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Updated: Jul 13, 2026
Intradermal Inoculation of Mycobacterium avium in the Mouse Ear
Published on: July 3, 2025
Molecular epidemiology of Mycobacterium avium subsp. avium and Mycobacterium intracellulare in captive birds
Mark Schrenzel1, Melissa Nicolas, Carmel Witte
1Zoological Society of San Diego, Wildlife Disease Laboratories, 15600 San Pasqual Valley Road, Escondido, CA 92027, USA. mschrenzel@sandiegozoo.org
Abstract:
Mycobacterium avium subsp. avium and Mycobacterium intracellulare are primary causes of mycobacteriosis in captive birds throughout the world, but little is known about how they are transmitted. To define the local epidemiology of infection, we strain-typed 70 M. avium subsp. avium and 15 M. intracellulare culture isolates obtained over a 4-year period from captive birds. Typing was performed using randomly amplified polymorphic DNA (RAPD) PCR, amplified fragment length polymorphic (AFLP) fragment analyses, and for a subset of isolates, DNA sequencing of a segment of the 16S-23S rRNA internal transcribed spacer region. Six strain clusters comprising 43 M. avium subsp. avium, isolates were identified; 42 isolates had unique typing patterns, including all M. intracellulare isolates. Phylo-geographical analyses using RAPD and AFLP fingerprints and animal confinement histories showed no correlation between housing of infected birds and mycobacterial strain-type, except for two animals. The diversity of M. avium subsp. avium and M. intracellulare isolates and minimal evidence for bird-to-bird transmission suggest that environmental reservoirs may be important sources of infection in captivity.
Insights
Mycobacterium avium subsp. avium and Mycobacterium intracellulare cause disease in captive birds. Limited bird-to-bird transmission suggests environmental sources are key infection reservoirs.
Area of Science:
- Veterinary Microbiology
- Avian Diseases
- Epidemiology
Background:
- Mycobacterium avium subsp. avium (MAA) and Mycobacterium intracellulare (MI) are significant pathogens causing mycobacteriosis in captive avian populations globally.
- Current understanding of transmission routes for these bacteria in captive birds remains limited, hindering effective disease control strategies.
Purpose of the Study:
- To investigate the genetic diversity and epidemiological patterns of MAA and MI isolates from captive birds.
- To identify potential sources and transmission dynamics of mycobacterial infections within captive avian environments.
Main Methods:
- Strain typing of 70 MAA and 15 MI isolates using Randomly Amplified Polymorphic DNA (RAPD) PCR and Amplified Fragment Length Polymorphic (AFLP) analyses.
- DNA sequencing of the 16S-23S rRNA internal transcribed spacer region for a subset of isolates.
- Phylogenetic and geographical analyses incorporating animal housing and confinement histories.
Main Results:
- Six distinct strain clusters were identified among the MAA isolates, with 42 isolates exhibiting unique typing patterns, including all MI isolates.
- Phylogeographical analyses revealed no significant correlation between bird housing and specific mycobacterial strain types, with only two exceptions.
- The high diversity of isolates and limited evidence for direct bird-to-bird transmission were observed.
Conclusions:
- The findings suggest that environmental reservoirs play a crucial role in the transmission of MAA and MI to captive birds.
- Further research into environmental sampling and source identification is warranted to mitigate mycobacterial infections in avian collections.
- Understanding transmission dynamics is essential for developing targeted interventions to protect captive bird health.
