ITS-2 rDNA sequencing of Gnathostoma species (Nematoda) and elucidation ofthe species causing human gnathostomiasis in the Americas

From several gnathostome species the complete internal transcribed spacer I TS-2 ribosomal DNA (rDNA) repeat sequence and a fragment of the 5.8S rDNA w ere obtained by direct polymerase chain reaction cycle-sequencing and silve r-staining methods. The size of the complete ITS-1 sequence in agarose gel electrophoresis was also obtained. The ITS-2 enabled the differentiation of Gnathostoma spinigerum from Thailand and Gnathostoma binucleatum from Mexi co and Ecuador and confirmed the validity of the latter. Gnathostoma turgid um, Gnathostoma sp. I (= Gnathostoma procyonis sensu Almeyda-Artigas ct al. , 1994), and Gnathostoma sp. II(= G. turgidum sensu Foster, 1939 pro parte) , all from Mexico, proved to be independent species, but Gnathostoma sp. II I, also from Mexico, could not be differentiated from G. turgidum. In Mexic o and Ecuador, gnathostomes involved in human infection and that had been c lassified as G. spinigerum belong to G. binucleatum. The 5.8S rDNA sequence s of the 6 Gnathostoma species studied were identical. The results of the I TS-1 agreed with those results of ITS-2.