Real-time PCR detection of Toxoplasma gondii in surface water samples in São Paulo, Brazil

Water is considered an important vehicle for the spread of human toxoplasmosis in several countries. Toxoplasma gondii oocysts can persist in the environment for long periods, being highly resistant to the various chemical inactivation processes commonly used by water supply systems, distinctly from simple filtration and flocculation that are efficient in removing oocysts from drinking water. The existing methodologies for identification and quantification of this parasite in water samples are not standardized and have limitations. This study aimed to evaluate the presence of T. gondii oocysts in surface water samples used as a source for the production of drinking water in the State of São Paulo, through the implementation of a specific methodology using real-time PCR technique (qPCR). Volumes of 20 L of the sample were concentrated by filtration in Envirocheck® HV capsules. For DNA extraction, the PowerSoil DNA isolation® kit (currently DNeasy PowerSoil®) was used. The target sequence selected for qPCR was a 62-base-pair fragment of the B1 gene. In the initial recovery evaluation of the method in four replicates of reverse osmosis water, the mean recovery was 48.5% (SD ± 11.5), while the mean recovery for method performance in matrices was 3.2% (SD ± 3.2) (rainy season) and 62.0% (SD ± 6.2) (dry period), suggesting that the characteristics of the samples and the climatic conditions interfere in the recovery efficiency. Of the 39 samples analyzed (May to December 2015), 7.7% (3/39) were positive for T. gondii, and among the ten sources studied; the occurrence of the oocysts was detected in 30% (3/10).