Molecular analysis of echinostome metacercariae from their second intermediate host found in a localised geographic region reveals genetic heterogeneity and possible cryptic speciation.
Echinostome metacercariae are the infective stage for humans and animals. The identification of echinostomes has been based until recently on morphology but molecular techniques using sequences of ribosomal RNA and mitochondrial DNA have indicated major clades within the group. In this study we have used the ITS2 region of ribosomal RNA and the ND1 region of mitochondrial DNA to identify metacercariae from snails collected from eight well-separated sites from an area of 4000 km2 in Lamphun Province, Thailand. The derived sequences have been compared to those collected from elsewhere and have been deposited in the nucleotide databases. There were two aims of this study; firstly, to determine the species of echinostome present in an endemic area, and secondly, to assess the intra-specific genetic diversity, as this may be informative with regard to the potential for the development of anthelmintic resistance and with regard to the spread of infection by the definitive hosts. Our results indicate that the most prevalent species are most closely related to E. revolutum, E. trivolvis, E. robustum, E. malayanum and Euparyphium albuferensis. Some sites harbour several species and within a site there could be considerable intra-species genetic diversity. There is no significant geographical structuring within this area. Although the molecular techniques used in this study allowed the assignment of the samples to clades within defined species, however, within these groupings there were significant differences indicating that cryptic speciation may have occurred. The degree of genetic diversity present would suggest the use of targeted regimes designed to minimise the selection of anthelmintic resistance. The apparent lack of geographic structuring is consistent with the transmission of the parasites by the avian hosts.
Department of Biology, Faculty of Science, Chiang Mai University, Chiang Mai Province, Chiang Mai, Thailand; Program of Applied Biology, Faculty of Science and Technology, Pibulsongkram Rajabhat University, Phitsanulok Province, Phitsanulok, Thailand.
Waraporn
W
Noikong
Department of Biology, Faculty of Science, Chiang Mai University, Chiang Mai Province, Chiang Mai, Thailand; Applied Technology in Biodiversity Research Unit, Institute of Science and Technology, Chiang Mai University, Chiang Mai Province, Chiang Mai, Thailand.
Chalobol
C
Wongsawad
Department of Parasitology, Seoul National University College of Medicine, and Institute of Endemic Diseases, Seoul National University Medical Research Center, Seoul, Korea.
Jong-Yil
JY
Chai
Department of Biology, Faculty of Science, Chiang Mai University, Chiang Mai Province, Chiang Mai, Thailand.
Supap
S
Saenphet
School of Biological Sciences, Medical Biology Centre, The Queen's University of Belfast, Belfast, Northern Ireland.
Alan
A
Trudgett
D000818:Animals; D016000:Cluster Analysis; D004272:DNA, Mitochondrial / Q000737:chemistry / Q000235:genetics; D021903:DNA, Ribosomal Spacer / Q000737:chemistry / Q000235:genetics; D004449:Echinostoma / Q000145:classification* / Q000235:genetics* / Q000302:isolation & purification; D004451:Echinostomiasis / Q000469:parasitology; D018740:Genetic Heterogeneity; D049810:Genetic Speciation; D006801:Humans; D058488:Metacercariae / Q000145:classification* / Q000235:genetics* / Q000302:isolation & purification; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D013785:Thailand
D004272:DNA, Mitochondrial; D021903:DNA, Ribosomal Spacer