Skin involvement in lymphomas caused by Marek's disease virus infection in Silkie chickens

The Silkie is a typical Chinese breed of chicken. In 2012, batches of Silkies were found to have diffuse tumor-like nodules on their skin after feather removal, when they were slaughtered at about 60 days old. Gross examination showed no visible neoplastic lesions on the visceral organs and peripheral nerves, except slight splenomegaly in individual chickens. The disease was prevalent, with high condemnation rates for skin lesions, which caused great economic losses to the company. Tissues, including skin, visceral organs, and peripheral nerves, were collected for histologic examination. Heparinized blood samples were collected for virus isolation and identification. Marek's disease virus (MDV), Reticuloendotheliosis virus (REV), and Avian leukosis virus (ALV) were analyzed, using polymerase chain reaction (PCR) tests. Histologic examination showed that all of the tumor-like nodules on the skin were lymphomas. Lymphoproliferative lesions occurred mostly on the skin and only a few on the viscera, including the liver and proventriculus. Infected chick embryo fibroblasts showed clear cytopathic effects; indirect fluorescent antibody test for envelope glycoprotein B was positive. In addition, PCR indicated the presence of MDV serotype 1 infection without REV and ALV. A phylogenetic tree of the Meq gene showed that the isolate (SD121201) and Chinese reference strains, which are very virulent MDVs, are in the same clade. It was concluded that the Silkies tested were infected with MDV serotype 1. The Marek's disease epidemic has been controlled using CVI988/Rispens vaccines.