Is Echinococcus intermedius a valid species?

Authors: NAKAO, MINORU - Asahikawa Medical College; LAVIKAINEN, ANTTI - University Of Helsinki; Hoberg, Eric

Submitted to: Trends in Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2015
Publication Date: 8/15/2015
Citation: Nakao, M., Lavikainen, A., Hoberg, E.P. 2015. Is Echinococcus intermedius a valid species? Trends in Parasitology. 31:342-343.

Interpretive Summary: Medical and veterinary sciences require scientific names to discriminate pathogenic organisms in our living environment. Various species concepts have been proposed for metazoan animals. There are, however, constant controversies over their validity because of lack of a common criterion to define species across different phyla. Current disagreements within the genus Echinococcus, a group of highly pathogenic and zoonotic tapeworms, highlight the challenge and the reason why such taxonomic issues are not trivial. Concepts about species must be grounded in a phylogenetic/evolutionary context, follow clear rules of nomenclature, and be directly linked to specimens which have been permanently archived in museum repositories. A recent proposal for taxonomy in this group of tapeworms does not apply these criteria, and would lead to confusion about the identity of the parasites. This example is important for parasite taxonomists, disease ecologists and medical/veterinary professionals in establishing why decisions about taxonomy are critical as foundations, and have direct consequences for our understanding of the biosphere and the distribution of potential parasitic disease.

Technical Abstract: Medical and veterinary sciences require scientific names to discriminate pathogenic organisms in our living environment. Various species concepts have been proposed for metazoan animals. There are, however, constant controversies over their validity because of lack of a common criterion to define species across different phyla. Current disagreements within the genus Echinococcus, a group of highly pathogenic and zoonotic tapeworms, highlight the challenge and the reason why such taxonomic issues are not trivial. In this regard E. granulosus the etiological agent of cystic hydatid disease has over the past decade been shown to represent a number of cryptic species. Among these, Echinococcus canadensis is the most difficult species with respect to recognizing clear delimiting boundaries relative to other congeners. In the course of taxonomic revision of Echinococcus granulosus sensu lato, it was demonstrated that the domestic camel and pig strains (genotype G6/G7) and the sylvatic cervid strain (genotypes G8 and G10) were genetically very closely related. Collectively these genotypes were unified as E. canadensis by elevating the subspecies E. granulosus canadensis to specific rank. A recent proposal to provide a name, E. intermedius, for the combined pig and camel strains cannot be supported. There is obviously no foundation for resurrecting and using the name of E. intermedius for G6/G7, because no intermediate hosts (i.e. pig and camel) were recorded in the original description. The species was described based on only a few adult worms from a dog in Spain, and thus to a considerable degree remains of unknown provenance. Further, the putative type specimen of E. intermedius now appears lost, despite extensive efforts and continuous searches among collections in Spanish museums and related institutes.