Characterization of the avian polyomavirus-associated glomerulopathy of nestling parrots.

The glomerulopathy occurring in nestling nonbudgerigar parrots with avian polyomavirus (APV) disease was examined in 10 parrots. Glomerular lesions were characterized by the presence of dense, periodic acid-Schiff (PAS)-positive material that expanded the mesangium and that narrowed and at times occluded capillary lumina. PAS-staining was found to be more sensitive than hematoxylin and eosin in the detection of the lesions. Ultrastructurally, finely granular electron-dense material was found in massive intracapillary and mesangial condensates. Capillary endothelial cells exhibited changes consistent with cellular swelling. No evidence of chronic glomerular changes was observed. Immunofluorescent staining demonstrated that the PAS-positive, electron-dense condensates were complexes of IgG, avian polyomavirus antigen, and, in one bird, IgM. Viral DNA was detected in the serum of all six birds examined. Anti-APV antibodies were also present in all five serum samples examined. These findings suggested that the pathogenesis of this acute immune complex glomerulopathy and other APV-associated lesions depends on the presence of an appropriate ratio of circulating virus and anti-APV antibody.