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Mycobacterium avium (M. avium) infection have been describe in a number of species, including dogs,
cats, primates, swine, cattle, horses, and human. Mycobacterium avium is a ubiquitous, saprophytic, acid-fast,
aerobic bacillus that is widely distributed in the environment, especially in water and soil. Pigs and birds are very
susceptible to M. avium infections and may serve as reservoir hosts, although the organism may remain viable in
the soil for up to 4 years. Although M. avium is considered an opportunistic organism, it is the most likely of
the complex of closely related organisms to produce bacteremia and disseminated disease.
Mycobacterium avium is important organism, because the granulomatous lesions it produces are indistinguishable
from the tubercular lesions of M. tuberculosis and M. bovis. Mycobacteria produce a cell-mediated,
delayed-type hypersensitivity response, characterized by granulomatous inflammation. The progression of disease depends on
the ability of the macrophages to inhibit intracellular growth of the organisms.
The primary symptoms of disseminated Mycobacterium avium infection are enlarged lymph nodes, tonsillary
inflammation, and anorexia. Generally the cervical nodes are affected, as well as the mesenteric nodes, but they are not
as easily palpable. Other symptoms not occurring among all cases are: fever, vomiting, bloody stool, breathing difficulty
due to compression of lungs by enlarged nodes, and lameness. Necropsy demonstrates that infection does not occur in lung
tissue. Infection disseminates throughout other tissues, including spleen, liver, and bone marrow.
Mycobacteria often gain entry to the body through either the respiratory tract, the gastrointestinal tract, or the skin,
where they are phagocytized by local tissue macrophages and then disseminated to adjacent tissues. It is possible that
in this case, the ileum was the site of entry, because it was the only part of the gastrointestinal tract affected. The
incubation period is not known. Treatment attempts have failed in all cases I am aware of to date. Most dogs infected
were not seen by a veterinarian until the stage of lymphadenopathy, by which time the pathogen had probably infiltrated
other organs through the lymphatic system.
Mycobacterium avium is called an "opportunistic" pathogen because it does not normally causes disease in dogs
unless there is an acquired immune deficiency or a genetic defect or disease that predisposes an individual to M.
avium infection. There have been 4 cases in Miniature Schnauzers that are reported in veterinary literature. During
last two years, HealthGene Laboratory confirmed 12 additional cases of M. avium infection in Miniature Schnauzer
dogs. There is strong circumstantial evidence that the apparent increased incidence of M. avium infection in
Miniature Schnauzer dogs is due to an inherited defect that result in defective immune system mechanism for killing
intracellular bacteria.
HealthGene Laboratory offers a DNA-based test for the detection of M. avium infection in Miniature Schnauzer dogs.
Breeder should submit a blood sample from the dog through own veterinarian. The test result is usually available in two
business days.
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