HHV-6 & Encephalitis
HHV-6 encephalitis is a significant consequence of transplant immunosuppression, although it is seen in immunocompetent patients as well. Interestingly, the characteristics of HHV-6 encephalitis differ between patients who develop the condition through primary infection compared to viral reactivation (Kawamura 2011).
HHV-6 & Epilepsy
There are several lines of evidence that indicate the strong possibility of an etiological role of HHV-6 in patients with epilepsy. Herpesviruses have been implicated in the development of seizures. Seizures are thought to result from either primary infection or reactivation of latent virus (Leibovitch 2015). HHV-6B, in particular, continues to be associated with epilepsy, in addition to several other CNS diseases.
HHV-6 & Cognitive Dysfunction
HHV-6 reactivation is the most common cause of mental confusion among post-transplant patients (Zerr 2011). HHV-6 limbic encephalitis, which occurs in approximately 1-4% of all transplant patients, often results in intermittent confusion, poor coordination, flat affect and somnolence. HHV-6 and EBV have also been identified as risk factors for cognitive deterioration and progression to Alzheimer’s disease in elderly persons (Carbone 2014). A clinical association between the medial temporal lobes and dysfunction of memory formation was first documented in 1957 (Scoville & Milner). Since then, dozens of studies have supported the concept that the medial temporal lobes, specifically the hippocampus and surrounding structures, are intrinsically important to the processing of declarative functions such as conscious memory–which is responsible for remembering specific facts and events.
HHV-6 & Multiple Sclerosis
Over the years, a number of infectious agents have been implicated as potential role players in the development of MS. Today, attention focuses primarily on HHV-6A, Epstein Barr virus (EBV), Varicella Zoster Virus (VZV), Chlamydia pneumonia (Cpn) and human endogenous retroviruses (HERVs). Since these viruses and pathogens are also known to potentiate each other, it is possible that there are many infections involved in a chain reaction, resulting in an autoimmune process that continues long after the initial infections have passed.
HHV-6 & Chronic Fatigue Syndrome
HHV-6 has long been suspected as one trigger for CFS. HHV-6 reactivation in transplant patients can cause symptoms similar to CFS, including fatigue, cognitive dysfunction and autonomic dysfunction (Zerr 2012). Direct evidence of persistent central nervous system (CNS) infection is difficult to obtain, however, with current standard laboratory tests, as HHV-6 can persist in the CNS long after it has disappeared from the blood stream.