BJD Testing
BJD tests detect the actual bacteria or the body’s response to their presence. Animals are tested in two stages – screening tests of large numbers and follow-up tests of reactors.
There are four types of screening test available to test for BJD in live animals.
1. Antibody tests (serological or blood tests)
The main antibody test used for BJD is the absorbed ELISA test in cattle. There is also a Gel or AGID test used for goats. In the Market Assurance Program the number of animals sampled is determined by the size of the herd. Blood samples are collected from all animals, or an appropriate sample of animals within a herd. The blood test detects antibodies to the Johne’s disease bacteria and results are reported relatively quickly (one or two weeks). It is used as a screening test.
2. Individual Faecal culture
Dung or faecal samples collected from individual animals are cultured for the bacteria. This is more expensive and slower than antibody tests, taking from two to five months, depending on the culture method used.
As there are no antibody tests approved for alpaca and deer, faecal culture is the preferred test for these species. It is also used as a definitive test to confirm infection in cattle that react to the ELISA and can be in conjunction with antibody tests in cattle herds to increase the chance of detecting infected animals.
3. Pooled faecal culture
Faecal samples from up to five animals may be cultured in one pool as a herd screening test. While the test still takes two to five months, it is a cheaper herd test option than individual faecal culture. If a positive pool is identified then the individual animals need to be cultured to identify the source of the infection.
4. Herd Environmental Culture (HEC) Test
The Herd Environmental Culture (HEC), another type of faecal test, has been approved by Animal Health Committee’s (AHC) Sub-committee on Animal Health Laboratory Standards (SCAHLS) for use in dairy herds for the following purposes:
- as a surveillance tool in dairy herds in Free and Protected Zones
- as a test equivalent to the Check Test and a Maintenance Test (i.e. use for maintenance of herd status)
Details of the testing protocol are available here: BJD Herd Environment Culture Test
Follow-up Tests
Any animals or groups of animals that test positive to an antibody test are tested again with a definitive test to confirm the result. For instance, ELISA reactors are tested by individual faecal culture or by a post-mortem examination, microscopic examination of the gut tissue and possibly culture of gut tissue. These tests detect the actual bacteria or the characteristic microscopic lesions that they cause.
Page Updated: 10 August 2011