Marek’s disease is a highly contagious, economically important paralytic viral disease of poultry and is seriously threatening the poultry industry of the world including Ethiopia. In the present study, Marek’s disease virus isolated and characterized from clinically diseased chickens reared under different production systems in central Ethiopia. It is caused by herpes virus, belongs to the genus Mardivirus, family Herpesviridae. The virus causes massive destruction of lymphoid cells and macrophages inducing severe immunosuppression. Partial or complete paralysis is a fairly common symptom of Marek’s diseases due to accumulation and proliferation of tumour cells in peripheral nerves. Marek’s disease is diagnosed by isolation of the virus from tissue of infected chickens and viral antigen detection through available methods. Vaccination is the single most important method of controlling the diseases and preventing the development of tumours due to virus infection. Outbreaks still occur in vaccinated flocks under the right conditions due to a newly evolved highly virulent Marek’s diseases virus strain. The Ripens vaccine appeared to perform marginally better than the RMIT vaccine. To determine the 50% protective dose of vaccine the challenge virus strain and dose, the genetic susceptibility and sex of the chickens and environmental factors should be considered.
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