Detection, fate, and transport of Toxoplasma gondii oocysts in soil water systems: Influence of soil physicochemical properties, water chemistry, and surfactant

Authors: KINSEY, ERIN - Clemson University; KORTE, CAROLINE - Clemson University; GOUASMIA, SOHIB - Aix-Marseille University; L'OLLIVIER, CORALIE - Marseille University Hospital Timone; Dubey, Jitender; DUMÈTRE, AURÉLIEN - Aix-Marseille University; DARNAULT, CHRISTOPHE - Clemson University

Submitted to: Environmental Microbiology Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2023
Publication Date: 9/22/2023
Citation: Kinsey, E., Korte, C., Gouasmia, S., L'Ollivier, C., Dubey, J.P., Dumètre, A., Darnault, C. 2023. Detection, fate, and transport of Toxoplasma gondii oocysts in soil water systems: Influence of soil physicochemical properties, water chemistry, and surfactant. Environmental Microbiology Reports. 15(6):597-613. https://doi.org/10.1111/1758-2229.13204.
DOI: https://doi.org/10.1111/1758-2229.13204

Interpretive Summary: Food safety remains a worldwide problem. Among the pathogens transmitted from animals to humans, coccidia are a group of protozoans (single celled parasites) that affect human health and economic losses to farmers of massive magnitude. Coccidia in general have an environmentally resistant stage (oocyst) excreted in feces of certain (definitive) hosts. Humans and animals become infected by ingesting food and water contaminated with oocysts. Controlling transmission is technically difficult because commonly used disinfectants are ineffective in killing oocysts and oocysts can survive for many months even in harsh climates. The coccidia includes members of the genus Toxoplasma, Cyclospora, and Sarcocystis that can cause severe illness in humans. Toxoplasma is one of the most studied parasites because it infects one-third of humanity and virtually all warm blooded animals. Efficient and sensitive methods have been developed for the detection of the oocysts in environment. Prior to redirection of USDA’s food safety research program, ARS scientists contributed to a research consortium seeking to understand how oocysts are transported in different types of soils. Findings present a better understanding of the mechanisms and factors that influence the transmission of this zoonotic pathogen in soils and receiving waters. These results will be of interest to parasitologists and biologists. This research was completed before redirection of Toxoplasma research at ARS.

Technical Abstract: A series of laboratory experiments were conducted to study the fate and transport of Toxoplasma gondii oocysts in soils as a function of soil physicochemical properties and soil water chemistry properties. Soil columns were homogeneously packed with loamy sand soils (Lewiston and Greenson series) and sandy loam soils (Sparta and Gilford series), and subject to hydrologic conditions characterized by the absence and presence of an anionic surfactant—Aerosol 22 in the artificial rainfall. Quantitative polymerase chain reaction (qPCR) was utilized for the detection and enumeration of oocysts in soil leachates to evaluate their breakthrough and in soil matrices to examine their spatial distribution. Differences in the rate and extent of transport of oocysts were observed as a function of physical and chemical parameters tested. The breakthrough of oocysts was observed for all the soils irrespective of the presence of surfactant. However, in the absence of surfactant, the predominant fate of oocysts in soils subject to simulated rainfall was their retention in the soil profile. The presence of surfactant induced a change in the fate of oocysts in these soils exposed to rainfall simulation as the predominant fate of oocysts was found to be in the soil leachates.