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Title: Echinococcus canadensis (Cestoda: Taeniidae) is a valid species consisting of the mitochondrial genotypes G6, G7, G8 and G10

Author
item YANAGIDA, TETSUYA - Yamaguchi University
item LAVIKAINEN, ANTTI - University Of Helsinki
item Hoberg, Eric
item KONYAEW, SERGEY - Russian Academy Of Sciences
item ITO, AKIRA - Asahikawa Medical College
item SATO, OTAKE - Dokkyo Medical University
item ZAIKOV, VLADIMIR - Kenozero National Park
item BECKMEN, KIMBERLEE - Alaska Department Of Fish And Game
item MAKAO, M - Asahikawa Medical College

Submitted to: International Journal for Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2017
Publication Date: 8/7/2017
Citation: Yanagida, T., Lavikainen, A., Hoberg, E.P., Konyaew, S., Ito, A., Sato, O., Zaikov, V.A., Beckmen, K., Makao, M. 2017. Echinococcus canadensis (Cestoda: Taeniidae) is a valid species consisting of the mitochondrial genotypes G6, G7, G8 and G10. International Journal for Parasitology. doi.org/10.1016/j.ijpara.2017.07.001.

Interpretive Summary: Species of Echnococcus tapeworms are the causative agents of cystic and avelolar hydatid disease, a serious zoonotic infection in people on a global scale. Although the species diversity within the genus has been increasingly well resolved, the status of Echinococcus canadensis has long been controversial. Confusion over identity has continued mainly because it consists of the mitochondrial genotypes named G6, G7, G8 and G10 with different host affinity: G6 (camel strain) and G7 (pig strain) with domestic cycles and G8 (cervid strain) and G10 (Fennoscandian cervid strain) with sylvatic or semi-domestic cycles. There is an argument whether the genotypes should be recognized as separate taxa which correspond to the biological or epidemiological aggregation. To contribute to resolution of this controversy which has implications for patterns of transmission, identification and possible treatment in human infections, we explored gene flow among global samples of E. canadensis genotypes using a mitochondrial DNA (mtDNA) gene and single copy nuclear DNA (nDNA) markers. Nucleotide sequences were determined for 48 isolates of E. canadensis collected from different hosts in a wide range of regions. The mitochondrial phylogeny of cox1 showed that all the isolates were clearly divided into 3 clades corresponding to G6/G7, G8 and G10. Five and three alleles were confirmed at pepck and pold loci, respectively. The resultant gene flow patterns demonstrated that each of the E. canadensis genotypes is not reproductively isolated, supporting their attribution (G6/G7, G8 and G10) to a single species. A mosaic parasite fauna due to natural and anthropogenic disturbance including introductions and invasion precludes us to split the genotypes into different species. Our findings have implications for understanding local to regional patterns of infection in people and global distribution of hydatid disease. Genetic data, new interpretations of diversity and species status will be critical for the medical establishment, wildlife veterinarians, and the zoonotic disease community at national and international levels in leading to control of human infections on a global scale.

Technical Abstract: The species status of Echinococcus canadensis has long been controversial, mainly because it consists of the mitochondrial genotypes G6, G7, G8 and G10 with different host affinity: G6 (camel strain) and G7 (pig strain) with domestic cycles and G8 (cervid strain) and G10 (Fennoscandian cervid strain) with sylvatic or semi-domestic cycles. There is an argument whether the genotypes should be recognised as separate taxa which correspond to the biological or epidemiological aggregation. In the present study, gene flow among E. canadensis genotypes was investigated using a mitochondrial DNA (mtDNA) gene and single copy nuclear DNA (nDNA) markers. Nucleotide sequences of complete mitochondrial cytochrome c oxidase subunit 1 (cox1) and partial nuclear phosphoenolpyruvate carboxykinase (pepck) and DNA polymerase delta (pold) were determined for 48 isolates of E. canadensis collected from different hosts in a wide range of regions. The mitochondrial phylogeny of cox1 showed that all the isolates were clearly divided into 3 clades corresponding to G6/G7, G8 and G10. Five and three alleles were confirmed at pepck and pold loci, respectively. Although a couple of alleles were found corresponding to certain genotypes or host localities, most of the alleles were shared among individuals showing different genotypes. The allele sharing occurred primarily in regions where different genotypes were found in sympatry. The resultant gene flow patterns demonstrated that each of the E. canadensis genotypes is not reproductively isolated, supporting their attribution (G6/G7, G8 and G10) to a single species. A mosaic parasite fauna due to natural and anthropogenic disturbance including introductions and invasion precludes us to split the genotypes into different species.