Ovine Pulmonary Adenocarcinoma in Sheep: Jaagsiekte Signs and Management

Ovine pulmonary adenocarcinoma, often shortened to OPA, is a contagious lung tumor of sheep caused by jaagsiekte sheep retrovirus (JSRV). You may also hear it called jaagsiekte, ovine pulmonary adenomatosis, or ovine pulmonary carcinoma. The disease mainly affects sheep, though rare cases have been reported in goats and mouflon.

OPA is unusual because it is both infectious and cancerous. The virus infects lung cells and, over time, can trigger tumor growth in the lungs. Many sheep are infected long before they look sick, so the disease can move quietly through a flock before obvious cases appear.

Clinical signs usually become noticeable in adult sheep, often around 2 to 4 years of age, although younger animals can be affected. As tumors enlarge, normal lung tissue is replaced, making breathing harder and reducing body condition. In advanced cases, affected sheep may decline over weeks to months.

For pet parents and flock managers, the hardest part is that OPA often looks like other chronic respiratory problems at first. That is why early veterinary evaluation matters, especially when one or more sheep show unexplained weight loss and progressive breathing changes.

OPA is caused by jaagsiekte sheep retrovirus (JSRV), a betaretrovirus that spreads mainly through respiratory secretions. Sheep inhale infectious droplets or aerosols from affected flockmates, including some animals that are infected but not yet showing obvious signs.

The virus can also be passed in colostrum and milk, which helps explain why lambs may become infected early in life. Young sheep appear particularly susceptible. Once infected, a sheep may remain subclinical for months or longer before tumors become large enough to affect breathing.

Close housing, repeated nose-to-nose contact, and keeping infected and uninfected animals together can increase transmission risk. Because the incubation period is long, flock managers may not realize the disease is present until several animals are already infected.

This is not a condition caused by feed, weather, or routine stress alone. Those factors can worsen breathing or make secondary infections more likely, but the underlying cause of OPA is viral infection with JSRV.

Diagnosis usually starts with history and physical exam. Your vet will look at age, flock pattern, weight loss, breathing effort, and whether fever is present. Because OPA can mimic chronic pneumonia and other lung diseases, diagnosis often requires more than listening to the chest.

Transthoracic ultrasound is one of the most useful live-animal tools. It can help identify superficial lung lesions and support a diagnosis of OPA, including lesions as small as 1 to 2 cm near the lung surface. Ultrasound is especially helpful for sorting likely OPA cases from other chronic respiratory problems in adult sheep.

Definitive confirmation often relies on necropsy and histopathology of affected lung tissue. PCR testing for JSRV may be used on tumor tissue, bronchoalveolar samples, lymphoid tissue, or blood in some settings, but it is not perfect for every individual animal. There is no reliable serologic blood test because infected sheep do not develop a useful antibody response for routine diagnosis.

In flock situations, your vet may recommend a combination approach: identify clinical suspects, scan high-risk animals, submit tissues from culled or dead sheep, and then build a flock management plan from those results. That approach is often more practical than trying to rely on one test alone.

Prevention focuses on keeping JSRV out of the flock or reducing spread if it is already present. The most important steps are buying replacements carefully, avoiding introduction of animals from flocks with chronic unexplained respiratory disease, and quarantining new arrivals. Because infected sheep may look normal for a long time, source flock history matters.

If OPA is suspected or confirmed, work with your vet on a flock plan that may include regular inspection of adults, ultrasound screening of suspects, and prompt culling of affected sheep. In some programs, offspring of affected ewes are also managed separately because early-life transmission can occur.

Lamb management can matter. JSRV has been detected in colostrum and milk, so some higher-control programs use uninfected colostrum sources, milk replacer, or separate rearing strategies for lambs from high-risk ewes. Those steps are more labor intensive, but they may fit valuable breeding flocks.

There is no vaccine and no treatment that clears infection. Good ventilation, lower stocking density, and reducing close contact can support respiratory health, but they do not replace testing, surveillance, and removal of suspect animals when OPA is in the flock.