Systematic review and modelling of seroprevalence in humans, Europe, 2000 to 2021

Background: Toxoplasma gondii is a zoonotic protozoan capable of infecting warm-blooded animal species and humans. Although toxoplasmosis presents mostly as mild or asymptomatic infection in immunocompetent individuals, in unborn children and people with weakened immune systems, the disease can be severe with ocular, neurological or multi-systemic manifestations and even death. Aim: We aimed to collate and analyse data on T. gondii seroprevalence in humans to model and compare age-dependent prevalence in geographic regions in Europe. Methods: A systematic review identified 1,822 scientific publications, from which seroprevalence data were extracted from 69 studies. Data were analysed using a Bayesian hierarchical model. Results: The modelling of the seroprevalence indicated the highest incidence rates in eastern (50%) and western (48%) Europe, with the lowest estimates in northern Europe (18%) and the United Kingdom (UK) (18%). Eastern and western Europe were regions where T. gondii infections occurred earliest in life, with half of the population expected to be seropositive by the age of 44 and 47 years, respectively. In contrast, in northern Europe and the UK the modelled median time to infection exceeded 170 years. Conclusions: Results of the study provide a robust baseline for future epidemiological research on human T. gondii infections in Europe and may be useful to validate subsequent research, such as risk assessment studies.