Comparison of nested PCR and real-time PCR for the detection of Toxoplasma gondii in biological samples from naturally infected cats

There are different protocols of molecular diagnosis methods available including DNA extraction methods to diagnose of Toxoplasma gondii, being necessary to perform comparative studies in biological samples. The aim of this study is to compare real-time PCR (rtPCR) and nested PCR (nPCR) to evaluate the detection of T. gondii in naturally infected cats. Biological samples of Toxoplasma-seropositive cats were assayed for detection of T. gondii DNA--extracted by both the lysis buffer and proteinase K (LB proteinase K) method and the acid guanidinium thiocyanate (GuSCN) method--using rtPCR and nPCR. T. gondii DNA was detected by nPCR in 43.6% and 40.8% of the samples from which it was extracted by the LB proteinase K and the GuSCN method, respectively. With rtPCR these figures fell significantly to 33.8% and 14.1%. Despite of nPCR showed higher sensitivity, the agreement observed between two PCRs was good; this agreement, however, was affected by the DNA extraction method used, LB proteinase K method showed better results.