Mycobacterium avium and Mycobacterium intracellulare infection in mammals

Mycobacterium avium subsp. avium and M. intracellulare are ubiquitous organ isms in the environment. The reservoir of M. avium subsp. avium is generall y accepted to be environmental, in particular, water and soil are sources o f the organism. In contrast to M. avium infection in wild and domestic bird s, M. avium infection in mammals occurs only sporadically and is rarely tra nsmissible. Generalised disease is usually uncommon, owing to the non-progr essive, chronic character of the infection. However, some cases of dissemin ated disease have been reported, e.g. in captive non-domestic hoofed animal s as well as in immunosuppressed dogs and cats. The majority of M. avium an d M. intracellulare infections in livestock are detected at slaughter and t he diagnosis is confirmed by bacteriological procedures. Condemnation of af fected portions of the carcass can result in significant economic losses, a lthough gross lesions are mostly restricted to lymph nodes close to the ali mentary tract. Successful treatment with antibiotics in combination with su rgery has been reported in some affected domestic cats, but is not consider ed to be effective or economical in other species. In the past, differentia tion of M. avium bacteria from the closely related M. avium su bsp. paratub erculosis was ba sed on the mycobactin dependence a nd prolonged incubation period of the latter. More recently, amplification of the genomic insertio n sequence IS900 has proved to be a powerful tool for identification of M. avium subsp. paratuberculosis. The potential zoonotic importance of M. aviu m infections has been indicated, but requires clarification.