From several gnathostome species the complete internal transcribed spacer ITS-2 ribosomal DNA (rDNA) repeat sequence and a fragment of the 5.8S rDNA were obtained by direct polymerase chain reaction cycle-sequencing and silver-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 Mexico and Ecuador and confirmed the validity of the latter. Gnathostoma turgidum, Gnathostoma sp. I (=Gnathostoma procyonis sensu Almeyda-Artigas et al., 1994), and Gnathostoma sp. II (=G. turgidum sensu Foster, 1939 pro parte), all from Mexico, proved to be independent species, but Gnathostoma sp. III, also from Mexico, could not be differentiated from G. turgidum. In Mexico and Ecuador, gnathostomes involved in human infection and that had been classified as G. spinigerum belong to G. binucleatum. The 5.8S rDNA sequences of the 6 Gnathostoma species studied were identical. The results of the ITS-1 agreed with those results of ITS-2.

From several gnathostome species the complete internal transcribed spacer ITS-2 ribosomal DNA (rDNA) repeat sequence and a fragment of the 5.8S rDNA were obtained by direct polymerase chain reaction cycle-sequencing and silver-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 Mexico and Ecuador and confirmed the validity of the latter. Gnathostoma turgidum, Gnathostoma sp. I (=Gnathostoma procyonis sensu Almeyda-Artigas et al., 1994), and Gnathostoma sp. II (=G. turgidum sensu Foster, 1939 pro parte), all from Mexico, proved to be independent species, but Gnathostoma sp. III, also from Mexico, could not be differentiated from G. turgidum. In Mexico and Ecuador, gnathostomes involved in human infection and that had been classified as G. spinigerum belong to G. binucleatum. The 5.8S rDNA sequences of the 6 Gnathostoma species studied were identical. The results of the ITS-1 agreed with those results of ITS-2.

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Proteins from crude extracts of advanced third-stage larvae and adult Gnathostoma binucleatum nematode worms showed protein profiles in SDS-PAGE analysis similar to Echinococcus granulosus, Trichinella spiralis, Dipylidium caninum, Ancylostoma caninum, Ascaris lumbricoides and Toxocara canis. The immunoblot analysis of the human serum infected or suspected to be infected with G. binucleatum using the total larvae extract recognized the 40, 60, 80 and 115 kDa proteins and using the total adult worm extract recognized only the 80 and 115 kDa proteins. However, the 115 kDa protein showed cross-reactions with A. caninum, A. lumbricoides, T. canis and D. caninum with human serum positive to gnathostomosis, while the 40 kDa protein was only recognized with the G. binucleatum total larvae extract. The results obtained suggest that the use of antigens from the advanced third-stage larvae of the parasite were best recognized for immunodiagnosis of gnathostomosis.

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