Mycobacterium avium infection in Miniature
Schnauzer dogs
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 Mycobacterium 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 Mycobacterium 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 infection in Miniature Schnauzer
dogs. The breeder should submit a blood sample from the dog
through his/her own veterinarian. The test result is usually available
in two business days.
