Dogs that develop unusual infections or infections that are recurring or persistent and unresponsive to antimicrobial therapy likely suffer from a hereditary (primary) immunodeficiency disorder. Immunodeficiencies represent a large heterogeneous group of dysfunctions of the host's immune system which increases the risk for infections. They can arise through disturbances in antigen-specific defense mechanisms mediated by lymphocytes, the nonspecific defense system (which includes phagocytes, plasma proteins, and physical barriers), or both. 

Many genetically determined immune defects have been described in the dog, whereas only a few are known in cats. While the clinical signs may be suggestive of a primary immunodeficiency, a definitive diagnosis often requires specific immune testing in addition to routine laboratory tests.  The molecular defects for several primary immunodeficiencies have been elucidated allowing for DNA screening.
A few hereditary immunodeficiency disorders are prevalent within certain breeds of dogs, whereas others occur in isolated families or cases. Furthermore, because of the underlying immunodeficiency, the resulting infections are poorly responsive to treatment and often recur. Thus, therapeutic interventions are limited.
At the 2017 AKC Canine Health Foundation National Parent Club Canine Health Conference, Dr. Urs Giger explained more about inherited immunodeficiencies and discussed what has been learned about the genetic predisposition of Miniature Schnauzers to infection with avian tuberculosis - a serious and fatal infection in affected dogs. Additionally, because this has zoonotic potential, humans that come into contact with affected dogs are also at risk for infection. Dr. Giger shares more about his research, the DNA test that is currently available, as well as general recommendations regarding testing and breeding of Miniature Schnauzers: