Historical review and current status of gnathostomiasis in Asia

The genus Gnathostoma contains at least twelve distinctive species. Among these, 6 species, namely G. spinigerum, G. hispidum, G. doloresi, G. vietnamicum, G. malaysiae and G. nipponicum, are found in wild animals in Asia. Related to human gnathostomiasis, G. spinigerum has long been believed as the only causative species. Until the early 1980s, all gnathostomiasis cases found in major endemic areas in Asia, such as Thailand, China and Japan, were caused by infection with G. spinigerum. In the early 1980s in Japan, new gnathostomiasis cases appeared in urban areas and these cases were shown to be caused by G. hispidum, of which larvae were found in loaches imported from Taiwan, Korea, or mainland China. Recently infections with G. nipponicum caused by eating locally obtained loaches raw, were found in 2 humans in Mie Prefecture, and 14 cases of infection with G. doloresi, probably caused by eating raw slices of freshwater fishes, were found in Miyazaki Prefecture. So far four Gnathostoma species are responsible for zoonotic infections in humans. Since G. hispidum and G. doloresi, like G. spinigerum, are widely distributed in Asia, care should be taken with the identification of species causing gnathostomiasis.