Signalment:  

9-week-old, female, Leghorn chicken, avianIn March 2003, extensive swelling or bulbous protrusions of the integument were noticed in the layer chickens of approximately 11 weeks of age of a commercial flock. The affected chickens had almost no clinical signs other than the tumor and ate, drank, and walked normally. Approximately 80 of 27,000 (0.3%) chickens in the affected flock were slaughtered because of the tumor. Similar tumors had also occurred in the chickens of another farm originating from the same lot of breeder hens.¹⁵ Both affected flocks had been vaccinated by the wing-web method for fowl pox and Marek's diseases and were sprayed with the infectious bronchitis vaccine at hatching

Gross Description:  

The tumors were primarily observed in the head or wing, had a maximum diameter of 10 cm, were usually solitary, soft to firm but not hard, and creamy white to a dull red in color and grew slowly. The overlying skin was wounded in some cases, resulting in ulceration.

Histopathologic Description:

The tumor was unencapsulated and composed of loose areas with abundant mucinous matrix. Stellate or spindleshaped cells were predominant, whereas mitotic figures were uncommon. Short collagen fibers, which are stained blue by the azan stain and Masson trichrome stain, were observed in the matrix. The mucinous matrix was stained positively with alcian blue pH 2.5 and colloidal iron and showed metachromasia by toluidine blue staining: it was negative with alcian blue pH 1.0, high iron diamine, and periodic acid-Schiff reaction. The positive reactions disappeared after digestion with hyaluronidase. These results demonstrate that the matrix contained hyaluronic acid.

Tumors were specifically stained by a rabbit anti-ALSV serum and two mouse monoclonal antibodies against subgroup A ALSV, and the inner bulb of Herbst corpuscles was strongly stained. Normal cutaneous and subcutaneous tissues of the affected chickens were negative. 

Electron microscopy revealed viral particles in the tumor that were 74-97 nm in diameter, had a core (34-46 nm in diameter) and envelopes, and sometimes showed the budding process. Their ultrastructural characteristics were identical with those of type C retroviruses.⁸

Morphologic Diagnosis:  

Skin: myxoma, Leghorn, chicken, avian

Lab Results:  

RT-PCR analyses were performed on the tumor tissues of two affected chickens with a primer pair targeted the gp85 region of the env gene of subgroups A to E avian leukosis/sarcoma virus (ALSV). Tumor samples were PCR positive. Nucleotide sequence analyses indicated that these viruses belonged to subgroup A of ALSV and had 97.5% nucleotide sequence homology with myeloblastosis-associated virus type 1-like strain 1 of Canadian isolate.¹⁷ Fifteen of 20 serum samples obtained from 19 weeks of age clinically normal chickens from the affected layer farm were strongly reactive against subgroup A of ALSV, and eight of them were also strongly reactive against subgroup B by an enzymelinked immunosorbent assay (ELISA).¹⁹

Condition:  

Myxoma

Contributor Comment:  

Generally, neoplastic diseases other than Marek's disease or lymphoid leukosis are sporadic; however, in the present case, subcutaneous tumors were observed in many layer chickens in a flock. A congenital or genetic disease was suspected at first because a similar disease had occurred in the chickens of another farm originating from the same lot of breeder hens. The results of immunohistochemistry, electron microscopy, RT-PCR analysis, and ELISA indicate that the neoplastic diseases in the present case are associated with subgroup A of ALSV infection. It seems that the virus is exogenous because the ALSV antigen positive area is localized and, in the tumor, it corresponds with the C-type viral particles observed area. Eight of 20 chickens from the affected farm had an antibody to subgroup B; however, it might be a cross-reaction caused by group-specific antigens of ALSV. We conclude that 17 samples had antibodies against subgroup A ALSV. The existence of matrix-inclusion bodies containing ribonucleic acid in the myocardium is further evidence in favor of this viral infection.³ It is possible that the virus is transmitted vertically from hen to progeny through the egg or horizontally from bird to bird at the breeding site. Chickens inoculated in the wing web with avian sarcoma virus develop sarcomas at the site of inoculation⁵. Epizootic outbreaks of solid tumors have been reported, and the physical transmission of ALSV among newly hatched chickens during the vaccination procedure has been suggested⁷. However, in our case, tumors were observed not only at the site of inoculation, but also in other areas. Further studies are required to elucidate the epizootiology of our case.

