[Acute human herpesvirus 6 (HHV-6) infections: when and how to treat?].

The pathogenicity of human herpesvirus 6 (HHV-6) still raises numerous questions. Acute HHV-6 infections correspond to primary infections, reactivations or exogenous reinfections. The expression of related clinical symptoms is highly variable but may be extremely severe, particularly among immunocompromised patients. The prototypic severe disease associated with these infections is limbic encephalitis occurring in stem cell transplant recipients. The diagnosis of acute HHV-6 infections relies on the quantitation of viral load in whole blood by means of quantitative PCR. The demonstration of HHV-6 causative role in the genesis of clinical symptoms requires additional investigations such as the search for HHV-6 DNA in cerebrospinal fluid in case of encephalitis. The chromosomal integration of HHV-6 DNA is a rare event among HHV-6-infected subjects but may alter the interpretation of virological results. Therapy with ganciclovir, foscarnet or cidofovir has not yet clear indications but, at the current stage of knowledge, only concerns the treatment of highly symptomatic infections. The usefulness of prophylactic or pre-emptive antiviral chemotherapy has not yet been convincingly demonstrated. Treatment efficacy must be checked through a clinical and virological follow up, based in part on quantitative PCR approaches. Controlled studies are urgently needed with the goal of evaluating the cost-effectiveness of HHV-6 follow up and therapy in different clinical situations.