Systematic Veterinary Virology

SYMPTOMS

• Marek’s disease occurs in two main forms, depending on which parts of the body are affected by the tumours. The symptoms and lesions of the eye are sometimes referred as occular form (occular lymphomatosis)
• Nervous form (Classical form – neural lymphomatosis) : In this form the nerves, particulary the sciatic nerves (the main nerves to the legs), are affected. The birds are unable to stand, become paralysed and slowly waste away from lack of food and water. In most cases the paralysis comes on quickly. Sometimes the wings or neck are involved. In some cases the iris is involved and this can lead to blindness.
• Visceral form (Acute form): In this form, greyish-white tumours are found in the ovaries, liver, spleen, kidney, heart and other organs. Sometimes the liver and spleen are swollen without distinct tumours being present. Birds may show signs of depression, paralysis, loss of appetite, loss of weight, anaemia (pale combs), dehydration (shrunken combs), and sometimes diarrhoea. Some birds die without any clinical signs being noticed.