The tumor contained large amounts of mucin and involved histologic lesions similar to those previously reported in cases of myxoma in chickens^{2, 16} and was therefore diagnosed as myxoma. Myxoma is composed of embryonal connective tissues.⁹ Myxoma in the subcutis, spleen, kidney, ovary, and mesentery in chickens has been previously reported.^{1, 16, 20} Replication-defective avian retroviruses and Rous sarcoma virus affect mesenchymal cells and cause sarcomas.¹² Various tumors have been reported in chickens inoculated with specific strains of ALSV; for example, strain F-1A of subgroup A has been associated with lymphoid leukosis, erythroblastosis, fibrosarcoma, and hemangioma in inoculated chickens.⁷

Today, it seems that leukosis-free flocks have been established, most commercial flocks consist of genetically resistant lines, the eradication of horizontally transmitted viruses has been accomplished,¹² and, accordingly, there has been a sharp reduction in the incidence of diseases associated with ALSV infection with the exception of subgroup J ALSV.^14,18 However, in our unpublished data, layer flocks frequently have ALSV antigens in Japan, and we are concerned about an outbreak of diseases associated with ALSV. The present epizootic outbreak of neoplastic disease is therefore unusual and worthy of study.

JPC Diagnosis:  

Feathered skin: Myxoma, leghorn chicken (Gallus domesticus), avian.

Conference Comment:  

The contributor gives a good overview of the ALSV-induced myxoma in this flock of commercial chickens. 

Viruses of the avian leukosis/sarcoma virus (ALSV) group are members of the Alpharetrovirus genus of the family Retroviridae. Other species within this genus include the Rous sarcoma virus and other replication defective viruses that carry various oncogenes. ALSVs are divided into 6 subgroups, A-E and J, based on differences in their viral envelope. Viral replication requires a reverse transcriptase that synthesizes a DNA provirus of the RNA virus. This DNA provirus is then integrated into the host cell genome where viral RNAs are transcribed, which are then translated into precursor and mature viral proteins.

In addition to subgroups, strains of ALSV are generally classified according to the predominant neoplasm they produce, such as lymphoid leukosis virus (LLV), avian erythroblastosis virus (AEV), avian myeloblastosis virus (AMV), and avian sarcoma virus (ASV). Although the oncogenic spectrum of the strains are usually characteristic, they can overlap and are affected by viral origin, dose, and route of inoculation, as well as by host age, genotype, and sex.

Gross and histologic differential diagnoses for neoplasms and lesions that may be caused by ALSV strains include:

• Lymphoid, erythroid, and myeloid infiltrates
  • Mareks disease, lymphoid leukosis virus, and reticuloendotheliosis virus have very similar gross and histologic lesions. They may be differentiated via PCR or serology
  • Erythroblastosis the liver and bone marrow are usually cherry red
  • Myeloblastosis the liver is usually pale red and the bone marrow is whitish, grossly the lesions are similar to lymphoid leukosis
• Myelocytomatosis: Distinctive character and location, is usually nodular and multiple, occurs on the surface of bone in association with the periosteum and near cartilage
• Hemangioma: Wounds, bleeding from feather follicles, hemorrhages, and sarcomas
• Renal tumors: Renal enlargement caused by hematomata, lymphoid leukosis, or accumulation of urates
• Osteopetrosis: Other osteopathies such as rickets, and osteoporosis
• Connective tissue tumors: Granulomas, tuberculosis, pullorum disease

Retrovirus of Animals¹²

Alpharetrovirus	Avian leukosis viruses, avian carcinoma viruses, avian sarcoma viruses, Rous sarcoma virus, duck spleen necrosis virus
Betaretrovirus	Mouse mammary tumor virus, Jaagsiekte
Gammaretrovirus	Feline leukemia virus, feline sarcoma virus, porcine type C virus, many murine leukemia viruses, many murine sarcoma viruses
Deltaretrovirus	Bovine leukemia virus, human and simian T lymphotropic viruses
Epsilonretrovirus	Walleye dermal sarcoma virus, walleye epidermal hyperplasia viruses
Lentivirus	Human immunodeficiency virus, simian immunodeficiency viruses, maedi/visna virus, caprine arthritis-encephalitis virus, feline immunodeficiency virus, equine infectious anemia virus, bovine immunodeficiency virus
Spumavirus	Bovine, feline, simian, and human foamy viruses

References:

