Isolation, genotyping and phenotyping Toxoplasma gondii in Europe – A critical perspective

Toxoplasma gondii is a zoonotic parasite of worldwide distribution which can be transmitted from host to host, by consumption of raw or undercooked meat and vertically, or via the environment to the host. The genus Toxoplasma of the phylum Apicomplexa is represented by just the one species, T. gondii, which encompasses a multitude of genotypes of different virulence phenotypes. Understanding and importantly, the aim to predict the manifestations and outcome of infection in the human host, fueled the effort to isolate and genetically characterize the parasite over several decades. Early genotyping was heavily focused on humans and food animals. Over time and with the implementation of the One Health approach, the entire chain of transmission, which encompasses wildlife and the environment, has been included. Since the 1990s there has been a tremendous increase in knowledge of the parasite's genetic diversity–both at a low and high level of resolution–worldwide. The data has provided a new epidemiological perspective on T. gondii and fostered the development of molecular detection tools with source attribution capabilities, as well as strategies for environmental surveillance and transmission prevention. The genotyping effort in Europe delivered much of the data available today and sophisticated high resolution genotyping methods based on microsatellite (MS) analysis and rapid whole genome sequencing (WGS) were developed. After over two decades of genotyping T. gondii in Europe, we here present an overview of what has been learned and where do we go from here.