HHV-7 may have a narrower tropism than HHV-6: the virus efficiently infects and replicates in CD4+ cells; it can be found in brain tissue but at a lower frequency than HHV-6.
It has been suggested that HHV-7 could reactivate HHV-6 from latency. Increased prevalence has been reported in people with autoimmune disease.
qPCR test is available to quantify the number of copies present in body fluids or tissues. This test can be done on blood, saliva, tissue biopsies. The test can also uncover the potential chromosomal integration of HHV6.