Johne's disease ELISA - serum

This test is cheaper for members of the Premium Cattle Health Scheme / Premium Sheep & Goat Health Scheme. For more information on the benefits of health scheme membership, please follow these links: Premium Cattle Health Scheme | SRUC or Sheep & goat health schemes | SRUC

Pricing: 1-39 samples = £5.85 per sample; 40+ samples = £5.20 per sample

Interpretation of Johne's disease antibody ELISA in ruminants
Positive: >/= 70%
Inconclusive: 60% and <70%
Negative: <50%

Interpretation in Cattle
Negative: The sensitivity of the test for clinical disease is 90%, but may be as low as 20% for the early pre-clinical phase of the disease. Where negative results are obtained and infection with Mycobacterium avium subspecies paratuberculosis is still suspected the animal should be subjected to a second test for Johne's disease (faecal culture, faecal PCR test, faecal smear examination or necropsy). It is rare for infected animals aged less than two years old to test positive by any test.

Inconclusive:  Where inconclusive results are obtained the animal should be subjected to a second test for Johne's disease (faecal culture, faecal PCR test, faecal smear examination or necropsy) or blood sampled again after one month and tested for antibody.

Positive: Positive results are indicative of infection with Mycobacterium avium subspecies paratuberculosis. The specificity of the assay is high (99%), i.e. very few results will be false positives.

Please note that the intra-dermal tuberculin test can result in the production of cross-reacting antibody that may lead to an animal uninfected with Johne's disease testing positive by the antibody Elisa. This is a particular issue for antibody screening of newly purchased animals that have been TB tested prior to movement. In these cases faecal culture should be carried out and the antibody level re-assessed after three months by which time in uninfected animals the antibody level will have declined significantly.

Interpretation in Sheep
The antibody response to Mycobacterium avium subspecies paratuberculosis (Map) and the development of clinical paratuberculosis is highly variable amongst infected sheep. The specificity of the assay in sheep is high, particularly in the clinical phase of disease i.e. very few results will be false positives. While the sensitivity of the test in the clinical phase is acceptable, it is low for the pre-clinical phase of the disease. Where negative results are obtained and infection with Map is still suspected the animal may be subjected to a second test for Johne's disease (faecal PCR or necropsy).