Two Cases of Feather Dystrophy in Free-Living Griffon Vultures (Gyps fulvus fulvus) Associated with Viral-like Inclusion Bodies

Abstract

The griffon vulture (Gyps fulvus fulvus) is a scavenger species that plays a vital ecological role in carrion removal. Successful survival and reproduction in captive and wildlife conditions require optimal physical status and plumage integrity. Nutritional and environmental factors, systemic diseases, and various etiological agents can influence feather alterations. Although frequently documented in captive psittacine species, feather abnormalities are extremely rare in wild birds. Since 2020, two free-living griffon vultures in northeastern Italy have been found in poor physical condition, unable to fly due to partial feather loss and malformation of remiges and rectrices. Histopathologic examination of follicles and peri-follicular tissue revealed atrophy, keratin replacement, vasculitis, and calamus dystrophy with lymphohistiocytic perivasculitis. Immunohistochemical and ultrastructural analysis identified the presence of virus-like particles in epithelial and inflammatory cells. Although virome analysis did not confirm the presence of this virus in pooled affected samples, this study provides the first report of an emerging plumage disorder in free-ranging griffon vultures, which requires further characterization.

Keywords: avian polyomavirus; birds of prey; feathers abnormalities; griffon vulture; inclusion bodies.

Figure 1

Gross aspect of altered tail feathers. (A) Injury patterns of differing severity, ranging from mild manifestations with alterations affecting the barbs of the vane and a markedly curved rachis, to an interruption of growth in the early stages of development due to necrosis of vascular structures, up to the formation of encapsulated amorphous material inducing follicular structural deformity. (B) Follicular dilation observed in the tail feathers.

Figure 2

Histological aspects of dystrophic feathers from a griffon vulture (Gyps fulvus fulvus). Comparison of (A) a normal feather and (B) a dystrophic feather sampled at the same level and in the same anatomical area, from a healthy and a deplumed vulture. In the diseased bird, necrosis in the calamus pulp (arrows) and dystrophy of barbs and barbules (arrowheads) are evident (H&E stain, scale bar = 15 μm). (C) Complete view of the calamus of a dystrophic feather showing the dystrophic–necrotic aspect of the pulp area of the calamus (arrows) and the presence of dermatitis in the residual, perifollicular tissue (arrowheads) (H&E stain; scale bars = 1 mm). (D) Histology of the rachis, at the level of the calamus, of the dystrophic feather. High magnification of a pathological area of the calamus pulp, with associated inflammation (lymphohistiocytic infiltration) (circle) surrounding the necrotic–eosinophilic material (arrows) (H&E stain; scale bars = 0.5 mm). (E) Numerous cells in the calamus pulp show intra-nuclear inclusion bodies (arrows) (H&E stain; scale bars = 150 µm). (F) Several inclusions show weak to moderate immunolabeling to APV-VP-1 (arrows) (IHC stain, Harris’s hematoxylin nuclear counterstain; scale bars = 150 µm).

Figure 3

Electron micrographs of one of the altered and immunohistochemically VP-1 positive cell nuclei, observed in the area of necrotic calamus pulp. (A) The nucleus is increased in size with marginated or fragmented chromatin, with small paracrystalline structures aggregated in the nucleoplasm (arrowheads) (scale bar = 1.25 µm). (B) Perinuclear chromatin margination (arrow), homogeneous cytoplasmic appearance with viral-like particles lining the plasma membrane (arrowhead), and early degradation of mitochondria showing initial crystolysis (scale bar = 1.25 µm). (C,D) Higher magnification of paracrystalline structures aggregated in the nucleoplasm and composed of regular, symmetrical, icosahedral viral-like particles, (arrowheads) (scale bars: 0.25 µm (C); 0.05 µm (D)).

Figure 4

Taxonomy distribution of sequencing contigs obtained from pooled samples: feathers (A), blood (B), and calamus (C).