sporadic bovine leukosis

a disease similar to enzootic bovine leukosis, with malignant proliferation of lymphoid tissues but no culturable infectious agent; it occurs in three forms that vary in the age of the animal and organ affected: calf, seen in animals under six months of age and marked by generalized lymphadenopathy and widespread metastasis; thymic, seen in animals 6 to 18 months of age and confined mainly to the thymus; and cutaneous or skin, the only nonlethal form, affecting young adults and marked by cutaneous tumors that regress spontaneously.