Detection of HHV-6 by the polymerase chain reaction

Selection of the same mutation in the U69 protein kinase gene of human herpesvirus-6 after prolonged exposure to ganciclovir in vitro and in vivo

After serial passage in the presence of increasing concentrations of ganciclovir (GCV) in vitro, a human herpesvirus-6 (HHV-6) mutant exhibiting a decreased sensitivity to the drug was isolated. Analysis of drug susceptibility showed that the IC(50) of this mutant was 24-, 52- and 3-fold higher than that of the wild-type (wt) IC(50) in the case of GCV, cidofovir and foscarnet, respectively. Genotypic analysis showed two single nucleotide changes as compared to the wild-type: an A-->G substitution of the U69 protein kinase (PK) gene resulted in an M(318)V amino acid substitution and the other change, located in the C-terminal part of the U38 gene, resulted in an A(961)V amino acid substitution within the DNA polymerase. The M(318)V change was located within the consensus sequence DISPMN of the putative catalytic domain VI of the PK. This change was homologous to the M(460)V and M(460)I changes that had been reported previously within the consensus sequence DITPMN of the human cytomegalovirus (HCMV) UL97 PK and associated with the resistance of HCMV to GCV. The M(318)V change was also detected by PCR in HHV-6-infected PBMCs from an AIDS patient who had been treated with GCV for a long period of time and exhibited a clinically GCV-resistant HCMV infection. These findings provide strong circumstantial evidence that the M(318)V change of the PK gene is associated with resistance to GCV and raise the question of cross resistance to this drug among different betaherpesviruses.

Asymmetric periflexural exanthem of childhood: microbiologic case-control study

Our objective was to study possible etiologic factors of asymmetric periflexural exanthem of childhood (APEC) among a large panel of microbiologic agents not yet investigated. To do so, we designed a prospective case-control study using throat, stool, blood, and skin samples, and enlisted 37 children with APEC and 37 age-matched controls without eruption seen consecutively from February 1995 to April 1996 from a mixed referral center and community-based population. No interventions were done. Used as the main outcome measure was the differences in the two groups for microbiologic investigations. No significant statistical differences between cases and controls for virus and bacteria investigated were found. No microorganism was identified as a possible etiologic agent in any of the APEC patients. APEC is not a nonspecific cutaneous eruptive pattern to several common microbiologic agents. More sophisticated molecular approaches are needed to address its etiology.

Detection of human herpesvirus 6 DNA in serum by a microplate PCR-hybridization assay

PCR was performed on DNA extracts derived from clinical serum samples submitted for human herpesvirus 6 (HHV-6) serological examination. To detect amplified HHV-6 products, a hybridization-based microtiter plate assay (PCR ELISA; Boehringer Mannheim) was used. The assay system was found to be rapid, specific, and sensitive. Approximately three copies of a plasmid-based HHV-6 sequence could be detected, and no cross amplification was observed with HHV-7 genomic DNA. There was no correlation found between HHV-6 DNA detection and serological status in clinical serum samples from individuals more than 2 years old. On the other hand, in serum samples from infants less than 2 years old, a high rate of detection of HHV-6 DNA was observed in those who lacked immunoglobulin G and M antibodies to HHV-6 (55%). In this regard, PCR of serum DNA extracts may be used as a sensitive indicator of active HHV-6 infection in infants prior to their seroconversion.

Herpesvirus 6 variant A infection after heart transplantation with giant cell transformation in bile ductular and gastroduodenal epithelium

Herpesvirus 6 (HHV-6) is a ubiquitous virus known to cause febrile syndromes and exanthema subitum in children. Less commonly, and particularly in organ transplant recipients, it may result in hepatitis, bone marrow suppression, interstitial pneunonitis, and meningoencephalitis. This report expands the spectrum of clinical disease associated with HHV-6 by documenting viral infection in a 44-year-old heart transplant recipient presenting with gastroduodenitis, pancreatitis, and hepatitis. On histopathologic examination, the gastric, duodenal, and bile ductular epithelium showed a multinucleate giant cell transformation similar to the cytopathic effect caused by the virus in human T-lymphocytes infected in vitro. Electron microscopy showed herpes particles with a thick tegument layer in the duodenum. Polymerase chain reaction amplified HHV-6 variant A sequences from multiple sites. Serology confirmed the presence of an acute HHV-6 infection. Thus, HHV-6 variant A can cause gastroduodenitis and pancreatitis in immunosuppressed individuals. Multinucleate giant cells and enveloped virions with a prominent tegument can be used as morphologic criteria to raise the possibility of HHV-6 infection in human biopsy tissue.

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.

