GROSS EXAMINATIONA 10-month-old, 1.75 kg hen was necropsied on 12/17/2025. This bird had a weeklong history of lethargy and poor appetite. She passed away naturally. Additional history is on file.
Autolysis was mild. The bird was emaciated with severe muscle wasting. The coelomic cavity was distended with approximately 8mL of light yellow to fan fluid that contained small, soft, light yellow, egg yolk-like material and fibrin. The liver contained multiple4-10 mm in diameter, soft, light tan, slightly raised nodules. Diffusely, the mesentery and intestinal serosa were thickened by tanto red, smooth to slightly raised, indistinct nodular lesions. Within the center of the mesentery, there was a 3-4 cm, firm, multinodular mass that was mottled tan to dark red to yellow on cut section. The ovary was atrophied. All other organs were grossly within normal limits. Gross Diagnoses:Liver, mesentery, and intestines: Multifocal nodular to diffuse masses, consistent with lymphoma Body, as a whole: Emaciation with severe muscle wasting Coelomic cavity: Coelomic effusion with yolk Cytology examination: An impression smear of one of the liver masses was examined. The highly cellular smear contains frequent lymphocytes, fairly frequent hepatocytes, and moderate to high amounts of blood on a light blue background. Approximately 80% of the cells are intermediate to large lymphocytes with small volumes of granular blue cytoplasm, and large round nuclei containing moderately stippled chromatin and 1 to 2 distinct nucleoli. Lesser numbers of small lymphocytes are observed.FINAL NECROPSY CONCLUSION(S): Multicentric lymphoma, consistent with Marek’s disease Comments:The combined gross and cytologic findings in this case are consistent with multicentric lymphoma (cancer). Lymphoma in chickens is often virally induced (Marek’s disease and avian leukosis). Both of these are transmissible forms of lymphoma in chickens (avian leukosis is caused by a retrovirus and Marek’s disease is caused by a herpesvirus). For both viruses, virtually all flocks are considered to be exposed to the virus, though the incidence of tumors and mortality is often low. The viruses are transmitted in eggs and through contact with infected birds. The incidence of disease of Marek’s disease can be reduced in birds through vaccination, but there is no vaccine to protect against tumor mortality associated with avian leukosis. While vaccination for Marek’s disease is the most effective way of preventing disease, it is not 100% effective, and we do occasionally see cases in vaccinated birds. In this case, given the pleomorphic nature of the neoplastic lymphocytes and the young age of the bird, this is consistent with Marek’s disease. The coelomic (body cavity) effusion (fluid accumulation) with egg yolk material is likely secondary to the lymphoma. As a specific diagnosis was made based on gross and cytologic examination and further testing is unlikely to significantly alter this diagnosis, no further testing is pending.
