Rev 10/14/2025
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).
Nematodes of the superfamily Trichinelloidea possess a characteristic stichosome esophagus which consists of a tube surrounded by a single row of gland cells (stichocytes).
Males:
Female:
Ref: Marchiondo et al, 2020
Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:
Historically, trichinosis was considered a disease acquired by humans from consumption of pork. However, with the decline in infections through management of swine, and improved reporting mechanisms, there has been fewer infections from consumption of swine and a greater incidence of infections acquired from wild game.
Intemperate zones, bear, wild boar (feral swine), and fox have been implicated in noncommercial infections, whereas in regions above the 26C isotherm, infections from bear, seal, walrus, and igunaq (fermented meat from marine mammals) are more common.
In the past, it was believed that rats and other rodents served as endemic reservoirs for commercial farms; however, recent studies indicate that rodents are usually only accidental hosts (Marchiondo et al., 2020)
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 undergo 4 molts to become adults withis 36 hours, mate, embed in the intestinal epithelium and villi, Females produce eggs which hatch (1000 larvae per female in 5 days).
The hatched larvae are distributed via the circulatory system and migrate into skeletal muscle cells, which die unless they are striated muscle fibers. The larvae mechanically penetrate the muscle cells, roll into a spiral shape, reprogram the cells into survival (nurse cells), and become encapsulated by a collagen sheath. Entering the muscle cell may occur within 1 hour of the immature L1 have passing into the circulatory system In the muscle cells, the encapsulated L1 can remain infective for years; however, with time, calcification of the cysts occurs and the larvae die.
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 is direct, withot requiring and intermediate host, and 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.
Marchiondo, A.A., Cruthers, L.R., Zarlenga, D.S., Yazwinski, T,A, 2020. Nematoda, Trichinelloidea. Chapter 2 in Marchiondo, Cruthers and Fourie (eds) Parasiticide Screening Vol 2. Academic Press.
Owen, R. 1835. Description of a microscopic entozoon infesting the muscles of the human body. Trans. Zool. Soc. London 1:315-324.