Detection of human herpes virus 6 in AIDS-associated retinitis by means of in situ hybridization, polymerase chain reaction and immunohistochemistry

The ubiquitous nature of HHV-6 and its genomic relationship with cytomegalovirus led us to evaluate an etiological link between HHV-6 and AIDS-associated retinitis in a prospective study. HHV-6 infection was studied in patients with AIDS-associated retinitis and in two control populations. Eye pairs were obtained at necropsy from nine patients with AIDS-associated retinitis, four human immunodeficiency virus (HIV)-sero-positive patients with normal fundus examination and three HIV-seronegative patients. HHV-6 infection was detected by polymerase chain reaction (PCR), in situ hybridization and immunohistochemistry. Human cytomegalovirus (CMV) and HIV-1 infections were detected in parallel by the same methods. HHV-6 infection was detected in three cases of AIDS-associated retinitis. In two of these patients, HHV-6 infection was detected both by immunohistochemistry and PCR while in the third case it was detected by in situ hybridization and PCR. In the three patients, fundus examination showed bilateral retinitis in two of them and unilateral retinitis in one of them. HHV-6 infection was not detected in the retina of the two control groups. CMV was also detected in the three cases positive for HHV-6 by all three methods. HIV DNA was detected by PCR in two of three cases and was confirmed in one of these cases by in situ hybridization. These results confirm that HHV-6 infects the retina but suggests that HHV-6 does not have an exclusive causative role in AIDS-associated retinitis, since CMV coinfection of the retina was detected in all three of the patients positive for HHV-6.

Difference in permissiveness of human fibroblast cells to variants A and B of human herpesvirus-6

Human herpesvirus-6 (HHV6) is a lymphotropic virus genetically related to human cytomegalovirus (CMV) and for which two variants, A and B, have been distinguished. Human CMV is usually cultivated with human fibroblasts (HF). The lack of cell lines useful for HHV6 isolation and propagation led us to investigate whether HHV6 variants A and B could infect HFs as CMV does. Isolates of HHV6 variants A and B were used to infect MRC-5 HFs. HHV6 infection was detected by means of immunoperoxidase assay using three specific monoclonal antibodies. HHV6-specific antigens were detected in 88 and 38% of cases after infection with variants A and B, respectively. The highest number of HHV6-antigen-positive cells was obtained at 4-5 days p.i. The titre of HHV6 stocks was determined in parallel by immunoperoxidase assay on HFs and by observation of cytopathic effect using serial dilutions on peripheral blood mononuclear cells (PBMC). The number of infectious particles inducing the appearance of antigen-positive HF cells was consistently lower than the titre of virus stocks, expressed as TCID50. The amount of HF-associated HHV6 DNA was measured using limiting dilution PCR assay; it was significantly increased during 4-day infection in the case of variant A but not variant B. The yield of virus from infected HFs was demonstrated only for variant A by the serial propagation of virus from HFs to PBMCs and by the increase in cell-free HHV6 DNA in HF culture supernatant. Our results show that HHV6 can reproducibly infect HFs, albeit at a low level, and that HFs are more permissive to variant A than to variant B, as reported previously for PBMCs and human T-cell lines.

Evaluation of a commercial enzyme-linked immunosorbent assay for detection of serum immunoglobulin G response to human herpesvirus 6

A rapid (60-min) commercially available enzyme-linked immunosorbent assay (ELISA) for the detection of immunoglobulin G (IgG) class antibodies to human herpesvirus 6 (HHV-6) was evaluated. The specificity of the ELISA for HHV-6 was confirmed by absorption studies, with the reactivities of HHV-6-positive sera being unaffected by other herpesviruses (cytomegalovirus, herpes simplex virus, and varicella-zoster virus) or the HSB2 cell line used to culture HHV-6. HHV-6 IgG antibody levels in a panel of 502 serum samples were determined by ELISA and an indirect immunofluorescence assay (IFA). Results obtained by the two methods were in close agreement, suggesting that the ELISA provides a suitable test method for the determination of HHV-6 IgG antibodies in a routine clinical laboratory. Both tests were positive in 398 cases (79%), and both were negative in 71 cases (14%), with a different result obtained by IFA and ELISA in only 33 cases (7%). Furthermore, absorption of sera with HHV-6 prior to assay revealed that the majority of these results were false positive (n = 8) or false negative (n = 23) in the IFA (true positives or negatives in the ELISA). Subsequently, the ELISA showed a sensitivity of 99.76% and a specificity of 98.75%. HHV-6-specific IgG levels were also determined in paired serum samples collected from 49 donors--14 with exanthem subitum (ES), 15 with ES which was complicated with central nervous system involvement, and 20 undergoing bone marrow transplantation--in whom HHV-6 infection had been demonstrated by virus isolation and/or PCR. All patients with ES or central nervous system complications showed an increase in HHV-6-specific IgG, indicating that this ELISA may be a useful aid in the diagnosis of these conditions. Furthermore, 14 of 20 patients undergoing bone marrow transplantation showed an increase in HHV-6-specific IgG levels, possibly reflecting a reactivation of HHV-6 in these patients.

