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Jaagsiekte (Ovine Pulmonary adenmatosis)

Disease Name: Jaagsiekte (Ovine Pulmonary adenmatosis)

Introduction: This is a slowly progressing disease of adult sheep. It is caused by the Jaagsiekte sheep retro virus. Also know as ovine pulmonary adenocarcinoma virus. Jaagsiekte is an Afrikaaner word meaning panting sheep. With the exception of Australasia this disease has a wide geographical spread. The disease can occur, albeit rarely, in goats. It is spread via the respiratory route. Close contact facilitates the spread of the disease. The incidence of the disease is much higher in housed stock. Breed of sheep can also be a factor. Animals can be infected from a period of months up to two years before they display any clinical signs. While it has been seen in younger sheep, most affected sheep tend to be three to four years of age and in poor body condition 

Clinical signs: Signs are very similar to chronic pneumonia.

  • Poor body condition
  • Difficulty breathing
  • Exercise intolerance
  • Open mouth breathing
  • Moist rales can be heard from the sheep
  • Sudden death from bacterial pneumonia

Added 12.10.2017

Diagnosis: There are no commercially available serology or pcr test kits. This makes diagnosis difficult and expensive. CT scans are effective; however the cost is prohibitive for commercial sheep. Ultrasound has produced some good results but it is still not considered to be wholly reliable. There has been some success with testing the products of a lung wash and the wheelbarrow test, if positive, is a pathopneumonic symptom, however not all animals will give a positive wheel barrow test. Post mortem and histopthological examination are still the only way to fully diagnose the disease.

Added 12.10.2017

Treatment/control: Purchase of OPA-infected but clinically normal breeding replacement stock (both ewes and rams) is the major risk factor for introducing OPA into clean flocks.  Ideally, breeding replacements would be obtained from flocks declared free of OPA but confirmation of such status in the absence of commercially available tests is not possible. Best practice is to identify and cull out sheep with any sign of the disease as early as possible. Some flocks impose a harsh policy to try to reduce the incidence of OPA where they cull thin, tachypnoeic or coughing sheep.  Culling out on the basis of weight loss and respiratory signs inevitably means that a proportion of the sheep culled will not in fact have OPA.

Ultrasound screening would allow more accurate selection. In addition, detection of OPA lesions by ultrasound examination should allow culling at an earlier stage than recognition of clinical signs by the farmer, and would permit culling while the sheep is still in good body condition, is fit to travel and has greater value for slaughter.  In addition, the ability to identify affected animals at an earlier stage will be a positive step forward in reducing transmission of JSRV.  Tumour cells produce the virus and release it into the respiratory secretions, so sheep with larger tumours are likely to be a greater risk for transmission to other sheep.

Prevention of spread from neighbouring premises can be effected by maintaining a closed disease-free flock with double ring fencing around the perimeter of the farm.

Added 12.10.2017

Bio containment - the main route of infection is by respiratory aerosol with close confinement during housing or trough feeding increasing the rate of spread of infection therefore housing must only be undertaken if essential for flock management purposes. Maintaining sheep in single age groups has been shown to be the most important management factor in reducing clinical disease.

Useful links:

http://www.nadis.org.uk/bulletins/ovine-pulmonary-adenocarcinoma-(opa).aspx

https://www.msdvetmanual.com/respiratory-system/respiratory-diseases-of-sheep-and-goats/ovine-pulmonary-adenocarcinoma

http://www.merckvetmanual.com/respiratory-system/respiratory-diseases-of-sheep-and-goats/overview-of-respiratory-diseases-of-sheep-and-goats