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==Overview==
==Overview==
Trichinella spp. is usually transmitted to the human host by eating undercooked meat containing cysts of Trichinella spp. Following ingestion, exposure to gastric acid and pepsin release the larvae from the cysts and invade the small bowel mucosa.When a person eats meat from an infected animal, Trichinella cysts break open in the intestines and grow into adult roundworms. Females are 2.2 mm in length; males 1.2 mm. The life span in the small intestine is about four weeks. After 1 week, the females release more larvae that migrate to voluntarily controlled muscles where they encyst. The roundworms produce other worms that move through the gut wall and into the bloodstream. These organisms tend to invade muscle tissues, including the heart and diaphragm. They can also affect the lungs and brain. <ref name="wiki1234">Trichinosis. Wikipedia. https://en.wikipedia.org/wiki/Trichinosis. Accessed on January 22, 2016</ref> Characteristic findings on microscopic histopathological analysis of the muscle, the nurse cell has a collagen capsule with larvae inside and is surrounded by cellular infiltrates.<ref name="pmid19136437">{{cite journal| author=Gottstein B, Pozio E, Nöckler K| title=Epidemiology, diagnosis, treatment, and control of trichinellosis. | journal=Clin Microbiol Rev | year= 2009 | volume= 22 | issue= 1 | pages= 127-45, Table of Contents | pmid=19136437 | doi=10.1128/CMR.00026-08 | pmc=PMC2620635 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=19136437  }} </ref>  
[[Trichinella|''Trichinella spp.'']] is usually transmitted to the human host by eating undercooked meat containing [[cysts]] of [[Trichinella|''Trichinella spp.'']] Following ingestion, exposure to [[gastric acid]] and [[pepsin]] release the larvae from the [[cysts]] and invade the small bowel mucosa. When an individual eats meat from an infected animal, [[Trichinella|''Trichinella'']] [[cysts]] break open in the intestines and grow into adult [[roundworms]]. Females are approximately 2.2 mm in length; males 1.2 mm. The life span in the small intestine is approximately four weeks. After 1 week, the females release more larvae that migrate through the [[bloodstream]] to voluntarily controlled [[muscles]] where they encyst. These organisms tend to invade muscle tissues, including the [[heart]] and [[diaphragm]]. They can also affect the [[lungs]] and [[brain]].<ref name="wiki1234">Trichinosis. Wikipedia. https://en.wikipedia.org/wiki/Trichinosis. Accessed on January 22, 2016</ref> Characteristic findings on microscopic histopathological analysis of the [[muscle]], the nurse cell has a collagen capsule with larvae inside and is surrounded by cellular infiltrates.<ref name="pmid19136437">{{cite journal| author=Gottstein B, Pozio E, Nöckler K| title=Epidemiology, diagnosis, treatment, and control of trichinellosis. | journal=Clin Microbiol Rev | year= 2009 | volume= 22 | issue= 1 | pages= 127-45, Table of Contents | pmid=19136437 | doi=10.1128/CMR.00026-08 | pmc=PMC2620635 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=19136437  }} </ref>  


