Classification of Parasites

Although all infectious agents of humans are parasites, by convention, parasitic diseases are often defined as diseases caused by ectoparasites, parasites that live on the outside or within the skin of the host, and endoparasites, parasites that live on the inside of the host. Parasites occupy a diverse array of eukaryotic organisms that span many phyla ( Box 256.1 ). Together, ectoparasites and endoparasites exert an enormous toll on human life and health.