Editing Trichinosis (section)

==Cause==
[[Image:Trichinella larvaeD.jpg|thumb|''Trichinella spiralis'' [[larvae]] in muscle tissue]]
[[File:Trichinella Spiralis x.s. & l.s. 40x.png|thumb|Animal tissue infected with the parasite that causes the disease trichinosis: Most parasites are shown in cross-section, but some randomly appear in long section.]]

The classical agent is ''T. spiralis'' (found worldwide in many carnivorous and omnivorous animals, both domestic and [[sylvatic]] (wild),{{citation needed|date=January 2023}} but seven primarily sylvatic species of ''Trichinella'' also are now recognized:

===Species and characteristics===
* [[Trichinella spiralis|''T. spiralis'']] is most adapted to swine, most pathogenic in humans, and is cosmopolitan in distribution.{{citation needed|date=January 2021}}
* [[Trichinella britovi|''T. britovi'']] is the second-most common species to infect humans; it is distributed throughout Europe, Asia, and northern and western Africa, usually in wild carnivores, crocodiles, birds, wild boar, and domesticated pigs.{{citation needed|date=January 2021}}
* ''T. murrelli'' also infects humans, especially from black bear meat; it is distributed among wild carnivores in North America.<ref>{{Cite journal|last1=Scandrett|first1=Brad|last2=Konecsni|first2=Kelly|last3=Lalonde|first3=Laura|last4=Boireau|first4=Pascal|last5=Vallée|first5=Isabelle|date=June 2018|title=Detection of natural Trichinella murrelli and Trichinella spiralis infections in horses by routine post-slaughter food safety testing|journal=Food and Waterborne Parasitology|volume=11|pages=1–5|doi=10.1016/j.fawpar.2018.06.001 |pmc=7033993|pmid=32095599}}</ref>
* [[Trichinella nativa|''T. nativa'']], which has a high resistance to freezing, is found in the Arctic and subarctic regions; reservoir hosts include polar bears, Arctic foxes, walruses, and other wild game.<ref>{{cite book |doi=10.1006/rwfm.1999.1595 |chapter=Trichinella |title=Encyclopedia of Food Microbiology |date=1999 |pages=2181–2186 |isbn=978-0-12-227070-3 | vauthors = Gamble HR }}</ref>
* ''T. nelsoni'', found in East African predators and scavengers, has been documented to cause a few human cases.
* ''[[Trichinella papuae|T. papuae]]'' infects both mammals and reptiles, including crocodiles, humans, and wild and domestic pigs; this species, found in Papua New Guinea and Thailand, is also nonencapsulated.<ref name=":0">{{Cite web|title = CDC – DPDx – Trichinellosis – index|url = https://www.cdc.gov/dpdx/trichinellosis/index.html|website = www.cdc.gov|access-date = 2015-07-25|url-status = live|archive-url = https://web.archive.org/web/20150704215541/http://www.cdc.gov/dpdx/trichinellosis/index.html|archive-date = 2015-07-04}}</ref>
* ''T. pseudospiralis'' infects birds and mammals, and has demonstrated infection in humans;<ref>{{cite journal | author = Jongwutiwes S | date = Jan 1998 | title = First outbreak of human trichinellosis caused by Trichinella pseudospiralis | journal = Clin Infect Dis | volume = 26 | issue = 1| pages = 111–15 | doi=10.1086/516278| pmid = 9455518 |display-authors=etal| doi-access = free }}</ref> it is a nonencapsulated species.
* ''T. zimbabwensis'' can infect mammals, and possibly humans; this nonencapsulated species was detected in crocodiles in Africa.<ref name=CDC2013DP/>

===Taxonomy===
* Kingdom: Animalia
* Phylum: Nematoda
* Class: Adenophorea
* Order: Trichurida
* Family: Trichinellidae
* Genus: ''Trichinella''

===Lifecycle===
[[File:Trichinella LifeCycle.gif|thumb|upright=1.4|Lifecycle of ''Trichinella spiralis'']]

The typical lifecycle for ''T. spiralis'' involves humans, pigs, and rodents. A pig becomes infected when it eats infectious cysts in raw meat, often porcine [[carrion]] or a [[rat]] ([[sylvatic cycle]]). A human becomes infected by consuming raw or undercooked infected pork (domestic cycle). In the stomach, the [[cyst]]s from infected undercooked meat are acted on by [[pepsin]] and [[hydrochloric acid]], which help release the larvae from the cysts into the [[stomach]].<ref name=five>{{cite journal |author1=Capo, V. |author2=Despommier, D. D. |date=1996 |title=Clinical Aspects of Infection with ''Trichinella spp.'' |journal=Clinical Microbiology Reviews |volume=9 |issue=1 |pages=47–54 |doi=10.1128/cmr.9.1.47|pmid=8665476 |pmc=172881 }}</ref> The larvae then migrate to the [[small intestine]], and burrow into the [[intestinal mucosa]], where they molt four times before becoming adults.<ref name=five/>

Thirty to 34 hours after the cysts were originally ingested, the adults mate, and within five days produce larvae.<ref name="five"/> Adult worms can only reproduce for a limited time because the [[immune system]] eventually expels them from the small intestine.<ref name="five"/> The larvae then use their piercing mouthpart, called the "stylet", to pass through the [[Gastrointestinal wall|intestinal mucosa]] and enter the [[lymphatic vessel]]s, and then enter the [[Circulatory system|bloodstream]].<ref name="four"/>

The larvae travel by [[Capillary|capillaries]] to various organs, such as the [[retina]], [[Cardiac muscle|myocardium]], or [[lymph node]]s; however, only larvae that migrate to [[skeletal muscle]] cells survive and [[Microbial cyst|encyst]].<ref name="two"/> The larval host cell becomes a [[nurse cell]], in which the larva will be encapsulated, potentially for the life of the host, waiting for the host to be eaten. The development of a capillary network around the nurse cell completes encystation of the larva. Trichinosis is not soil-transmitted, as the [[Parasitism|parasite]] does not lay eggs, nor can it survive long outside a host.<ref name=Mason2014/><ref>{{cite journal |title=Epidemiology, diagnosis, treatment, and control of trichinellosis |journal=Clinical Microbiology Reviews |date=January 2009 |pmc=2620635 |pmid=19136437 |pages=127–45, Table of Contents|volume=22 |issue=1 |doi=10.1128/CMR.00026-08 |first1=Bruno |last1=Gottstein |first2=Edoardo |last2=Pozio |first3=Karsten |last3=Nöckler}}</ref>