Avian bornavirus (ABV) is currently considered a probable etiologic agent of proventricular dilatation disease (PDD) of psittacines. We tested 24 stored avian brain samples, processed for histopathology and retained following their submission for necropsy or histopathology to the Schubot Exotic Bird Center diagnostic laboratory in 1992. Thirteen of these samples were from birds diagnosed at that time as suffering from PDD. The remaining 11 samples were diagnosed as suffering from diseases other than PDD. Immunohistochemistry was performed using an antiserum directed against the ABV nucleoprotein (Nprotein). Stained slides were read by an investigator unaware of their prior histopathology results. Cells containing ABV N-protein were present in the nervous tissues of all 13 PDD cases. One bird not previously diagnosed with PDD also had ABV N-protein in its brain. A review of this bird's necropsy report indicated that it was, most probably, also suffering from PDD. The remaining 10 non-PDD birds had no detectable Nprotein in their brains. The N-protein was present in the cerebrum, cerebellum and spinal cord. These findings support other studies that indicate that ABV is an etiological agent of PDD.
The ongoing evolution of Ebolaviruses poses significant challenges to the development of immunodiagnostics for detecting emergent viral variants. There is a critical need for the discovery of monoclonal antibodies with distinct affinities and specificities for different Ebolaviruses. We developed an efficient technology for the rapid discovery of a plethora of antigen-specific monoclonal antibodies from immunized animals by mining the VH:VL paired antibody repertoire encoded by highly expanded B cells in the draining popliteal lymph node (PLN). This approach requires neither screening nor selection for antigen-binding. Specifically we show that mouse immunization with Ebola VLPs gives rise to a highly polarized antibody repertoire in CD138+ antibody-secreting cells within the PLN. All highly expanded antibody clones (7/7 distinct clones/animal) were expressed recombinantly, and shown to recognize the VLPs used for immunization. Using this approach we obtained diverse panels of antibodies including: (i) antibodies with high affinity towards GP; (ii) antibodies which bound Ebola VLP Kissidougou-C15, the strain circulating in the recent West African outbreak; (iii) non-GP binding antibodies that recognize wild type Sudan or Bundibugyo viruses that have 39% and 37% sequence divergence from Ebola virus, respectively and (iv) antibodies to the Reston virus GP for which no antibodies have been reported.
antibodies to this antigen. Of 15 birds believed to be free of PDD, two were weakly positive. While the nature of this antigen remains unclear, the authors suggest that it may be a viral antigen or a neurotoxin. The serum of affected birds does not react significantly with any antigens in normal macaw brains; therefore, it is unlikely to be an autoantigen. The antigen is found at all levels in the spinal cord and in the mid-and hindbrain. Its absence in Western blots of affected gastrointestinal tract may simply reflect the relative paucity of nervous tissue within these organs. Its presence in one of five hearts suggests that the heart sample taken may possibly have included some nerve tissue, although heart lesions were present in this bird. The antigen was not detected in any tissue from the three apparently PDD-negative birds tested. The presence of antibodies to this protein in 12 of 16 PDDconfirmed parrots and their absence in apparently normal birds may provide a basis for a serodiagnostic test for this disease. It is important to note that the sera were tested at a dilution of 1:5000. Less diluted samples may result in a higher seroprevalence. The four birds with negative serology were crop biopsy-positive. In testing 15 birds believed to be negative for PDD, two blood samples gave weak positive reactions. Given the insidious nature of PDD, it is not surprising that otherwise healthy birds may in fact be positive for the disease. Nevertheless, two possibly false positives out of 15, and four false negatives out of 16, suggest that detection of antibodies to this antigen by Western blotting or by other serological methods may be useful in confirming the diagnosis of PDD.
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