Monitoring of cell-free viral DNA in primary Epstein-Barr virus infection.

Primary Epstein-Barr virus (EBV) infection in childhood is usually asymptomatic, but sometimes causes infectious mononucleosis (IM). Very occasionally, IM develops into a life-threatening EBV-associated hemophagocytic syndrome (EBV-AHS). We studied the importance and usefulness of measuring cell-free viral DNA in the serum of patients with these primary EBV infections. Using real-time quantitative polymerase chain reaction, cell-free EBV-DNA was quantified in the serum of nine children with IM and three with EBV-AHS. In the acute phase of IM, an average of 10(2.4) copies/ml of EBV-DNA was detected in 95% of sera. The EBV load gradually decreased and disappeared within 1 month. Patients with EBV-AHS had an extremely high viral load in their sera (10(5.5)-10(7.4) copies/ ml). The viral load persisted longer in these patients, although it decreased in parallel with the improvement of symptoms. These results indicate that cell-free EBV-DNA was frequently detected in patients with primary EBV infection and could, therefore, be used as a marker for EBV infection. Measuring the cell-free EBV-DNA is useful for monitoring the primary EBV infection, especially in EBV-AHS.