Generating super-shedders: co-infection increases bacterial load and egg production of a gastrointestinal helminth

Lass, Sandra; Hudson, Peter J.; Thakar, Juilee; Saric, Jasmina; Harvill, Eric; Albert, Réka; Perkins, Sarah E.

Our experiment showed that helminth establishment was initially the same in single and co-infected groups (figure 6a), but clearance was faster in single-infected individuals. Thus, the difference in helminth infection intensity in co-infection versus single infection was likely to be mediated by the host's immune system. While parasites in the same location within a host may interact due to competition for resources, including space and nutrients, interactions between parasites in different physical locations are likely to be mediated by the immune system [13, 19] , and these interactions may be antagonistic towards parasite defence [13, [47] [48] [49] . Previous work has shown that clearance of B. bronchiseptica from the lungs requires IFN-g, part of a Th1-mediated response [21] , whereas an immune response to H. polygyrus is initiated by Th2 cytokines, such as IL-4 and IL-10 in the murine host [50] . The anticipated antagonism between these immune responses to the bacterialhelminth co-infection may therefore have produced the impaired clearance of B. bronchiseptica and H. polygyrus [13, 20] . Alternatively, the immunomodulatory pathways known to be activated by H. polygyrus [51] [52] [53] could lead to suppression of immune responses to both parasites, thereby producing the helminth super-shedders and the high bacterial loads observed.