A parasite is a species that lives on or in another organism (which is known as the host). Parasites cause hosts some harm. Moreover, parasites are structurally adapted to the way of life of their host. Some common parasites that affect humans are hookworms, lice and protozoans such as the agents that carry diseases like malaria, sleeping sickness and amoebic dysentery. Herbivores are not considered parasites because they do not live on or in the body of a host.
