Johne’s Disease on U.S. Dairy Operations - 2002. The U.S. Dept. Agriculture published its most recent study on Johne’s disease in the U.S. The 178 page report is a wealth of information. It provides survey results about risks for M. paratuberculosis transmission on U.S. dairies, diagnostic testing practices, test accuracy, test agreement, and estimation of the prevalence of M. paratuberculosis infection among the dairies selected for study. The document is free to download as a pdf file but be warned – it is very large (5MB) and so takes considerable time to download depending on your internet connection speed.