An Overview of Gnathostomiasis in the World

Gnathostomiasis is a typical fish-borne parasitic zoonosis. Gnathostoma spinigerum has long been considered the only species to cause human infection. Because of the distribution of this species and the eating habits of the people, gnathostomiasis was thought an unique parasitic disease in Asia, especially in Thailand and Japan. Around the 1970s, however, the presence of this disease was reported from Ecuador and Mexico, and now the endemicity in Latin America is considered the worst in the world. The causative species was recently proven to be G. binucleatum. In Japan, while gnathostomiasis due to G. spinigerum had almost disappeared by the 1970s, small outbreaks and/or sporadic cases caused by infection with G. hispidum, G. doloresi, and G. nipponicum were, one after another, discovered during the 1980s-1990s, suggesting that any Gnathostoma spp would cause human disease. Apart from those known endemics, an outbreak of gnathostomiasis among Korean emigrants in Yangon, Myanmar, was reported. Furthermore, collaborative study with Danish and Vietnamese parasitologists revealed that G. spinigerum infection is common in freshwater fishes in Vietnam, suggesting that gnathostomiasis would occur all over the Indochina peninsula. In fact, this expectation will be substantiated by the country report from Vietnam in this meeting. In addition to those known or predicted endemic areas, literature survey revealed that gnathostomiasis patients have been seen sporadically in Europe and North America. Those patients seen in non-endemic areas were mostly emigrants from endemic areas, but a few travelers from non-endemic areas also seemed to be infected during their travel to endemic areas. Gnathostomiasis has now become an important disease in travel medicine. definitive hosts, they become adult worms to complete their life cycle (Fig 1). Although any second intermediate or paratenic host can be the source of human infection with Gnathostoma spp, the majority of patients have a history of ingesting raw or undercooked fish meat. Gnathostomiasis is, therefore, a typical fish-borne parasitic zoonosis. In Japan, a few cases were supposed to be infected by ingesting raw snake meat with a belief in its tonic effect (Kurokawa et al, 1998). GNATHOSTOMA AS A PATHOGEN OF HUMAN DISEASE When the third-stage larvae are ingested by humans, they are unable to develop into the adult stage and migrate through human tissues, preferentially in the skin, to cause serpiginous eruption and/or mobile erythema. Although gnathostomiasis is generally known as cutaneous larva migrans, an accidental migration of the larvae into vital organs, such as the central nervous system (CNS) results in fatal or deleterious illness. Among 13 species, only one G. spinigerum, had been known to cause human disease in Asian countries, especially Thailand and Japan (Daengsvang, 1980). However, since the 1980s, in Japan, G. hispidum, G. nipponicum, and G. doloresi were, one after another, proven to cause human disease (Nawa, 1991). In Correspondence: Dr Yukifumi Nawa, University of Miyazaki, 1-1 Gakuen-Kibanadai-Nishi, Miyazaki 889-2192, Japan. Tel: +81-985-587588; Fax: +81-985-582886 E-mail: [email protected] BIOLOGY OF THE GENUS GNATHOSTOMA The genus Gnathostoma is a nematode parasite of carnivorous/omnivorous mammals. Till now, 13 species of the genus Gnathostoma have been identified with varying geographical distributions (Table 1; Daengsvang, 1980). Six species are found in Asia and seven in the Americas. Adult worms of the majority of Gnathostoma spp parasitize the stomach of the definitive hosts (G. nipponicum reside in the esophagus and some other species reside in the kidney or liver). They lay eggs in the feces of the definitive hosts and the first-stage larvae hatch from the eggs in freshwater. After being ingested by copepods (Cyclops), the first intermediate host, the larvae develop into early thirdstage larvae. They are then ingested by freshwater fishes or amphibians, where they become advancedthird-stage larvae. Along with the food-chain, the advanced-third-stage larvae are distributed in a wide range of animals (paratenic hosts) including icthiophagous fishes, reptiles, birds, and rodents, without further development. When the second intermediate or paratenic hosts are ingested by the SOUTHEAST ASIAN J TROP MED PUBLIC HEALTH 88 Vol 35 (Suppl 1) 2004 Table 1 Currently accepted Gnathostoma species with reference to human infection. Species Natural Habitat Locality Human definitive hosts infection G. spinigerum Owen, 1836 feline, canine stomach Asia, Oceania Yes G. hispidum Fedtschenko, 1872 pig, wild pig stomach Asia, Europe Yes G. trugidum Stossich, 1902 opossum stomach Americas G. americanum Travassos, 1925 feline stomach South America G. doloresi Tubangui, 1925 pig, wild pig stomach Asia, Oceania Yes G. didelphis Chandler, 1932 opossum liver USA G. nipponicum Yamaguti, 1941 weasel esophagus Japan Yes G. procyonis Chandler, 1942 raccoon stomach USA G. brasiliense Ruiz, 1952 otter liver Brazil G. miyazakii Anderson, 1964 otter kidney North America G. malaysiae Miyazaki et Dunn, 1965 rat stomach Malaysia, Thailand G. vietnamicum Le Van Hoa, 1965 otter kidney Vietnam, Thailand G. binucleatum Almeyda-Artigas 1991 canine stomach Mexico Yes (modified from Table I, Daengsvang, 1980) Fig 1Life cycle of the genus Gnathostoma.