Interaction forces drive the environmental transmission of pathogenic protozoa RUNNING TITLE: Protozoa-environment interaction forces

International audienceThe protozoan parasites Giardia duodenalis, Cryptosporidium spp. and Toxoplasma gondii are environment-resistant pathogens that pose significant risks to public health worldwide. Their environmental transmission is closely governed by the physicochemical properties of their cysts and oocysts respectively, allowing their transport, retention and survival for months in water, soil, vegetables and mollusks, which are the main reservoirs for human infection. Importantly, the cyst/oocyst wall plays a key role in that regard by exhibiting a complex polymeric coverage that determines the charge and hydrophobic characteristics of parasites' surface. Interaction forces between parasites and other environmental particles may be, in a first approximation, evaluated following the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloidal stability. However, due to the molecular topography and nano- to micro- structure of the cyst/oocyst surface, non-DVLO hydrophobic together with additional steric attractive/repulsive forces may play a pivotal role in controlling the parasite behavior when submitted to various external conditions. Here, we review several parameters that enhance or hinder the adhesion of parasites to other particles and surfaces, and address the role of fast-emerging techniques for mapping the cyst/oocyst surface e.g. by measuring their topology and the generated interaction forces at the nano- to micro- scale. We discuss why characterizing these interactions could be a crucial step for managing the environmental matrices at risk of microbial pollution