Accurate and rapid detection of ovine Johne’s disease (OJD) infection, in both individual sheep and flocks, continues to be a major challenge for the management and control of the disease in the sheep industry. Current diagnostic tests for OJD have a limited ability to detect individual infected sheep, particularly in the early stages of infection. However, they can be used with good accuracy to assess the infection status of flocks.
The main test currently used for on-farm flock screening is the Pooled faecal culture (PFC) to detect OJD bacteria in dung. A single dung pellet is collected from at least 350 adult sheep in the flock and cultured in ‘pools’ of 50 for the OJD bacteria. On average, the PFC is able to detect OJD in 98% of infected flocks if 2% or more of sheep in the flock are infected.
A blood test to detect antibodies to OJD bacteria in the blood (serology) is also available, but has its drawbacks. It is less sensitive than PFC and so more sheep must be tested to provide a similar level of confidence in the results. Antibodies are also produced in the blood following vaccination. Approval by the state Chief Veterinary Officer may be needed before using the blood test.
Abattoir surveillance is also a practical and cost effective means of checking for OJD. Trained inspection personnel at abattoirs in all states now inspect lines of adult sheep for visible signs of OJD in the intestines and lymph nodes. Find out more about the abattoir monitoring program in Australia.
Ongoing research is focusing on the development of new tests that can quickly and accurately detect infected sheep, particularly in the early stages of infection.
More information is available from Meat & Livestock Australia’s fact sheet on Diagnosing Ovine Johnes Disease.