Terrestrial runoff influences the transport and contamination levels of Toxoplasma gondii in marine organisms

Abstract

There is a growing concern regarding the potential adverse impact of Toxoplasma gondii contamination of the marine environment on marine wildlife and public health. Terrestrial runoff is a significant route for dissemination of T. gondii oocysts from land to sea. Yet, the influence of terrestrial runoff on T. gondii prevalence in marine animals in China is largely unknown. To address this concern, we examined the presence of T. gondii in marine oysters Crassostrea spp., rockfish Sebastes schlegelii (S. schlegelii), fat greenling fish Hexagrammos otakii (H. otakii), and Asian paddle crab Charybdis japonica (C. japonica) using a PCR assay targeting T. gondii B1 gene. A total of 1920 samples were randomly collected, in Jan-Dec 2020, from terrestrial runoff areas (TRA, TRB, and TRC) and non-terrestrial runoff area (Grape bay) in Weihai, China. T. gondii prevalence in TRB and TRC was 6.04 % and 5.83 %, respectively, which was higher than 2.29 % detected in the non-terrestrial runoff area. The highest prevalence was detected in Crassostrea spp., and a correlation was observed between T. gondii prevalence and weight of Crassostrea spp. The temperature, but not precipitation, significantly correlated with T. gondii prevalence. Understanding the fate of T. gondii delivered to oceans by terrestrial runoff is critical for predicting future disease risks for marine wildlife and humans.