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Avian Mycobacteriosis

Mycobacterium Infection

Avian mycobacteriosis, also known as avian tuberculosis (ATB), is an important chronic, contagious disease that affects both domestic and wild birds worldwide. The disease is caused by infection with Mycobacterium avium or M. genavense. M. avium is capable of infecting any species of bird, as well as other mammals, including humans. In cattle and goats, M. avium subsp. paratuberculosis (MAP) is responsible for causing paratuberculosis (PTB), also known as Johne's disease. Chickens that are stressed or have poor immune systems are more susceptible to infection with M. avium.

Avian Mycobacteriosis Risk Factors

Risk factors include overcrowded living conditions, inadequate or unbalanced nutrition, adverse weather or environmental conditions such as drought, extreme cold or heat, chronic inflammation, internal or external parasites, or infection with an existing disease.

Clinical Signs of Avian Mycobacteriosis

Avian mycobacteriosis has a slow disease course, and symptoms of illness may last for several weeks to months in affected birds. The most common signs include:
  • Progressive weight loss
  • Depression
  • Loss in condition
  • Muscle atrophy along the keel bone
  • Roosters may develop a change in voice, such as making hoarse attempts at crowing.

How Avian Mycobacteriosis is Transmitted

M. avium is transmitted primarily by infected wild birds or newly introduced, older adult domesticated poultry, which shed the organism into the environment through their droppings. Susceptible chickens become infected by ingesting or inhaling the organism from the contaminated environment.

Clinical Signs

Progressive weight loss
Enlarged abdomen
Change in voice
Hoarse crowing (roosters)
Dull ruffled feathers
Pale or bluish comb or wattle
Drooping wings
Lameness (often unilateral)


  • History
  • Acid fast staining
  • Bacterial culture
  • Tuberculin test (wattle)
  • Rapid Agglutination test
  • ELISA - useful for screening flocks
  • PCR


Supportive careIsolate the bird from the flock and place in a safe, comfortable, warm location (your own chicken "intensive care unit") with easy access to water and food. Limit stress. Call your veterinarian.
Antibiotic sensitivity testingIndicated for treatment, since each strain of M. avium shows differing resistance to different antibiotics.



  • Biosecurity
  • Do not use peat as a bedding material for poultry
  • Minimizing overcrowding
  • Providing proper ventilation
  • Supplementing adequate amounts of vitamins and minerals in diet
  • Quarantine new additions to the flock for at least 60 days

Scientific References

Age Range

Most commonly affects older birds between 18-20 months of age.

Risk Factors

  • Exposure to wild bird populations, including sparrows, starlings and pigeons
  • Roof-harvested rainwater
  • Compromised immune system
  • Stress