1. Campbell JE, Appleby EC: Tumours in young chickens bred for rapid body growth (broiler chickens): a study of 351 cases. J Pathol Bacteriol 92:77-90, 1966
2. Fadly AM, Payne LN: Leukosis/sarcoma group. In: Diseases of Poultry, eds. Saif YM, Barnes HJ, Glisson JR, Fadly AM, McDougald LR, Swayne DE, 11th ed., pp. 465-505. Iowa State Press, Ames, IA, 2003
3. Gilka F, Spencer JL: Viral matrix inclusion bodies in myocardium of lymphoid leukosis virus-infected chickens. Am J Vet Res 46:1953-1960, 1985
4. Ginn PE, Mansell JEKL, Rakich PM: Skin and appendages. In: Jubb, Kennedy, and Palmers Pathology of Domestic Animals, ed. Maxie MG, 5th ed., vol. 1, p. 762. Elsevier Limited, St. Louis, MO, 2007
5. Halpern MS, Ewert DL, Flores LJ, Fujita DJ, Aldrich CE, Mason WS: Sarcoma growth in 15I5372 chickens infected with avian sarcoma viruses of subgroup B or G. Virology 134:472-476, 1984
6. Henderson BE, Gardner MB, Charman HP, Johnson EY, Rucio T, Sarma P, Alena B, Huebner RJ: Investigation of an increase of solid tumors in chickens vaccinated against Mareks disease. Avian Dis 18:58-66, 1974
7. Hihara H, Yamamoto H, Arai K, Yoshino T, Shimizu T: Oncogenicity of three strains of avian leukosis virus in white leghorn chicks of BK line. Natl Inst Anim Health Q (Tokyo) 20:87-95, 1980
8. Jawetz E, Melnick JL, Adelberg EA: Tumor viruses. In: Review of Medical Microbiology, 16th ed., pp. 488-498. Maruzen Asia Ltd., Singapore, 1984
9. Jones TC, Hunt RD, King NW: The skin and its appendages. In: Veterinary Pathology, 6th ed., pp 817-871. Williams and Wilkins, Baltimore, 1997
10. Maxie MG, Robinson WF: Cardiovascular system. In: Jubb, Kennedy, and Palmers Pathology of Domestic Animals, ed. Maxie MG, 5th ed., vol. 3, p. 51. Elsevier Limited, St. Louis, MO, 2007
11. Goldschmidt MH, Hendrick MJ: Tumors of the skin and soft tissues. In: Tumors in Domestic Animals, ed. Meuten DJ, 4th ed., pp. 91-92. Blackwell Publishing, Ames, IA, 2002
12. Murphy FA, Gibbus EPJ, Horzinek MC, Studdert MJ: Retroviridae. In: Veterinary Virology, 3rd ed., pp. 363-389, Academic Press, San Diego, 1999
13. Nakamura K, Higahi T, Yamada M, Imai K, Yamamoto Y: Basophilic intracytoplasmic viral matrix inclusions distributed widely in layer hens affected with avian-leukosis-virus-associated tumours. Avian Pathol 36:53-58, 2007
14. Nakamura K, Ogiso M, Tsukamoto K, Hamazaki N, Hihara H, Yuasa N: Lesions of bone and subcutaneous tumors in chickens 945 bone marrow in myeloid leukosis occurring naturally in adult broiler breeders. Avian Dis 44:215-221, 2000
15. Ono M, Tsukamoto K, Tanimura N, Haritani M, Kimura KM, Suzuki G, Okuda Y, Sato S: An epizootic of subcutaneous tumors associated with subgroup A avian leukosis/sarcoma virus in young layer chickens. Avian Dis 48:940-6, 2004
16. Reece RL: Some observations on naturally occurring neoplasms of domestic fowls in the State of Victoria, Australia (1977-87). Avian Pathol 25:407-447, 1996
17. Spencer JL, Benkel B, Chan M, Nadin-Davis S: Evidence for virus closely related to avian myeloblastosis-associated virus type 1 in a commercial stock of chickens. Avian Pathol 32:383-390, 2003
18. Takami, S, Goryo M, Masegi T, Okada K: Histopathological characteristics of spindle-cell proliferative disease in broiler chickens and its experimental reproduction in specific pathogen-free chickens. J Vet Med Sci 66:231-235, 2004
19. Tsukamoto K, Kono Y, Arai K, Kitahara H, Takahashi K: An enzyme-linked immunosorbent assay for detection of antibodies to exogenous avian leukosis virus. Avian Dis 29:1118-1129, 1985
20. West JL: An avian splenic myxoma. Avian Dis 18:139-141, 1974

A virtual slide is not available for this case.

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