Jaagsiekte Sheep Retrovirus - Pathogenesis

Pathogenesis

JSRV is transmitted by the respiratory route and may also infect lymphocytes and myeloid cells, in addition to the lung epithelia. Expression of the JSRV Envelope protein activates signalling cascades that promote cellular proliferation and malignant transformation of the cells. Initially, the tumour cells grow along the alveolar walls in a pattern reminiscent of human BAC, but subsequently become more invasive and metastasize to the local lymphnodes. Larger tumours maybe necrotic and fibromatous at their centre.As the tumour grows, fluid production in the lung increases and this is likely to promote virus spread to other sheep. Only when the tumour reaches a size large enough to compromise lung function, do clinical signs appear. Critically,the majority of infected animals in endemic areas never show outward signs of infection, but they may be shedding virus, thus promoting inadvertent introduction of the disease into previously unaffected flocks and new geographical areas.