Seasonal and spatial variation in Toxoplasma gondii contamination in soil in urban public spaces in California, United States.

Background Toxoplasma gondii is a zoonotic parasite that can have severe implications for human health. Acutely infected cats shed environmentally resistant T. gondii oocysts in their faeces that contaminate soil, and soil can serve as a reservoir of infection for humans. Free-roaming domestic cats are thought to play an important role in environmental contamination with T. gondii, but few studies have directly measured the direct contribution of free-roaming cats to T. gondii in soil. Methods Our goals were to determine whether T. gondii soil contamination occurs in public areas with free-roaming cat colonies in central California and examine spatial and temporal variation in soil contamination. We initially performed spiking experiments to compare the limit of T. gondii detection in soil using three conventional nested PCR assays and one real-time quantitative PCR. The nested PCR targeting the internal transcribed spacer (ITS-1) of the small subunit ribosomal RNA was the most sensitive assay, with a limit of detection between 20 and 200 oocysts per gram of soil. We applied the ITS1 PCR assay on soil from sites in city and state parks, public playgrounds and community gardens in central California, USA. Samples were collected during spring, summer and fall and in sites located along the coast and inland. Results We detected and sequence-confirmed T. gondii in 5.6% of all of our soil sub-samples, but with large seasonal and spatial variation in soil contamination: we only detected T. gondii during fall and only in coastal sites (44.3% soil prevalence), despite similar sampling intensity across space and time. Conclusions Our results suggest that free-roaming cat colonies are an important source of T. gondii in spaces where people recreate and grow food and that soil contamination is highly seasonal and spatially variable. Management of free-roaming cats could prevent T. gondii infections by reducing environmental contamination with this zoonotic pathogen.