Rev 12/21/2022
Trichinella spiralis was discovered by James Paget and Richard Owen in 1835 in the muscles of human cadavers in London and by Joseph Leidy in 1846 in the muscles of swine in Philadelphia (Gould, 1970). Since then it has been reported from over 100 mammalian hosts. Intensive studies reveal that there is variation amonmg isolates from duifferent hosts awhich has led to the description of new species (see Trichinella menu).
Males:
Female:
Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:
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.
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.
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.
Ecophysiological Parameters:
Chitwood, B.G. 1930. The structure of the esophagus in the Trichuroidea. Journal of Parasitology 17:35-42.
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.
Gould, S.E., 1970. History. In: Gould, S.E. (Ed.), Trichinellosis in Man and Animals. Charles C. Thomas, Springfield, IL, pp. 3–46.
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.
Owen, R. 1835. Description of a microscopic entozoon infesting the muscles of the human body. Trans. Zool. Soc. London 1:315-324.