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Jaagsiekte sheep retrovirus (JSRV) causes ovine pulmonary adenocarcinoma (OPA or Jaagsiekte), a disease of increasing concern to sheep farmers. It is an infectious lung cancer caused by viral transformation of type II pneumocytes and Clara cells primarily affecting sheep but goats also (reviewed by Griffiths and others 2010). Generally, older sheep that are clinically affected but lambs less than a year old can show clinical signs. OPA is invariably fatal but the clinical course is highly variable lasting days to weeks. Naive flocks may incur losses of 20–25 per cent to OPA upon initial infection with subsequent annual losses of 1–5 per cent. Affected animals become emaciated, dyspnoeic upon exercise and copious amounts of fluid, which contains large amounts of infectious JSRV (Cousens and others 2009), may drain from the nostrils when the head is lowered. However, many OPA cases fail to produce fluid, and dyspnoeic sheep in poor condition have an extensive differential diagnosis. Preclinical OPA is undetectable by veterinary clinical examination and clinical cases are frequently difficult to diagnose (Cousens and others 2008), yet may still transmit JSRV (Salvatori 2004).
Although the causative agent of OPA was determined some time ago (Palmarini and others 1999), no reliable farm-level ante-mortem diagnostic test exists. Antibodies against JSRV are not detectable by serological diagnostic tests (Ortin and others 1998, Scott and others 2013) and PCR-based techniques, although useful research tools, lack sufficient sensitivity in field diagnosis (Lewis and others 2011). Therefore, OPA diagnosis still requires postmortem examination of lungs including histopathology and occasionally immunohistochemistry (IHC).
Many dyspnoeic sheep in poor condition are culled without veterinary investigation, so the …