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Antigenicity
- The virus cannot be grown in culture, although it can be seen by EM on tumor cells of infected sheep
Pathogenesis
- Causes a proliferation of alveolar lining cells, producing massive amounts of fluid
- Proliferative foci project into alveoli and bronchi and from slow-growing tumors
- Death occurs between 3-4 years of age
Clinical signs:
- Low exercise tolerance
- Gradual weight loss
- Dyspnoea
- Coughing
- Nasal fluid discharges during wheelbarrow test
- Secondary bacterial infection by Pasteurella hemolytica often precipitates death
- PM reveals fawn-gray tumor (for more see here)
Epidemiology
- Found in 25% of pneumonia cases in Scotland
- Absent in USA, common in UK
Diagnosis
- Electron microscopy on lung biopsy
Control
- Cull clinically affected animals
- Also called pulmonary carcinomatosis
- Infectious bronchiolar-alveolar carcinoma caused by a retrovirus
- Commonest under intensive management systems which favour aerosol transmission and close contact of disease
- Behaves like chronic pneumonia
- Takes months to years to express itself clinically as coughing and exercise intolerance
- Gross pathology:
- Heavy lungs which fail to collapse
- The lesions progress from small firm grey/white nodular lesions to extensive confluent areas with replacement by neoplastic tissue
- Cut surface oozes fluid
- There is often coexistent infection present
- Occasional metastases to bronchial and mediastinal lymph nodes can occur
- Histopathology:
- Widespread proliferation of alveolar (Type 2) and terminal bronchiolar epithelium, lining the alveoli and lower airways
- Multiple neoplastic foci of cuboidal/columnar cells forming papillary projections into the lumen
- Metastases of the same in the bronchial and mediastinal lymph nodes
- There is no serological test, and diagnosis depends upon raising the animal by the hind limbs whereupon a clear fluid issues from the nose = "Wheelbarrow test"
- More information