Rev: 11/01/2022

  Classification Biology and Ecology
Morphology and Anatomy Life Cycle
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Gnathostoma Owen, 1836

Type species of the genus: Gnathostoma spinigerum Owen, 1936) (described as a stomach parasite of a tiger at the London Zoo).


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Morphology and Anatomy:

Diagnostic traits od the genus nclude host specificity, site of infection, body size, cuticular spines, presence of 1 or 2 bulges in the polar ends of eggs, as well as eggshell and caudal bursa morphology (Bertoni-Ruiz et al., 2011).



Body size range for the species of this genus in the database - Click:



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More than twenty species have been described parasitizing mammals (rodents, domestic and wild swine, felids, otters, raccoons, marsupials, and weasels), mainly in Asia and America (Bertoni-Ruiz et al., 2011).

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Adult worms of most species inhabit the gastric wall of definitive hosts; however, some species parasitize esophagus, kidneys or the urinary bladder.

Some species of Gnathostoma are the causal agents of gnathostomiasis in humans and animals. Gnathostomiasis is a foodborne helminthic infection of humans that is endemic in Asia and the Americas. Frequently transmitted by ingestion of raw fish infected with muscle-encysted juveniles.

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Biology and Ecology:


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Life Cycle:

Adult worms (13-55 mm long) encysted in the stomachs of definitive animal hosts release eggs that are shed in the host's feces.

The eggs develop in water and first-stage larvae (L1) are released in about 7 days.  The L1 larvae are ingested by the first intermediate hosts, freshwater copepods (Cyclops species) and larval-infected copepods are ingested by a broad range of second intermediate hosts including fish, eels, frogs, snakes, and birds.

In the gastrointestinal tract of the second intermediate or paratenic hosts, L1 larvae develop into second-stage larvae (L2)  and mature into third-stage larvae (L3) which encyst in the host tissues.

When the second intermediate hosts are ingested by predatory, definitive hosts, typically wild and domestic cats and dogs and wild carnivores, the L3 penetrate the gastrointestinal tract, migrate through the liver into the peritoneal cavity, and reenter the stomach in about 4 weeks to encyst, mature into adults within 6 months, and release eggs.

The entire life cycle occurs within a period of 8 to 12 months.

Humans are accidental or dead-end hosts that do not support reproductive cycle of the nematode. They become infected by eating raw or undercooked second intermediate hosts that harbor muscle-encysted infective L3 larvae. Although human transmission is typically by raw seafood consumption, two alternative routes of transmissioninclude ingestion of freshwater contaminated with L1-infected copepods and direct skin penetration of food handlers by L3 larvae during the preparation of infected fish, frogs, or other second intermediate hosts (Diaz, 2015, Daengsvang, 1980).

For Ecophysiological Parameters for this genus, click 
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Ecosystem Functions and Services:


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Bertoni-Ryuiz, F., Lamothe, M.R., Argumedo, L.G., Osorio-Sarabia, D., Leon-Regagnon, V. 2011. Systematics of the genus Gnathostoma (Nematoda: Gnathostomatidae) in the Americas. Rev. Mex. Biodiv. 82:


Daengsvang, S. 1980. A monograph on the genus Gnathostoma and gnathostomiasis in Thailand.

Diaz. J.H. 2015. Gnathostomiasis: An Emerging Infection of Raw Fish Consumers in Gnathostoma Nematode-Endemic and Nonendemic Countries. I. Travel Medicine 22:118-224.


Copyright 1999 by Howard Ferris.
Revised: November 01, 2022.