ISSN 2398-2942      

Mycobacterium avium


Synonym(s): M. avium




  • Order: Actinomycetales
  • Family: Mycobacteriaceae
  • Genus: Mycobacterium
  • Species: avium


  • Gr: myces- fungus; bakterion - a small rod.
  • Non-tubercle forming mycobacteria.

Active Forms

This article is available in full to registered subscribers

Sign up now to start a free trial to access all Vetlexicon articles, images, sounds and videos, or Login

Clinical Effects



  • Can survive in soil and water, particularly in acidic swamp areas and coastal plains.
  • Can remain viable for up to 4 years in the environment.
  • Feces of infected birds contain large numbers of bacilli.


  • Ingestion of meat or contact with infected soil or fomites contaminated by bird carcasses or feces.
  • Soil disturbance can play a role in transmission by essentially aerosolizing contaminated soil.

Pathological effects

  • Enter the body via the gastrointestinal tract, and less commonly by inoculation into the skin or by aerosol.
  • Engulfed by phagocytic cells (dendritic cells and macrophages) where they subvert immune mediated killing in order to multiply.
  • Granuloma formation occurs to contain the organism.
  • Spread to adjacent tissues or throughout the body via hematogenous or lymphatic dissemination.
  • Local multiplication of the bacillus may develop at the initial site (primary complex).
  • Primary clinical presentation of disseminated M. avium include enlarged lymph nodes, inappetence and/or anorexia, hepatomegaly, splenomegaly and diarrhea with or without vomiting. 
  • Submandibular, cervical and mesenteric nodes are most frequently affected.
  • Other reported clinical signs include fever, inappetence, melena, dyspnea, and lameness.
  • Infection disseminates throughout other tissues, including spleen, liver, and bone marrow.
  • Progression of the disease depends on the ability of macrophages to inhibit intracellular growth of the organisms.
  • M. avium granulomatous lesions are indistinguishable from tubercular lesions formed by infection with of M. tuberculosis-complex.
  • Incubation period between infection and onset of clincial signs is unknown.
  • It is suspected that affected individuals are in some way immunocompromised in order to allow the pathogen the opportunity to cause disseminated disease in a species.

Other Host Effects

Clinical signs

  • In order of observed frequency, the most common clinical signs include:
    • Lethargy, depression and anorexia are almost ubiquitous.
    • Pyrexia.
    • Lymphadenopathy Lymphadenopathy (mesenteric most frequently but also the tonsils and submandibular lymph nodes).
    • Pale mucous membranes (due to mild/moderate normocytic normochromic non-regenerative anemia).
    • Cranial abdominal pain (due to hepatomegaly and/or splenomegaly).
    • Diarrhea +/- melena or hematochezia.
    • Vomiting.
    • Icterus.
  • Sporadically reported signs include:
    • Neck pain.
    • Shifting lameness.
    • Limb paralysis.
    • Dyspnea.
    • Polyuria and polydipsia.
    • Cutaneous swellings.


Control via animal

  • Avoid contact with bird feces.

Control via chemotherapies

  • Several drug protocols have been attempted; amoxicillin Amoxicillin, potentiated amoxicillin and cephalosporins are often used initially giving brief clinical improvement.
  • Multi-drug combinations have been used which contain fluoroquinolones (pradofloxacin, moxifloxacin or enrofloxacin Enrofloxacin), macrolides (clarithromycin Clarithromycin or azithromycin Azithromycin) and rifampicin Rifampicin, occasionally with the addition of doxycycline Doxycycline and/or streptomycin Streptomycin in severe cases.
  • Initial response to treatment may be good, but relapses may occur.
  • Survival times on multi-drug protocols have been reported between 4 days and 10 months.
  • There are no reported cases of long term resolution where therapy could be discontinued.
  • Ethical question over treatment; many drugs have associated toxicity and treatment is continuous until deterioration and euthanasia.
  • Theorectically there is a possible zoonotic potential of infection from dogs to humans.

Control via environment

  • None; ubiquitous in soil/water.


  • No vaccine available.


This article is available in full to registered subscribers

Sign up now to start a free trial to access all Vetlexicon articles, images, sounds and videos, or Login

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Biet F, Boschiroli M L, Thorel M F et al (2005) Zoonotic aspects of Mycobacterium bovis and Mycobacterium avium-intracellulare complex (MAC). Vet Res 36 (3), 411-436 PubMed.
  • O'Toole D, Tharp S, Thomsen B V et al (2005) Fatal mycobacteriosis with hepatosplenomegaly in a young dog due to Mycobacterium avium. J Vet Diag Invest 17 (2), 200-204 PubMed.
  • Eggers J S, Parker G A, Braaf H A et al (1997) Disseminated Mycobacterium avium infection in three miniature schnauzer litter mates. J Vet Diag Invest (4), 424-427 PubMed.

Can’t find what you’re looking for?

We have an ever growing content library on Vetlexicon so if you ever find we haven't covered something that you need please fill in the form below and let us know!


To show you are not a Bot please can you enter the number showing adjacent to this field

 Security code