Validation of a PCR assay for Mycobacterium avium subsp. paratuberculosis from faeces samples of red deer.
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Mycobacterium avium subsp. paratuberculosis (MAP) is a common bacteria in deer in New Zealand, over 60% of herds may be infected. MAP causes Johne’s disease (JD), a chronic, granulomatous enteritis. Deer which are infected at an age of 2 years or younger seem to be most susceptible to the disease. Large numbers of MAP may be shed in the faeces in the end stage of the disease and the pasture will be contaminated, which gives the opportunity for transmission of MAP infection to other hosts. The aim of this study is to validate the faecal RT-PCR for MAP from faeces samples of red deer and to determine if the faecal RT-PCR could replace Paralisa© or culture for a quick and reliable indication of high shedding. Paired faecal and serum samples were collected from 20 individual deer, with an age of 12-24 months, in 18 herds on North Island and 20 herds on South Islands. There is a significant, positive linear correlation between the positive results of the RT-PCR and their culture values (r=0.641) and a significant, negative correlation between the positive results of the RT-PCR and their Paralisa© values (Johnin r= -0.587 and ppa r= -0.542). However, the RT-PCR cannot replace Paralisa© or faecal culture. More research is needed, especially with the ‘gold standard’ assay (tissue culture) to find an easy, quick and reliable test method for the control of JD.