission, including preventing nursing from positive ewes when advised by your vet
- Review of ventilation, stocking density, replacement purchases, and biosecurity
Advanced / Critical Care
- Expanded diagnostics such as PCR, necropsy with histopathology, or broader respiratory disease workup
- Whole-flock test-and-cull or aggressive test-and-segregate program
- Artificial rearing or supervised lamb-rearing strategies for high-value genetics under veterinary guidance
- Intensive supportive care for valuable individuals with secondary complications
- Detailed biosecurity redesign for closed-flock management and monitored replacements
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 signs, how likely is OPP compared with lungworms, bacterial pneumonia, or ovine pulmonary adenocarcinoma?
- Which test do you recommend first for my flock, and when should we repeat testing if results are negative but suspicion remains?
- Should we test the whole flock, only adults, or only close contacts right now?
- What is the best plan for lambs born to positive or suspect ewes on this farm?
- Would segregation be enough for our goals, or do you recommend removing positive sheep?
- What signs tell us a sheep's quality of life is declining and euthanasia should be discussed?
- How should we handle new purchases, quarantine, and pre-purchase testing to protect the flock?
- What other diseases should we rule out in sheep with chronic weight loss or breathing trouble?
How to Prevent Maedi-Visna in Sheep
Prevention is centered on biosecurity and flock testing, because there is no vaccine and no treatment that clears infection. The most effective programs use regular serologic screening, careful records, and either removal of positive sheep or strict separation from test-negative animals. Your vet can help you choose a realistic schedule based on flock size and goals.
Protecting lambs is especially important. Because transmission can occur through colostrum and milk, many control programs focus on preventing lambs from nursing infected ewes and raising replacements from lower-risk or test-negative dams when possible. Close-contact respiratory spread also matters, so reducing crowding and improving ventilation can help lower transmission pressure.
Buy replacements carefully. Ask for flock health history and recent OPP testing before bringing in new sheep, then quarantine and retest as your vet recommends. Closed-flock management, testing before shows or breeding introductions, and avoiding commingling with unknown-status sheep can all reduce risk over time.
Even with good prevention, flock cleanup is usually a long-term project rather than a one-season fix. A steady, practical plan with your vet is often more successful than trying to change everything at once.