Scientific name. Gnathostoma spinigerum, G. hispidum, G. doloresi, G. nipponicum

Disease name. Gnathostomiasis

Geographic distribution.
G. spinigerum: Palestine, India, Bangladesh, Burma, Thailand, Laos, Cambodia, Viet Nam, Malaysia, Indonesia, Philippines, China, Japan, Australia, Equador
G. hispidum: Turkestan, Hungary, Austria, Germany, Romania, Thailand, Viet Nam, Malaysia, Philippines, Korea, Taiwan and China
G. doloresi: India, Burma, Thailand, Viet Nam, Singapore, Philippines, Taiwan, Japan and New Guinea
G. nipponicum: Japan

Infection rate. Infection status can not be correctly estimated because the gnathostomes are tissue invading nematodes; their infections are nto easily diagnosed. In Korea, one case of Thai woman infected with G. spinigerum was reported in 1988, and the larvae of G. hispidum wre detected in a snake host, Agkistrodon brevicaudus.

Life cycle. The adult worms live in the stomach or esophagus of the final hosts. The eggs pass out with the feces, cleave and embryonate in the water in appropriate temperature. The second stage larvae, after molt in embrynoated eggs, are hatched and swim actively in the water, and are ingested by fresh water copepods, i.e., Mesocyslops leuckarti, Eucyclops serrulatus, Cyclops strenuus and C. vicinus. The larvae take off the sheath in the digestive tract of the copepod and migrate to the body cavity, to become an early third-stage larvae after the second molt. When the copepods are eaten by tadpoles or fishes (the second intermediate host), the early third-stage larvae in the digestive tract of the second intermediate hosts enter the muscle, and grow into the advanced third-stage larvae. On the other hand, some kinds of animals other than final hosts play a role of paratenic hosts, which ingest the second intermediate hosts holding the larvae. The final hosts get infection by ingesting raw or undercooked intermediate or paratenic hosts. The important final hosts are dogs and cats (G. spinigerum), pigs and wild pigs (G. hispidum and G. doloresi), and weasels (G. nipponicum).

Morphology. Most of the worms in humans are advanced third-stage larvae or very young adult worms. Their general morphology is similar to that of adult, with subglobular head bulb containing more than 4 rows of hooklets (G. nipponicum: 3 rows). Gnathostome larvae are identified on the basis fo several characteristics: the shape of body, the number of rows of hooklets at the head bulb, the number of hooklets in each row, and the characters with the extension of spines covering the body.

Pathology and clinical symptoms. The pathologic manifestations of gnathostomiasis consist of inflammation, edema, and tissue destructions along with the path of larvae. Much of the tissue reaction is believed to be allergic, but the number and size of larvae, and their invading sites are important factors also. The main organs affected are as follow: subcutaneous tissues, skin, central nerve system, eye, lungs and gastrointestinal tract.

Diagnosis. The clinical diagnosis is often based on the patient`s history of eating raw fishes, frogs and snakes, as well as the clinical symptoms. In rare cases, the migrating larvae are recovered but histologic diagnosis are also useful. Intradermal test and enzyme-linked immunosorbent assay (ELISA) are applicable.

Prevention. Avoiding ingestion of untreated water, raw freshwater fishes, tadpoles or snakes.

Comments. Differential diagnosis from other tissue invading helminths is necessary.

The early 3rd stage larva (EL3) of Gnathostoma. nipponicum from a loach imported from China.

The early 3rd stage larva of G. nipponicum from a loach imported from China.

Head bulb of G. nipponicum.

Siniperca scherzeri, mandarin fish.