Anatomical distribution of avian bornavirus in parrots, its occurrence in clinically healthy birds and ABV-antibody detection

Abstract

Proventricular dilatation disease (PDD) is a fatal infectious disease of birds that primarily affects psittacine birds. Although a causative agent has not been formally demonstrated, the leading candidate is a novel avian bornavirus (ABV) detected in post-mortem tissue samples of psittacids with PDD from the USA, Israel and, recently, Germany. Here we describe the presence of ABV in a parrot with PDD as well as in clinically normal birds exposed to birds with PDD. In two ABV-positive post-mortem cases, the tissue distribution of ABV was investigated by quantitative real-time reverse transcription-polymerase chain reaction. Viraemia was observed in a PDD-affected bird whereas a restriction of ABV to nerve tissue was found in the non-PDD-affected bird. Healthy birds from the same aviary as the affected birds were also found to harbour the virus; 19/59 (32.2%) birds tested positive for ABV RNA in cloacal swabs, providing the first evidence of ABV in clinically healthy birds. In contrast, 39 birds from the same geographic area, but from two different aviaries without PDD cases in recent years, had negative cloacal swabs. ABV RNA-positive, clinically healthy birds demonstrated the same serological response as the animal with confirmed PDD. These results indicate that ABV infection may occur without clinical evidence of PDD and suggest that cloacal swabs can enable the non-invasive detection of ABV infection.

Figure 1

Sera from PDD-affected Bird Z178/08, asymptomatic ABV PCR-positive Birds Z14/09-13 and Z14/09-05, and healthy PCR- negative Bird Z14/09-47, were evaluated by western blot analysis using recombinant ABV P and N, as well as BDV P and N (p23, p40), demonstrating a strong reaction to ABV N with limited cross-reactivity to BDV N.

Figure 2

Maximum likelihood tree based on nucleotide sequences of five ABV strains (strain Z178/08, accession number FJ770253, identical to strain Z1/09, accession number FJ932550; strain Z14/09/28 accession number FJ932551; strain 1367, accession number FJ169440.1; strain 1034_1322, accession number FJ169441.1; strain bil, accession number EU781967.1) and four BDV strains from mammals (strain No/98, accession number AJ311524.1; strain V, accession number U04608.1; strain He80, accession number L27077.2; strain He/80/FR, accession number AJ311522.1). Numbers near the nodes indicate the branch support. Unit of the scale bar is substitutions per site.