==Pathogenesis==
==Pathogenesis==
[[Image:Trichinella_lifecycle.gif|350px|left|thumb|Trichinella life cycle.]]
[[Image:Trichinella_lifecycle.gif|550px|Trichinella life cycle]]<br>
*Trichinellosis is acquired by ingesting meat containing cysts (encysted larvae) (1) of Trichinella.
*Trichinosis is acquired by ingesting meat containing [[cysts]] (encysted larvae) (life cycle stage: 1) of [[Trichinella|''Trichinella'']].
*During the enteral phase:
===Enteral Phase===
**After exposure to gastric acid and pepsin, the larvae are released (2) from the cysts and invade the small bowel mucosa
*After exposure to [[gastric acid]] and [[pepsin]], the larvae are released (life cycle stage: 2) from the [[cysts]] and invade the small bowel mucosa.
**Thirty to 34 hours after the cysts were originally ingested, they develop into adult worms (3) within (female 2.2 mm in length, males 1.2 mm; life span in the small bowel: 4 weeks).
*Thirty to 34 hours after the [[cysts]] were originally ingested, they develop into adult worms (life cycle stage: 3) (female approximately 2.2 mm in length, males 1.2 mm); life span in the small bowel is approximately 4 weeks.
**The adults worms mate, and within five days produce larvae.
*The adults worms mate. The production of larvae generally occurs within 5 days.
**The worms can only reproduce for a limited time because the immune system will eventually expel them from the small intestine.
*The worms can only reproduce for a limited time. The immune system will eventually expel them from the small intestine.
**After 1 week, the females release larvae (4)  
*After 1 week, the females release larvae (life cycle stage: 4).
***Trichinella pseudospiralis, however, does not encyst.
*The newborn larvae then use their piercing mouthpart (called the "stylet") to pass through the intestinal mucosa.
**The newborn larvae then use their piercing mouthpart, called the "stylet", to pass through the intestinal mucosa  
===Parental Phase===
*During the parental phase:
*The newborn larvae enter the [[lymphatic vessels]] and then enter the [[bloodstream]].
**The newborn larvae enter the lymphatic vessels, and then enter the bloodstream.
*The larvae travel by [[capillaries]] to various organs, such as the [[retina]], [[myocardium]], or lymph nodes; however, only larvae that migrate to skeletal muscle cells survive and encyst.  
**The larvae travel by capillaries to various organs, such as the retina, myocardium, or lymph nodes; however, only larvae that migrate to skeletal muscle cells survive and encyst.  
*[[Muscle cells|Skeletal muscle cells]] act as nurse cells where larvae can develop and after weeks, months or years calcify.
**Skeletal muscle cells act as nurse cells where larvae can develop and after weeks, months or years calcify.
*Encystment is completed in 4 to 5 weeks and the encysted larvae may remain viable for several years (life cycle stage: 5).<ref name="wiki1234">Trichinosis. Wikipedia. https://en.wikipedia.org/wiki/Trichinosis. Accessed on January 22, 2016</ref><ref name="pmid19136437">{{cite journal| author=Gottstein B, Pozio E, Nöckler K| title=Epidemiology, diagnosis, treatment, and control of trichinellosis. | journal=Clin Microbiol Rev | year= 2009 | volume= 22 | issue= 1 | pages= 127-45, Table of Contents | pmid=19136437 | doi=10.1128/CMR.00026-08 | pmc=PMC2620635 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=19136437  }} </ref><ref name="a">Trichinellosis. CDC. http://www.cdc.gov/parasites/trichinellosis/biology.html. Accessed on January 26, 2016</ref>
**Encystment is completed in 4 to 5 weeks and the encysted larvae may remain viable for several years. (5)
*Ingestion of the encysted larvae perpetuates the cycle.
*Rats and rodents are primarily responsible for maintaining the endemicity of this infection.
*Carnivorous/omnivorous animals, such as pigs or bears, feed on infected rodents or meat from other animals.
*Different animal hosts are implicated in the life cycle of the different species of Trichinella.
*Humans are accidentally infected when eating improperly processed meat of these carnivorous animals (or eating food contaminated with such meat).
<ref name="a">Trichinellosis. CDC. http://www.cdc.gov/parasites/trichinellosis/prevent.html. Accessed on January 26, 2016</ref><ref name="wiki1234">Trichinosis. Wikipedia. https://en.wikipedia.org/wiki/Trichinosis. Accessed on January 22, 2016</ref><ref name="pmid19136437">{{cite journal| author=Gottstein B, Pozio E, Nöckler K| title=Epidemiology, diagnosis, treatment, and control of trichinellosis. | journal=Clin Microbiol Rev | year= 2009 | volume= 22 | issue= 1 | pages= 127-45, Table of Contents | pmid=19136437 | doi=10.1128/CMR.00026-08 | pmc=PMC2620635 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=19136437  }} </ref>


==Microscopic Pathology==
==Microscopic Pathology==
*Males T. spiralis:  
*Males [[Trichinella spiralis|''T. spiralis'']]'':''
**Measure between 1.4 and 1.6 mm long and are more flat anteriorly than posteriorly.  
**Measure between 1.4 and 1.6 mm long and are more flat anteriorly than posteriorly.  
**The anus can be found in the terminal (side) and they have a large copulatory pseudobursa on each side.  
**The anus can be found in the terminal (side) and they have a large copulatory pseudobursa on each side.  
*Females T. spiralis:
*Females [[Trichinella spiralis|''T. spiralis'']]'':''
**Are about twice the size of the males  
**Are about twice the size of the males  
**Have an anus found terminally.
**Have an anus found terminally  
**The vulva is located near the esophagus.
**The vulva is located near the esophagus  
**The single uterus of the female is filled with developing eggs in the posterior portion, while the anterior portion contained the fully developed juveniles.<ref name=b>Trichinella spiralis. Wikipedia. https://en.wikipedia.org/wiki/Trichinella_spiralis. Accessed on January 26, 2016</ref>
**The single uterus of the female is filled with developing eggs in the posterior portion, while the anterior portion contained the fully developed juveniles.<ref name="b">Trichinella spiralis. Wikipedia. https://en.wikipedia.org/wiki/Trichinella_spiralis. Accessed on January 26, 2016</ref>
*Muscle biopsy (hematoxylin-eosin staining):
*[[Muscle biopsy]] ([[hematoxylin and eosin stain]]):
**Nurse cell has a collagen capsule (thickness depends on Trichinella species) with larvae inside and surrounded by cellular infiltrates.<ref name="pmid19136437">{{cite journal| author=Gottstein B, Pozio E, Nöckler K| title=Epidemiology, diagnosis, treatment, and control of trichinellosis. | journal=Clin Microbiol Rev | year= 2009 | volume= 22 | issue= 1 | pages= 127-45, Table of Contents | pmid=19136437 | doi=10.1128/CMR.00026-08 | pmc=PMC2620635 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=19136437  }} </ref>
**Nurse cell has a collagen capsule (thickness depends on [[Trichinella|''Trichinella'']] species) with larvae inside and surrounded by [[Cellular infiltration|cellular infiltrates]].<ref name="pmid19136437">{{cite journal| author=Gottstein B, Pozio E, Nöckler K| title=Epidemiology, diagnosis, treatment, and control of trichinellosis. | journal=Clin Microbiol Rev | year= 2009 | volume= 22 | issue= 1 | pages= 127-45, Table of Contents | pmid=19136437 | doi=10.1128/CMR.00026-08 | pmc=PMC2620635 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=19136437  }} </ref>
[[Image:10180_lores.jpg|200px|This is a photomicrograph depicting a Trichinella spiralis cyst seen embedded in a muscle tissue specimen, in a case of trichinellosis.]]
[[Image:10180_lores.jpg|200px|This is a photomicrograph depicting a Trichinella spiralis cyst seen embedded in a muscle tissue specimen, in a case of trichinellosis.]]


