Avian mycobacteriosis is a significant cause of avian morbidity and mortality, affecting commercial, aviary/pet, zoological and wild birds.1-7 Over a period of 7 years, Taronga Zoo had a 9.4% incidence of avian mycobacteriosis in birds based on histopathological and/or microbiological examinations. Although Mycobacterium avium was successfully cultured in 30% of histopathology positive cases, 70% were unspeciated and suspected cases couldn’t be confirmed using culture. This study aimed to identify mycobacterial species in unspeciated and suspect cases using molecular diagnostics. It also explored fecal testing as a potential method of ante-mortem detection and examined epidemiological features of avian mycobacteriosis within the collection, including species predilection, environmental risk factors and application of molecular diagnostics for use in wild birds.
Conventional pan-mycobacterial nested-PCR and sequencing identified mycobacterial species in archived tissue samples from cases between 2007-2013. From 80 birds, mycobacterial DNA was identified in 104 samples as M. genavense (66), M. avium (48) or M. terrae (2); 12 samples had dual infection. PCR increased the rate of post-mortem mycobacteriosis detection by 30% and increased the rate of Mycobacteria speciation by 331%. Ante-mortem fecal testing using real-time PCR didn’t detect M. genavense in clinically affected birds, including those later confirmed to have M. genavense on tissue PCR. Two clinically healthy birds had M. genavense in fecal samples.
In total, 38 bird species were represented, with affected birds displaying a wide range of clinical signs and gross findings. The highest incidence of mycobacteriosis was in Columbiformes (16.1%) suggesting greater susceptibility. Psittaciformes had a low incidence (3.4%), contrasting previous studies suggesting high susceptibility.1
This study highlighted the need for molecular diagnostics on tissues for avian mycobacteriosis diagnosis and confirmed M. genavense as the leading cause of mycobacteriosis in the collection. Further research includes relevance to wild populations and further development of reliable ante-mortem diagnostics.