Johne’s Disease – agar gel immunodiffusion (AGID)

Species: Ovine, cervine

Specimen: Serum

Container: Red top or gel tube

Collection protocol: Venepuncture

Special handling/shipping requirements:  Standard

General information about the disease:

Johnes disease is an enteric infection of grazing ruminants caused by Mycobacterium paratuberculosis. This test has a reported specificity of >97% indicating that an animal with a positive result almost certainly has Johne’s infection. The sensitivity of the test depends on the stage of the disease. In preclinical cases, sensitivity is low.  However, with clinically affected animals, the sensitivity improves to approximately 66%.

General information about when this test is indicated:

AGID is used for specific requirements of some countries and for ancillary testing. ELISA is the first test of choice.

Comparison with other related tests:  ELISA and CFT are other serological tests. Faecal PCR increases sensitivity and may be used to quantify shedding in individual animals or to test pools of up to 5 samples. Faecal Ziehl-Neelsen stains are also possible to check for acid fast organisms, but lack sensitivity.

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