Megabacteriosis in budgerigars: diagnosis and treatment

Abstract

This study was performed on a breeding colony (about 500 budgerigars) affected by chronic fatal wasting disease. Necropsy was undertaken on ten severely affected budgerigars, and fresh-impression smears of the ventricular and proventricular mucosa were prepared and observed unstained and stained by Giemsa and Gram’s methods using light microscopy. Tissue samples for histopathology were taken from the proventriculus, gizzard, intestine, liver, spleen and lung, fixed in 10%-buffered formalin, and processed by standard paraffin wax technique. Sections were stained with H&E, Brown–Brenn and PAS methods. At necropsy, atrophy of the pectoral muscle, thickening of the proventricular and ventricular wall, covering of the proventricular mucosa by thick white mucus, ulceration and haemorrhage of the proventricular mucosa, and loosening of the koilin layer were observed. The most severe histopathological lesions were observed in the proventriculus and gizzard, especially at the proventricular–ventricular junction, including penetration of an organism to the lumen of the superficial proventricular crypts and occasionally to deeper parts of the glands; lymphocytic–plasmacytic proventriculitis, lymphocytic–plasmacytic ventriculitis and disruption of the koilin layer were also noted. The organism was gram-positive, PAS-positive and acidophilic in Gram’s, PAS and Giemsa stained sections, respectively. Other birds in the colony were treated with nystatin after which, the rate of mortality decreased and reached zero. At necropsy of treated birds, no megabacteria were observed in smears and tissue sections. In conclusion, definitive diagnosis of megabacteriosis is most consistently demonstrated by histopathology and fresh smear of the proventricular mucus. An effective treatment is antifungal agents such as nystatin.