In some cases the iris is involved and this can lead to blindness. When the birds are autopsied the affected nerves can sometimes be seen to be swollen. Changes can be seen under the microscope. 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.
Some birds die without signs being noticed.
Similar disease Lymphoid leucosis also causes tumours in organs, but does not cause paralysis. It is usually seen in birds over 16 weeks of age, whereas MD is commonly seen under that age. Treatment Treatment is not effective. Diseased birds should be removed from the flock and humanely destroyed. The introduction of more potent vaccines is giving better control.