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Avian Mycobacteriosis

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.

Often, chickens with avian mycobacteriosis may not show any clinical signs of infection until death. However in those that do, the classical presentation is characterized by chronic and progressive emaciation with a prominent keel bone apparent, as a result of muscle atrophy, and weakness. Chickens that are stressed or have poor immune systems are more susceptible to infection with M. avium. Possible stresses may be related to 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
The most commonly reported clinical signs of the disease include progressive weight loss and muscle atrophy along the keel bone. More specific, additional signs exhibited by an infected white-crested Hollard dwarf rooster were hoarse attempts at crowing during it's last three weeks in the disease course. Over the course of the final week, the rooster showed dramatic loss of condition and depression.

Transmission
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.

Incubation period
Avian mycobacteriosis has a long incubation period and a slow course, with symptoms prolonging in birds for weeks or months.

Necropsy findings
Firm, grayish-yellow to white granulomatous lesions in the intestines, liver, and spleen, and bone marrow.

Symptoms

Progressive weight loss
Prominent keel bone
Diarrhea
Enlarged abdomen
Loss of voice
Dull ruffled feathers
Pale or bluish comb or wattle
Lethargy
Depression
Paralysis
Drooping wings
Lameness (often unilateral)

Diagnosis

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

Treatment

Antibiotic sensitivity testing: Indicated for treatment, since each strain of M. avium shows differing resistance to different antibiotics.

Prevention

  • 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