This is a symbiotic relationship between two organisms in which one species (parasite) benefits for growth and reproduction to the harm of the other species (host). It must be emphasized that parasite and host interact and that excessive harm done to a host, which makes it less competitive , also endangers the survival of the parasite species. Parasitism can be differentiated into

depending respectively, on whether they live on or in the host. Lice, flea, ticks, etc. are examples of ectoparasites. Tape-worms, bilharzia and the malaria parasite are examples of endoparasites.