Outbreaks of Marek’s Disease in Layer Chickens Farms in Khartoum and Gezira State in Sudan: Clinical and Pathological Aspects

Outbreaks of Marek’s disease were investigated in five commercial poultry farms in Khartoum and Gezira States during the period 2009-2012. All the affected birds were of layers aged 4-7 months. The mortality rate ranged from 0.3-2.8%, the clinical signs observed were diarrhea (60%), paralysis (60%) and drop in egg production (40%). Enlargement in visceral organs, and nerves were the main postmortem lesion in all examined birds , 100% enlargement was noticed in liver and spleen ,sciatic nerve(80 %), whereas lesion in eyes (20%), ovaries (20%), heart (40%) and lungs (20%) were not common. Infiltration of lymphoid cells was observed in livers, kidneys, spleen and nerves. The most remarkable finding in the present investigation was the excessive losses from MD in adult laying flocks over the age of 40 weeks suggesting that infection of MD in vaccinated adult commercial type chickens might be due to de novo infection (Super infection) with highly virulent strains despite existing considerable levels of vaccine immunity and age resistance, also vaccination failure may perhaps considered one of the important causes of disease outbreaks. These results may assist in disease control policies and planning research priorities.Keywords: Marek’s disease,field cases, clinical signs, postmortem lesions, histopathology,Suda