Editing Parasitism (section)

== Taxonomic range ==

Parasitism has an extremely wide taxonomic range, including animals, plants, fungi, protozoans, bacteria, and viruses.<ref name="Rollinson2">{{cite book |last1=Rollinson |first1=D. |last2=Hay |first2=S. I. |title=Advances in parasitology |date=2011 |publisher=Elsevier Science |location=Oxford |isbn=978-0-12-385897-9|pages=4–7}}</ref>

=== Animals ===

{{further|List of parasitic organisms}}

{|class="wikitable sortable <!--collapsible collapsed-->"
|+ Major parasitic animal groups{{sfn|Poulin|2007|page=6}}
! Phylum !! Class/Order 
 ! style="width: 60px;" |No. of<br/>species 
! Endo-<br/>paras. ||Ecto-<br/>paras. !! [[Invertebrate|Invert]]<br/>def. host !! [[Vertebrate|Vert]]<br/>def. host !! No. of<br/>hosts !! Marine !! Fresh-<br/>water !! Terres-<br/>trial
|-
|[[Cnidaria]] ||[[Myxozoa]] ||1,350 ||Yes ||||||Yes ||2 or more ||Yes ||Yes ||
|-
|[[Cnidaria]] ||[[Polypodium (animal)|Polypodiozoa]] ||1 ||Yes ||||||Yes ||1 ||||Yes ||
|-
|[[Flatworms]] ||[[Trematodes]] ||15,000 ||Yes ||||||Yes ||2 or more ||Yes ||Yes ||Yes
|-
|[[Flatworms]] ||[[Monogenea]]ns ||20,000 ||||Yes ||||Yes ||1 ||Yes ||Yes ||
|-
|[[Flatworms]] ||[[Cestoidea|Cestodes]] ||5,000 ||Yes ||||||Yes ||2 or more ||Yes ||Yes ||Yes
|-
|[[Nematomorpha|Horsehair worms]] ||<!--Class--> ||350 ||Yes ||||Yes ||||1 or more ||||Yes ||Yes
|-
|[[Nematodes]] ||<!--Class--> ||10,500 ||Yes ||||Yes ||Yes ||1 or more ||Yes ||Yes ||Yes
|-
|[[Acanthocephala]] ||<!--Class--> ||1,200 ||Yes ||||||Yes ||2 or more ||Yes ||Yes ||Yes
|-
|[[Annelids]] ||[[Hirudinea|Leeches]] ||400 ||||Yes ||||Yes ||1 ||Yes ||Yes ||
|-
|[[Molluscs]] ||[[Bivalves]] ||600 ||||Yes ||||Yes ||1 ||||Yes ||
|-
|[[Molluscs]] ||[[Gastropods]] ||5,000 ||||Yes ||||Yes ||1 ||Yes ||||
|-
|[[Arthropods]] ||[[Ixodida|Ticks]] ||800 ||||Yes ||||Yes ||1 or more ||||||Yes
|-
|[[Arthropods]] ||[[Acari|Mites]] ||30,000 ||Yes ||Yes ||Yes ||Yes ||1 ||Yes ||Yes ||Yes
|-
|[[Arthropods]] ||[[Copepods]] ||4,000 ||||Yes ||Yes ||Yes ||1 ||Yes ||Yes ||
|-
|[[Arthropods]] ||[[Phthiraptera|Lice]] ||4,000 ||||Yes ||||Yes ||1 ||||||Yes
|-
|[[Arthropods]] ||[[Siphonaptera|Fleas]] ||2,500 ||||Yes ||||Yes ||1 ||||||Yes
|-
|[[Arthropods]] ||[[Diptera|True flies]] ||2,300 ||||Yes ||||Yes ||1 ||||||Yes
|-
|[[Arthropods]] ||[[Strepsiptera|Twisted-wing insects]]||600 ||Yes ||||Yes ||||1 ||||||Yes
|-
|[[Arthropods]] ||[[Hymenoptera|Parasitoid wasps]] ||130,000<ref>{{cite journal |last1=Polaszek |first1=Andrew |last2=Vilhemsen |first2=Lars |title=Biodiversity of hymenopteran parasitoids |journal=Current Opinion in Insect Science |date=2023 |volume=56 |page=101026 |doi=10.1016/j.cois.2023.101026 |pmid=36966863 |s2cid=257756440 |doi-access=free |bibcode=2023COIS...5601026P }}</ref> - 1,100,000<ref name="Forbes Bagley Beer Hippee 2018">{{cite journal | last1=Forbes | first1=Andrew A. | last2=Bagley | first2=Robin K. | last3=Beer | first3=Marc A. | last4=Hippee | first4=Alaine C. | last5=Widmayer | first5=Heather A. | display-authors=3 | title=Quantifying the unquantifiable: why Hymenoptera, not Coleoptera, is the most speciose animal order | journal=BMC Ecology | volume=18 | issue=1 | date=12 July 2018 | page=21 | issn=1472-6785 | doi=10.1186/s12898-018-0176-x| pmid=30001194 | pmc=6042248 | doi-access=free | bibcode=2018BMCE...18...21F }}</ref> ||Yes ||Yes ||Yes ||||1 ||||||Yes
|}

