A reader asked about retroviruses – these are virus that which reproduces its RNA the opposite way of normal viruses (i.e. Retro). Antiretroviral drugs are medications for the treatment of this type on infection. Retroviruses are best known in connection with HIV infections.
The XMRV Hype
Due to lab errors, a lot of money and time was spent trying to show that XMRV (RV for retrovirus) was associated with CFS/ME. The titles of many recent studies say it all:
- No association found between the detection of either xenotropic murine leukemia virus-related virus or polytropic murine leukemia virus and chronic fatigue syndrome in a blinded, multi-site, prospective study by the establishment and use of the SolveCFS BioBank.
- No evidence of XMRV provirus sequences in patients with myalgic encephalomyelitis/chronic fatigue syndrome and individuals with unspecified encephalopathy. 
- Lack of evidence for retroviral infections formerly related to chronic fatigue in Spanish fibromyalgia patients.
- Absence of xenotropic murine leukemia virus-related virus in Italian patients affected by chronic fatigue syndrome, fibromyalgia, or rheumatoid arthritis. 
- Absence of xenotropic murine leukaemia virus-related virus sequences in healthy blood donors andchronic fatigue syndrome patients in Catalonia, Spain]. 
- Researchers find no link between XMRV and chronic fatigue syndrome. 
- Xenotropic and polytropic murine leukemia virus-related sequences are not detected in the majority of patients with chronic fatigue syndrome. 
- Lack of evidence for a role of xenotropic murine leukemia virus-related virus in the pathogenesis of prostate cancer and/or chronic fatigue syndrome. 
- A multicenter blinded analysis indicates no association between chronic fatigue syndrome/myalgic encephalomyelitis and either xenotropic murine leukemia virus-related virus or polytropic murine leukemia virus. 
- Human endogenous retrovirus-K18 superantigen expression and human herpesvirus-6 and human herpesvirus-7 viral loads in chronic fatigue patients. 
The last study had a bit wider scope on other virus associated with CFS/ME “We fail to demonstrate a difference in HERV-K18 envtranscripts, HHV-6 viral copy number, and HHV-7 viral copy number between CFS patients and healthy controls. Our data do not support the hypothesis of reactivation of HHV-6 or HHV-7 in CFS.” which is echoed in some studies:
- No serological evidence for a role of HHV-6 infection in chronic fatigue syndrome. 
- Serological and virological investigation of the role of the herpesviruses EBV, CMV and HHV-6 in post-infective fatigue syndrome.  ” These data do not support the hypothesis of ongoing or reactivated EBV, HHV-6, or CMV infection in the pathogenesis of CFS.”
And there are other older studies who speculate “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.” and “These findings suggest that the amount of HHV-6 and HHV-7 reactivation can be an objective biomarker for fatigue.”  “Parvovirus B19 may be involved in the pathogenesis of CFS, at least for a subset of patients.” 
Anti-viral Drugs — works by side effects???
On the flip side, an antiviral drugs such as Valacyclovir have positive results on a subset of ME/CFS patients . “We concluded that the 16 CFS patients (included in both phases of this study) with EBV-persistent infection (EBV single-virus subset) are improved after 6 months of continuous pharmacokinetic dosing with valacyclovir.”   Patients with multiple viruses did not benefit – even when one was EBV.
My model of CFS is that it is a microbiome dysfunction, a major shift of bacteria types and volumes in the person. I was unable to find any studies on how antivirals shifts (or do not shift) the microbiome by the use of antiviral drugs. Drugs intended for one purpose often are later to have other consequences — for example, a drug intended for the treatment of various cardiovascular disorders… is commonly known as Viagra.
IMHO, retrovirus and virus are red-herrings in CFS/ME. They have been heavily studied “and found wanting” as explanations and models for treatment. Virus may become reactivated as a side effect of the bacteria shift is a small subset of CFS/ME patients, but it is not a global answer.