Epidemiology of Mycobacterium bovis infection in feral ferrets (Mustela furo) in New Zealand: I. Pathology and diagnosis.

Necropsies from 228 ferrets captured from eight areas in the North and South Islands provided material for an investigation into the epidemiology of tuberculosis in feral ferrets. Mycobacterial culture of pooled lymph nodes (retropharyngeal, respiratory and jejunal) identified the prevalence of infection to be much higher than that estimated from gross lesions only. Seventy-three of the 228 animals examined (32%) were diagnosed as tuberculous. Fifty-three culture-positive ferrets and 18 seemingly uninfected animals were subjected to detailed histopathological examination. The outcomes of these investigations, including the characteristics of the disease, distribution of lesions and aids to diagnosis, are presented. Of the feral carnivores found in New Zealand, the disease persists at high prevalence only in ferrets, and is probably the maintained principally by ingestion of tuberculous carrion. The course of the disease may be prolonged in some ferrets, but tuberculosis eventually causes death of many infected animals. Microscopic hepatic granulomas may be considered pathognomonic of the disease, and have potential to be used as a rapid diagnostic tool in ferrets with no gross lesions.