Lymphoid leukosis discovered in Legbar chicken
By Martin Ficken, DVM, PhD
Recently, one dead, female, Cream Legbar chicken was presented to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) in Gonzales for necropsy. The bird had excellent feathering, was in good post-mortem condition, and weighed 1.06 kilograms.
Upon gross examination, mild breast muscle atrophy was present.The liver was enlarged approximately five times normal size and contained small white coalescing foci interpreted as neoplastic cells (Figure 1). The spleen was of normal size, but contained similar white foci.The kidney contained a nodular mass in the middle of the right renal chain that measured approximately 2 cm in diameter (Figure 2).The bursa contained a nodular mass that measured approximately 1 cm in diameter (Figure 3).The right lung was diffusely congested and edematous.All other systems contained no significant lesions.
Microscopic sections of liver were characterized by numerous coalescing foci of a uniform population of lymphoblasts that had large vesicular nuclei with marginated chromatin, one or more nucleoli, and poorly defined cytoplasmic membranes. Many individual cells had undergone necrosis. Occasional mitotic figures were observed. Foci of neoplastic cells appeared to be spreading by expansion with compression of the surrounding parenchyma rather than by infiltration of the sinusoids.
The spleen, bursa, and kidneycontained numerous coalescing foci of neoplastic cells similar to those described in the liver. A section of lung was characterized by diffuse congestion. No significant lesions observed in the brain, sciatic nerve, or heart.
Lesions in the liver, spleen, bursa, and kidney were characteristic of, and consistent with, lymphoid leukosis. Changes in the lung were considered terminal and incidental.
Lymphoid leukosis is caused by an avian retrovirus that induces a lymphoblastic lymphosarcoma in susceptible chickens, four months of age or older. Grossly visible tumors almost invariably involve the liver, spleen, and cloacal bursa. Other organs often grossly involved include the kidney, lung, gonad, heart, mesentery, and bone marrow. Tumor growth may be nodular, miliary, diffuse, or a combination of these forms. Microscopically all tumors are focal and multicentric in origin and the microscopic pattern is one of coalescing foci. Cells consist of large lymphoblasts with large vesicular nuclei with margination and clumping of chromatin (Nair & Fadly, 2013).
The main differential for lymphoid leukosis is Marek’s disease caused by avian herpesvirus and is far more common than lymphoid leukosis. Marek’s disease does not induce tumors in the bursa, growth is by infiltration of the tissue rather than by expansion, and the histopathologic features are of a pleomorphic population of various lymphocytes, lymphoblasts, reticular cells, and macrophages.
For more information about this case, contact Gonzales Resident Director Dr. Martin Ficken. To learn more about TVMDL’s testing services, visit tvmdl.tamu.edu or call 888.646.5623.
Nair, V and Fadly AM. Leukosis/Sarcoma Group in Diseases of Poultry 13th edition Wiley-Blackwell, ed. Swayne, DE et al. pp. 553-592, 2013.
Pope, CR. Lymphoid System in Avian Histopathology 2nd edition, ed. C. Riddell, pp. 17-44, 1996.