Amidst the various challenges of modern poultry health, such as avian influenza, Newcastle disease, and colibacillosis, there is one disease that is relatively rarely discussed yet carries severe implications for both poultry health and public health: avian tuberculosis (also known as avian mycobacteriosis). This disease is chronic, slow-developing, and frequently goes undetected until it reaches an advanced stage, thereby posing a potential threat of significant economic loss to livestock operations.

When chicken performance drops, egg production declines, or several birds appear increasingly emaciated without any obvious cause, farmers typically focus their attention on common diseases like colibacillosis or Newcastle disease. However, there is a chronic disease that often evades notice due to its extremely slow progression, namely avian tuberculosis / avian mycobacteriosis.

This disease is primarily caused by Mycobacterium avium subsp. avium, a bacterium capable of infecting almost all bird species, ranging from chickens, turkeys, and waterfowl to pigeons, ornamental birds, and wildlife. One of the reasons why mycobacteriosis is incredibly difficult to control is the causative bacteria’s ability to persist in the environment for extended periods.

Transmission generally occurs through the ingestion of feed or water contaminated with the feces of infected birds. Wild birds and carrier poultry also play a vital role as disease reservoirs. Furthermore, farm equipment, workers’ footwear, contaminated litter, and multi-age management systems can substantially elevate the risk of infection spread.

Clinical Signs and Pathology

Unlike acute diseases that develop rapidly, avian tuberculosis / avian mycobacteriosis is chronic and progressive. Clinical signs are often non-specific, making them easy to overlook. Infected poultry typically manifest gradual weight loss, severe emaciation (going light), weakness, chronic diarrhea, anemia, and reduced egg production. In some cases, respiratory distress and swelling around the eyes may be observed.

In advanced stages, the infection can lead to organ failure and ultimately end in death. The characteristic lesions of this disease can be identified during necropsy. Organs such as the intestines, liver, and spleen frequently exhibit yellowish-white nodules or granulomas resembling tubercles. The liver and spleen are commonly enlarged (hepatomegaly and splenomegaly) due to the formation of granulomatous tissue. In certain cases, lesions can also be found in the bone marrow, lungs, skin, or eyes.

Avian tuberculosis / Avian mycobacteriosis represents a threat that must not be disregarded. Its chronic nature, subtle detection profile, and long-term environmental persistence pose hidden challenges to both traditional and modern poultry industries. Vigilance and early detection remain the ultimate keys to safeguarding flock health and ensuring the sustainability of livestock businesses.

REFERENCES

• Abd El-Ghany, W. A. (2022). A review of avian mycobacteriosis: An emerging bacterial disease of public health concern. International Journal of One Health, 8(2), 70–75. https://doi.org/10.14202/IJOH.2022.70-75

• Sattar, A., Zakaria, Z., Abu, J., Aziz, S. A., & Rojas-Ponce, G. (2021). Isolation of Mycobacterium avium and other nontuberculous mycobacteria in chickens and captive birds in peninsular Malaysia. BMC Veterinary Research, 17, Article 13. https://doi.org/10.1186/s12917-020-02695-8

• Tsiouris, V., Kiskinis, K., Mantzios, T., Dovas, C. I., Mavromati, N., Filiousis, G., Brellou, G., Vlemmas, I., & Georgopoulou, I. (2021). Avian mycobacteriosis and molecular identification of Mycobacterium avium subsp. avium in racing pigeons (Columba livia domestica) in Greece. Animals, 11(2), 291. https://doi.org/10.3390/ani11020291

• World Organisation for Animal Health. (2024). Avian tuberculosis. In WOAH terrestrial manual 2024 (Chapter 3.3.6). World Organisation for Animal Health. https://www.woah.org