Use of inverse polymerase chain reaction to characterize a novel human herpesvirus 7 isolate

Human herpesvirus-7 (HHV-7) is a T-lymphotropic virus detected in peripheral blood mononuclear cells and in saliva, but no reliable link between this agent and a disease has been demonstrated so far. Starting from a 186 bp-fragment described previously, we used an inverse polymerase chain reaction to clone and sequence the adjacent sequences of this known region. A 1062 bp-fragment containing two ORFs was characterized and its sequence was compared with those of two other beta-herpesviruses, human cytomegalovirus (HCMV) and human herpesvirus-6 (HHV-6). With respect to the first ORF, amino-acid identity was estimated to be 22% between HHV-7 and HCMV, and 47% between HHV-7 and HHV-6. In contrast, only a weak homology between HHV-7 and the two other beta-herpesviruses was demonstrated for the second ORF. The newly characterized 1062 bp-fragment was used to define a novel HHV-7-specific PCR assay. Preliminary data indicate that this region is highly conserved among HHV-7 isolates.