What is avian tuberculosis?

Avian tuberculosis is a chronic, infectious disease in birds, most commonly caused by the Mycobacterium avium complex (MAC), particularly Mycobacterium avium. It's important to note that classic tuberculosis with tubercles in organs is not commonly seen in small passerines. More often, it's found incidentally during necropsy, especially in canaries and finches (Estrildidae).

Understanding Avian Tuberculosis

Avian tuberculosis differs somewhat from mammalian tuberculosis. Here's a breakdown:

• Causative Agent: Primarily caused by bacteria within the Mycobacterium avium complex (MAC).
• Prevalence: While less common than other diseases in many bird species, it can be a significant issue in captive bird populations (like aviaries and zoos) and occasionally in wild birds. It's often an incidental finding in canaries and finches.
• Transmission: Birds typically become infected by ingesting contaminated food, water, or soil. Aerosol transmission is also possible but less common.
• Clinical Signs: Symptoms can be vague and vary depending on the affected organs. Common signs include:
  • Weight loss despite a normal appetite.
  • Lethargy and weakness.
  • Diarrhea.
  • Lameness or swelling of joints.
  • Depression
  • In advanced cases, internal organ involvement can lead to specific signs related to the affected organ system.
• Diagnosis: Diagnosis often involves:
  • Necropsy: Post-mortem examination to identify lesions characteristic of tuberculosis.
  • Microscopic examination: Acid-fast staining of tissues to visualize the bacteria.
  • Culture: Culturing the bacteria from tissues for definitive identification.
  • PCR: Molecular testing (Polymerase Chain Reaction) can be used to detect the presence of Mycobacterium avium DNA.
• Treatment: Treatment is challenging and often not successful. Due to the chronic nature of the disease and the risk of antimicrobial resistance, euthanasia is often recommended, especially in pet birds. In valuable collections, long-term antibiotic therapy may be attempted, but success rates are low.
• Prevention: Prevention is key and involves:
  • Maintaining excellent hygiene in bird enclosures.
  • Providing clean food and water.
  • Quarantining new birds before introducing them to an existing flock.
  • Regular veterinary check-ups.
  • Removal of contaminated soil or bedding.

Key Differences from Mammalian Tuberculosis

While both avian and mammalian tuberculosis are caused by Mycobacterium species, they have distinct characteristics: