Cutaneous tumor-like lesions associated with poxvirus infection in laughing doves (Streptopelia senegalensis).

Abstract: Cutaneous, tumor-like nodules were observed on the digits and distal wings in 6 of 52 laughing doves (Streptopelia senegalensis) kept in an aviary. The nodules were surgically removed, and the birds were treated postoperatively with tetracycline. Histopathologic examination of the resected tissue revealed eosinophilic intracytoplasmic inclusion bodies associated with a heavy infiltration of heterophils, lymphocytes, and fewer plasma cells. Electron microscopy revealed pox virions. No additional cases were reported after the birds were surgically treated and quarantined from the remainder of the aviary. The location of lesions on the digits and distal wing tips is unusual for poxvirus. To our knowledge, infection with poxvirus has not previously been diagnosed or reported in wild birds in the Sultanate of Oman.

Key words: poxvirus, avian, laughing doves, Streptopelia senegalensis

Case Report

Two laughing doves (Streptopelia senegalensis), 4-6 months old, were admitted to the Seeb Veterinary Clinic, Sultanate of Oman, because of cutaneous nodules on a digit of one and the distal wing of the other. The birds, from a flock of 52 imported laughing doves maintained in an aviary, were housed in a single large wire-mesh cage equipped with several pigeonholes. The cage was cleaned daily, and fresh water was supplied ad libitum. The birds were fed a diet of commercial seed supplemented with minerals and vitamins. No other birds were kept with the doves. Subsequently, 4 additional birds in the aviary developed similar lesions of various sizes; a single digit was affected in 1 bird and digits and wings in 3 birds. No mortalities were recorded.

On physical examination, 1 bird exhibited a tumor-like cutaneous nodule measuring 11 X 6 X 4 mm on a digit of the left leg. The other bird displayed a similar nodule measuring 12 x 8 X 3 mm on the distal tip of the right wing. The nodules were firm and ulcerated. No other lesions were observed.

Swabs from the nodules were streaked on blood and MacConkey agar plates and incubated at 37[degrees]C for 48 hours; no significant bacteria were isolated. Lidocaine local anesthetic was applied to the skin, and the nodules were resected. Samples of each lesion were fixed in 10% buffered formalin, sectioned, and stained with hematoxylin and eosin. Tissue samples, approximately 1 mm in diameter, were also fixed in buffered Karnovsky solution, post-fixed in 1% aqueous osmium tetroxide, and processed for transmission electron microscopy. Fixed tissue was cut into 60- to 90-nm sections and viewed by using a Joel JEM-1230 transmission electron microscope at 80 kV.

Histopathologic lesions in nodules affecting both the wings and digits consisted of papilloma-like clusters of epithelial cells extending from the epidermis into the dermis. Epithelial debris, necrotic cells, and colonies of bacteria surrounded the cell clusters, and marked epidermal and dermal hyperplasia were observed along with ballooning degeneration (Fig 1). Numerous eosinophilic intracytoplasmic inclusions (Bollinger bodies) were present in most of the cells. Fibroblast proliferation and fibrosis were occasionally detected. A heavy infiltration of heterophils, lymphocytes, and plasma cells was seen among cell clusters. In some areas, intracytoplasmic inclusions of various sizes and shapes occupied almost the entire cell, resulting in the nucleus being either destroyed or displaced. Some cells were markedly enlarged and completely vacuolated. Electron microscopy revealed membranebound inclusions containing numerous mature and immature virus particles (Fig 2). Mature virions were recognizable by dumbbell- or brick-shaped nucleoids surrounded by distinctive membranes enclosing lateral bodies and a biconcave central core, whereas immature virions were small, spherical, electron-dense bodies, which were seen inside the inclusions, free in the cytoplasm, or inside clear vacuoles. In some inclusions, 2 mature virions were partially enclosed by 1 membrane. Inclusions contained clear vacuoles of various sizes, and some inclusions showed partial degeneration. Affected cells exhibited degenerative nuclei and reduced numbers or absence of cytoplasmic organelles. Heterophils contained round-to-oval granules, and some exhibited partial disintegration of the cell membranes with extruded granules; others contained clear cytoplasmic vacuoles.

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After surgery, the doves were prophylactically treated with tetracycline (150 mg/L of drinking water x 5 days). Other affected doves were isolated and treated similarly. Two months after surgery, no recurrence of pox lesions was observed in the previously affected birds.

Discussion

Avian pox is a common viral disease of domestic and wild birds, (1,2) but to the best of our knowledge, infection with poxvirus has never been diagnosed or reported in wild birds in the Sultanate of Oman. Both cutaneous and diphtheritic forms of poxvirus were previously reported in a mourning dove (Xenaida macrouva). (3) The presence of inclusion bodies containing virus particles was considered diagnostic for poxvirus in the case reported here. (4) A similar finding of tumor-like lesions due to poxvirus infection was reported in Chilean flamingos (Phoenicopterus chilensis). (5) Proliferation of fibroblasts may induce these tumor-like lesions.

We describe the light and electron microscopic findings of an avipoxvirus infection in laughing doves, lesions of which were manifested atypically on the digit of one dove and the wing of another. Lesions on the digit were similar to those described in a goshawk (Acciptev gentilis). (6) To the best of our knowledge, pox lesions on the wings have not been previously described. Cutaneous pox usually occurs on featherless parts of the face and legs.

The original source of the poxvirus in the aviary was not determined. Because avian pox is not generally thought to be transmitted through unbroken epithelium, it can be speculated that abrasions, perhaps a consequence of the birds flying in the cage, might have provided a route of viral transmission.

Resection of the pox lesions, wound dressing, and empirical antibiotic treatment to prevent secondary bacterial infection all contributed to clinical resolution. Similar results were described in a goshawk. (6) In this case, infected birds were quarantined in cages far from the aviary, and strict sanitary measures also played an important role in preventing further disease transmission.

Acknowledgments: We are grateful to Mrs Kawther Al-Adawi and Mr Virgillio Cruz for preparation of specimens for transmission electron microscopy.

References

(1.) Kirmse P. Pox in wild birds, an annotated bibliography. J Wildl Dis. 1967;49(suppl):1-10.

(2.) Yoshikkawa MGT, Alam J. Histopathological studies of fowl pox in Bantams. Int J Poult Sci. 2002;1:197199.

(3.) Tangredi BP. Avian pox in a mourning dove. Vet Med Small Anita Clin. 1974;69:700-701.

(4.) Tripathy DN, Reed WM. Pox. In: Saif YM, Barnes HJ, Glisson JR, et al, eds. Diseases of Poultry, 11th ed. Ames, IA: Blackwell Publishing; 2003:253-269.

(5.) Arai S, Arai C, Fujimaki M, et al. Cutaneous tumor-like lesions due to poxvirus infection in Chilean flamingos. J Comp Path. 1991;104:439-441.

(6.) Schoemaker NJ, Dorrestein GM, Lumeij JT. An avipoxvirus infection in a goshawk (Accipiter gentilis). Avian Pathol. 1998;27:103-106.

From the Department of Animal & Veterinary Sciences, College of Agricultural Marine Sciences (Tageldin, Johnson), the Department of Pathology, College of Medicine and Health Sciences (Al-Amri), and the Department of Marine Science and Fisheries (Aisha), Sultan Qaboos University, PO Box 34, Postal Code 123, Sultanate of Oman.