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<p>Abstract</p> <p>Background</p> <p>Toxoplasmosis is an important parasitic zoonosis caused by the protozoan <it>Toxoplasma gondii </it>that is distributed world-wide and infects a variety of hosts. However, the prevalence of <it>T. gondii </it>in the environment (such as soil, water and food) is largely unknown. Due to the technical difficulty in oocyst counting directly, an alternative assay using the serologic status of <it>T. gondii </it>in free-living animals, such as stray or free-living dogs, as an indicator, can be used to evaluate environmental contamination indirectly, as they are exposed to the same risk of infection as humans and other animals.</p> <p>Results</p> <p>In the present study, 231 stray or free-living dogs across an urban-rural gradient were examined to assess the frequency of <it>T. gondii </it>in the environment. Specific antibodies to <it>T. gondii </it>were found in 93 dogs (40.3%) by enzyme-linked immunosorbent assay (ELISA), and no statistically significant differences were observed in seroprevalences of <it>T. gondii </it>between urban dogs (38.7%) and rural dogs (41%) (<it>p </it>> 0.05).</p> <p>Conclusions</p> <p>A high seroprevalence of <it>T. gondii </it>in stray or free-living dogs in the present study indicates that there would be a wide distribution and a constant infection pressure of <it>T. gondii </it>across an urban-rural gradient, and the oocysts of <it>T. gondii </it>in the environment would be an important source of infection for humans and other animals both in urban and rural areas in China.</p>