Parasitology is the study of parasites, their hosts, and the relationship between them. As a biological discipline, the scope of parasitology is not determined by the organism or environment in question but by their way of life. This means it forms a synthesis of other disciplines, and draws on techniques from fields such as cell biology, bioinformatics, biochemistry, molecular biology, immunology, genetics, evolution and ecology.
Adult black fly (Simulium yahense) with Onchocerca volvulus emerging from the insect's antenna. The parasite is responsible for the disease known as river blindness in Africa. Sample was chemically fixed and critical point dried, then observed using conventional scanning electron microscopy. Magnified 100×.
The Italian Francesco Redi, considered to be the father of modern parasitology, was the first to recognize and correctly describe details of many important parasites.
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson characterised parasites as "predators that eat prey in units of less than one". Parasites include single-celled protozoans such as the agents of malaria, sleeping sickness, and amoebic dysentery; animals such as hookworms, lice, mosquitoes, and vampire bats; fungi such as honey fungus and the agents of ringworm; and plants such as mistletoe, dodder, and the broomrapes.
A fish parasite, the isopod Cymothoa exigua, replacing the tongue of a Lithognathus
Head (scolex) of tapeworm Taenia solium, an intestinal parasite, has hooks and suckers to attach to its host
The parasitic castrator Sacculina carcini (highlighted) attached to its crab host
Human head-lice are directly transmitted obligate ectoparasites
