Abstract
Avian mycobacteriosis (AM) is a zoonotic disease caused by Mycobacterium aviumcomplex (MAC), which can spread from avians to other farmed animals such as cattle and pigs as well as to humans. This study is the first report of granulomatous inflammation, as a result of avian mycobacteriosis, in the follicular pharyngeal tonsils of a farmed ostrich. The head of an apparently healthy farmed adult ostrich was obtained after slaughter. Each pharyngeal fold displayed a large tissue mass. This tissue was routinely prepared for light microscopy and stained with haematoxylin and eosin, periodic acid Schiff, Grocott methenamine silver, Gram and Ziehl-Neelsen. Immunohistochemistry (IHC) and polymerase chain reaction (PCR) were performed to identify Mycobacterium spp. and Mycobacterium tuberculosis complex, respectively. Histologically, the tissue masses consisted of confluent mature micro-granulomata that were characterised by central caseous necrosis surrounded by multinucleated giant cells, macrophages and lymphoid cells and an outer mature fibrous connective tissue capsule. Within some foci of caseous necrosis were variably sized colonies of small, Gram-negative, acid-fast bacilli, which showed positive IHC labelling for Mycobacterium spp., leading to a presumptive diagnosis of AM. PCR thus proved useful in excluding the presence of notifiable Mycobacteriumspp. The significance and role of the pharyngeal tonsils of ratites in diseases such as AM warrant specific attention. Moreover, as ratites are known to present with AM infections with apparently no visible loss in body condition, as presumably occurred in the present case, it is imperative that unusual masses in apparently healthy ratites be thoroughly investigated.
Highlights
The tissue masses originated from and were intimately attached to the dorsal surface of the pharyngeal folds, with the rostral, left tissue mass originating from the left pharyngeal fold and the caudal, right tissue mass originating from the right pharyngeal fold (Figure 2)
Mycobacteriosis is a chronic, progressive disease resulting in systemic granulomatous inflammation and in ratites usually presents as unthriftiness, loss of weight and diarrhoea (Shivaprasad 2002)
The reported case of granulomatous conjunctivitis was caused by M. phenylpyruvica, the authors noted the resemblance between these lesions and those seen in tuberculosis (Gürel, Gülçubuk & Turan 2004)
Summary
Mycobacterium avium complex (MAC) is the causative agent of a bacterial infection known as avian mycobacteriosis (AM) (García, LeClear & Gaskin 2001; Tell, Woods & Cromie 2001; Thornton et al 1999) or avian tuberculosis (ATB) (Cooper 2005; Thornton et al 1999). Avian mycobacteriosis mainly affects the digestive system (Bowes 1993; Cooper 2005; Cromie et al 2000; García et al 2001; Shivaprasad 2002; Tully & Shane 1996) with secondary spread of infection to other visceral organs (Bowes 1993) where the typical nodular lesions are detected (Doneley et al 1999; Huchzermeyer 1997). MAC bacilli are usually shed in the faeces of affected birds (Thornton et al 1999) and ingestion of contaminated faeces is the most common mode of infection (Bowes 1993; Cooper 2005; García et al 2001; Tully & Shane 1996)
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