OPA = Ovine Pulmonary Adenocarcinoma (Jaagseikte or Yaksie, or tea-pot disease, as we used to call it), is a contagious viral neoplastic disease of the lungs of sheep and rarely goats. A retro and/or herpes virus probably causes the adenomatous tumour, but work is still ongoing to determine this exactly. Often known from the Afrikaans name, Jaagsiekte.

Natural transmission is generally by the respiratory route. Close contact of individuals e.g. indoors or at feeding troughs may assist the spread of virus. The incubation period can be as long as 3-4 years, although cases are seen in much younger animals and early lesions are frequent at post-mortems of young sheep. The respiratory exudates are infectious to other sheep.

Signs of disease are only seen when the tumor is very large or numerous small tumors, (which affect respiratory function of the lungs), are present. The incidence of the disease can be up to 10% but deaths are sporadic. Although several sheep in a flock may be affected, usually a single sheep is showing clinical signs at any one time.

Clinical signs are severe respiratory distress with no coughing or fever. The affected individuals lose weight as the respiratory embarrassment increases. Clinical disease ends in death after days to weeks of signs being exhibited. OPA predisposes affected individuals to pasteurellosis so in the terminal stages some sheep have a fever and have a transient response to antibiotics. Any flock with a pasteurellosis problem could have OPA as a predisposing factor and individuals in a OPA infected flock, which develop pasteurellosis should be treated as though they are suffering from OPA until proven otherwise. Flocks with OPA have a much higher incidence of pasteurella deaths.

Diagnosis of the disease can only be done at post-mortem, as there is no serological test available at the moment. In an OPA infected flock diagnosis can be made on clinical signs – age of sheep, moist rales on auscultation of lung fields and evidence of abnormal volumes of respiratory fluids in afebrile (not running a fever) sheep. The ‘wheel-barrow test’ is a useful aid to diagnosis where by the individual sheep has its’ hind legs lifted up while its’ front feet are on the ground, thus their head is lower than their lungs, if large volumes (30-300ml) of clear mucus exudate pour from their nose and mouth then this is highly suggestive of OPA. NB. This exudate is infectious.

Treatment is not practical, controlling flocks in which the disease is known to occur must be based on reducing crowding and early elimination of any sheep that is thin, losing weight, or showing respiratory signs. Running a separate ‘clean flock’ of bought in disease free sheep until natural culling of the existing flock occurs is, in theory, the way to get a disease free flock, though breakdowns are not uncommon. At the moment there is no test to certify a sheep or flock is disease-free - and no prevention.