Biological Threat Agents in the Environment: Detection, Fate, and Transport of Toxoplasma gondii in Soils

Toxoplasma gondii is a zoonotic protozoan that causes toxoplasmosis, a waterborne and foodborne disease. T. gondii is widely prevalent in humans and warm-blooded animals worldwide, and is found in soil and water systemsas an environmentally resistant oocyst stage. The mechanisms by which oocysts are transmitted throughout the environment are largely unknown. Our study aims at exploring the fate and transport of T. gondii oocysts in soil and water systems and explores the soil physicochemical properties and flow phenomena that impact their transport. To characterize and measure the transport of oocysts in soil and water systems, qPCR was used to detect and quantify oocysts in experimentally contaminated soil and water samples. Our findings demonstrated that soil physicochemical properties and water chemistry impacted the mobility of T. gondii oocysts in natural (soils) and engineered (sand) porous media. Our results determined that an increase in salt concentration and ion valency (i.e., sodium, calcium, and magnesium ions) reduced the soil breakthrough of oocysts while the presence of surfactants (i.e., anionic surfactant sodium dodecylbenzene sulfonate (SDBS), non-ionic surfactant Triton X-100, and anionic surfactant Aerosol 22) enhanced their transport. The transport of oocysts in saturated sand porous media was simulated using Hydrus 1D with adsorption-only, adsorption/desorption, and straining models. The adsorption model seems to show a good fit of the experimental data. Our research findings show the significance of the environmental transport of T. gondii oocysts and present an understanding of the mechanisms and factors that influence the environmental transmission of this zoonotic pathogen.