Ovine Pulmonary Adenocarcinoma in Sheep: Lung Cancer Signs and Diagnosis
- Ovine pulmonary adenocarcinoma (OPA), also called jaagsiekte or sheep pulmonary adenomatosis, is a contagious lung cancer caused by jaagsiekte sheep retrovirus (JSRV).
- Most sheep with clinical disease are adults, often 2-4 years old, and common signs include weight loss, faster or harder breathing, exercise intolerance, and a watery nasal discharge from tumor fluid in the lungs.
- There is no curative treatment or vaccine. Your vet usually focuses on confirming the diagnosis, separating or removing affected sheep, and protecting the rest of the flock.
- On-farm diagnostic workups often involve a farm call, physical exam, and lung ultrasound. In the U.S., a practical diagnostic cost range is often about $200-$600 per sheep, while necropsy and lab confirmation may add roughly $150-$400 depending on transport, disposal, and lab fees.
What Is Ovine Pulmonary Adenocarcinoma in Sheep?
Ovine pulmonary adenocarcinoma, or OPA, is a contagious viral lung cancer of sheep. It is caused by jaagsiekte sheep retrovirus (JSRV), a retrovirus that infects lung cells and can trigger tumor growth over time. The disease is also called jaagsiekte or sheep pulmonary adenomatosis.
OPA usually develops slowly. Many sheep look normal for months or even years after infection, then begin to show progressive weight loss and breathing trouble as tumors and fluid build up in the lungs. Clinical cases are most often seen in sheep older than 2 years, although younger sheep can be affected, especially if exposed early in life.
This condition matters because it is both fatal for the affected sheep and important for flock health. There is no vaccine and no proven curative treatment. That means early recognition, veterinary evaluation, and flock-level management are the main tools pet parents and producers can use.
Symptoms of Ovine Pulmonary Adenocarcinoma in Sheep
- Progressive weight loss despite a normal or fair appetite
- Faster breathing or increased effort to breathe
- Exercise intolerance or falling behind the flock
- Panting or open-mouth breathing in advanced cases
- Watery or frothy nasal discharge, especially when the head is lowered or hindquarters are lifted
- Crackles or abnormal lung sounds heard by your vet
- Chronic poor thrift without fever
- Sudden worsening if secondary bacterial pneumonia develops
OPA often starts quietly. Early signs can look like other chronic lung problems, so a sheep may only seem thin, less active, or short of breath during handling. A copious watery nasal discharge caused by fluid from the tumor-affected lungs is one of the more suggestive findings, but it is not present in every case.
You should be more concerned when breathing effort is increasing, the sheep is losing condition over time, or there is nasal fluid without fever in an adult sheep. If your sheep is open-mouth breathing, collapsing, or rapidly worsening, see your vet immediately.
What Causes Ovine Pulmonary Adenocarcinoma in Sheep?
OPA is caused by jaagsiekte sheep retrovirus (JSRV). This virus is mainly spread in respiratory secretions, so sheep can become infected by inhaling droplets and fluid from affected flockmates. Research and veterinary references also support transmission through colostrum and milk, which helps explain why some lambs are infected early in life.
One challenge is that infected sheep may look healthy for a long time. During that silent period, they can still contribute to spread within the flock. Not every infected sheep develops obvious tumors during its commercial lifespan, but subclinically infected animals can act as a reservoir.
OPA is not caused by feed, dust, or a simple bacterial pneumonia, although those problems can complicate the picture. Secondary bacterial infection may make a sheep look temporarily different or more acutely ill, but the underlying cancer process is driven by the virus.
How Is Ovine Pulmonary Adenocarcinoma in Sheep Diagnosed?
Your vet usually starts with the history and physical exam. A sheep with chronic weight loss, increased breathing effort, crackly lung sounds, and watery nasal discharge without fever raises concern for OPA. Some veterinarians may also use the traditional "wheelbarrow test" to see whether fluid runs from the nostrils when the hindquarters are lifted, although this is only supportive and not a stand-alone diagnosis.
For live animals, transthoracic lung ultrasound is one of the most practical and useful tools. It can help identify superficial lung lesions and distinguish OPA from some other chronic respiratory problems. In field conditions, ultrasound is often the best next step when OPA is suspected.
Definitive confirmation is often made after death through necropsy and histopathology, sometimes with PCR or immunohistochemistry on lung tissue. Blood PCR and other live-animal tests have limited usefulness because infected cells may be scarce, especially early on, and serology is not reliable because infected sheep usually do not develop detectable antibody titers. That is why flock history, clinical signs, ultrasound findings, and postmortem testing are so important together.
Treatment Options for Ovine Pulmonary Adenocarcinoma in Sheep
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Veterinary exam to assess breathing status and likely diagnosis
- Immediate separation from the flock if feasible
- Humane culling or euthanasia discussion for clinically affected sheep
- Basic flock review to identify other thin or respiratory sheep
Recommended Standard Treatment
- Farm call and full physical exam by your vet
- Transthoracic lung ultrasound to support diagnosis
- Targeted supportive care only if secondary bacterial infection is suspected
- Prompt culling of confirmed or highly suspicious cases
- Necropsy and histopathology/PCR on selected animals to confirm flock diagnosis
- Biosecurity review for purchased replacements and age-group management
Advanced / Critical Care
- Repeated ultrasound screening of at-risk groups
- Multiple necropsies and laboratory confirmation to map flock impact
- Consultation on segregation, closed-flock strategies, and lamb-rearing changes
- Removal of offspring from infected ewes at birth with colostrum substitute or cow colostrum and milk replacer in selected high-value programs
- Embryo transfer or other genetic-preservation planning for valuable lines in heavily affected flocks
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Ovine Pulmonary Adenocarcinoma in Sheep
Bring these questions to your vet appointment to get the most out of your visit.
- You can ask your vet whether my sheep's signs fit OPA or whether pneumonia, parasites, or another chronic lung disease is more likely.
- You can ask your vet whether a lung ultrasound can be done on-farm and what findings would make OPA more or less likely.
- You can ask your vet whether this sheep should be isolated right away while we sort out the diagnosis.
- You can ask your vet whether euthanasia or culling is the kindest option based on this sheep's breathing effort and body condition.
- You can ask your vet whether a necropsy would help confirm the diagnosis and guide decisions for the rest of the flock.
- You can ask your vet how to manage flockmates that look normal but may have been exposed.
- You can ask your vet whether replacements should come only from flocks with no known history of OPA.
- You can ask your vet whether single-age grouping or removing lambs from infected ewes makes sense for my operation.
How to Prevent Ovine Pulmonary Adenocarcinoma in Sheep
Prevention focuses on biosecurity and flock management, because there is no vaccine and no reliable screening test that can find every infected sheep before signs appear. The safest approach is to avoid bringing in sheep from flocks with a known history of OPA. Even then, risk is not zero because the incubation period can be long and some infected sheep look healthy.
If OPA is diagnosed or strongly suspected, work with your vet on a flock plan. This often includes prompt removal of clinically affected sheep, careful observation of flockmates, and keeping sheep in single-age groups when possible to reduce transmission pressure. In some high-value programs, removing lambs from infected ewes at birth and rearing them separately with colostrum substitutes or cow colostrum and milk replacer has been used as a control strategy.
Good hygiene and routine infection-control practices matter, but they cannot replace flock-level management. Because subclinical carriers are the hardest part of this disease, prevention is really about reducing introductions, limiting close exposure, and making long-term decisions with your vet that fit your flock's goals and budget.