Article Index

Viral persistence: reactivation of HHV-6

In concluding her discussion on the role of the immune system in ME/CFS, Dr. Klimas reviewed the recent work of Dr. Konstance Knox, who has shown that the Human Herpes Virus 6 (HHV-6) is periodically reactivated in some ME/CFS patients. The work is especially intriguing, since many patients and a number of ME/CFS researchers have suspected that a major component of ME/CFS involves chronic viral persistence.

Dr. Knox and her team conducted a significant study involving 4 sites with a total number of 368 subjects. Thirty-five percent of the ME/CFS subjects expressed the HHV­-6 virus in their serum while no HHV-6 virus was found in the control group. While this finding was signifi­cant, it really did not demonstrate expression of this virus as a funda­mental key to the ill­ness, since two-thirds of ME/CFS patients did not show expression.

An interesting discovery was when 26 ME/CFS patients, who had first tested negative were re-tested, they were then found to have reacti­vated virus. The testing technique in the study involved the direct identification of the virus itself, rather than antibodies to it. These results may be significant in identifying a char­acteristic of the disease process, since periodic reactivation of HHV-6 may occur in more than 37% of ME/CFS patients.

Dr. Knox and her colleagues then did a smaller study of 35 subjects with ME/CFS who had neurological problems. They looked for HHV-6 in the patients' central nervous systems and found the virus actively expressing in 7 patients. Therefore, at least in some patients, the virus is getting into the brain. According to Dr. Klimas, the virus has the propensity to go into the tiny little ves­sels in the brain that supply blood and cause inflammatory reactions. In ME/CFS patients, abnormalities in PET, MRI, and SPECT scans often show decreased blood perfusion. This decreased perfusion may be caused by local inflammatory responses caused by HHV-6. Interestingly, Drs. Ablashi, Krueger, and Knox found no active expression of the HHV-7 or HHV-8 virus in ME/CFS patients.

Other Herpes Viruses

The Herpes family of viruses may play a role in the pathophysiology of ME/CFS. Dr. Klimas already cited EBV (HHV-3) and cytomegalovirus (CMV or HHV-4) as known triggers for ME/CFS. The viruses in this family are generally latent viruses. An individual usually is first infected in childhood or adolescence. At this age, the initial infection is usually quickly overcome by the immune system, but the virus itself manages to "hideout" in some part of the body's tissues, becoming inactive or "latent".

For instance, HHV-6 hides out in natural killer cells. Dr. Klimas theorized about HHV-6 and ME/CFS: why would someone at age 20, 30, or 40 begin to express a virus that should be latent? Something must have happened immunologically to allow the virus to reactivate. She recalled Dr. Lloyd's hypothesis that people can get infections which then persist if the immune system is already not performing properly.

If HHV-6 were active in some ME/CFS patients, would the virus be contagious? Dr. Klimas said she has not found anything in the secretions of ME/CFS patients that is infectious or contagious, including HHV-6, EBV, or any­thing else.