Infectious Disease Online
Pathology of Human Gnathostomiasis
Gnathostomiasis is a food-borne parasitic disease caused by the third
stage larvae of the genus Gnathostoma.
Although 15 species of the genus Gnathostoma have been reported , only 5 of them infect humans. These are Gnathostoma spinigerum, G. nipponicum, G. hispidum, G. doloresi, and G. binucleatum.
( Clue to Diagnosis: The species of Gnathostoma can be distinguished by the number of nucleus in the gut epithelium: G. hispidum and G. nipponicum 1 ; G. doloresi 2 and G. spinigerum 3-7 )
Gnathostoma spinigerum was first identified in the gastric tumour of a tiger in 1836.
Human gnathostomiasis was first reported from Thailand in 1890 in a woman presenting with a breast mass.
Gnathostomiasis is endemic in Japan and Southeast Asia, particularly in Thailand, and in Cambodia, Laos, Myanmar, Indonesia, Philippines, and Malaysia.
Cases have also been reported in India, China and Sri Lanka.
In more recent years there has been a number of reports of human gnathostomiasis from Central and South America, particularly in Mexico and also in Guatemala, Peru, and Ecuador.
A few cases were reported in Myanmar, Zambia, and Botswana.
The main source of human infection is thought to be ingestion of inadequately cooked flesh of either the "primary" or "secondary" second intermediate hosts harbouring third-stage larvae.
Fresh water fish and domestic poultry may be the most important sources.
Adult nematodes live in the stomach of definitive fish-eating hosts (carnivorous mammals including the tiger, opossum, pig, wild boar, weasel, racoon, otter, cats and dogs).
When faeces containing eggs are deposited in water, first and then second-stage larvae develop.
Ingested by the first intermediate host (a cyclop), they develop into early third stage larva (L3).
Second intermediate hosts (freshwater fish ; frogs ; snakes; chickens; snails; or pigs) ingest the cyclops, liberating the larvae, which encyst in muscle and mature into L3 forms.
When infected fish are eaten by a definitive host, the larvae mature into adults in 6 months.
The larvae cannot mature in humans and keep migrating in the skin, subcutaneous tissues, or other organs.
Gnathostomiasis is characterized by intermittent creeping eruptions and/or migrating swellings and eosinophilia. Larval migration to other tissues (visceral larva migrans) can result in a serious consequence.
If untreated, gnathostomiasis may remit and recur several times until death of the larvae up to 12 years after infection.
Routes of human infection : Ingestion of water that contains infected copepods or direct skin penetration of food handlers through L3-infected meat.
Symptoms in humans occur as the larva migrates through tissues, causing cutaneous and/or visceral larva migrans, which may begin within 24–48 hours after ingestion of infected meat.
Initial nonspecific symptoms include fever, malaise, nausea, vomiting, diarrhea, and epigastric pain lasting 2–3 weeks and usually accompanied by a marked eosinophilia.
Within 1 month, the cutaneous lesion may develop, with characteristic nonpitting edematous migratory swellings that may be painful, pruritic, or erythematous and may last 1–2 weeks.
Visceral gnathostomiasis occurs when the larvae migrate through the internal organs such as the lungs, gut, genitourinary tract, eye, ear, and central nervous system.
This form causes more illness and deaths, with higher mortality rates than the cutaneous form.
Biopsy of a skin lesion or a visceral eosinophilic mass found at surgery can be helpful diagnostically. It is curative if the larva is removed.
Biopsies of migrating lesions frequently miss the larvae and are helpful only in demonstrating an eosinophilic infiltration.
Gnathostomiasis should be considered as a possible diagnosis of migatory skin lesions and eosinophilia in individuals living in, or recently returning from, endemic areas.
The triad of eosinophilia, migratory lesions, and obvious exposure risk are highly suggestive of the diagnosis of gnathostomiasis.
Exposure risk must include residence in or travel to an area of endemicity and consumption of food that potentially contains the larval form of the parasite (raw or undercooked fish, frogs, chickens, cats, or dogs.
Adequate cooking is the best way to ensure that the larvae are killed, although freezing infected meat to −20°C for 3 to 5 days is also effective.
Public health education is essential to change the eating habits of people in areas with high levels of endemicity.
Travelers should to be aware of the potential consequences of eating local delicacies.
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