Johnes Disease

Clinically affected deer lose weight and develop a chronic scour, which is unresponsive to treatment; it can look like the after effects of a bad dose of facial eczema. Two clinical syndromes are seen, the odd sporadic case in older deer, or serious outbreaks in 8 to 15 month old deer with up to 15% of the mob affected. Control options on seriously affected farms are currently limited to culling affected stock, culling test positive animals, or depopulation of farms and restocking after two years. 
Laboratory tests must be used to screen herds for sub-clinical cases, although they do not always immediately detect presence of the disease. The appropriate tests are the Paralisa or faecal culture. Sub-clinically infected deer may test negative to the Paralisa test if they have recently been infected or their antibody levels are below the detection limits of the test. Additionally, sub-clinically affected deer tend to excrete the organism in their faeces intermittently, making detection using faecal culture rather "hit or miss".

For these reasons, in herds where positives have been identified, repeat testing of previously test negative deer should be undertaken at strategic intervals to increase the chance of detecting sub-clinically infected deer. These are guidelines only