Parasitism is widespread in the animal kingdom,<ref>{{cite book |last1=Morand |first1=Serge |last2=Krasnov |first2=Boris R. |last3=Littlewood |first3=D. Timothy J. |title=Parasite Diversity and Diversification |url=https://books.google.com/books?id=o2t2BgAAQBAJ&pg=PA44 |year=2015 |publisher=Cambridge University Press |isbn=978-1-107-03765-6 |page=44}}</ref> and has evolved independently from free-living forms hundreds of times.<ref name=PoulinRandhawa2015/> Many types of [[helminth]] including [[trematoda|flukes]] and [[Cestoidea|cestodes]] have complete life cycles involving two or more hosts. By far the largest group is the parasitoid wasps in the Hymenoptera.<ref name=PoulinRandhawa2015/> The [[phylum|phyla]] and [[class (biology)|classes]] with the largest numbers of parasitic species are listed in the table. Numbers are conservative minimum estimates. The columns for Endo- and Ecto-parasitism refer to the definitive host, as documented in the Vertebrate and Invertebrate columns.{{sfn|Poulin|2007|page=6}}

=== Plants ===

{{main|Parasitic plant}}

[[File:Cuscuta parasite plant.JPG|thumb|left|upright|''[[Cuscuta]]'' (a dodder), a stem [[holoparasite]], on an [[acacia]] tree]]

A [[hemiparasite]] or ''partial parasite'' such as [[mistletoe]] derives some of its nutrients from another living plant, whereas a [[obligate parasite|holoparasite]] such as ''[[Cuscuta]]'' derives all of its nutrients from another plant.<ref name="Rastogi">{{cite book |last1=Rastogi |first1=V. B. |title=Modern Biology |url=https://books.google.com/books?id=D-85x6Jhji0C&q=partial+parasite&pg=SA1-PA115 |publisher=Pitambar Publishing |date=1997 |isbn=978-81-209-0496-5 |page=115}}</ref> [[Parasitic plant]]s make up about one per cent of [[angiosperms]] and are in almost every [[biome]] in the world.<ref name="Kokla Melnyk 2010">{{Cite journal |last1=Kokla |first1=Anna |last2=Melnyk |first2=Charles W. |date=1 October 2018 |title=Developing a thief: Haustoria formation in parasitic plants |journal=Developmental Biology |language=en |volume=442 |issue=1 |pages=53–59 |doi=10.1016/j.ydbio.2018.06.013 |pmid=29935146 |s2cid=49394142 |issn=0012-1606|doi-access= }}</ref><ref name="Heide-Jørgensen, H. 2008">{{cite book |last=Heide-Jørgensen |first=Henning S. |year=2008 |title=Parasitic flowering plants |publisher=Brill |isbn=978-90-04-16750-6}}</ref><ref name=Nickrent2002>{{cite web |last1=Nickrent |first1=Daniel L. |author-link1=Daniel Lee Nickrent |title=Parasitic Plants of the World |url=http://nickrentlab.siu.edu/NickrentPDFs/Chapter2.pdf |date=2002 |access-date=10 April 2018 |url-status=live |archive-url=https://web.archive.org/web/20160306062557/http://nickrentlab.siu.edu/NickrentPDFs/Chapter2.pdf |archive-date=6 March 2016}} which appeared in Spanish as Chapter 2, pp. 7–27 in: J. A. López-Sáez, P. Catalán and L. Sáez [eds.], ''Parasitic Plants of the Iberian Peninsula and Balearic Islands''.</ref> All these plants have modified roots, [[haustorium|haustoria]], which penetrate the host plants, connecting them to the conductive system—either the [[xylem]], the [[phloem]], or both. This provides them with the ability to extract water and nutrients from the host. A parasitic plant is classified depending on where it latches onto the host, either the stem or the root, and the amount of nutrients it requires. Since holoparasites have no [[chlorophyll]] and therefore cannot make food for themselves by [[photosynthesis]], they are always obligate parasites, deriving all their food from their hosts.<ref name="Heide-Jørgensen, H. 2008"/> Some parasitic plants can locate their [[host (biology)|host]] plants by detecting [[Chemical substance|chemicals]] in the air or soil given off by host [[Shoot (botany)|shoot]]s or [[root]]s, respectively. About 4,500 [[species]] of parasitic plant in approximately 20 [[Family (biology)|families]] of [[flowering plant]]s are known.<ref name="Heide-Jørgensen, H. 2008"/><ref name="NickrentMusselman2004">{{cite journal |last1=Nickrent |first1=D. L. |last2=Musselman |first2=L. J. |title=Introduction to Parasitic Flowering Plants |journal=The Plant Health Instructor |year=2004 |doi=10.1094/PHI-I-2004-0330-01}}</ref>

