What significance do helminths species-complexes have for the prevention, diagnosis and treatment of human infections?

With the application of increasingly sophisticated molecular tools to the study of systematics (taxonomy, phylogeny), a multitude of new, initially genetically defined species have been uncovered, while molecular sequence data, including ‘barcoding’ of the ITS-2 and cox-1 genes, allow species identification and the discovery of cross-host species interactions. Cryptic species are typically genetically definable entities that occur within a taxon previously recognized as a single morphologically defined entity. 1 This is the case with many medically important macroparasite species, which we now know to be separate taxa but which are very difficult or cannot be determined morphologically. Historically, unraveling the species complexes within the mosquito genus Anopheles provides a good example of the importance of recognizing cryptic species as different; morphologically near identical species have different capacities for transmitting malaria leading to the confusing situation of the presence of supposed Anopheles vectors without malaria. 2 With the recognition that the areas without malaria were occupied by non-vector cryptic species this problem was solved and control and screening programs could be concentrated in those areas with known vectors. The situation with helminths is in most cases less clear, although numerous species complexes are known. These include trematodes such as Opisthorchis viverrini sensu lato (s.l.) 3 and Paragonimus westermani s.l., 1,4 members of the Echinostomatidae, 5 and possibly Schistosoma japonica, 6 cestodes such as Echinoccocus granulosus s.l., 7 as well as nematodes from the genera Anisakis and Pseudoteranova. 8,9 Once the genetic differences between the spe