The ‘bridge effect’ by intermediate hosts may explain differential distributions of Echinococcus species

Zoonotic cestodes in the genus Echinococcus show marked differences in their distribution patterns, which have not been satisfactorily explained. Echinococcus multilocularis is limited to moist and cool areas of the Holarctic region, whereas species in the E. granulosus sensu lato (s.l.) complex mostly have a worldwide distribution encompassing hot and arid areas. We suggested that the low virulence of species in the E. granulosus s.l. complex for their intermediate hosts, and a longer lifespan of infected hosts, explain the differential distributions (‘bridge effect’ hypothesis). Human-mediated dispersal and egg shedding by definitive hosts might also be involved. In the light of globalization and climate change, a clear understanding of the drivers of zoonotic parasites distribution is critical to prevent pathogen outbreaks.