Species within the ''[[Orobanchaceae]]'' (broomrapes) are among the most economically destructive of all plants. Species of ''[[Striga]]'' (witchweeds) are estimated to cost billions of dollars a year in crop yield loss, infesting over 50&nbsp;million hectares of cultivated land within Sub-Saharan Africa alone. ''Striga'' infects both grasses and grains, including [[Zea mays|corn]], [[Oryza sativa|rice]], and [[sorghum]], which are among the world's most important food crops. ''[[Orobanche]]'' also threatens a wide range of other important crops, including [[peas]], [[Cicer arietinum|chickpeas]], [[Solanum lycopersicum|tomatoes]], [[carrot]]s, and varieties of [[cabbage]]. Yield loss from ''Orobanche'' can be total; despite extensive research, no method of control has been entirely successful.<ref name="WestwoodYoder2010">{{cite journal |last1=Westwood |first1=James H. |last2=Yoder |first2=John I. |last3=Timko |first3=Michael P. |last4=dePamphilis |first4=Claude W. |title=The evolution of parasitism in plants |journal=Trends in Plant Science |volume=15 |issue=4 |year=2010 |pages=227–235 |doi=10.1016/j.tplants.2010.01.004|pmid=20153240 |bibcode=2010TPS....15..227W }}</ref>

Many [[plants]] and [[fungi]] exchange carbon and nutrients in mutualistic [[mycorrhizal]] relationships. Some 400 species of [[myco-heterotrophy|myco-heterotrophic]] plants, mostly in the tropics, however effectively [[Cheating (biology)|cheat]] by taking carbon from a fungus rather than exchanging it for minerals. They have much reduced roots, as they do not need to absorb water from the soil; their stems are slender with few [[vascular bundle]]s, and their leaves are reduced to small scales, as they do not photosynthesize. Their seeds are small and numerous, so they appear to rely on being infected by a suitable fungus soon after germinating.<ref>{{cite journal |last=Leake |first=J. R. |date=1994 |title=The biology of myco-heterotrophic ('saprophytic') plants |journal=New Phytologist |volume=127 |issue=2 |pages=171–216 |doi=10.1111/j.1469-8137.1994.tb04272.x|pmid=33874520 |bibcode=1994NewPh.127..171L |s2cid=85142620 }}</ref>

[[File:Armillaria mellea, Honey Fungus, UK 1.jpg|thumb|The honey fungus, ''[[Armillaria mellea]]'', is a parasite of trees, and a [[saprophyte]] feeding on the trees it has killed.]]

=== Fungi ===

{{further|Pathogenic fungus|Plant pathology}}

Parasitic [[fungi]] derive some or all of their nutritional requirements from plants, other fungi, or animals.

