Association of Persistent Viral Infections with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Doctoral Thesis

Abstract

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a multifactorial disease with unexplained aetiology. Human herpesvirus (HHV)-6, HHV-7, human parvovirus B19 (B19V) and xenotropic murine leukemia virus-related virus (XMRV) are thought to be possible trigger factors in ME/CFS development. The aim of this study was to determine the involvement of HHV-6, HHV-7, B19V and XMRV in etiopathogenesis of ME/CFS. Various polymerase chain reaction (PCR) methods to detect presence of viral genomic sequences were used, viral load and expression of virus-specific genes. Presence of HHV-6A and HHV-6B by PCR and restriction analysis was distinguished with following visualization of amplification products electrophoretically. Immunoenzymatic methods were used to estimate presence of virus-specific antibodies, reaction patterns of these antibodies, as well as the level of cytokines in blood plasma, while the HHV-6 antigen expression was detected by indirect immunofluorescence. The analysis of patients with ME/CFS and apparently healthy individuals revealed absence of XMRV proviral gag and env gene sequences in DNA from patients and apparently healthy individuals. These data are in concordance with the results obtained in many laboratories worldwide. HHV-6 specific antibodies in 92.1% of ME/CFS patients’ and 76.7% of apparently healthy individuals’ plasma samples were found. Markers of persistent HHV-6 infection in a latent phase had 42% of patients and 28.7% of healthy individuals, though in an active phase – 11% of ME/CFS cases and none of healthy individuals. HHV-6B is prevalent in Latvian ME/CFS patients. HHV-7 specific antibodies had 84.6% of patients and 93.8% of analysed controls. Markers of persistent HHV-7 infection in latent and active phase had 58% vs 34% of ME/CFS patients and 67.3% vs 8% of apparently healthy individuals. B19V specific antibodies in 78% of patients with ME/CFS and 67.4% of healthy individuals were detected. Presence of latent/persistent B19V infection markers had 12% of patients and 1.9% of controls but 17% of patients and 1.9% of healthy individuals had an active infection. According to the antibody pattern, 36% of ME/CFS patients had recent B19V infection and 43% – sustained infection. In patients with a persistent viral infection in an active phase median HHV-6 load (1927 vs 279 copies/10^6 cells), median HHV-7 load (238.6 vs 196.7 copies/10^6 cells) and median B19V load (251.8 vs 37.2 copies/10^6 cells) was higher than in patients with a persistent viral infection in a latent phase. Analysing HHV-6, HHV-7 and B19V co-infection, latent infection/co-infection was observed to 51.5% of patients and 76.7% of apparently healthy individuals, whereas active – 45% of ME/CFS patients and 8.7% of healthy individuals. HHV-6 load in patients with persistent infection/co-infection in a latent and active phase was 262 and 653.2 copies/10^6 cells, respectively, whereas HHV-7 load was 166.5 and 248.5 copies/10^6 cells, respectively. In case of latent/persistent B19V co-infection, the viral load was 96.8, in case of active co-infection – 250.8 copies/10^6 cells. ME/CFS patients with a persistent infection in an active phase had higher level of pro-inflammatory (IL-6, TNF-α and IL-12) and anti-inflammatory (IL-10) cytokines than with a persistent infection in a latent phase, however without any statistical difference in part of cases. No difference was found in the level of IL-6 among patient groups without infection, with latent infection/co-infection, active single, double and triple co-infection, in turn a significant difference was revealed in the levels of TNF-α, IL-12 and IL-10 among these five groups. Furthermore, the level of TNF-α, IL-12 and IL-10 is significantly higher in patients with severe compared with moderate course of ME/CFS. All patients had unexplained chronic fatigue lasting for more than 6 months. Impaired memory, decreased concentration and sleep disturbances were most frequently observed symptoms in patients with ME/CFS. Patients with B19V genomic sequence and NS1 specific antibodies significantly often had lymphadenopathy and multi-joint pain. Moreover, onset of symptoms corresponded to B19V infection appearance time. The obtained data allow to conclude that XMRV infection is not associated with ME/CFS. Significantly more frequent findings of persistent HHV-6, HHV-7 and B19V infection/co-infection in an active phase with a higher viral load and elevated levels of pro- and anti-inflammatory cytokines among patients with ME/CFS than apparently healthy individuals indicate the importance of these infections/co-infections in ME/CFS development. Moreover, they are accompanied by a more severe ME/CFS clinical course.