Fish as the natural second intermediate host of Gnathostoma spinigerum

Gnathostomiasis is a helminthic disease most frequently occurring in Thailand. Human infections are usually found to be caused by Gnathostoma spinigerum, although five species of the genus Gnathostoma exist in Thailand, and three of these are capable of infecting man. In Thailand, 47 species of vertebrates--fish (19), frogs (2), reptiles (11), birds (11) and mammals (4)--have been reported to serve naturally as the second intermediate (and/or paratenic) hosts of G. spinigerum. Of these, fish, especially swamp eels (Monopterus albus), were found to be the best second intermediate/paratenic hosts: they had the highest prevalence rate and the heaviest infection intensity. However, the scientific names of these fish have been revised from time to time. Therefore, for clarity and consistency, we have summarized the current scientific names of these 19 species of fish, together with their illustrations. We describe one additional fish species, Systomus orphoides (Puntius orphoides), which is first recorded as a naturally infected second intermediate host of G. spinigerum.