==References==
==References==
{{reflist|2}}
{{reflist|2}}
[[Category:Conditions diagnosed by stool test]]
[[Category:Infectious disease]]
[[Category:Needs overview]]

Latest revision as of 19:01, 18 September 2017

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Danitza Lukac

Overview

Trichinella spp. is usually transmitted to the human host by eating undercooked meat containing cysts of Trichinella spp. Following ingestion, exposure to gastric acid and pepsin release the larvae from the cysts and invade the small bowel mucosa. When an individual eats meat from an infected animal, Trichinella cysts break open in the intestines and grow into adult roundworms. Females are approximately 2.2 mm in length; males 1.2 mm. The life span in the small intestine is approximately four weeks. After 1 week, the females release more larvae that migrate through the bloodstream to voluntarily controlled muscles where they encyst. These organisms tend to invade muscle tissues, including the heart and diaphragm. They can also affect the lungs and brain.[1] Characteristic findings on microscopic histopathological analysis of the muscle, the nurse cell has a collagen capsule with larvae inside and is surrounded by cellular infiltrates.[2]

Pathogenesis

Trichinella life cycle

  • Trichinosis is acquired by ingesting meat containing cysts (encysted larvae) (life cycle stage: 1) of Trichinella.

Enteral Phase

  • After exposure to gastric acid and pepsin, the larvae are released (life cycle stage: 2) from the cysts and invade the small bowel mucosa.
  • Thirty to 34 hours after the cysts were originally ingested, they develop into adult worms (life cycle stage: 3) (female approximately 2.2 mm in length, males 1.2 mm); life span in the small bowel is approximately 4 weeks.
  • The adults worms mate. The production of larvae generally occurs within 5 days.
  • The worms can only reproduce for a limited time. The immune system will eventually expel them from the small intestine.
  • After 1 week, the females release larvae (life cycle stage: 4).
  • The newborn larvae then use their piercing mouthpart (called the "stylet") to pass through the intestinal mucosa.

Parental Phase

  • The newborn larvae enter the lymphatic vessels and then enter the bloodstream.
  • The larvae travel by capillaries to various organs, such as the retina, myocardium, or lymph nodes; however, only larvae that migrate to skeletal muscle cells survive and encyst.
  • Skeletal muscle cells act as nurse cells where larvae can develop and after weeks, months or years calcify.
  • Encystment is completed in 4 to 5 weeks and the encysted larvae may remain viable for several years (life cycle stage: 5).[1][2][3]

Microscopic Pathology

  • Males T. spiralis:
    • Measure between 1.4 and 1.6 mm long and are more flat anteriorly than posteriorly.
    • The anus can be found in the terminal (side) and they have a large copulatory pseudobursa on each side.
  • Females T. spiralis:
    • Are about twice the size of the males
    • Have an anus found terminally
    • The vulva is located near the esophagus
    • The single uterus of the female is filled with developing eggs in the posterior portion, while the anterior portion contained the fully developed juveniles.[4]
  • Muscle biopsy (hematoxylin and eosin stain):

This is a photomicrograph depicting a Trichinella spiralis cyst seen embedded in a muscle tissue specimen, in a case of trichinellosis.

References

  1. ↑ 1.0 1.1 Trichinosis. Wikipedia. https://en.wikipedia.org/wiki/Trichinosis. Accessed on January 22, 2016
  2. ↑ 2.0 2.1 2.2 Gottstein B, Pozio E, Nöckler K (2009). "Epidemiology, diagnosis, treatment, and control of trichinellosis". Clin Microbiol Rev. 22 (1): 127–45, Table of Contents. doi:10.1128/CMR.00026-08. PMC 2620635. PMID 19136437.
  3. ↑ Trichinellosis. CDC. http://www.cdc.gov/parasites/trichinellosis/biology.html. Accessed on January 26, 2016
  4. ↑ Trichinella spiralis. Wikipedia. https://en.wikipedia.org/wiki/Trichinella_spiralis. Accessed on January 26, 2016
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