Cost is a factor in use of this test. Serologic tests should not be used to confirm a diagnosis of Johne's disease. The antigens used in these assays are prepared differently, vary in composition, and give different results when used with bovine serum. Culture of feces for bacteria . As with the traditional tuberculin tests for tuberculosis, a small amount of bacterial antigen is injected into the skin, and examined at 72 hours later for signs of swelling.
Infected animals develop a distinct swelling at the site of injection.
A new more specific antigen provides for improved accuracy of the skin test. Detection of bacterial DNA . Modern molecular probes detect very small amounts of bacteria genetic material. Generally, these tests are not used in routine screening in veterinary diagnostic laboratories. New molecular techniques for Mycobacterium.