OPA (Jaagsiekte)

OPA (Ovine Pulmonary Adenocarcinoma or Jaagsiekte), is a contagious lung cancer of sheep caused by jaagsiekte sheep retrovirus (JSRV).  OPA occurs in most countries where sheep are farmed and is of significant economic and animal welfare importance.

The typical clinical signs of OPA are that of a progressive respiratory disease that resembles pneumonia.  However, a unique feature in many affected sheep is the overproduction of fluid in the lung that can be seen running from the nose when the animal lowers its head.  Once these signs appear the disease is invariably fatal.  Affected flocks many lose up to 20% of sheep per year to OPA, although 1-2% is more usual.  Despite the unique clinical appearance, infection with JSRV is frequently subclinical, and OPA is commonly spread to new flocks and areas through the purchase of infected but apparently healthy animals.

Current control strategies for OPA are confined to managemental interventions, such as culling of clinically-affected animals, and are relatively ineffective in controlling the disease.  A major aim of our research is to develop improved methods for controlling OPA, including vaccines and diagnostic tests that can detect infected animals prior to the onset of clinical signs.  This work has led to the development of PCR tests that can detect JSRV in the blood of infected animals.  We have recently used this test to survey JSRV infection in 125 farms across Scotland.  The results found that 38% of farms tested had evidence of JSRV infection, although only a small proportion of these had a history of clinical OPA.  Unfortunately, although the existing PCR test can detect infection within a flock, it is not yet suitable for diagnosing infection within individual animals and work is continuing to develop diagnostic tests with greater sensitivity.

Another area of interest is directed at understanding the interaction of JSRV with its host during the early stages of infection. For example, we are currently studying the cell types that are initially infected and transformed and we are characterizing the innate immune response to infection.  Greater understanding of these events may be informative for the design of novel control strategies for OPA.  In addition, OPA is regarded as an animal model for some forms of human lung cancers and studies on the early events in JSRV-induced transformation in sheep may be relevant to the human disease.