Ovine pulmonary adenocarcinoma diagnosis and control in practice

Jaagsiekte sheep retrovirus (JSRV) is an oncogenic retrovirus that causes ovine pulmonary adenocarcinoma (OPA). This is a progressive, fatal, bronchiolo-alveolar carcinoma of sheep (Griffiths et al, 2010), caused by virally-induced transformation of secretory epithelial cells of the distal respiratory tract (Ortin et al, 2019). JSRV can be transmitted from sheep with OPA tumours mainly by the respiratory route (Ortin et al, 2019) and in colostrum and milk, transplacental transmission has not been ruled out. There are insufficient data to determine the relative importance of these routes, and they should all be considered when designing plans to control the disease (Ortin et al, 2019).

OPA is generally considered a chronic wasting disease with progressive respiratory distress, and is invariably fatal. Initial clinical signs of the disease include weight loss, a gentle cough and tachypnoea. This progresses to marked elevations in respiratory effort while the animal is at rest; however, the animal's appetite remains good and unless there is a secondary bacterial infection, the sheep remains afebrile (Scott et al, 2013). Over-production of pulmonary epithelial lining fluid (lung fluid) is a common sign of OPA. Fluid gathers within the respiratory tract and first appears as a scant serous nasal discharge, and during the advanced stages of clinical disease may flow freely from both nostrils when the head is lowered during feeding. This quantity may exceed 50 ml if the hindquarters are raised when the head is simultaneously lowered (colloquially referred to as the ‘wheelbarrow test’, although a negative test does not rule out the disease). OPA lesions may predispose to secondary bacterial pneumonia causing sudden death despite antibiotic treatment.