Geographic/ethnic differences in human herpesvirus-6 antibody patterns

An evaluation of HHV-6 as an etiologic agent in Hodgkin lymphoma and brain cancer using IARC criteria for oncogenicity

BACKGROUND

Human herpesvirus-6 (HHV-6) is a ubiquitous double-stranded DNA virus that can cause roseola infantum, encephalitis, and seizure disorders. Several studies have shown an association between HHV-6 and cancer but confirmation of an etiologic role is lacking. We reviewed the criteria for viral causation of cancer used by The International Agency for Research on Cancer (IARC) for six oncogenic viruses and applied criteria to published reports of HHV-6 and its association with Hodgkin lymphoma and brain tumors.

METHODS

Our major criteria for oncogenicity were finding evidence of the virus in every tumor cell and prevention of the tumor by an antiviral vaccine. Our six minor criteria included: 1) suggestive serologic correlation, such as higher virus antibody levels in cases compared to controls; 2) evidence of the virus in some but not all tumor cells, and 3) time space clustering. We focused on Epstein-Barr virus (EBV) as the primary virus for comparison as HHV-6 and EBV are both Herpesviridae, ubiquitous infections, and EBV is well-accepted as a human oncovirus. Particular attention was given to Hodgkin lymphoma (HL) and brain cancer as these malignancies have been the most studied.

RESULTS

No studies reported HHV-6 satisfying either of the major criteria for oncogenicity. Of the minor criteria used by IARC, serologic studies have been paramount in supporting EBV as an oncogenic agent in all EBV-associated tumors, but not for HHV-6 in HL or brain cancer. Clustering of cases was suggestive for both HL and brain cancer and medical intervention suggested by longer survival in patients treated with antiviral agents was reported for brain cancer.

CONCLUSION

There is insufficient evidence to indicate HHV-6 is an etiologic agent with respect to HL and brain cancers. We suggest that methods demonstrating EBV oncogenicity be applied to HHV-6. It is important that one study has found HHV-6 in all cancer cells in oral cancer in a region with elevated HHV-6 antibodies and therefore HHV-6 can still be considered a possible human oncogenic virus.

Loss of maternally derived human herpesvirus-6 immunity and natural infection in Argentinian infants

BACKGROUND

Human herpesvirus-6 (HHV-6) infection is widespread throughout the world. No data are available in Argentina about the loss of maternally derived HHV-6 immunity and natural infection in infants.

METHODS

A population of 100 pregnant women and 407 children between 1 and 15 months of age were assayed by indirect immunofluorescence to detect and quantify specific IgG anti-human herpesvirus-6 (anti-HHV-6) antibodies in Córdoba City, Argentina.

RESULTS

There was no significant difference in the positive rate between infants aged 1 to 9 months (range, 43.6 35.5%) and pregnant women (37%). Seropositive ratio dropped in the 10-month group (23.33% seropositive) and rose sharply in the 11-month group (38.89%), 12-month (60.61%), and 13- to 15-month group (63.46%). The geometric mean titer (GMT) for infants in the 12 to 15 months age group (23.4 41.64) was significantly higher than the GMT for infants 10 months of age (11.04) (P < 0.05 with the Tukey-HSD test).

CONCLUSIONS

This study shows a significant association between loss of passive HHV-6 antibody and age among infants. The results support evidence that HHV-6 enters the susceptible population at 11 months, leading to a high prevalence of antibodies in children between 13 and 15 months of age.

Human herpes virus-6 seroprevalence and leukaemias: a case-control study. GIMEMA (Gruppo Italiano Malattie Ematologiche dell' Adulto)

The relationships between acute myeloid leukaemia (AML), acute lymphocytic leukaemia (ALL), chronic myeloid leukaemia (CML) and refractory anaemia with excess of blasts (RAEB) and human herpes virus (HHV)-6 antibody level were investigated in a multicentre case-control study. An association between increased HHV-6 seropositivity and geometric mean titre ratio with AML was shown: P for trend = 0.022, adjusted odds ratio 1.20, 95% confidence interval 1.07-1.33 respectively. No association was found between HHV-6 and ALL, CML or RAEB.

