Ovine Pulmonary Adenocarcinoma (OPA), also known as Jaagsiekte, is a contagious and often fatal lung cancer that affects sheep. It is caused by a retrovirus called the Jaagsiekte sheep retrovirus (JSRV), which leads to the development of tumours in the lungs.
Last weekend I came across a ewe that was lagging behind the flock, and peeled off towards the nearest boundary fence when approached. When I caught her, she was also quite lean.
Alarm bells time – what is wrong with this ewe? She appeared to have symptoms consistent with pneumonia – heavy breathing and a slightly snotty nose – so I treated her for such with antibiotic and anti-inflammatory, but I suspected a condition I have seen before known as OPA or Jaagsiekte disease.
The next day she was dead, and post-mortem examination confirmed my suspicions.
So, what is OPA?
Key aspects of OPA (Ovine Pulmonary Adenocarcinoma) include:
- Transmission:
- OPA is transmitted primarily through respiratory secretions such as saliva and nasal discharge. It can also spread through contaminated equipment or by direct contact with infected sheep, and is often passed from mother to lamb via mucus, nasal secretions, or colostrum.
- Clinical Signs:
- Progressive respiratory distress: Affected sheep often show signs of laboured breathing and coughing.
- Lagging behind the flock when gathered, moved or handled.
- Fluid accumulation in the lungs: One of the hallmark signs is a buildup of fluid in the lungs, which can sometimes be detected by a characteristic “cribbing” or fluid sound during coughing.
- Weight loss: Even though sheep may appear to eat normally, they often lose weight as the disease progresses.
- Excessive mucus production: Sheep with OPA may produce a thick nasal discharge. The ‘wheelbarrow test’ – holding the ewe up at the rear and letting her head hang down – may result in a significant amount of fluid draining from her lungs.
- Diagnosis:
- Diagnosis is typically confirmed through clinical signs, post-mortem examination, and laboratory tests. Histopathological examination of lung tissue often reveals adenocarcinoma (lung cancer).
- PCR testing can identify the presence of the Jaagsiekte sheep retrovirus (JSRV).
- Management and Control:
- There is no cure for OPA. Management focuses on controlling the spread and maintaining herd health.
- Infected animals are often culled to prevent further spread of the virus.
- Biosecurity measures, such as isolating infected animals and disinfecting equipment, are critical.
- It is important to test and screen sheep for the virus, especially in high-risk herds.
- Impact on Production:
- OPA can lead to significant losses in sheep farming due to both the mortality rate and the reduced productivity of affected animals.
What are we going to do about it on this farm?
This is the third confirmed case, so suggests the flock does have an issue. After weaning time and before the ewes go to the tup again next autumn, the whole breeding flock, including rams, will be ultrasound scanned by an experienced vet and any affected animals removed from the flock and not used for breeding again.
Going forwards, there needs to be a policy of only sourcing breeding replacements from farms that have a screening and monitoring programme, and consideration should be given to ‘closing the flock, i.e. not buying-in sheep from elsewhere other than health-tested rams.
It is also worth considering a better tagging and recording system so that no home-bred female lambs from OPA-affected mothers are retained for breeding, and aiming for a more extensive system so that the sheep are not kept in such close proximity to one-another.