Ovine pulmonary adenocarcinoma (OPA), or Jaagsiekte as it is often commonly known, is a relatively new disease in terms of industry awareness. The disease, which results from the Jaagsiekte sheep retrovirus (RSV), is transmitted from sheep to sheep mainly through the respiratory system and causes a lung tumour likened to cancer that will eventually be fatal.

The reason it is described as a relatively new disease for the sheep industry is that it is challenging to identify and, as such, has not been suspected or identified in cases of mortality it is likely to have been the cause of.