Quantitative analysis of Epstein-Barr virus load by using a real-time PCR assay

To measure the virus load in patients with symptomatic Epstein-Barr virus ( EBV) infections, we used a realtime PCR assay to quantify the amount of EBV DNA in blood. The real-time PCR assay could detect from 2 to over 10(7) co pies of EBV DNA with a wide linear range. We estimated the virus load in pe ripheral blood mononuclear cells (PBMNC) from patients,vith symptomatic EBV infections. The mean EBV-DNA copy number in the PBMNC was 10(3.7) copies/m u g of DNA in patients with EBV-related lymphoproliferative disorders, 10(4 .1) copies/mu g of DNA in patients with chronic active EBV infections, and 10(2.2) copies/mu g of DNA in patients,vith infectious mononucleosis. These numbers were significantly larger than those in either posttransplant pati ents or immunocompetent control patients without EBV-related diseases. In a patient with infectious mononucleosis, the virus load decreased as the sym ptoms resolved. The copy number of EBV DNA in PBMNC from symptomatic EBV in fections was correlated with the EBV-positive cell number determined by the in situ hybridization assay (r = 0.842; P < 0.0001). These results indicat e that the real-time PCR assay is useful for diagnosing symptomatic EBV inf ection and for monitoring the virus load.