Real-Time Polymerase Chain Reaction, High Sensitivity for Toxoplasmosis

Toxoplasma gondii oocyst under the microscope, isolated
Toxoplasma gondii oocyst under the microscope, isolated
Peripheral blood mononuclear cell samples outperform serum and whole blood samples as a method of PCR extraction, a study shows.

Using peripheral blood mononuclear cells (PBMC) in conjunction with real time polymerase chain reaction (PCR) testing significantly improves toxoplasmosis diagnosis in patients with retinochoroiditis, according to a study in BMC Infectious Diseases.

The investigation compared real time PCR with nested PCR for sensitivity to detect Toxoplasma gondii în patients with toxoplasmic retinochoroiditis. Ten patients who presented with toxoplasmic chorioretinal lesions were recruited, along with 10 healthy participants. Patients with active lesions displayed them close to a hyperpigmented retinal scar. Mean age of the test cohort was 24.5±6.19 years, and the average age of the control group was 28.6±8.3 years. Researchers analyzed blood samples via 3 different means on all participants; PBMC, serum, and whole blood samples. Both real time and nested PCR were used as a means of diagnosis.  

PBMC samples proved better for extracting DNA than serum or blood, and enhanced the molecular technique for diagnosis. PBMC samples collected after toxoplasmosis treatment and examined with real-time PCR using B1 revealed DNA was still present, but the copy number was reduced.   

Using the bradyzoite-specific SAG-4 gene, real-time PCR was slightly more sensitive than nested PCR (P =.36), the study shows. Real-time and nested methods were comparable with MAG-1 primer (P =.50) for patients with toxoplasmic chorioretinitis. Use of the B1 gene revealed that 90% of patients with retinochoroiditis had positive test results with real time PCR, and just 1 was positive using nested PCR (P =.0003). 

Real-time PCR is being established as a rapid and easily performed diagnostic tool. “The use of B22 and B23 target genes due to their high sensitivity and specificity along with SAG-4 and MAG-1 bradyzoite genes is recommended for toxoplasmosis diagnosis using PBMC samples with real-time PCR,” according to the researchers. 

Study limitations include a low number of participants.


Khanaliha K, Bokharaei-Salim F, Hedayatfar A, et al. Comparison of real-time PCR and nested PCR for toxoplasmosis diagnosis in toxoplasmic retinochoroiditis patients. BMC Infect Dis. 2021;21(1):1180. doi:10.1186/s12879-021-06873-3