The aim of this study was to determine the natural infection route of parrot bornavirus (PaBV), the causative agent of proventricular dilatation disease (PDD) in psittacines. For this purpose, nine cockatiels (Nymphicus hollandicus) were inoculated orally, and nine cockatiels were inoculated intranasally, with a PaBV-4 isolate. To compare the results of both trials, the same isolate and the same experimental design was used as in a previous study where infection was successful by intravenous as well as intracerebral inoculation. After inoculation, the birds were observed for a period of six months and tested for PaBV RNA shedding, virus replication, presence of inflammatory lesions and PaBV-4 antigen in tissues as well as specific antibody production. In contrast to the previous study involving intravenous and intracerebral infections, clinical signs typical for PDD were not observed in this study. Additionally, anti-PaBV-antibodies and infectious virus were not detected in any investigated bird during the study. Parrot bornavirus RNA was detected in only four birds early after infection (1-34 days post infection). Furthermore, histopathological examination did not reveal lesions typical for PDD, and PaBV-antigen was not detected in any organ investigated by immunohistochemistry.
In summary, oral or nasal inoculation did not lead to a valid infection with PaBV in these cockatiels. Therefore it seems to be questionable that the formerly proposed faeco-oral transmission is the natural route of infection in immunocompetent adult or subadult cockatiels.