Novel human herpesviruses (human herpesviruses 6, 7 and 8)

The number of members in the family Herpesviridae has increased in the last 10 years due to the description of three novel human herpesviruses: human herpesvirus 6 (HHV-6) in 1986, human herpesvirus 7 (HHV-7) in 1990, and human herpesvirus 8 (HHV-8), also known as Kaposi's sarcoma-associated herpesvirus (KSHV), in 1994. HHV-6 and HHV-7 were first isolated from blood lymphocyte cultures, while HHV-8 was identified following a specific molecular biology approach in the search for the etiologic agent of Kaposi's sarcoma. The three viruses are lymphotropic, T-cells being the targets of HHV-6 and HHV-7, and B-cells being probably those of HHV-8. The ability to be propagated in cell cultures in vitro differs according to the virus concerned: this can be done readily with HHV-6, with more difficulties in the case of HHV-7, and has not yet been achieved in the case of HHV-8. Human infection with HHV-6 and HHV-7 is ubiquitous, widespread and acquired early in life. HHV-8 epidemiology is still unclear, and there are two hypotheses: a restricted dissemination in the general population like herpes simplex virus type 2, or a widespread infection like all other human herpesviruses. The polymerase chain reaction is the common method for the detection of infection using specific primers and probes for HHV-6, HHV-7 and HHV-8 respectively. Serologic assays are only available for HHV-6 and HHV-7, with limitations being due, in particular, to possible cross-reactions with cytomegalovirus. HHV-6 is the causative agent of exanthem subitum (sixth disease). Its role as an opportunistic agent and immune dysfunction inducer is debated and currently under investigation. The pathogenic role of HHV-7 seems to be modest, with one case of exanthem subitum reported so far. HHV-8 is strongly associated with three diseases: Kaposi's sarcoma, Castleman's disease and body-cavity-based lymphomas. The therapy against these novel viruses has to be considered in the future.

Large-scale study suggests no direct link between human herpesvirus-6 and primary Sjögren's syndrome

The aim of this study was to evaluate the role of human herpesvirus-6 (HHV-6) in the development of primary Sjögren's syndrome (PSS). Serum HHV-6 antibody levels, as measured by immunofluorescence assay (IFA) and the prevalence of HHV-6 DNA in peripheral blood mononuclear cells (PBMCs) determined by polymerase chain reaction (PCR), were studied in 49 PSS patients and 50 control subjects, all in-patients in the University Hospital Internal Medicine ward, Limoges, France. In addition, portions of labial salivary gland were obtained from 34 patients and 15 controls, the presence of viral DNA being detected by the same PCR technique. The results were then compared with clinical observations of systemic disease manifestations in patients and a histological study of salivary gland involvement. No significant difference in HHV-6 seroprevalence was found between control subjects (50.0%) and patients (63.3%) nor was there any statistically significant difference between patient and control groups for total viral DNA in PBMCs (22.4%, 12.0%) and salivary glands (8.8%, 6.6%). Analysis of clinical and histological data revealed no detectable correlation between disease severity and viral involvement. Tests for HHV-6A and HHV-6B proved positive in patient and control groups, HHV-6B being the most frequently encountered type in both groups. In conclusion, the results of this large-scale trial does not confirm the suspected direct role of HHV-6 in the etiology of PSS.

Diagnosis of human herpesvirus-6 infection in two patients with central nervous system complications

BACKGROUND

Although exanthem subitum (ES) is generally a mild, self-limiting disease of early childhood, some cases of ES are complicated by seizures and encephalopathy. The presence of human herpesvirus-6 (HHV-6) DNA in cerebrospinal fluid (CSF) of these patients suggests that HHV-6 can infect the central nervous system (CNS) causing encephalitis.

OBJECTIVES

To demonstrate HHV-6 infection in two patients with serious CNS complications. The patients, a child and an adult, failed to develop the characteristic rash normally associated with ES.

STUDY DESIGN

Peripheral blood mononuclear cells (PBMCs) and CSF were examined for the presence of HHV-6 or viral DNA, using virus isolation techniques and the polymerase chain reaction (PCR). Serum samples were tested by immunofluorescence (IF) and enzyme linked immuno-sorbent assay (ELISA) for the presence of anti-HHV-6 IgM and anti-HHV-6 IgG respectively.

