Gnathostoma Owen, 1836
Type species of the genus: Gnathostoma spinigerum
Owen, 1936) (described as a stomach parasite of a tiger at the London Zoo).
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).
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).
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
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).
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.
November 01, 2022.