Relationship between the pathology of bovine intestinal tissue and current diagnostic tests for Johne's disease

Authors: JENVEY, CAITLIN - US Department Of Agriculture (USDA); HOSTETTER, J - Iowa State University; Stabel, Judith

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 10/1/2017
Publication Date: 12/3/2017
Citation: Jenvey, C.J., Hostetter, J.M., Stabel, J.R. 2017. Relationship between the pathology of bovine intestinal tissue and current diagnostic tests for Johne's disease. Meeting Abstract. 194/109.

Interpretive Summary: Confocal microscopy is a widely used method utilizing fluorescence to identify the presence of cell types within tissues and/or bacterial or viral pathogens. This method has been used successfully to detect the presence of bacterial pathogens such as mycobacteria and to correlate that presence with the pathogenesis of disease. Understanding the pathogenesis of the disease and the host immune response to infection will allow us to develop improved diagnostic tools and vaccines. In the present study, mid-ileal tissue from naturally infected cattle was stained for macrophage and Mycobacterium avium subsp. paratuberculosis (MAP) and visualized by confocal microscopy. Quantitative staining of the tissues was correlated with current diagnostic tests for Johne’s disease. The test with the highest correlation to tissue pathogenesis was the serum ELISA test that measures serum antibodies to MAP. The models developed for this analysis were useful in assessing the utility of current diagnostic tests to predict clinical disease in cattle, something that will be helpful to producers that may need to consider culling of infected animals from the herd.

Technical Abstract: Johne’s disease is an enteric disease caused by the intracellular pathogen Mycobacterium avium subsp. paratuberculosis (MAP). Recently, we observed increased numbers of macrophages in mid-ileal intestinal tissue of cows naturally infected with MAP, when compared to uninfected controls. This study aimed to determine whether the presence of macrophages and MAP correlated with common methods used for the diagnosis of MAP infection. Diagnostic tests assessed were ELISA, IFN-' assay, RT-PCR (fecal and tissue), and histological classification. Immunofluorescent (IF) labeling was performed on frozen bovine mid-ileal intestinal tissue collected from 28 Holstein dairy cows. Macrophages were labeled using a monoclonal anti-macrophage surface antigen (AM-3K) and MAP was labeled using a polyclonal rabbit heat-killed MAP antigen. Confocal microscopy imaging software was used to quantify IF labeling surface area (SA). Linear and non-linear regression models were developed for statistically significant correlations. Simple logistic regression models were used to determine the predictive probability of all statistically significant categorical dependent variables. An increase in macrophage SA was demonstrated in tissue sections from both subclinically and clinically infected cows, when compared to uninfected controls. Significant correlations were observed between ELISA S/P ratios, and tissue PCR, with both macrophage SA and MAP SA. In addition, ELISA S/P ratios were correlated with macrophage and MAP co-localization SA. Macrophage and MAP SA was not correlated with IFN- ' assay or fecal PCR. The predicted probability of cow status shifting from control to subclinical, and from subclinical to clinical was significantly increased with an increase in macrophage SA. Our findings indicate that ante-mortem serum ELISA could be used as a predictor of macrophage and MAP presence in the target tissue for infection. Additionally, macrophage SA could in turn be used as a predictor of cow status. The models presented in this study provide definitive information on the active pathogenesis of disease and how this is reflected in ante-mortem and post-mortem diagnostic tests.