Susceptibility of human herpesvirus 6 to antivirals in vitro

Human herpesvirus 6 (HHV-6) is a herpes virus that has been isolated from human lymph tissue. HHV-6 may be the causative agent of exanthem subitum, a disease in children that involves fever and rash. Acyclovir is a commonly used antiviral agent that must be activated by an enzyme called thymidine kinase (TK) in order for it to be effective. Viruses that lack the TK enzyme are resistant to acyclovir treatment. The sensitivity of HHV-6 to acyclovir and several other antiviral agents was assessed. DNA was isolated from HHV-6 and used to make a probe (a radioactive strand of DNA) that would bind specifically to DNA in HHV-6. DNA hybridization (the use of a DNA probe to identify a complementary or identical strand of DNA in a virus, cell or tissue sample) was used to monitor DNA synthesis in HHV-6 treated with the antiviral agents. The disappearance of DNA synthesis in a virus following treatment with an antiviral agent indicates that the virus was sensitive to the antiviral agent (which means that the virus was killed). Cytomegalovirus (a form of herpesvirus) was resistant to acyclovir, while herpes simplex virus type 1 (HSV-1) was sensitive to acyclovir. HHV-6 was found to be resistant to acyclovir and bromovinyl-deoxyuridine (BVdU), but was sensitive to ganciclovir (DHPG) and phosphonoacetic acid (PAA). These results demonstrate that HHV-6 infection should not be treated with acyclovir. Although HHV-6 might respond to DHPG, researchers do not advise using this drug to treat exanthem subitum. (Consumer Summary produced by Reliance Medical Information, Inc.)