Epidemiology of Mycobacterium bovis infection in feral ferrets (Mustela furo) in New Zealand: II. Routes of infection and excretion.

Detailed necropsies of 228 ferrets captured from eight areas in the North and South Islands provided material for an investigation into the epidemiology of tuberculosis in wild ferrets. Seventy-three of the 228 (32%) animals examined were diagnosed as tuberculous, by culture of pooled lymph nodes and detailed histopathological examination. The prevalence of bovine tuberculosis was 96% in 24 ferrets taken from areas in which tuberculous possums were common. None of 35 animals under 4 months of age were found to be infected, and the prevalence of infection was shown to rise with age, such that for each 6 month age increment there was a 2.8 times greater risk of becoming infected. The most common route of infection appeared to be via the alimentary tract, as 79% of 38 animals, in which the initial lesions could be reasonably determined, had these lesions associated with the digestive tract. Samples from potential sites of excretion from infected ferrets were submitted for culturing. The most common route of excretion was via the oral cavity, with M. bovis recovered from 15 of 64 (23%) oral swabs. Mycobacterium bovis was also isolated from four of 64 (6%) tracheobronchial lavage samples, ten of 63 (16%) faecal samples, two of 29 (7%) urine samples and one of 8 (12.5%) mammary glands. The disease in ferrets appears to be principally maintained by ingestion of tuberculous carrion. Although a moderate number of ferrets excrete M. bovis orally, there appears to be only minor intraspecific transmission by bite wounding. The findings provided no evidence to support the occurrence of pseudo-vertical transmission.