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Parasitic Echinococcus multilocularis in Hokkaido originated from an Alaskan island more than 3000km away — Verification by Hokkaido University


Echinococcus multilocularis is a parasite that infects humans leading to serious diseases. It is currently prevalent in Hokkaido, causing serious health concerns. During the early 20th century, there was a thriving fox breeding fur industry on the Kuril Islands, which led to the introduction of high-quality foxes and voles as food sources for them on these islands. Scientists have hypothesized that these anthropogenic movements of host animals resulted in the transfer of parasites from St. Lawrence Island in Alaska to the Kuril Islands. Subsequently, the parasite populations from the Kuril Islands invaded the main island of Hokkaido. However, there was a lack of scientific evidence to support this hypothesis.

A research group led by Professor Nariaki Nonaka and Associate Professor Ryo Nakao of the Faculty of Veterinary Medicine at Hokkaido University has genetically verified the origin of Echinococcus multilocularis in Hokkaido. These findings indicate the possibility that this parasite originated on St. Lawrence Island in Alaska, over 3,000 kilometers away. The results were published in the journal iScience.

The research group used a high-throughput sequencer to read the base sequences of the mitochondrial genomes of 66 parasites from Hokkaido, 5 from St. Lawrence Island, and 1 from Europe. In total, 12 protein-coding gene sequences were studied in the mitochondrial genomes. A haplotype network of these 12 protein-coding gene sequences was constructed to describe the relationships among the genotypes. Additionally, a similar network was constructed using Bayesian phylogeographic analysis to estimate their global dispersal routes of three Echinococcus multilocularis from a database of published sequences from 17 regions around the world.

The network analysis of the 12 genes revealed that Hokkaido Echinococcus multilocularis individuals form a radial network and are broadly classified into two groups: St. Lawrence genotypes (group 1), which make up approximately 90% of the total population, and non-St. Lawrence genotypes (group 2).

Group 1 was detected throughout Hokkaido, suggesting that the species expanded its distribution throughout the island after the invasion, whereas group 2 was detected only in eastern Hokkaido. The network analysis of the three genes, with additional information from 17 regions around the world, revealed that group 2 is very closely related to parasites found in Sichuan Province, China. Moreover, the Bayesian phylogeographic analysis based on the genetic and geographic information strongly supported the unidirectional introduction of both group 1 from St. Lawrence Island and group 2 from Sichuan Province to Hokkaido.

Currently, there are no data to infer the route of entry of group 2 into Hokkaido. However, it is possible that, as with group 1, which originated on St. Lawrence Island, the movement of animals for fox breeding caused the parasite's entry into Hokkaido and the subsequent epidemic.

Journal Information
Publication: iScience
Title: Mitogenomic exploration supports the historical hypothesis of anthropogenic diffusion of a zoonotic parasite Echinococcus multilocularis
DOI: 10.1016/j.isci.2023.107741

This article has been translated by JST with permission from The Science News Ltd. ( Unauthorized reproduction of the article and photographs is prohibited.

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