Studies on psittacine beak and feather disease

Psittacine beak and feather disease (PBFD) is a serious, often fatal condition, affecting a large number of species of psittacine birds throughout Australia, Europe, America and Africa. In Australia both captive and wild populations of birds are affected. The disease primarily effects young birds and results in feather abnormalities and atrophy of lymphoid organs. Some large birds also suffer beak deformities. The disease is widely believed to be viral in origin, although attempts to isolate a virus from affected tissues have so far failed. The development of growing feathers in normal cockatoos and cockatoos affected by PBFD was studied following plucking of the existing feathers. Differences in development were detected using light and electron microscopic techniques as early as 5 days after plucking and continued for the duration of a 28 day study. The major differences detected in the PBFD affected feathers were slow organization and growth, the presence of areas of necrosis and disorganization in epidermal areas and keratinization of epidermal cells at a more proximal level than was seen in normal feathers. Special stains confirmed that cells containing purple intracytoplasmic granules typically seen in affected feathers are macrophages, as previously postulated. Virus-like particles were detected in these cells, as well as in epidermal and endothelial cells in affected feathers. PBFD was experimentally transmitted to nestling budgerigars and galahs using several different inocula prepared from the feathers of birds naturally and experimentally infected with PBFD. PBFD could also be experimentally transmitted to young adult Peach-faced lovebirds. PBFD was transmitted to nestling budgerigars by oral, subcutaneous and intra-cloacal routes, however budgerigars became less susceptible to clinical disease with increasing age. Experimentally infected birds developed gross, histologic and electron microscopic lesions identical to those seen in birds naturally affected by PBFD. An inoculum prepared from the feathers of budgerigars with experimentally induced PBFD was used to reproduce PBFD in nestling galahs. Similarly an inoculum prepared from the feathers of galahs with experimentally induced PBFD was used to reproduce PBFD in nestling budgerigars, confirming that the disease in different species of psittacines is the same. Virus can be detected in the faeces of birds affected with PBFD over several months, and probably longer, and the faecal-oral route of transmission is postulated as the most likely method by which PBFD is transmitted naturally. Isolation of the causative virus of PBFD would not only prove a valuable diagnostic and experimental tool, but also aid in the development of a serologic test. Isolation attempts in chicken embryo fibroblast, chicken monocyte-derived macrophage, sulphur-crested cockatoo monocyte-derived macrophage and Crandal feline cell lines were unsuccessful, despite the same inoculum proving infectious to budgerigars. The culture of sulphur-crested monocyte-derived macrophage cell cultures has not been described previously. Attempts to develop an enzyme immunoassay using a virus-containing feather homogenate as an antigen was unsuccessful, as virus present in the antigen was already bound by psittacine IgG and therefore unsuitable. From the work presented it was not possible to determine the type of binding. The results obtained from experimental studies reported in this thesis are consistent with the hypothesis that PBFD is an infectious disease of viral aetiology which affects many species of psittacine birds