Ultrasound image abnormalities associated with the development of ovine pulmonary adenocarcinoma

Ovine pulmonary adenocarcinoma (OPA), caused by Jaagsiekte sheep retrovirus (JSRV), is a contagious neoplastic pulmonary disease of sheep. Early OPA diagnosis is challenging as the disease can remain subclinical until advanced disease. Lung ultrasound offers the potential of identifying OPA lesions as small as 1-2 cm in diameter involving the visceral pleural surface. Although the procedure lends itself to screening large commercial flocks, further research is needed to investigate whether commonly used ultrasound features can be used to diagnose and stage OPA disease, potentially before gross lung tumours develop. Using our JSRV experimental model we adopted a semiquantitative approach to grade, at monthly intervals up to 9 months post-JSRV infection, the incidence and progression of B lines, white lung, and irregular pleural lines. Results were compared against non-infected control sheep. While the presence of irregular pleural lines was inconsistent following JSRV infection, white lung developed only in the lung instilled with JSRV, whereas B lines developed in both lungs. These features occurred both in sheep which developed gross tumours, and also in those which did not develop gross tumours. Changes in B lines and white lung ultrasound features in lungs that had no evidence of gross lung tumour development may reflect structural and/or functionally dynamic aspects of the underlying pathophysiology. Future assessment of the direct association between histopathological characteristics and ultrasound image features will provide a foundation to investigate the practical utility of this knowledge, particularly in the context of screening flocks as a means to control this disease.