Epidemiology
Avian tuberculosis occurs worldwide. All species of birds appear to be susceptible, although to variable degrees. Most avian tuberculosis cases occur in small backyard poultry flocks, in zoos or in wild birds.
Overall Mycobacterium spp. infection was detected in 0.7 % (82 on 11,664) of the wild birds examined between 1975 and 1985 in the Netherlands [6]. These represented 25 species of birds, of 10 different orders. However the isolation of some strains was considered incidental by the authors and the pathological significance remained undetermined. Comparable prevalences were obtained by studies in the United States and in Canada where, respectively, 0.3 % (of 3,000 waterfowl) and 0.6 % (of 600 wild birds) were found to be infected with Mycobacterium spp. [1].
Mycobacteria are excreted in the faeces of infected birds with advanced lesions. Cadavers and offal may infect predators and cannibalistic flock-mates. However, recent molecular studies [5] highlight the heterogeneity in the M. avium complex, and the epidemiology and the pathogenesis may vary among strains.