Refractory giardiasis: Exploring the contribution of bacterial community shifts

Giardia duodenalis infection is a common cause of diarrhoea in returning travellers from low-income regions. The increasing prevalence of resistance to nitroimidazoles, as first-line therapy, are of global concern. The interaction between Giardia and the host's gut microbiota plays a crucial role in the pathophysiology of giardiasis. Yet, longitudinal data assessing the course of the infection are scarce, and non-existent in patients refractory to treatment. Here, we provide the first longitudinal bacterial community study, carried out in two Giardia-infected Spanish adult patients refractory to treatment after travelling to India, a Giardia-hyperendemic country, which offers insights into the gut microbiota's response to infection and therapy over time. A significant reduction in alpha diversity was evidenced during and post-infection, accompanied by changes in bacterial taxa contribution, with an important individual effect. We evidenced microbial shifts that may be associated with infection, treatment effectiveness or microbial restoration after infection, which can potentially be used to monitor disease evolution and adjust the therapeutic strategy.