Rev: 12/21/2022
Synonyms:
Trichinellosis is a parasitic infection caused by a nematodes of the genus Trichinella. Virtually all mammals are susceptible to infection by one or more species of the genus; however, humans are especially prone to developing clinical disease.
The number of outbreaks around the world appear to is increasing markedly, reflecting a changing epidemiological paradigm.
All stages in the life cycle of Trichinella occur in individual mammalian hosts. When skeletal muscle containing infective larvae is ingested by another mammal, the larvae are released by the action of gastric fluids and pass into the small intestine.There, the parasites invade the small intestine epithelial wall, and molt four times before becoming sexually mature. After copulation, the females begin to expel newborn larvae about six or seven days after initial infection (Bruschi and Murrell, 2002).
In Trichinella spiralis, encysted preparasitic nematode larvae are ingested in infected muscle tissue (raw or undercooked pork is the classic example in the case of trichinosis in humans).
The cyst surrounding the larva is digested in the new host and the larvae molt to adults, mate, embed in the intestinal epithelium and females produce eggs which hatch (1000 larvaeper female in 5 days).
The hatched larvae are distributed via the circulatory system and migrate into surrounding cells, which die unless they are striated muscle fibers.
Secretory products of the stichocytes induce DNA endoreduplication and transformation of the muscle fiber and into a multinucleate nurse cell which becomes encapsulated by collagen and supplied with capillaries (Despommier, 1998; Lee, 2002).
The life cycle continues when the muscle is eaten by another animal.
Trichinella spiralis larvae encysted in pork.
Photomicrograph by Jonathan Eisenback.
The nature and function of stichocyte secretions, particularly of vertebrate parasites, is an area of continued interest in research on host-parasite relationships.
In humans, initial infection is through the intestine after consumption of infected raw or undercooked meat. Intestinal infection may result in abdominal pain and diarrhea. Larvae migrate to muscle tissues and may cause swellings, rash, fever, and inflammation of the eyes.
Bruschi, F. and Murrell, K.D. 2002.
De Ley, P. and Blaxter, M. 2002. Systematic position and phylogeny. Pp 1-30 in Lee, D.L. (ed.). The Biology of Nematodes. Taylor and Francis, London and NY. 635p.
Despommier, D.D. 1998. Trichinella and Toxocara. Pp597-607 in Cox, F.E.G., Kreier, J.P. and Wakelin, D. Volume 5, Parasitology in Collier, L., Balows, A. and Sussman, M. (eds.). Topley and Wilson’s Microbiology and Microbial Infections. Arnold, London.
Ferris, H. 2007. Stichosomida. McGraw-Hill Encyclopedia of Science & Technology. http://accesscience.com/abstract.aspx?id=757377&referURL=http%3a%2f%2faccesscience.com%2fcontent.aspx%3fid%3d757377.
Lee, D.L. 2002. Life cycles. Pp 61-72 in Lee, D.L. (ed.). The Biology of Nematodes.Taylor and Francis, London and NY. 635p.
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