Diagnosing Johne’s disease in a herd or flock has traditionally required culture of faecal samples to detect the presence of viable disease-causing bacteria. This organism (Mycobacterium avium subspecies paratuberculosis) is very slow growing and requires culture for 12 weeks. Clearly this is not a quick test when you want to determine if a farm has Johne’s disease.
In collaboration with the NSW Department of Primary Industries (Elizabeth Macarthur Agricultural Institute, EMAI), we have recently developed the HT-J direct faecal test which can provide a result within a week of the sample arriving in a diagnostic laboratory. The HT-J test detects the presence of genetic material (DNA) of the bacterium present in faecal samples from cattle or sheep and it is as sensitive as liquid cultures for detecting the disease-causing organism.
The name HT-J is shortened from “High-throughput Johne’s” test and an additional advantage of the test is that it can be carried out in a high-throughput format (96 samples and controls in a plate) which means it is easier to test a large number of samples. We have carried out extensive validation of this test on nearly 2000 samples from across Australia.
The HT-J test has been approved by SCAHLS (The Subcommittee on Animal Health Laboratory Standards) for use in Australia and New Zealand for detection of Johne’s disease in sheep and cattle. http://www.scahls.org.au/LabTests/Pages/SCAHLS-approved-tests.aspx
In 2012 a workshop was run by the team here in collaboration with EMAI to train diagnostic laboratory technicians to carry out this test. A follow up technical workshop was held in 2014. The University continues to offer technical support for laboratories that are running the test through a technical working group that meets regularly.
To hear more about how the test can be used, you can listen to an interview with Prof. Richard Whittington, one of the test developers. http://www.abc.net.au/news/2014-05-20/new-johnes-test-a-big-step-forward/5464190
The development and validation of the new faecal PCR test has been published in the international scientific literature:
Plain, KM, Marsh IB, Waldron AM, Galea F, Whittington AM, SaundersVF, Begg D J, de Silva K, Purdie ACand Whittington R J (2014). High-throughput direct fecal PCR assay for detection of Mycobacterium avium subsp. paratuberculosis in sheep and cattle. Journal of Clinical Microbiology 52, 745-757.