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Mycobacterium avium

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Synonym(s): M. avium


Introduction

Classification

Taxonomy

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

Etymology

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

Active Forms

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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.
  • Skin wounds sustained during hunting avian prey (most commonly seen in cats).
  • Soil disturbance can play a role in transmission by essentially aerosolizing contaminated soil.

Pathological effects

  • Enter the body via skin penetration or the gastrointestinal tract, and less commonly 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. Termed incomplete primary complex.
  • Submandibular, cervical and mesenteric nodes are most frequently affected.
  • Other reported symptoms include fever, vomiting, 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.
  • M. avium infection can produce a lepromatous form of disease, generally resulting in diffuse panniculitis Skin: panniculitis due to rapidly growing mycobacteria.
  • Siamese and Abyssinian breeds have been over represented in reported cases of M. avium in cats and with an increased severity of clinical disease.
  • Older cats, especially those with chronic kidney disease (CKD) and cats infected with Feline immunodeficiency virus (FIV) are at increased risk of infection.
  • Incubation period between infection and onset of clincial signs is unknown.

Control

Control via animal

  • Avoid contact with bird feces.

Control via chemotherapies

  • There are a nunmber of reports of cats with M. avium infection being successfully treated using triple combination antibiotic therapy including rifampin  Rifampicin with another 2 drugs from: clofazimine  Clofazimine , doxycycline  Doxycycline , pradofloxacin or marbofloxacin, ethambutol or clarithromycin   Clarithromycin .
  • Initial response to treatment may be good, but relapses may occur.
  • Recurrence of signs has been reported up to 2 years post treatment. It is unclear if this constitutes recrudescence of infection or repeat infection.
  • Ethical question over treatment; many drugs have associated toxicity in the cat and treatment is prolonged, typically lasting at least 6 months but often a minimum of a year is needed.
  • Theorectically there is a possible zoonotic potential of infection from cats to humans though this has not been demonstrated in practice to date.
  • Bacteriological cure may not coincide with resolution of clinical signs.

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 PubMed and VetMedResource.
  • Rivière D, Pingret J L, Etievant M et al (2011) Disseminated Mycobacterium avium subspecies infection in a cat. J Feline Med Surg 13 (2), 125-128 PubMed.

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