Mauricio Seguel, Sarah A. Budischak, Anna E. Jolles, Vanessa O. Ezenwa
In nature, most animals are simultaneously infected with a diverse range of parasites. Some of these parasites, like gastrointestinal (GI) worms, can cause profound changes in the host that affect co-occurring parasites.
In this study, focusing on two different GI worms (Cooperia and Haemonchus) infecting wild African buffalo, we examined if and how worms modify host immunity and tissue morphology and the consequences of these modifications for a protozoan parasite, coccidia, that also resides in the GI tract. By comparing buffalo that received a treatment to clear their worm infections to untreated controls, we found that when treatment eliminated Haemonchus, coccidia shedding increased. Furthermore, animals relieved of their Haemonchus burdens experienced an enhancement in the branch of the immune system that controls worms (Th2 immunity). This increase in Th2 immunity was associated with a decline in certain immune cells (e.g. T lymphocytes) and an increase in wound healing, both of which likely contributed to increases in coccidia shedding. Importantly, animals that shed more coccidia experienced adverse reproductive and health consequences, as evidenced by an older age of first reproduction and lower body condition. Thus, eliminating Haemonchus from a host’s parasite community may counterintuitively reduce host fitness by facilitating coccidia.
Altogether, our findings suggest that tracking how parasites change host characteristics can help uncover the complex and nuanced ways in which parasites influence one another.