Plant pathogenic fungi are classified into three categories depending on their mode of nutrition: biotrophs, [[hemibiotrophs]] and necrotrophs. Biotrophic fungi derive nutrients from living plant cells, and during the course of infection they colonise their plant host in such a way as to keep it alive for a maximally long time.<ref>{{Cite journal |last1=Fei |first1=Wang |last2=Liu |first2=Ye |date=11 August 2022 |title=Biotrophic Fungal Pathogens: a Critical Overview |url=http://dx.doi.org/10.1007/s12010-022-04087-0 |journal=Applied Biochemistry and Biotechnology |volume=195 |issue=1 |pages=1–16 |doi=10.1007/s12010-022-04087-0 |pmid=35951248 |s2cid=251474576 |issn=0273-2289}}</ref> One well-known example of a biotrophic pathogen is [[Corn smut|''Ustilago maydis'']], causative agent of the corn smut disease. Necrotrophic pathogens on the other hand, kill host cells and feed [[saprophytic]]ally, an example being the root-colonising honey fungi in the genus ''[[Armillaria]].''<ref name="RHS">{{cite web |title=What is honey fungus? |url=https://www.rhs.org.uk/advice/profile?PID=180 |publisher=[[Royal Horticultural Society]] |access-date=12 October 2017}}</ref> Hemibiotrophic pathogens begin their colonising their hosts as biotrophs, and subsequently killing off host cells and feeding as necrotrophs, a phenomenon termed the [[biotrophy-necrotrophy switch]].<ref>{{Cite journal |last1=Chowdhury |first1=Supriyo |last2=Basu |first2=Arpita |last3=Kundu |first3=Surekha |date=8 December 2017 |title=Biotrophy-necrotrophy switch in pathogen evoke differential response in resistant and susceptible sesame involving multiple signaling pathways at different phases |url=http://dx.doi.org/10.1038/s41598-017-17248-7 |journal=Scientific Reports |volume=7 |issue=1 |page=17251 |doi=10.1038/s41598-017-17248-7 |pmid=29222513 |pmc=5722813 |bibcode=2017NatSR...717251C |issn=2045-2322}}</ref>

Pathogenic fungi are well-known causative agents of diseases on animals as well as humans. Fungal infections ([[Fungal infection|mycosis]]) are estimated to kill 1.6&nbsp;million people each year.<ref>{{cite journal |title=Stop neglecting fungi |journal=Nature Microbiology |date=25 July 2017 |volume=2 |issue=8 |pages=17120 |doi=10.1038/nmicrobiol.2017.120 |pmid=28741610 |doi-access=free}}</ref> One example of a potent fungal animal pathogen are [[Microsporidia]] - obligate intracellular parasitic fungi that largely affect insects, but may also affect vertebrates including humans, causing the intestinal infection [[microsporidiosis]].<ref name="Didier">{{cite journal |last1=Didier |first1=E. S. |last2=Stovall |first2=M. E. |last3=Green |first3=L. C. |last4=Brindley |first4=P. J. |last5=Sestak |first5=K. |last6=Didier |first6=P. J. |url=https://www.researchgate.net/publication/8159085 |title=Epidemiology of microsporidiosis: sources and modes of transmission |journal=Veterinary Parasitology |date=9 December 2004 |volume=126 |issue=1–2 |pages=145–166 |doi=10.1016/j.vetpar.2004.09.006 |pmid=15567583}}</ref>

[[File:Borrelia burgdorferi-cropped.jpg|thumb|upright|''[[Borrelia burgdorferi]]'', the bacterium that causes [[Lyme disease]], is transmitted by ''[[Ixodes]]'' ticks.]]

=== Protozoa ===

{{further|Human parasite#Protozoa}}

Protozoa such as ''[[Plasmodium]]'', ''[[Trypanosoma]]'', and ''[[Entamoeba]]''<ref name=Esch2013>{{cite journal |last1=Esch |first1=K. J. |last2=Petersen |first2=C. A. |title=Transmission and epidemiology of zoonotic protozoal diseases of companion animals |journal=Clinical Microbiology Reviews |volume=26 |issue=1 |pages=58–85 |date=January 2013 |pmid=23297259 |pmc=3553666 |doi=10.1128/CMR.00067-12}}</ref> are endoparasitic. They cause serious diseases in vertebrates including humans—in these examples, malaria, sleeping sickness, and [[amoebiasis|amoebic dysentery]]—and have complex life cycles.<ref name="PollittMacGregor2011"/>

