the occurrence of more than one distinct form of a natural object, such as a crystalline substance, a virus, the cells in a tumour, or an organism at different stages of the life cycle

parasitic flatworm of the class Trematoda, characterized by a body that is usually flat and often leaflike, which can infect the blood, liver, intestines, and lungs

Infection with the human immunodeficiency virus (HIV) that can occur through sexual intercourse, blood transfusion or the sharing of intravenous needles, skin piercing instruments or from mother to child.

parasitic protozoan that produces a refractory vaginal discharge in females, as well as bladder and urethral infections in males