Toxoplasmosis: A Study Reveals That Transmission of the Parasite Is Largely Environmental

A study conducted in Belgrade, Serbia, seeks to piece together the puzzle of toxoplasmosis in urban settings. By cross-referencing analysis data from wild birds, backyard chickens, rodents, and river water, the study shows that exposure to Toxoplasma gondii occurs more frequently through the environment (contaminated water and soil) than through the diet alone of the affected species.  

Urban Toxoplasmosis: Integrating Water and Soil Analysis

While cats remain the definitive hosts of Toxoplasma gondii, in urban settings the spread of this protozoan can only be understood by considering the entire chain: oocysts shedded, sporulation, stagnation and resuspension in water bodies, followed by repeated contact with birds, rodents, poultry, and humans. This environmental approach places surface waters, floodplains, and peri-urban agricultural areas at the center of the risk.  

A Multihost Field Study Design

The authors analyzed heart tissue from 224 wild birds representing 15 species captured in urban, peri-urban, and rural areas of Belgrade, as well as locally raised backyard chickens. Molecular detection relied on qPCR targeting T. gondii, a sensitive and specific method for detecting the parasite’s DNA in tissues. At the same time, rodents were tested, and river water samples were collected near the study sites at the Sava-Danube confluence.  

Prevalence: high among birds, very high among chickens

Molecular prevalence reached 24.1% in wild birds and 41.4% in chickens. Among birds, the rates are comparable across different areas (22.4% in urban areas, 27.3% in suburban areas, 22.7% in rural areas), suggesting widespread and continuous exposure that depends less on the immediate habitat than on hydrological connectivity and surrounding land use.  

Corvids as sentinels among urban wildlife

Among the animal species found in urban areas, corvids are the most frequently infected: crows and ravens have a positivity rate exceeding 30%, while that of the wood pigeon is around 15 to 16%. This rate, specific to avifauna, positions corvids as bioindicators of environmental contamination, useful for guiding targeted surveillance.  

Surface Water and Rodents: The Missing Pieces of the Puzzle

In the same areas, three out of four water samples contained T. gondii DNA, and more than one in two rodents tested positive. The convergence of birds, rodents, and water within a limited area indicates a mechanism of environmental persistence: infectious oocysts circulate and recontaminate the environment, leading to repeated exposure of wildlife and, by extension, domestic livestock and humans.  

One Health Approach: Mapping the Risk

Taken together, these results shift the focus of the fight to micro-territories. Around floodplains, canals, retention basins, and irrigated wastelands, surface water becomes the vector that can trigger an alert. Combining data on urban birds (especially corvids), rodents, and water analysis helps map the risk more accurately and proves more useful to local communities than city-wide averages.  

Integrated Monitoring and Targeted Prevention Messages

In practice, monitoring is most effective when it combines periodic bird captures, responsible rodent trapping, and regular screening of water flowing out of retention basins and urban wetlands. On the prevention front, the focus is on thoroughly washing fruits and vegetables, fully cooking meat from local sources, properly storing poultry feed, managing stray cats near water sources, and practicing hand hygiene after any gardening or fishing activity. Seasonal testing, genotyping that links environmental factors to hosts, and hydrological models coupled with oocyst load data will make it possible to estimate realistic exposure doses and identify high-risk periods following floods, construction projects, or heat waves followed by thunderstorms. The study highlights a reality that is often taken for granted: in urban areas, water management and land use are at least as important as controlling the feline population alone for managing toxoplasmosis. By integrating sentinel birds, rodents, and water into a “One Health” approach, public health authorities have a concrete tool to target interventions, optimize risk communication, and, ultimately, reduce the incidence of the disease in humans.