Abstract
Avian oncogenic viruses include Marek’s disease virus (MDV), a highly contagious herpesvirus, as well as retroviruses such as avian leukosis virus (ALV) subgroups A to J and reticuloendotheliosis virus (REV). In this study, we are surveying the incidence of these viruses during 2011-2015. A total of 64 flocks were vaccinated against MDV by using bivalent vaccine (HVT FC-126 + Rispens CVI988) (45 commercial Brown, white layers and 19 broiler breeder flocks) suffering from increase mortality with high No. of culling birds, bad uniformity and the post mortem examination revealed the presence of tumor lesions in different visceral organs. The age of birds varied from 11-24week, located in eight different governorates; [El-Sharkia, El-Dakahlia, El-Behera, Ismailia, Damietta, El-Monofia, El-Giza, Alexandria] .The total mortality reached 32.6% in brown commercial layers, 25.2% in white commercial layers (with average 28.9%) , 35.7% and 25.2% in females and males of broiler breeders respectively. Samples were collected from a total number of 20 out of 64 examined flocks, the twenty flocks representive 8, 6 and 6 commercial brown, white layer and broiler breeders respectively from tumor organs (liver, spleen, kidney, Bursa of Fabricious, heart, nerve, brain, mesentery and proventriculus). The histopathology-positive tissue sections were identified and further con-firmed by RT-PCR in addition to a blood samples were also collected for serological test using ELISA for ALV and REV. PCR using primers specific to (MDV, ALV, REV) appeared to be the method of choice for rapid and accurate diagnosis of these viruses. PCR and ELISA tests demonstrated the presence of MDV only in all collected samples except one sample was positive for both MDV and REV virus but all samples were negative for ALV.

Key words: Marek’s, tumor viruses, survey and epidemiology.