Mycobacterium avium causes disease, principally tuberculosis in immunocompromised individuals. It is the most frequent cause of disseminated infections in AIDS patients in the West. The pathogen is also associated with disease in animals, chiefly birds and livestock, and may be isolated from environmental samples such as soil and water. Analysis of strains ofM. avium isolated from clinical, veterinary, and environmental sources for the presence of the mycobacterial insertion sequences IS900 and IS901 demonstrates the specific association of IS901 to animal pathogenic M. avium strains. In contrast, most clinical M. avium strains and all AIDS-derived strains examined so far lacked IS901. Significant differences in the plasmid contents and serotypes of strains with and without IS901 were also found. We therefore suggest that the presence of IS901 divides M. avium into two clearly distinct subtypes with differing host range, virulence, plasmid possession, and serotyping antigens. By using DNA sequence data from IS901 and M. avium DNA, a set of polymerase chain reactions were developed for the specific detection and differentiation of these subtypes. The Mycobacterium avium-M. intracellulare complex, or M. avium complex, is a group of related mycobacteria that cause widespread disease in animals (7, 8, 33). M. avium is generally considered to be an opportunistic pathogen in humans, causing tuberculosis, lymphadenitis, and disseminated infections in immunocompromised patients, particularly AIDS patients (5, 6, 11, 15). M. avium is now recognized as the cause of the most common disseminated bacterial infections in Western AIDS patients. The pathogen is thought to be never or only very rarely transmitted from person to person. The source of M. avium infection in humans is unknown, but its presence in animals, birds, and environmental samples suggests a number of possible reservoirs. The M. avium complex was initially classified into seroagglutination types: serotypes 1 to 3 were designated M. avium, and serotypes 4 to 21 were designated M. intracellulare. The close phenotypic similarity of the two species led to their being grouped in a single (M. avium) complex (26). DNA homology studies, however, indicated that although many M. intracellulare serotypes were genetically distinct from those of M. avium (sharing less than 56% DNA homology), serotypes 4, 5, 6, and 8 were in fact indistinguishable from those of M. avium and are now considered to be M. avium complex serotypes (1). These higher M. avium complex serotypes are those that are most commonly associated with AIDS (15), whereas the classical M. avium serotypes (1, 2, and 3) are those most commonly associated with infections in birds and other animals (7, 8, 25, 33). The reasons for these associations are presently unknown. Two specific mammalian pathogens are also closely related to M. avium (>95% DNA homology): M. paratuberculosis, the causative agent of Johne's disease (chronic regional enteritis) in ruminants (3, 27), but implicated in Crohn's disease in humans (...

With the rising number of patients with human immunodeficiency virus (HIV)/AIDS in developing countries, the control of mycobacteria is of growing importance. Previous studies have shown that rodents and insectivores are carriers of mycobacteria. However, it is not clear how widespread mycobacteria are in these animals and what their role is in spreading them. Therefore, the prevalence of mycobacteria in rodents and insectivores was studied in and around Morogoro, Tanzania. Live rodents were trapped, with three types of live traps, in three habitats. Pieces of organs were pooled per habitat, species, and organ type (stratified pooling); these sample pools were examined for the presence of mycobacteria by PCR, microscopy, and culture methods. The mycobacterial isolates were identified using phenotypic techniques and sequencing. In total, 708 small mammals were collected, 31 of which were shrews. By pool prevalence estimation, 2.65% of the animals were carriers of mycobacteria, with a higher prevalence in the urban areas and in Cricetomys gambianus and the insectivore Crocidura hirta. Nontuberculous mycobacteria (Mycobacterium chimaera, M. intracellulare, M. arupense, M. parascrofulaceum, and Mycobacterium spp.) were isolated from C. gambianus, Mastomys natalensis, and C. hirta. This study is the first to report findings of mycobacteria in African rodents and insectivores and the first in mycobacterial ecology to estimate the prevalence of mycobacteria after stratified pool screening. The fact that small mammals in urban areas carry more mycobacteria than those in the fields and that potentially pathogenic mycobacteria were isolated identifies a risk for other animals and humans, especially HIV/AIDS patients, that have a weakened immune system.

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