it is one of aneoplastic viral disease primarly affect chicken and rarely affect turkey and firstly detection of the virus occur at year of 1980 by ( dr jozef Marek) and the virus is belongs to Herpes virus of DNA viruses this viruses characheterized by the infiltration of neoplastic cells of cells forming lymphocyt in many organs as nerves trank and internal organs and most of the virus type are antigenically related to each other and greatly differs according to their onchogonisty and ability to form tumors and some of serotypes are highly virulant and other are avirulant the female chicken is mostly affected than male one.
Some characters related to the virus .
Mode of transmission.
by horizontal transmission only and the infection occur through the respiratory tract of poultry by the inhalation of the virus which founded on the epithelial tissue of feather or skine dander and so it is very important from our field experience to burn the collected feather of birds at time of 80 days old when the feather renewed and prevent the ability of transmission of this virus infection and also burn the feather collected every 3 days during egg production. also the virus can infect birds through the digestive tract by ingestion the contaminated food and water which affected by the secrection of affected birds.