In the last 20 years Johne’s disease, caused by infection with Mycobacterium paratuberculosis (Map), has emerged as one of the most important bacterial diseases affecting productivity in New Zealand farmed deer. In addition to clinical losses, subclinical infection results in reduced growth rates of young deer, lower reproductive performance and lighter velvet weights. Traditionally, microbial culture of faecal material or gut tissue has been used to confirm the presence of infection. The Disease Research Laboratory has recently developed a refined ELISA test thatmonitors IgG1 antibody (Paralisa) specific for antigens expressed uniquely by M. paratuberculosis. This test has acceptable sensitivity (75-91%) and specificity (>98%) for the detection of subclinically affected animals. The use of this test in severely infected deer herds can reduce the prevalence of reactors from high (>40%) to low levels (<5%) within 2-3 years and result in the elimination of clinical disease. Clinically detectable Johne's disease represents a minor proportion of the total number of animals infected in a herd so it is also important to have diagnostic tests that detect subclinically infected animals. Using the Paralisatest, it is now possible to implement management systems to electively remove infected deer to increase production and reproductive performances.
Proceedings of the New Zealand Society of Animal Production, Volume 67, Wanaka, 95-101, 2007
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