Seroprevalence, Molecular Epidemiology and Immunological Aspects of Human Herpesvirus 8 in Ireland

Abstract

Human herpesvirus 8 (HHV-8) seroprevalence and molecular epidemiology vary both geographically and between sub-populations. Recent work has highlighted the importance of proinflammatory cytokines in the pathogenesis of HHV-8 infection. The purpose of this study was to determine the seroprevalence of HHV-8 in an Irish population, including specific risk groups, to examine the molecular epidemiology of HHV-8 in an Irish population by characterising four regions of the HHV-8 genome, K1, T0.7 (K12), open reading frame (ORF)75 and K15, and to perform cytokine analysis over time in a population with known human herpesvirus 8-related disease and thereby to investigate the role of proinflammatory cytokines in the diagnosis and monitoring of HHV-8-related disease. Cytokine levels were also compared between HHV-8 subtypes to investigate whether a relationship exists between subtype and immunological response.

A cross-sectional seroprevalence study of 200 blood donors and 200 Genitourinary Medicine (GUM) and Infectious Diseases (ID) clinic patients was performed. All 200 blood donor samples were negative for HHV-8 IgG antibodies. 21% of GUM and ID patients were positive for HHV-8 IgG antibodies. 100 of these patients were men who have sex with men (MSM), 35% of whom were HHV-8 seropositive (46% of human immunodeficiency virus (HIV) positive MSM and 24% of HIV negative MSM). Of 100 heterosexual patients, only 7% were HHV-8 seropositive.

HHV-8 sequencing data were obtained for 23 specimens from 19 patients with HHV-8-related diseases. K1 subtypes A, B, C and F were present in 37%, 11%, 47% and 5%, respectively. For T0.7, subtypes A/C, J, B, R and Q were present in 58%, 17%, 8%, 8% and 8%, respectively. For ORF75, subtypes A, B, C and D were present in 58%, 8%, 25% and 8%, respectively. For K15, 69% had the P allele and 31% had the M allele. The cytokine analysis study included 30 patients who had HHV-8 DNA detected in plasma. Plasma levels of interferon (IFN)-γ, interleukin (IL)-10, IL-12p70, IL-13, IL-1β, IL-2, IL-4, IL-6, IL-8 and tumour necrosis factor (TNF)-α over time were assessed. Results were obtained for 76 specimens from 28 patients. Cytokine levels were compared between K1 subtypes. A statistically significant difference between subtypes was identified for IFN-γ, IL-1β, IL-6, IL-8, IL-13 and TNF-α, with higher levels for subtype F compared to the other subtypes. IL-1β and TNF-α levels were significantly higher in patients with the K15 M allele compared to the K15 P allele. Cycle threshold (Ct) values for HHV-8 PCR were significantly higher following treatment and a negative correlation between Ct value and IL-10, IFN-γ, IL-4, IL-6, IL-13 and TNF-α levels was identified.

This is the first study of HHV-8 seroprevalence and molecular epidemiology performed in Ireland. The absence of seropositivity in 200 Irish blood donors suggests that Ireland has a low population HHV-8 seroprevalence. The proportion of HHV-8 seropositivity in the MSM population was significantly higher than in the heterosexual population and most marked in HIV positive MSM. A broad variety of HHV-8 subtypes are represented in patients exhibiting HHV-8-related disease in Ireland. The predominance of C and A K1 subtypes was as expected for a western European population. The 31% prevalence for K15 subtype M was higher than expected for a western European population. This may represent the changing and evolving epidemiology in Ireland due to altered migration patterns. To our knowledge, this is the first study comparing cytokine levels between different subtypes of HHV-8. Further research is warranted to determine whether different subtypes can be linked with differing disease severity and, if so, what role proinflammatory cytokines have to play. The results of this study support previous reports that higher levels of proinflammatory cytokines are associated with higher HHV-8 viral loads and disease flares compared to remission.