Several countries (Australia, New Zealand and the USA, among others) have ongoing eradication programmes for Johne’s disease. Efforts to evaluate the success of these measures have intensified recently, as concerns over the link between human Crohne’s disease and consumption of M. johnei contaminated milk have grown. Recent developments in diagnostic methodologies to identify sub-clinical cases have further increased interest in planned control policies (Giessen et al., 1992; Egan et al., 1999).
The main source of infection in a herd is via a purchased animal. After entering a herd, Johne's disease tends to be cyclic, in that the disease often appears and disappears after a few years in the absence of control measures. Animals that have tested positive for the disease should be culled, as they pose a risk to others. Offspring born from cows that develop the disease should not be retained in the herd, as they are likely to be infected, either from their dam's faeces or in utero. Testing of the herd should be continued after the cull. The closed herd strategy, often applied to organic herds, may reduce the risk of the disease entering the herd.
Recent findings indicating that wildlife may act as a carriers for the disease are unlikely to affect control, as the amount of pathogen excreted by these carriers is too small to infect cattle (Greig et al., 1999).
At the moment (April, 2000), the UK government does not have an official control policy for Johne’s disease, which is a notifiable disease. A vaccine against the disease is available, but its use is controlled by MAFF in herds that have had a recognised case of the disease.
The Premium Cattle Health Scheme and the Herdcare National Cattle Health Scheme offer screening and eradication or disease monitoring programmes for Johne’s disease. Within these programmes, the whole herd is tested by blood sampling, and reactors and their offspring are culled.