An Update on Avian Mycobacteriosis

Domestic and wild birds play crucial roles in transmission and spread of important zoonotic pathogens with significant implications on human and avian health. There are more than 35 Mycobacterial species which can cause Mycobacteriosis. Avian Mycobacteriosis, primarily caused by Mycobacterium avium subsp. avium (MAA) is a chronic progressive, zoonotic disease with significant implications for both animal and public health, affects avian species comprising domestic poultry, captive wild birds and exotic pet birds as well as various mammals including immunocompromised humans. The pathogen is able to resist harsh environments (low oxygen, high temperature, dryness and low pH) and commonly used disinfectants. Mycobacteria species can survive in soil for more than 4 years. Transmission occurs via contaminated feces, soil, water and fomites, with infection routes being mostly oral. Clinically, affected birds often exhibit emaciation, depression and diarrhoea. Gross lesions typically present as greyish-white or yellow nodules in organs such as the liver, spleen and intestines, often leading to organ enlargement and a characteristic “knife-edged” keel due to muscle atrophy. Microscopically, the disease is marked by granulomas with central caseous necrosis, surrounded by epithelioid macrophages, multinucleated giant cells and lymphocytes, often encapsulated by fibrous tissue. Diagnostic approaches including acid-fast staining, culture, serological tests and molecular assays such as PCR. The rising incidence of Mycobacterial infections globally, especially among immunocompromised populations, underscores the need for enhanced surveillance, diagnostic refinement and potential vaccine development to mitigate both avian and zoonotic threats posed by avian Mycobacteriosis.