Parasitism

Parasitism is a <a href="/facts/Symbiosis/MrBArRGa">close relationship</a> between <a href="/facts/Species/oDg6b96r">species</a>, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the <a href="/facts/Host_(biology)/L6mop0kh">host</a>, causing it some harm, and is <a href="/facts/Adaptation/5K2gNpDB">adapted</a> structurally to this way of life. The entomologist <a href="/facts/E._O._Wilson/YuXAKxp7">E. O. Wilson</a> characterised parasites' way of feeding as "predators that eat prey in units of less than one". Parasites include single-celled <a href="/facts/Protozoa/JczTf25H">protozoans</a> such as the agents of <a href="/facts/Malaria/rN3g58CX">malaria</a>, <a href="/facts/Sleeping_sickness/zuvUoRKC">sleeping sickness</a>, and <a href="/facts/Amoebic_dysentery/VdNpYVKC">amoebic dysentery</a>; animals such as <a href="/facts/Hookworm/vSo9fQmh">hookworms</a>, <a href="/facts/Lice/xuKMIK5M">lice</a>, <a href="/facts/Mosquito/u8hTMTfc">mosquitoes</a>, and <a href="/facts/Vampire_bat/JR94QhBs">vampire bats</a>; <a href="/facts/Fungi/BHo5DP59">fungi</a> such as <a href="/facts/Armillaria_mellea/n354VMGP">honey fungus</a> and the agents of <a href="/facts/Ringworm/hFyb8T6n">ringworm</a>; and plants such as <a href="/facts/Mistletoe/TEDNExY3">mistletoe</a>, <a href="/facts/Dodder/XXPdQAKa">dodder</a>, and the <a href="/facts/Orobanchaceae/NUMn5wgN">broomrapes</a>.
There are six major parasitic <a href="/facts/Behavioral_ecology/P5Jm5ba7">strategies</a> of exploitation of animal hosts, namely <a href="/facts/Parasitic_castration/6y2pPww8">parasitic castration</a>, directly transmitted parasitism (by contact), trophically-transmitted parasitism (by being eaten), <a href="/facts/Disease_vector/bepASE2M">vector-transmitted</a> parasitism, <a href="/facts/Parasitoid/bdkEbIN9">parasitoidism</a>, and micropredation. One major axis of classification concerns invasiveness: an endoparasite lives inside the host's body; an ectoparasite lives outside, on the host's surface.
Like predation, parasitism is a type of <a href="/facts/Consumer%E2%80%93resource_interactions/vy6f9kBb">consumer–resource interaction</a>, but unlike <a href="/facts/Predation/JEGdrX3f">predators</a>, parasites, with the exception of parasitoids, are much smaller than their hosts, do not kill them, and often live in or on their hosts for an extended period. Parasites of animals are highly <a href="/facts/Generalist_and_specialist_species/HBajVhNJ">specialised</a>, each parasite species living on one given animal species, and <a href="/facts/Reproduction/nNu0F5Dy">reproduce</a> at a faster rate than their hosts. Classic examples include interactions between <a href="/facts/Vertebrate/tT54FSTT">vertebrate</a> hosts and <a href="/facts/Tapeworms/DP40WIv2">tapeworms</a>, <a href="/facts/Trematoda/d3J87oDn">flukes</a>, and those between the malaria-causing <a href="/facts/Plasmodium/Je91qK4F">Plasmodium</a> species, and <a href="/facts/Flea/hFLUFK24">fleas</a>.
Parasites reduce host <a href="/facts/Fitness_(biology)/MYpAGGey">fitness</a> by general or specialised <a href="/facts/Pathology/U9b18LJG">pathology</a>, that ranges from <a href="/facts/Parasitic_castration/6y2pPww8">parasitic castration</a> to <a href="/facts/Behavior-altering_parasites/wr7YPIns">modification of host behaviour</a>. Parasites increase their own fitness by exploiting hosts for resources necessary for their survival, in particular by feeding on them and by using intermediate (secondary) hosts to assist in their <a href="/facts/Transmission_(medicine)/sSGEGhcd">transmission</a> from one definitive (primary) host to another. Although parasitism is often unambiguous, it is part of a spectrum of interactions between <a href="/facts/Species/oDg6b96r">species</a>, grading via parasitoidism into predation, through evolution into <a href="/facts/Mutualism_(biology)/29hCDDS2">mutualism</a>, and in some fungi, shading into being <a href="/facts/Saprotrophic_nutrition/sJkDfrJW">saprophytic</a>.
Human knowledge of parasites such as <a href="/facts/Roundworm/yLMJ43Eu">roundworms</a> and <a href="/facts/Tapeworm/XQpcfzUx">tapeworms</a> dates back to <a href="/facts/Ancient_Egypt/BDsEGK4g">ancient Egypt</a>, <a href="/facts/Ancient_Greece/PTVBrWXq">Greece</a>, and <a href="/facts/Ancient_Rome/cGqIuxPd">Rome</a>. In <a href="/facts/Early_modern/hhpHM721">early modern</a> times, <a href="/facts/Antonie_van_Leeuwenhoek/HQ9dH9oo">Antonie van Leeuwenhoek</a> observed <a href="/facts/Giardia_lamblia/JzQgQB9j">Giardia lamblia</a> with his microscope in 1681, while <a href="/facts/Francesco_Redi/x1q0Hmzh">Francesco Redi</a> described internal and external parasites including <a href="/facts/Sheep_liver_fluke/9tmET3em">sheep liver fluke</a> and <a href="/facts/Tick/LNe33WJf">ticks</a>. Modern <a href="/facts/Parasitology/8UzTjlH8">parasitology</a> developed in the 19th century. In human culture, parasitism has negative connotations. These were exploited to <a href="/facts/Satire/dqFS5vIL">satirical</a> effect in <a href="/facts/Jonathan_Swift/000AjJvj">Jonathan Swift</a>'s 1733 poem "On Poetry: A Rhapsody", comparing poets to <a href="/facts/Hyperparasitical/8eGG61Er">hyperparasitical</a> "vermin". In fiction, <a href="/facts/Bram_Stoker/eJmm3Myz">Bram Stoker</a>'s 1897 <a href="/facts/Gothic_fiction/98wXoS69">Gothic horror</a> novel <a href="/facts/Dracula/DUmP8T48">Dracula</a> and its many later adaptations featured a <a href="/facts/Hematophagy/plcTvPFg">blood-drinking</a> parasite. <a href="/facts/Ridley_Scott/cop0oqMc">Ridley Scott</a>'s 1979 film <a href="/facts/Alien_(film)/TyTdD8TR">Alien</a> was one of many works of <a href="/facts/Science_fiction/d9hE2Lwt">science fiction</a> to feature a parasitic alien species.

Parasitism open-in-new

Parasitism