Introduction
Currently, no single diagnostic test can detect Mycobacterium avium subspecies paratuberculosis (MAP) infection at every stage of paratuberculosis. Furthermore, severe obstacles to disease control include the lack of early diagnosis and effective vaccines.
MAP proteomic preparations are critical for diagnostic and vaccine applications. Killed whole-cell extracts or modified live versions of MAP are used as vaccine formulations (Bastida and Juste, 2011) and sonicated fractionated whole-cell extracts or cell-free supernatants, comprising secreted proteins, are used in diagnostic tests such as the interferon gamma (IFN-γ) assay or enzyme-linked immunosorbent assay (ELISA). Failure of antigenbased diagnostic accuracy is due, in part, to the inconsistency of the cell-free preps, termed purified protein derivative (PPD), and presence of many cross-reactive proteins from other closely related mycobacteria. While the failure of protective antigens is more difficult to pinpoint, it can be partially attributed to non-specific targets as well as the difficulty in measuring correlates of protection. However, a few in vitro screening methods have recently been introduced to triage vaccine candidates prior to expensive animal trials (Abdellrazeq et al., 2018; Pooley etal., 2018). In the USA, vaccination is not administered to dairy herds and thus paratuberculosis control efforts have been limited to herd management and serological testing. This situation is different for sheep and goats in Australia and other countries that do have paratuberculosis vaccine programmes (Windsor, 2015).With the goal of aiding vaccine and diagnostic test advances, this chapter will focus primarily on MAP proteomic discoveries made since 2008 unless a historical perspective is needed. A few new antigens have come to light as a result of these recent studies and they will be discussed further. Another line of proteomic research that is emerging involves host biomarker discovery. A good example of this is the transthyretin and alpha haemoglobin proteins identified and purified from the serum of infected sheep (Zhong et al.,
2011). However, these topics are beyond the scope of this pathogen-focused chapter. Finally, many studies use the whole cell as an antigen for specific assays and these types of studies are not discussed herein. Only when the MAP proteome is fractionated or if a specific, defined antigen produced by the bacterium is studied, then it is mentioned herein.
8.2
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