courtesy of Errolyn Martin
The primary symptoms of disseminated mycobacterium avium infection are enlarged lymph nodes, tonsillary inflammation, and inappetence/anorexia. Generally the submandibular and 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.
Necropy demostrates that infection does not occur in lung tissue. Infection disseminates throughout other tissues, including spleen, liver, and bone marrow. Common lab findings are a low-grade nonregenerative anemia and elevated WBC, other lab findings are inconsistent among known cases until the disease has progressed significantly. Ingestion seems to be considered the primary route of infection.
The incubation period is not known. Treatment attempts have failed in all cases I am aware of to date. This may be due in part to the stage of illness upon initial diagnosis. Most dogs infected were not seen by a vet until the stage of lymphadenopathy, by which time the pathogen had probably infiltrated other organs through the lymphatic system. In addition, isolation of the organism is slow. The less costly method of culturing takes up to 4 months, by which time the dog is dead. The DNA Probe method takes much less time, and I don't know why this method is not used more often. Initial diagnosis seems to consistently be lymphosarcoma, except in the latter cases of the 3 littermates. Lymph node apsirate/biopsy is needed to differentiate.
It is generally believed that dogs are innately resistant to this pathogen, and susceptibility to infection is the result of immune system dysfunction. Probably a T-cell mediated immune response, where either the pathogen is not being identified, or the signal to turn on immune response is not getting through.
In my investigation I acquired a few case reports from veterinary journals, and an article from a veterinary journal about a study done years ago. The article appeared in the 1930 issue of the Journal Of The Amercian Veterinary Medical Assoc. The study cited identified cases of TB in dogs, various workers reporting a total of 72 cases of TB, all of which were identified as either human, bovine, or transitional. The author goes on to write "As far as I have been able to ascertain. cases of spontaneous tuberculosis of the dog have not been described in which the etiologic agent was the avian variety.".
The study experimentally exposes numbers of dogs to mycobacterium avium via various inoculation methods, including ingestion, intraperitoneal injection, intrabronchial injection, intravenous injection, and intracerebral injection. The conclusion " The facts obtained by these experiments seem to warrant the conclusion that by the ordinary means of exposure the dog is extremely resistant to the bacilli of avian tuberculosis". (This study is gruesome reading).
About the pathogen - mycobacterium avium is slow-growing. It is an opportunistic saprophyte. Poultry are primarily susceptible following contact with infected food or water. Feces of infected birds contain large numbers of the bacilli. Infection of dogs and cats occurs from ingestion of infected meat, contact with infected soil or with fomites contaminated by carcasses or feces. M. avium is ubiquitous, and can survive in the environment for at least 2 years, unlike the bacilli of M tuberculosis (human) or M Bovis (cow) which are short lived outside of a host.
This disease has been studied in 5 Basset Hounds, at Angell Memorial, and a common ancestor was identified. The conclusion was " The apparent inherited predisposition of some Basset Hounds to avian tuberculosis led to the study of the available pedigrees of 3 of the 5 affected dogs. All 3 pedigrees had a common male that was the sire of one of the affected dogs, and a paternal grandsire to another, and both paternal and maternal grandsire to the third dog..."
Age of onset for known cases seems to be anywhere from 10 months to 3 years. There is a journal case report of 3 MS littermates which died from this disease, 2 which became ill within a month or two of each other, the other became ill a year later. All 3 had lived in separate homes from puppyhood. I was able to connect this report with a pedigree a breeder gave me. There is also a journal case report of an individual case in a MS, for which I do not have the pedigree. The breeder's brother owned the dog and he contacted me after I spoke with the doctor who originally wrote the report. At the time I turned over copies of all my materials to AU for their work, I was aware of 9 confirmed cases of M avium in MS and had the pedigrees for 7 of them. Since that time I have been put in contact with a pet owner who also lost her dog to avian TB, and have her file and pedigree, and I have heard unofficially of at least 4 other cases in various parts of the US.
There is very strong suggestion of an inherited immune system dysfunction based on linear and genetic pedigree anaylsis. Whether it is inherited through a simple recessive or polygenic form is unclear, although one pedigree, of the 3 littermates, demomstrates enough genetic variance on the sire's side to indicate a simple recessive. Polygenes are possible on the basis of most cases being traced back to a particular family of dogs which have been considerably inbred/linebred for several years. Sexes are about equally represented. According to a researcher I spoke with, it has been considered a recessive in the Basset Hound work that was done in the last 10 years.
Tuberculosis is one of the most important infectious diseases in the world. There are an estimated 2-3 million deaths in people from tuberculosis each year, and 10 million new cases of active disease.
Despite these high numbers 90% of tuberculosis is subclinical. Tuberculosis is primarily transmitted through aerosol droplets, but it can also be transmitted through milk and infected meat. The mycobacterial species most frequently associated with disease are M. tuberculosis and M. bovus .
Individuals as well as most animals are resistant to the ubiquitous mycobacterial species M. avium and M. intercellare commonly known as the M. avium complex. However, there is an increased incidence of M. avium complex infections in AIDS patients, Basset Hounds, and Siamese Cats due to their immune compromised states. Protective immunity to intracellular bacteria such as mycobacteria and Salmonella is dependent on activation of macrophages by type 1 cytokines.
Human familial and murine model studies have found that the cytokines IL-12, IFN-gamma, and TNF-alpha play an essential role in the host resistance to mycobacteria. Mycobacterial infections are for the most part uncommon in dogs and cats.
Recently there have been antedotal reports of Mycobacterium avium infections in related Miniature Schnauzers from several different locations in the United States. Preliminary evaluation of cell-mediated immunity (CMI) in dogs related to a 1 1/2 year old male Miniature Schnauzer which was treated at the College of Veterinary Medicine, Auburn University, but subsequently died from systemic Mycobacterium avium infection are suggestive of decreased TNF production in Schnauzers compared to normal mixed breed dogs. At this time it is not known if this is a problem in all Schnauzers or only certain breeding lines. We are requesting blood samples from Schnauzers from different parts of the country to better determine if there is a genetic basis for the apparent increased risk for mycobacterial infections in Schnauzers.  Please contact Dr. Clint Lothrop, Jr. at the address below if you are interested in submitting blood samples for testing. All testing results will be kept strictly confidential.
 Note: Dr Lothrop is not soliciting samples from the general Schnauzer population at this time.
Clint Lothrop, Jr.
Scott-Ritchey Research Center
College of Veterinary Medicine
Auburn, AL 36849
(phone) (334) 844-5951