HUMAN HERPES VIRUSES 6 - HHV6?

Abstract

HHV-6 has two variants, A and B.

HHV-6A seems to be implicated in ME, with significantly higher abnormal levels seen in sufferers than to healthy controls.  It works by attacking some of the major defenses of the immune system, for example T cells, as in the case of HIV/AIDS, which has lead researchers to propose that HHV-6 could also act as a cofactor in the progression of AIDS.

Three possibilities for the link between ME and HHV-6:-

  • it causes ME
  • it causes ME only when linked with another virus;
  • it does not cause ME but is taking advantage of the sufferers weakened immune system.

HHV-6

Human herpes viruses 6 (HHV-6), as its name suggests, is a member of the herpes family. There are two variants, HHV-6A and HHV-6B.As far as one can tell, HHV-6B is the more ‘common’ one of the two. It is a common cause of the viral disease roseola that is seen in over 95% of young children by the age of 2 - a self-limited fever and rash.  Much like chicken pox and shingles, the virus can be reactivated in adults that were infected as children.  The virus persists after the initial infection in a latent ('hibernating') form in the cells of the central nervous system, bone marrow and immune system and it can then reactivate and begin replicating again (Fig. 1).

HHV-6, MS and ME

The other strain, however, HHV-6A, is the one implicated in AIDS, MS and ME, amongst other diseases.  In the case of MS, a direct link has been found between it and HHV-6A [1].  In addition, Dr. Dharam Ablashi, co-discoverer of HHV-6 and Scientific Director of the HHV-6 has summarised from existing literature that when lab methods detecting the presence of active HHV-6A infection are used, an exceptionally strong, statistically significant association between HHV-6A and both multiple sclerosis and ME is consistently seen. From what I’ve found, it seems that it is not a case of HHV-6A being reactivated in an adult like I explained before but people with MS, ME etc. acquiring it as a primary infection.  So, they haven’t been infected as children etc.  Using the chicken pox ‘analogy’ again, it’s like when adults suffer from the chicken pox (not having caught it as children), and of course it can be a lot worse when this happens.  They haven’t built up immunity to it.

Fig. 1.   Demonstrating latency and reactivation of the virus. [2]

T-cell killer

But what does HHV-6 actually do? HHV-6A is known to be a cytopathic pathogen with a powerful ability to infect and kill cells. It can directly infect or interfere with the function of several elements of the immune system including CD4 and CD8 T-cells, NK-cells, some B-cells, and mononuclear phagocytes.  Basically, it’s messing with some of the major defences your body has towards pathogens in your body, interrupting the normal function of the immune system.  T cells, for example, are regarded as the ‘generals’ of the immune system.  So this is where the problems could arise and cause ME.
See Fig. 2 on the next page for an illustration of the progression of HHV-6.

SIDENOTE - HHV-6 and HIV/AIDS

The cells HHV-6 targets have brought about connections being made with HIV/AIDS as HIV destroys the same kind blood cells - CD4 T cells (helper cells).  Findings have lead to proposals that HHV-6 acts can be a cofactor in the progression of AIDS and in the switch of HIV from the latent to the replicative state.  Ultimately, HHV-6 can be a cause of death in AIDS patients.   HHV-6, however, does not cause AIDS if the person is not infected with HIV.  Of course, there is a lot more information on that subject but I could write a whole book alone on this area!

Fig 2.  Illustrating a progression from infection to the clinical disease [3]

Neurotropism The tendency to affect, be attracted to, or attack nervous tissue
Vasculopathy - Disease of the blood vessels

In the end, there are three ways that HHV-6 could be related to ME:

ME is caused by this virus. a. Perhaps causing a persistent viral infection of HHV-6.

HHV-6 causes ME when it comes into contact with another virus for example parvovirus. a. HHV-6 could be relatively harmless on its own but when it comes into contact with another specific virus it is then when the trouble occurs.

i. For example, in the case of bird flu, if a human infected with influenza virus also acquires H5N1, a mutant strain of bird flu that can be transmitted from human to human could form. It is an opportunistic pathogen that takes advantage of an already weakened immune system. Whatever the case is, there is quite a lot of significant data showing HHV-6 in ME patients compared to healthy controls.

References cited:

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