Resources Causal Agents Gnathostoma spp. Humans are accidental hosts; the only forms found in humans are larvae or immature adults that never reach reproductive maturity. Most human infections are caused by G. Two unconfirmed human cases of G.
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Resources Causal Agents Gnathostoma spp. Humans are accidental hosts; the only forms found in humans are larvae or immature adults that never reach reproductive maturity.
Most human infections are caused by G. Two unconfirmed human cases of G. Life Cycle View Larger In definitive hosts, adult worms of most Gnathostoma spp reside in a tumor-like mass in the gastric wall; adult worms of some species are found in the esophagus or kidney. Adults mate and produce unembryonated eggs, which pass through a small opening in the tumor-like mass and ultimately into the feces. Eggs become embryonated in water, and eggs release sheathed first-stage larvae L1.
Freshwater copepods, which serve as first intermediate hosts, ingest the free-swimming L1, and the larvae molt twice to become early third-stage larvae EL3.
Following ingestion of the copepod by a suitable second intermediate host, the EL3 migrate into the tissues of the host and develop further into advanced L3 larvae AL3. When the second intermediate host is ingested by a definitive host, the AL3 develop into adult parasites in the gastric wall. Alternatively, the second intermediate host may be ingested by a paratenic host, in which the AL3 do not develop further but remain infective. Humans become infected by eating raw or undercooked meat of second intermediate or paratenic hosts containing AL3.
In the human host, AL3 migrate in various tissues and may develop into immature adults but never achieve reproductive maturity; they may range in size from 2 mm to about 2 cm depending on the species and the extent of development. Whether humans can become infected by drinking water that contains infected copepods is not clear. Hosts Carnivorous and sometimes omnivorous mammals serve as definitive hosts for Gnathostoma spp. Several members of the freshwater copepod family Cyclopidae appear to be competent first intermediate hosts.
Gnathostoma spp. Second intermediate hosts are typically aquatic animals that feed on copepods e. Geographic Distribution Most human cases of gnathostomiasis are reported from Gnathostoma-endemic regions in which raw fish dishes e. In the United States, cases of gnathostomiasis are most commonly reported in Southeast Asian immigrants.
Gnathostoma spinigerum, G. In tropical Australia, G. Occasional cases of gnathostomiasis associated with exposures in Africa Zambia, Botswana, and Tanzania have been reported; the causative species was identified for only one of the cases as G. Several Gnathostoma spp. However, the only species known to be zoonotic in this range is G. On the basis of serologic evidence, G. On the basis of molecular data, the reported Latin American cases of gnathostomiasis historically attributed to G.
Clinical Presentation The clinical manifestations in humans are caused by migration of the advanced L3 larvae or immature adults, which can invade a variety of tissues. Eosinophilia is commonly observed during initial larval migration e. Cutaneous gnathostomiasis, the most common form of the disease, results from migration of the parasite in subcutaneous tissue, which can be associated with intermittent migratory swellings often on the torso or upper limbs.
In some patients, the parasite migrates near the surface of the skin and can be extracted or may spontaneously emerge. Migration in deeper tissues such as pulmonary, gastrointestinal, genitourinary, auricular, ocular tissue, or the central nervous system is referred to as visceral gnathostomiasis or larva migrans profundus.
Clinical manifestations are highly variable and depend in part on which tissues are affected. Neurognathostomiasis can be associated with potentially fatal eosinophilic meningitis and myeloencephalitis, and ocular gnathostomiasis may cause vision loss. Scanning electron micrographs of Gnathostoma spinigerum Scanning electron micrographs of a Gnathostoma spinigerum female worm, showing the cuticular armature of the body surface. The cuticular armature is important for identification of Gnathostoma spp.
