LABORATORY DIAGNOSTICS OF ACTIVE AND LATENT HHV 6-INFECTION IN PATIENTS WITH HEMATOLOGICAL MALIGNANCIES.

Introduction: Human herpes virus type 6 (HHV 6) can cause serious infectious complications in immunodeficient patients. It is also capable of integrating into the genome of the infected cell. Due to this, there can be a misdiagnosis between viral integration and active infection during laboratory diagnostics. Thus, determination of HHV 6 infection using proper laboratory tools is relevant. Also the data on viral interference of HHV 6 and other herpes viruses are very poor especially for patients with hematological malignancies. The aim of the study was to identify laboratory markers of HHV 6 and the form of infection in patients with hematological malignancies.

Materials And Methods: 98 patients with hematological malignancies positive for HHV 6 DNA during the infectious complication were enrolled in the study. Viral load in leukocytes and plasma of peripheral blood, antiviral M and G immunoglobulins and peripheral blood leukocytes count were evaluated.

Results: The majority of patients (66 out of 98, 67.3%) showed laboratory signs of latent HHV 6. Integrated HHV 6 was suspected in 2 patients due to high viral load (1.5x105 copies and 1.7x105 copies), but it was not confirmed subsequently. Additional testing of HCMV and EBV in patients with laboratory signs of active HHV 6 infection revealed the superiority of monoinfection over mixed infection (20 of 32, 62.5%). In cases of mixed infection, the most common co-infectant was HCMV observed in 9 out of 12 (75%) cases. Mild leukopenia accompanied HHV 6 active infection.

Conclusion: Laboratory signs of latent HHV 6 tend to be prevalent in patients with hematological malignancies. In patients with laboratory markers of active HHV 6, the monoinfection demonstrated the superiority over mixed one. In cases of mixed infection, HCMV appeared to be the most commonly co-infectant. No cases of an integrated form of HHV 6 have been observed. The viral load of HHV 6 in leukocytes and blood plasma is almost 3 times lower in patients with a mixed infection than with a monoinfection. Active replication of HHV 6 was accompanied with mild leukopenia.