The emergence of Mycobacterium paratuberculosis in farmed deer in New Zealand - a review of 619 cases

AIM: To review cases in which Mycobacterium paratuberculosis was identified in farmed deer in New Zealand. METHODS: Case histories were reviewed where M. paratuberculosis was identified in deer by either culture or a polymerase chain reaction (PCR) test using primers from IS900. RESULTS: Between 1986 and 2000, M. paratuberculosis was identified by bacterial culture and/or PCR in 619 farmed deer from 299 herds, representing approximately 6% of deer herds in New Zealand. Over 85% of cases were identified during the last 6 years. In 60% of the infected herds, only one infected animal was identified. The maximum number of cases identified in a single deer herd was 47, and these were identified over a period of 8 years. Only 36 (5.8%) cases came from clinically affected animals identified on farms by veterinarians. The majority (89.7%) of the 619 cases were identified from lesions in mesenteric lymph nodes, including the ileocaecal lymph nodes, identified at meat inspection as being macroscopically either typical or equivocal of bovine tuberculosis (M. bovis). While the overwhelming majority of lesions were identified in mesenteric lymph nodes, M. paratuberculosis was also identified in 27 lesions in lymph nodes of the head, especially the retropharyngeal lymph node. CONCLUSIONS: The figures presented underestimate the true prevalence of infection with M. paratuberculosis, especially since not all suspect cases were submitted for culture or PCR. However, they do show that M. paratuberculosis appears to be spreading in farmed deer in New Zealand and highlight the possibility that Johne's disease is emerging as a potential major problem affecting this species. Identification of the organism by bacterial culture or PCR is required in many cases to distinguish lesions in mesenteric lymph nodes and lymph nodes of the head caused by M. paratuberculosis from those caused by M. bovis and M. avium.