RESULTS

HHV-6 was isolated from the PBMCs of the adult patient and the presence of virus in these cells was confirmed using electron microscopy. HHV-6 DNA was detected in CSF taken early during the infection in both patients, together with anti-HHV-6 IgM antibodies and increasing levels of anti-HHV-6 IgG.

CONCLUSIONS

The diagnosis of HHV-6 infection in these patients was confirmed either by virus isolation or by the detection of HHV-6 DNA in the CSF, and the results of serology. These cases show that HHV-6 infection may result in serious CNS complications, in children and adults.

Identification of human herpesvirus 6 variants A and B by amplimer hybridization with variant-specific oligonucleotides and amplification with variant-specific primers

Two distinct PCR-based procedures were evaluated for the detection and identification of human herpesvirus 6 (HHV-6) variants A and B in uncultured human samples. Variant-specific oligonucleotide hybridization (VSOH) is based on the amplification of two distinct regions of the HHV-6 genome, followed by hybridization of amplimers with variant-specific oligonucleotide probes. Variant-specific primer PCR (VSPP) is based on the amplification of each variant by using variant-specific primers. The study of 10 well-characterized HHV-6 strains allowed us to demonstrate the high sensitivity and specificity of both methods. With variant mixtures, however, some limitations of VSOH were evidenced and VSPP was required to obtain unambiguous results. The combination of VSOH and VSPP was applied to the direct study of 300 peripheral blood mononuclear cell samples from French subjects. HHV-6 was detected in 15 samples: 11 corresponded to variant B, 3 corresponded to variant A, and 1 corresponded to a mixture of both variants.

Detection of human herpesvirus-6 in paraffin-embedded tissue of cervical cancer by polymerase chain reaction

The polymerase chain reaction (PCR) was used to detect human herpesvirus-6 (HHV-6) DNA sequences from paraffin-embedded tissue from cervical cancer patients. Two of eight cases were positive for HHV-6 using two sets of HHV-6 primers. Hybridization of PCR products with specific radioisotope-labeled oligonucleotide probes confirmed the results. Furthermore, HHV-6 typing was possible by adapting restriction endonuclease digestion of PCR product. This method is useful for retrospective studies in investigating the etiologic role of HHV-6 in the development of human diseases.

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.

Detection of active and latent feline herpesvirus 1 infections using the polymerase chain reaction

A polymerase chain reaction (PCR) assay was developed to detect the thymidine kinase gene of feline herpesvirus 1 (FHV-1) and to study the active and latent carrier state in a group of naturally FHV-1 infected specific pathogen free (SPF) cats. The detection limit of PCR products on ethidium bromide stained gels was 390 fg or about 3 x 10(3) copies of the FHV-1 genome. The PCR was 25% more sensitive than conventional cell culture based virus isolation techniques in detecting FHV-1 in oral/ocular swabs and 100 times more sensitive in detecting virus in cell culture supernatants. Sites of FHV-1 latency in FHV-1 carriers as determined by PCR were mainly tissues of the head, especially the trigeminal ganglia, optic nerves, olfactory bulbs and corneas. Oral fauces, salivary glands, lacrimal glands, cerebellum and conjunctiva were less consistently positive. The cerebral cortex, thymus, trachea, lung, liver, spleen, kidney, and peripheral blood mononuclear cells were consistently negative for FHV-1 genome. The distribution of FHV-1 DNA in the tissues of the head was similar whether or not corticosteroid-induced virus shedding was occurring at the time the tissues were collected. Infectious virus was never recovered from tissue homogenates regardless of the PCR status of the tissues.

Antigenic and genetic differentiation of the two putative types of human herpes virus 6

Ten human herpes virus 6 (HHV-6) strains from different origins were studied using reactivity to monoclonal antibodies and polymerase chain reaction analysis. Using immunofluorescence and neutralization assays, two monoclonal antibodies gave a positive reaction with the ten strains while three others only reacted with a fraction of these strains. This differential reactivity permitted segregation of the ten strains into two non-overlapping antigenic groups, designated as I and II. DNA was amplified from two regions of HHV-6 genome corresponding to the putative large tegument protein (LTP) gene and major capsid protein (MCP) gene, respectively. The restriction analysis of amplified products using HindIII for LTP and HaeII for MCP showed identical patterns among the strains belonging to the same antigenic group while BglII, TaqI and ClaI provided distinct patterns among group II strains. The nucleotide sequence of amplified products was determined and homology was found to be equal to or greater than 99% within each group whereas it was 96% between both groups. The number of amino-acid changes was higher when comparing two strains of different groups than when comparing two strains of the same group. The converging results of antigenic and genetic analyses led us to consider HHV-6 groups I and II as two distinct types of HHV-6 species.