This is a fatal mycobacterial infection affecting the intestines. Multiplication of bacteria and chronic inflammation slowly thicken the intestinal wall, preventing absorption of nutrients, and leading to wasting and diarrhoea. Affected animals show no signs for months or years after becoming infected until the extent of intestinal compromise causes progressive wasting. Eating and drinking continue normally until animals are too weak to move.
There are separate sheep and cattle strains of M. tuberculosis. Goats may be infected with either strain. Bovine Johne's disease (BJD) is endemic in south eastern Australia. There are control and eradication programs in Australia for both OJD and BJD. Information here is limited to OJD since it is very unlikely that BJD-infected cattle would be entering the export chain.
The disease is widespread in sheep and goats in Australia. Prevalence is lower in drier, lightly stocked areas.
ProbIems may occur in the live export process if infected animals are sourced in the belief they have easily remedied problems such as internal parasites or undernutrition. Also, stressors within the live export process may accelerate progression of the disease and onset of clinical signs. It takes six weeks to 3 months from the onset of signs to death so there is the potential for animals to die during the live export process.
Suspicions are often first raised when there is unresponsive or unexplained wasting and death in yearling and adult animals. Flocks may have a distinct tail of clinically affected animals. At necropsy, the important diagnostic lesions are found in the intestines which have thickened walls, enlarged lymph nodes and prominent lymphatics. Differential diagnoses include internal parasites, undernutrition, poor dentition, and internal abscesses from cheesy gland or following rumenitis. Caprine arthritis-encephalitis (CAE) is an additional differential diagnosis in goats. With many of these differentials there is often some level of inappetence.
Laboratory confirmation in live animals requires serum and faeces submitted chilled. In dead animals, recommended specimens include thickened gut, enlarged lymph nodes and liver chilled for microbiology and in buffered formalin for histology. In the absence of obvious gross lesions submit specimens of ileum, liver and ileal and caudal jejunal lymph nodes.
It is untreatable, including with antibiotics.
Prevention of infection occurs on farm by vaccination and management to avoid exposure of susceptible animals to infected stock. Prevention of onset of clinical signs in the live export process is by sourcing younger, vaccinated animals from drier regions, or from flocks and herds in the Johne's disease market assurance program. Minimising environmental and management stress will also reduce the likelihood of early infected animals from developing clinical signs.