=== Bacteria ===

{{main|Pathogenic bacteria}}

Many bacteria are parasitic, though they are more generally thought of as [[Pathogenic bacteria|pathogens]] causing disease.<ref name=McFall-Ngai2007>{{Cite journal |last=McFall-Ngai |first=Margaret |date=January 2007 |title=Adaptive Immunity: Care for the community |journal=Nature |volume=445 |issue=7124 |pages=153 |doi=10.1038/445153a|pmid=17215830 |bibcode=2007Natur.445..153M |s2cid=9273396 |doi-access=free }}</ref> Parasitic bacteria are extremely diverse, and infect their hosts by a variety of routes. To give a few examples, ''[[Bacillus anthracis]]'', the cause of [[anthrax]], is spread by contact with infected [[domestic animal]]s; its [[spore]]s, which can survive for years outside the body, can enter a host through an abrasion or may be inhaled. ''[[Borrelia]]'', the cause of [[Lyme disease]] and [[relapsing fever]], is transmitted by vectors, ticks of the genus ''[[Ixodes]]'', from the diseases' reservoirs in animals such as [[deer]]. ''[[Campylobacter jejuni]]'', a cause of [[gastroenteritis]], is spread by the fecal–oral route from animals, or by eating insufficiently cooked [[poultry]], or by contaminated water. ''[[Haemophilus influenzae]]'', an agent of [[bacterial meningitis]] and respiratory tract infections such as [[influenza]] and [[bronchitis]], is transmitted by droplet contact. ''[[Treponema pallidum]]'', the cause of [[syphilis]], is [[sexually transmitted disease|spread]] by [[sexual activity]].<ref name=Lippincott>{{cite book |last1=Fisher |first1=Bruce |last2=Harvey |first2=Richard P. |last3=Champe |first3=Pamela C. |title=Lippincott's Illustrated Reviews: Microbiology (Lippincott's Illustrated Reviews Series) |publisher=Lippincott Williams & Wilkins |year=2007|pages=332–353 |isbn=978-0-7817-8215-9 }}</ref>

[[File:Tevenphage.svg|thumb|[[Enterobacteria phage T4]] is a [[bacteriophage]] virus. It infects its host, ''[[Escherichia coli]]'', by injecting its DNA through its tail, which attaches to the bacterium's surface.]]

=== Viruses ===

{{main|Virus |Bacteriophage}}

[[Virus]]es are obligate intracellular parasites, characterised by extremely limited biological function, to the point where, while they are evidently able to infect all other organisms from bacteria and [[archaea]] to animals, plants and fungi, it is unclear whether they can themselves be described as living. They can be either [[Orthornavirae|RNA]] or [[DNA virus]]es consisting of a single or double strand of [[genetic material]] ([[RNA]] or [[DNA]], respectively), covered in a [[protein]] coat and sometimes a [[lipid]] envelope. They thus lack all the usual machinery of the [[cell (biology)|cell]] such as [[enzyme]]s, relying entirely on the host cell's ability to replicate DNA and synthesise proteins. Most viruses are [[bacteriophage]]s, infecting bacteria.<ref name=Koonin2006>{{cite journal |last1=Koonin |first1=E. V. |last2=Senkevich |first2=T. G. |author3=Dolja, V. V. |title=The ancient Virus World and evolution of cells |journal=Biology Direct |volume=1 |page=29 |year=2006 |pmid=16984643 |pmc=1594570 |doi=10.1186/1745-6150-1-29 |doi-access=free }}</ref><ref name="Breitbart M, Rohwer F 2005 278–84">{{cite journal|author-link1=Mya Breitbart |author1=Breitbart, M. |author2=Rohwer, F. |title=Here a virus, there a virus, everywhere the same virus? |journal=Trends in Microbiology |volume=13 |issue=6 |pages=278–284 |year=2005 |pmid=15936660 |doi=10.1016/j.tim.2005.04.003}}</ref><ref name="Lawrence">{{cite journal|author1=Lawrence, C. M. |author2=Menon, S. |author3=Eilers, B. J. |display-authors=etal |title=Structural and functional studies of archaeal viruses |journal=The Journal of Biological Chemistry |volume=284 |issue=19 |pages=12599–603 |year=2009 |pmid=19158076 |doi=10.1074/jbc.R800078200 |pmc=2675988|doi-access=free }}</ref><ref>{{cite journal |last1=Edwards |first1=R. A. |last2=Rohwer |first2=F. |url=https://www.cbcb.umd.edu/confcour/CMSC828G-materials/Edwards-Rohwer-2005-NatureReviewsMicro.pdf |archive-url=https://web.archive.org/web/20191003133000/https://www.cbcb.umd.edu/confcour/CMSC828G-materials/Edwards-Rohwer-2005-NatureReviewsMicro.pdf |archive-date=3 October 2019 |url-status=live |title=Viral metagenomics |journal=Nature Reviews Microbiology |volume=3 |issue=6 |pages=504–510 |year=2005 |pmid=15886693 |doi=10.1038/nrmicro1163|s2cid=8059643 }}</ref>