Molecular identification and genetic diversity of Gnathostoma spinigerum larvae in freshwater fishes in southern Lao PDR, Cambodia, and Myanmar

Gnathostomiasis, an emerging food-borne parasitic zoonosisin Asia, is mainly caused by Gnathostoma spinigerum(Nematoda: Gnathostomatidae). Consumption of raw meator freshwater fishesin endemic areas is the major risk factor. Throughout Southeast Asia, including Thailand, Lao PDR, Cambodia, and Myanmar, freshwater fishare often consumed raw or undercooked. The risk of this practice for gnathostomiasisinfection in Lao PDR, Cambodia, and Myanmar has never been evaluated. Here, we identified larvae of Gnathostomaspecies contaminating freshwater fishessold at local markets in these three countries. Public health authorities should advise people living in, or travelling to, these areas to avoid eating raw or undercooked freshwater fishes. Identification of larvae was done using molecular methods: DNA was sequenced from Gnathostomaadvanced third-stage larvae recovered from snakeheadfishes ( Channa striata) and freshwater swamp eels( Monopterusalbus). Phylogenetic analysis of a portion of the mitochondrial cytochrome c oxidase subunit Igene showed that the G. spinigerum sequences recovered from southern Lao PDR, Cambodia, and Myanmar samples had high similarity to those of G. spinigerum from China. Sequences of the nuclear ribosomal DNAinternal transcribed spacer 2 region closely resembled sequences of G. spinigerum from Thailand, Indonesia, the USA, and central Lao PDR. This is the first molecular evidence of G. spinigerum from freshwater fishesin southern Lao PDR, Cambodia, and Myanmar.