Avian bornavirus associated with fatal disease in psittacine birds

Abstract

Thanks to new technologies which enable rapid and unbiased screening for viral nucleic acids in clinical specimens, an impressive number of previously unknown viruses have recently been discovered. Two research groups independently identified a novel negative-strand RNA virus, now designated avian bornavirus (ABV), in parrots with proventricular dilatation disease (PDD), a severe lymphoplasmacytic ganglioneuritis of the gastrointestinal tract of psittacine birds that is frequently accompanied by encephalomyelitis. Since its discovery, ABV has been detected worldwide in many captive parrots and in one canary with PDD. ABV induced a PDD-like disease in experimentally infected cockatiels, strongly suggesting that ABV is highly pathogenic in psittacine birds. Until the discovery of ABV, the Bornaviridae family consisted of a single species, classical Borna disease virus (BDV), which is the causative agent of a progressive neurological disorder that affects primarily horses, sheep, and some other farm animals in central Europe. Although ABV and BDV share many biological features, there exist several interesting differences, which are discussed in this review.

FIG. 1.

Manifestation of PDD in parrots. (A) Severely enlarged proventriculus of an orange-cheeked parrot (Pionites melanocephala) with PDD. The muscular wall of the proventriculus is highly atrophic with ingesta shining through. Within the pylorus region, a rupture of the proventriculus wall which spontaneously occurred intra vitam is visible. (B) Perivascular lymphoplasmacytic infiltrates in the brain of a diseased white cockatoo. (C to J) ABV antigen in various organs of an Amazona ventralis with PDD. Consecutive sections of paraffin-embedded organs of the diseased parrot infected with ABV genotype 2 strain 6609 (62) were stained with either a cross-reactive rabbit antiserum against the P protein of BDV (C, E, G, and I) or preimmune serum (D, F, H, and J): brain (C and D), liver (E and F), heart (G and H), and intestine (I and J). Brown staining indicates specific staining of ABV antigens by the cross-reactive antiserum.

FIG. 2.

Phylogenetic tree based on partial N gene sequences of bornaviruses from mammals and birds. Bootstrap values are given as percentages for the main nodes. Brackets illustrate the rationale for grouping known psittacine bornaviruses into five distinct genotypes. The GenBank accession number, strain name, and country and year of isolation are given.