I have expanded that intent to reflect information about mycobacterium paratuberculosis , the bacteria that is present wherever there is Johne's disease. Johne's disease is a disease of ruminants. The Veterinary Science faculty of the University of Wisconsin USA seems to have the most comprehensive site on Johne's Disease at Frequently Asked Questions about Johne's Disease . Readers should note that this agnote was prepared by NSW government employees, and the advice and opinions selected for publication may tend to explain legislation enacted and policies initiated by the government, and might also favour those hypotheses that exculpate government for the introduction of the disease to Australia. OJD is known to be spread by ingestion of pasture contaminated with infected fecal matter, and is known to be spread by the transport of infected fecal matter in waterways.
Young animals are more susceptible, and it appears that they can be infected by mother's milk.
The bacterium has been reported to persist for longer than one year on the pasture. With present technology it is not possible to reliably diagnose OJD in individual live sheep. If OJD is present the entire flock is assumed to be infected. Considering the horrendous punishment meted out to anyone who permits testing of their flock, this disparity is not at all surprising. The failure to offer the vaccine except to reported flocks sounds like heavy handed political thinking.