Immunohistochemical localization of tumor necrosis factor-α in gastrointestinal tissues of budgerigars naturally infected with Macrorhabdus ornithogaster

Macrorhabdosis is a contagious fungal gastrointestinal disease of birds, that predominantly affecs the proventriculus of budgerigars (Melopsittacus undulatus). Although the pathological features of Macrorhabdus ornithogaster infection have been extensively described, information regarding local inflammatory cytokine responses in naturally infected birds remains limited. In the present study, archival gastrointestinal tissues obtained from 25 budgerigars naturally infected with M. ornithogaster and 5 non-infected controls were evaluated histopathologically and immunohistochemically. Routine histopathology was performed to characterize tissue lesions, while immunohistochemistry was used to evaluate tissue expression of tumor necrosis factor-alpha (TNF-α). Histological lesions were predominantly localized to the proventriculus and consisted of mucosal erosion, ulceration, epithelial degeneration, and inflammatory cell infiltration associated with abundant fungal organisms. PAS and Gomori methenamine silver staining confirmed the presence and distribution of fungal elements within affected tissues. TNF-α immunoreactivity was detected mainly in epithelial and inflammatory cells within lesion affected areas, whereas control tissues exhibited minimal or no immunostaining. These findings demonstrate localized TNF-α expression in gastrointestinal tissues affected by M. ornithogaster infection and support the presence of an active TNF-α inflammatory response associated with macrorhabdosis. This study provides a descriptive baseline data for future quantitative and functional investigations evaluating cytokine-mediated mechanisms in avian fungal gastrointestinal disease.