Human herpesvirus 6

Human herpesvirus 6 variant A (HHV-6A) and human herpesvirus 6 variant B (HHV-6B) are two closely related yet distinct viruses. These visuses belong to the Roseolovirus genus of the betaherpesvirus subfamily; they are most closely related to human herpesvirus 7 and then to human cytomegalovirus. Over 95% of people older than 2 years of age are seropositive for either or both HHV-6 variants, and current serologic methods are incapable of discriminating infection with one variant from infection with the other. HHV-6A has not been etiologically linked to any human disease, but such an association will probably be found soon. HHV-6B is the etiologic agent of the common childhood illness exanthem subitum (roseola infantum or sixth disease) and related febrile illnesses. These viruses are frequently active and associated with illness in immunocompromised patients and may play a role in the etiology of Hodgkin's disease and other malignancies. HHV-6 is a commensal inhabitant of brains; various neurologic manifestations, including convulsions and encephalitis, can occur during primary HHV-6 infection or in immunocompromised patients. HHV-6 and distribution in the central nervous system are altered in patients with multiple sclerosis; the significance of this is under investigation.

Presence of human herpesvirus 6 variants A and B in saliva and peripheral blood mononuclear cells of healthy adults

Saliva and peripheral blood mononuclear cells (PBMCs) from 44 healthy young adults were tested for human herpesvirus 6 variants A and B (HHV-6A and -6B) DNA by a sensitive nested PCR. HHV-6B infection was ascertained in 98% of the subjects, and 95% were found to excrete variant B in their saliva. HHV-6A was found in the PBMCs of 16%, but was not detected in saliva samples.

Competitive ELISA for detection of HHV-6 antibody: seroprevalence in a danish population

A competitive HHV-6 enzyme-linked immunosorbent assay (ELISA) was established, utilizing HHV-6 rabbit polyclonal antibodies and HHV-6 cellular antigen. In total, 285 sera from Danish children aged 1-6 years were screened for HHV-6 antibodies. The lowest seropositive rate, 78% was found in the youngest age group from 1 year to 15 months. All 120 (100%) children aged 3 years and above were seropositive. The ELISA was compared with indirect immunofluorescence assay (IFA) using a group of 83 serum samples from 65 Danish patients (aged 4 weeks to 72 years). All but one of the sera (100% of patients) were positive in the ELISA, but only 71% of sera (65% of patients) were positive with both assays. The ELISA detected one seroconversion in a baby, which was not detected by IFA. The ELISA was found to be more sensitive than IFA.

Comparison of HHV-6 antibody titers in West Africa and the Caribbean

Human herpesvirus-6 (HHV-6) infection seems to be ubiquitous early in life, but antibody responses vary by geographic area. We compared HHV-6 antibody titer in 123 West African and 122 Caribbean serum samples. A quantitative immunofluorescence assay (IFA) using antigens derived from an HSB-2 cell line was used to test for IgG HHV-6 (GS strain) antibodies. The prevalence of HHV-6 antibodies was high (98%) in both sites. African samples had a significantly higher geometric mean titer (GMT: 697) than did Caribbean samples (GMT: 99). There was no difference between males (GMT: 260) and females (GMT: 270) overall. Children up to and including 9 years old had significantly higher titers (GMT: 483) than did all others (GMT: 237), and female children tended to have higher titers than did male children. In both areas there was a trend towards highest titer at younger age, followed by a decrease in titer during adulthood and middle age, and a secondary rise in titer in the oldest age group. Environmental and host factors may explain these geographic differences in antibody responses between two groups of African origin.

Low-incidence latent infection with variant B or roseola type human herpesvirus 6 in leukocytes of healthy adults

Nested primer-based polymerase chain reaction was employed to determine the frequency of latent infection with human herpesvirus 6 (HHV-6) among healthy adults from Bratislava, Slovak Republic. A 592-bp region, upstream from the gene encoding the putative large tegument protein of HHV-6, was amplified from DNA extracted from peripheral blood mononuclear cells (PBMC) of only one of 29 seropositive adults, suggesting that as few as 1 in 10(5) PBMC may be infected with the virus. Direct sequencing of the 592-bp fragment indicated that the virus harbored by the seropositive Slovak subject (designated B38) differed by only 3 nucleotides from an HHV-6 variant B strain (R-147) isolated from an American infant with a roseola-like illness and by 32 bases from the variant A strain GS isolated from a patient with lymphadenopathy (5.4% sequence divergence). None of these strains had a deoxyadenosine at base position 1251, when compared to the published sequence of strain GS clone pZVH14. Although this discrepancy did not affect the large tegument protein gene, it altered the predicted amino acid sequences of two putative proteins coded by open-reading frames 1 and 2 (ORF 1 and ORF 2) located upstream from this gene.