Canis ISSN: 2398-2942

Mycobacterium avium

Synonym(s): M. avium

Contributor(s): Karen Coyne, Melissa Kennedy, Conor O'Halloran

Introduction

Classification

Taxonomy

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

Etymology

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

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Clinical Effects

Epidemiology

Habitat

  • 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.

Transmission

  • 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

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.

Vaccination

  • No vaccine available.

Diagnosis

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Further Reading

Publications

Refereed papers

  • Recent references from VetMed Resource and PubMed.
  • Biet F et al (2005) Zoonotic aspects of Myxobacterium bovis and Mycobacterium avium-intracellulare complex (MAC). Vet Res 36, 411-436 PubMed.
  • O'Toole D et al (2005) Fatal mycobacteriosis with hepatosplenomegaly in a young dog due to Mycobacterium avium. J Vet Diag Invest 17, 200-204 PubMed.
  • Eggers J S et al (1997) Disseminated Mycobacterium avium infection in three Miniature Schnauzer litter mates. J Vet Diag Invest 9, 424-427 PubMed.

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