Rodentolepis straminea (Cestoda: Hymenolepididae) in an urban population of Apodemus sylvaticus in the UK

The hidden faces of a biological invasion: parasite dynamics of invaders and natives

One of the primary drivers of emerging infectious diseases (EIDs) is human intervention via host or parasite translocations. A unique opportunity to study host and parasite dispersal during a bio-invasion currently exists in Ireland due to the introduction of the bank vole (Myodes glareolus) in the 1920s. The continuing range expansion of M. glareolus within Ireland presents a natural large-scale perturbation experiment. This study used the Irish M. glareolus model to conduct a spatiotemporal study analysing the parasite dynamics of native and invasive species throughout their range. Myodes glareolus and native Apodemus sylvaticus were trapped in woodlands across Ireland and surveyed for their helminth parasites. Myodes glareolus in Ireland were found to have lower parasite diversity in comparison to records of M. glareolus from across Europe and A. sylvaticus in Ireland. Increased density of M. glareolus resulted in a dilution effect, with significantly lower levels of parasitism overall in native hosts, where M. glareolus has been established longest. However, three helminth parasite species of A. sylvaticus increased in abundance in the presence of M. glareolus. Furthermore, M. glareolus at the expansion front were less parasitised (lower abundance and prevalence of certain parasites and lower parasite diversity) than M. glareolus from the core population. This "enemy release" is believed to be mediating the continued successful spread of the invader across Ireland. Our results identify two important variables, seasonality and the stage of the invasion, which should not be overlooked when investigating or managing the changing distribution of hosts and their parasites. Studies of bio-invasions and parasite transmission have primarily focused on the invasive host species or the native host species in cases where virulent pathogen spillover is observed. Our results demonstrate how the concurrent study of invasive and native hosts, and the careful identification of their parasite communities, allows the dynamic processes influencing the parasite component and intracommunity to be identified.

Impact of the degree of urbanization on composition and structure of helminth communities in the Mongolian racerunner (Eremias argus) Peters, 1869

The effects of the degree of urbanization on the composition and mean abundance of helminth species and the structure of helminth communities in the Mongolian racerunner were investigated along a rural–urban gradient in the region of Ulan-Ude city (the Republic of Buryatia, Russia) and neighbouring rural districts. Racerunners were obtained from key areas and categorized into three grades based on the degree of urbanization. In this study, a total of 208 lizards were examined. The helminth communities in the Mongolian racerunner were studied at the infracommunity and component community levels. The nematode Spauligodon pseudoeremiasi was a sensitive bioindicator of the degree of urbanization in our study. All parameters of helminth infracommunities in the Mongolian racerunner were significantly reduced with increasing degree of urbanization of the key areas. Two parameters of helminth component communities (the proportion of hosts infected with parasites and the Shannon index) were significantly reduced with increasing degree of urbanization. The decline recorded in parameters of helminth infracommunities and component communities in the Mongolian racerunner were probably connected with the attenuation of the relationships between helminths, having a complex life cycle with intermediate hosts along the rural–urban gradient.