Figure A: Cephalic bulb. Figure B: Cuticular spines of the posterior body part. Detail of cuticular spines of the anterior body part. Figure C: Detail of cuticular spines of the anterior body part. Detail of nondendiculated cuticular spines. Figure D: Detail of nondenticulated single-pointed cuticular spines. Figure E: Detail of nondenticulated single-pointed cuticular spines.
Cross sections of immature Gnathostoma spp. Diagnostic characteristics of immature Gnathostoma worms found in humans include the presence of large, cavernous lateral chords; multinucleated intestinal cells some species ; pigmented granular material in the intestinal cells; and spines on the cuticle although some species do not have spines on the entire length of the body.
In histologic sections, some Gnathostoma spp. Note the presence of cuticular spines arrow. The multinucleated columnar intestinal cells with from three to five nuclei per cell identify this as G. Note the thick cuticle, coelomyarian muscle cells, and well-developed intestine. Figure D: Closer view of the intestinal morphology of the G.
The multinucleated intestinal cells have a prominent microvillus border arrow and contain dark, granular pigment darts. Ingested host red blood cells circle are present in the lumen of the intestine. The intestine arrow has rounded to cuboidal cells with single nuclei, an identifying feature of G.
Note also the typical genus-level larval features including low, coelomyarian muscle cells dart , and spacious lateral chords bisected by a lateral line asterisks. Gnathostoma spinigerum Figure A: Gnathostoma spinigerum immature male worm extracted from a person with cutaneous gnathostomiasis. In worms extracted from mammalian hosts, red coloration is common and is caused by staining from oxidized hemoglobin.
Overall length is 0. Figure B: Three-pointed spines in the anterior portion of the worm in Figure A. The shape and location of spines along the body are the primary means of species-level diagnosis within the Gnathostoma genus. Figure C: Posterior extremity of the worm in Figure A. Note the presence of broad caudal alae, with large, round pedunculate papillae. The surface of the caudal alae is covered with single-pointed spines.
Figure D: Cephalic bulb of a Gnathostoma spinigerum larva in fish muscle tissue, hematoxylin stained. Most Gnathostoma spp. Morphologic Diagnosis Morphologic diagnosis is achieved by identifying Gnathostoma larval forms or immature adults in a biopsy specimen or after extraction from a cutaneous lesion.
In histologic sections, Gnathostoma spp. Please contact DPDx for contact information for laboratories in Thailand and Japan that perform serologic testing. Laboratory Safety Standard laboratory precautions apply for the processing and examination of histologic sections. No stages of Gnathostoma spp. Suggested Reading Dekumyoy, P. Molecular detection of parasitic pathogens. Herman, J.
Gnathostomiasis, another emerging imported disease. Clinical Microbiology Reviews, 22 3 , pp. Nawa, Y. Ocular gnathostomiasis—update of earlier survey. Rusnak, J.
Clinical gnathostomiasis: case report and review of the English-language literature. Clinical Infectious Diseases, 16 1 , pp. DPDx is an educational resource designed for health professionals and laboratory scientists. For an overview including prevention, control, and treatment visit www. Page last reviewed: May 2,
Related Pages Causal Agents Gnathostoma spp. Humans are accidental hosts; the only forms found in humans are larvae or immature adults that never reach reproductive maturity. Most human infections are caused by G. Two unconfirmed human cases of G.
Incubation period[ edit ] The incubation period for gnathostomiasis is 3—4 weeks when the larvae begin to migrate through the subcutaneous tissue of the body. The eggs are then released with feces and in about a week hatch in water to develop into first stage larva. Life cycle in humans[ edit ] Infection of humans by gnathostomiasis is accidental because humans are not one of the definitive hosts of the parasite and do not allow the parasite to complete its life cycle. Infection in humans follows ingestion of raw or insufficiently cooked infected intermediate hosts. Instead the larvae continue to migrate unpredictably unable to develop into adults, so eggs are seldom found in diagnostic tests. Diagnosis[ edit ] Diagnosis of gnathostomiasis is possible with microscopy after removal of the worm.