Human herpesvirus 7

Human herpesvirus 7 (HHV-7) is one of eight known members of the Herpesviridae family. It acts together with HHV-6 to cause the childhood illness, Roseola. HHV-7 resides mostly in the immune cell named CD4+ T, and causes the downregulation of CD4 transcription.

HHV-7 in ME/CFS
In 2012, a study at Riga Stradins University, Latvia, was done on 108 CFS patients and 90 controls concluded: "The association between occurrence of ME/CFS clinical symptoms, HHV-6, HHV-7 and B19 infection/coinfection reactivation and increased expression levels of TNF-α and IL-6 allows suggesting that these immunomodulating pathogens are involved in ME/CFS etiopathogenesis. Their role as trigger factors could not be excluded. The correlation of distinctive active viral infection with various types of clinical symptoms shows necessity of simultaneous study of these viral infections for identification of possible subsets of ME/CFS."

In 2006, a study at Riga Stradins University, Latvia, was done on 17 CFS patients, 12 patients with unexplained chronic fatigue and 20 blood donors: They found no difference in the prevalence of latent/persistent single viral infections between the different groups, but dual infection rate was significantly higher in CFS patients (emphasis added). Active HHV-6 and dual (HHV-6 + HHV-7) infections were detected in the CFS patient group only and the frequency of HHV-7 reactivation was also significantly higher in these patients(emphasis added). The researchers conclusion was: "HHV-6 and HHV-7 may be involved in the pathogenesis of CFS and reactivation of both viruses may provoke changes in the phenotype of circulating lymphocytes."

In 2000, a study done by the CDC Atlanta, Georgia concluded: "Primary infection with HHV-6 or HHV-7 is not likely to be causally associated with CFS, because infection is virtually ubiquitous by the age of 2–5 years. Moreover, it is unlikely that reactivation of latent HHV-6 or HHV-7 is causally associated with a substantial proportion of cases of CFS because of the lack of consensus among studies and because reactivation of most latent herpesviruses is common, occurs sporadically, and is usually asymptomatic."