Silent Phase of Johne’s Disease in Experimentally Infected Goats – A Study on New and Established Diagnostic Approaches Using Specific and Non-Specific Parameters

The current gold standard diagnostic test for Johne’s disease (JD) is detecting Mycobacterium avium subsp. paratuberculosis (MAP) from fecal samples via culture and/or PCR. Other commercially available JD diagnostic tests focus on the detection of specific antibodies within the serum or milk of infected ruminants. These tests have a high specificity but low their sensitivity and usually fail to diagnose the disease until later stages of the disease. The ideal diagnostic test should detect infected animals already during the silent phase. Here, we evaluate the use of new and established approaches to define the silent phase of JD in experimentally infected goats. None of the established diagnostic tests or new approaches for the detection of humoral and cellular immune responses were positive during the first year of infection. Only the characterization of various subsets of peripheral blood leukocytes and the weight development gave some indication for the presence of a chronic, but silent, infection. Weight differences were present throughout the first year. In addition, some of the subsets of leukocytes (WC1 + γδ T cells, MHC class II + leukocytes, CD1 + leukocytes, CD14 + granulocytes, and CD14 + /MHC class II + granulocytes) demonstrated significant differences, but only at certain time points.