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Trichinella spiralis: Wikis


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Scientific classification
Kingdom: Animalia
Phylum: Nematoda
Class: Adenophorea
Order: Trichurida
Family: Trichinellidae
Genus: Trichinella
Species: T. spiralis
Binomial name
Trichinella spiralis
(Owen, 1835)

Trichinella spiralis is a nematode parasite, occurring in rats, pigs, and humans, and is responsible for the disease trichinosis. It is sometimes referred to as the "pork worm" due to it being found commonly in pork or rat products that are undercooked.



Trichinella species are the smallest nematode parasite of human, which has an unusual life cycle and one of the most widespread and clinically important parasites in the world. [1]The small adult worms mature in the intestine of an intermediate host such as a pig. Each adult female produces batches of live larvae, which bore through the intestinal wall, enter the blood (to feed on it) and lymphatic system, and are carried to striated muscle tissue. Once in the muscle, they encyst, or become enclosed in a capsule. Humans can be infected by eating infected pork or wild carnivores such as fox, cat or bear.[1]


Males of T. spiralis measure between 1.4 mm to 1.6 mm long and are flat anteriorly than posteriorly.[1] The anus can be found in the terminal (side) and they have a large copulatory pseudobursa on each side. [1] The females of T. spinalis are about twice the size of the males and 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. [1]

Life cycle

Trichinella spinalis is a parasitic nematode that has a direct life cycle, meaning that it completes all stages of development in one host. The larval forms of T. spinalis are encapsulated as a small cystic structure within the infected host. Human typically become infected when they eat improperly cooked pork or Trichinella infected meat. When a human eats the infected meat, the larvae are released from the nurse cell (due to stomach pH) and migrate to the intestine where they burrow into the intestinal mucosa, mature, and reproduce [2]. Interestingly, juveniles within nurse cells have an anaerobic or facultative anaerobic metabolism but when they become activated adopt an aerobic metabolism characteristics of the adult. [1] Female trichinella worms live for about six weeks and in that time can produce up to 1,500 larvae; where eventually a spent female dies and passes out of the host. The larvae can then gain access to the circulation and migrate around the body of the host [2]. The migration and encystment of larvae can cause fever and pain brought upon by the host inflammatory response. In some cases migration to specific organ tissues can cause myocarditis and encephalitis that can result in death.


Nurse Cell Formation

Trichinella spiralis larvae within the diaphragm muscle of a pig.

Nurse cell formation in skeletal muscle tissue is mediated by the hypoxic environment surrounding the new vessel formation. [3] The hypoxic environment stimulates cells in the surrounding tissue to up-regulate and secrete angiogenic cytokines, such as VEGF. This allows for the newborn T. spinalis larva to enter and form the nurse cell. Interestingly VEGF expression is detected surrounding the nurse cell right after Nurse cell formation and the continued secretion of VEGF can maintain the constant state of hypoxia. [4] Previous study have shown that VEGF can stimulate proliferation of synthesis of collagen type 1 in activated myofibroblast like cells. [5]


The first symptoms may appear between 12 hours and two days after ingestion of infected meat. The migration of worms in the intestinal epithelium can cause traumatic damage to the host tissue and the waste products they excrete can provoke an immunological reaction.[1] The resulting inflammation can cause symptoms such as nausea, vomiting, sweating and diarrhea. Five to seven days after the appearance of symptoms facial edema and fever may occur. After 10 days intense muscular pain, difficulty breathing, weakening of pulse and blood pressure, heart damage and various nervous disorders may occur, eventually leading to death due to heart failure, respiratory complications or kidney malfunction.[1]

Diagnosis and treatment

Muscle biopsy is used for trichinosis detection. Several immunodiagnostic tests are also available. Typically patients are treated with either Mebendazole or Albendazole but efficacy of such products are uncertain. Symptoms can be relieved by use of analgesics and corticosteroids.[1]

Prevention and Control

Trichinellosis is a disease caused by tissue-dwelling roundworms of the species Trichinella spiralis. In the United States, the national trichinellosis surveillance system has documented a steady decline in the reported incidence of this disease. During 1947 to 1951, a median of 393 cases was reported annually, including 57 trichinellosis-related deaths. During 1997--2001, the incidence decreased to a median of 12 cases annually with no reported deaths. The decline of infection was largely associated with changes implemented by the U.S. pork industry that have resulted in reduced prevalence of Trichinella among domestic swine. [6] In the United States, the congress passed the Federal Swine Health Protection Act restricting the use of uncooked garbage as food stock for pigs and creating a non-mandatory Trichinae Herd Certification Program [6]. The Trichinae Herd Certification Program is a voluntary pre-harvest pork safety program that provides documentation of swine management practices to minimize Trichinella exposure. The goal of the program is to establish a system under which pork production facilities that follow good production practices might be certified as Trichinella-safe. [7] In addition to the reduction in Trichinella prevalence in commercial pork, processing methods also have contributed to the dramatic decline in human trichinellosis associated with pork products. Through the U.S. Code of Federal Regulations, USDA has created guidelines for specific cooking temperatures and times, freezing temperatures and times, and curing methods for processed pork products to control post-harvest human exposure to Trichinella. [6]

See also


  1. ^ a b c d e f g h i Roberts, Larry S., John Janovay. Foundations of Parasitology. New York: McGraw-Hill, (2005), 405-407.
  2. ^ a b Crowley, Leonard. An Introduction to Human Disease: Pathology and Pathophysiology Correlations. 8th ed. Jones and Bartlett, 2009.
  3. ^ Fong, 2008 G.H. Fong, Mechanism of adaptative angiogenesis to tissue hypoxia, Angiogenesis 11 (2008), pp. 121–140.
  4. ^ V.A. Capo, D.D. Despommier and R.I. Polvere, Trichinella spiralis: vascular endothelial growth factor is up-regulated within the nurse cell during the early phase of its formation, J. Parasitol. 84 (1998), pp. 209–214
  5. ^ E. Novo, S. Cannito, E. Zamara, L. Valfre di Bonzo, A. Caligiuri and C. Cravanzola et al., Proangiogenic cytokines as hypoxia-dependent factors stimulating migration of human hepatic stellate cells, Am. J. Pathol. 170 (2007), pp. 1942–1953
  6. ^ a b c Roy, Sharon L., Adriana S. Lopez, and Peter M. Schantz. "Trichinellosis Surveillance --- United States, 1997--2001." Center for Disease Control
  7. ^ National Pork Board. Trichinae Herd Certification. Des Moines, Iowa: National Pork Producers Council, 2000. Available at


  • Despommier, D.D., Gwadz, R.G, Hotez, P., Knirsch, C. Parasitic Diseases 5th ed. New York: Apple Trees Pub. (2002)

External links


Up to date as of January 23, 2010

From Wikispecies

Trichinella spiralis


Main Page
Cladus: Eukaryota
Supergroup: Unikonta
Cladus: Opisthokonta
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Cladus: Protostomia
Cladus: Ecdysozoa
Phylum: Nematoda
Classis: Enoplea
Subclassis: Dorylaimia
Ordo: Trichocephalida
Familia: Trichinellidae
Genus: Trichinella
Species: Trichinella spiralis


Vernacular Name

English: Whipworm


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