Molecular Detection of Toxoplasma gondii Oocytes in Soil Samples from Guilan Province, Northern Iran

Soil is an appropriate substrate for the storage and transmission of oocytes of Toxoplasma gondii. Ingestion of soil contaminated with T. gondii oocysts is a major transmission route of human and animal toxoplasmosis. The present study was carried out to investigate soil contamination with T. gondii oocysts in urban and rural areas of Guilan Province, northern Iran.

Overall, 208 soil samples were collected from 16 cities and villages in Guilan Province, northern Iran from Oct 2020 to Nov 2021. Soil samples were investigated using modified sucrose flotation technique. Real-time polymerase chain reaction was used to detect presence of T. gondii DNAs in the samples. Positive samples were further analyzed using nested polymerase chain reaction for GRA6 gene. Moreover, six selected positive samples were used for amplifying and sequencing of the GRA6 gene.

Overall, 31 samples were positive for T. gondii with frequency of 14.9% and ranging from 10.9% in rural areas to 16.3% in urban areas. Statistical analysis showed significant differences between the seasons (P=0.003). The phylogenetic analysis illustrated that our six sequences were similar and closely related to Type I strain of T. gondii.

Results showed relatively high levels (14.9%) of T. gondii oocytes in soil samples of Guilan Province, northern Iran, which provided essential data for the effective prevention and control of toxoplasmosis in the region.