Direct identification by PCR of EBV types and variants in clinical samples

Use of saliva-based qPCR diagnostics for the accurate, rapid, and inexpensive detection of strep throat

OBJECTIVES

Outpatient health care facilities are essential for quickly diagnosing common infectious diseases such as bacterial and viral pharyngitis. The only form of pharyngitis requiring antibiotics is strep throat (ST); however, antibiotic prescription rates are much higher than ST prevalence, suggesting antibiotics are being inappropriately prescribed. Current rapid ST diagnostics may be contributing to this problem due to the low sensitivity and variable specificity of these tests. It is best practice to verify a negative ST diagnosis with a group A Streptococcus (GAS) culture, but many clinics do not perform this test due to the additional cost and 24-72 h required to obtain results. This indicates there is great need for more accurate rapid diagnostic tools in outpatient facilities. We hypothesized that next generation qPCR technology could be adapted to detect GAS DNA from saliva samples (instead of the traditional throat swab) by creating a simple, fast, and inexpensive protocol.

METHODS

Saliva specimens collected from patients at James Madison University Health Center were used to test the effectiveness of our Chelex 100-based rapid DNA extraction method, followed by a fast protocol developed for the Open qPCR machine to accurately detect ST.

RESULTS

Our final saliva processing and qPCR protocol required no specialized training to perform and was able to detect ST with 100 % sensitivity and 100 % specificity (n=102) in 22-26 min, costing only $1.12 per sample.

CONCLUSIONS

Saliva can be rapidly analyzed via qPCR for the accurate and inexpensive detection of ST.

EBV and HHV-6 Circulating Subtypes in People Living with HIV in Burkina Faso, Impact on CD4 T cell count and HIV Viral Load

Epstein Barr Virus (EBV) and Human Herpes Virus 6 (HHV-6) are responsible for severe diseases, particularly in immunocompromised persons. There is limited data of the infection of these opportunistic viruses in Burkina Faso.

The purpose of this study was to characterize EBV and HHV-6 subtypes and to assess their impact on CD4 T cell count, HIV-1 viral load and antiretroviral treatment in people living with HIV-1. The study population consisted of 238 HIV-positive patients with information on the CD4 T cell count, HIV-1 viral load and HAART. Venous blood samples collected in EDTA tubes were used for EBV and HHV-6 Real Time PCR subtyping.

An infection rate of 6.7% (16/238) and 7.1% (17/238) were found respectively for EBV and HHV-6 in the present study. Among EBV infections, similar prevalence was noted for both subtypes (3.9% (9/238) for EBV-1 vs 4.6% (11/238) for EBV-2) with 2.1% (5/238) of co-infection. HHV-6A infection represented 6.3% (15/238) of the study population against 5.0% (12/238) for HHV-6B. EBV-2 infection was significantly higher in patients with CD4 T cell count ≥ 500 compared to those with CD4 T cell count less than 500 cells (1.65% vs 8.56%, p = 0,011). The prevalence of EBV and HHV-6 infections was almost similar in HAART-naive and HAART-experienced patients.

The present study provides information on the prevalence of EBV and HHV-6 subtypes in people living with HIV-1 in Burkina Faso. The study also suggests that HAART treatment has no effect on infection with these opportunistic viruses in people living with HIV-1.

A multiplex calibrated real-time PCR assay for quantitation of DNA of EBV-1 and 2

Accurate and highly sensitive tests for the diagnosis of active Epstein-Barr virus (EBV) infection are essential for the clinical management of individuals infected with EBV. A calibrated quantitative real-time PCR assay for the measurement of EBV DNA of both EBV-1 and 2 subtypes was developed, combining the detection of the EBV DNA and a synthetic DNA calibrator in a multiplex PCR format. The assay displays a wide dynamic range and a high degree of accuracy even in the presence of 1μg of human genomic DNA. This assay measures with the same efficiency EBV DNA from strains prevalent in different geographic areas. The clinical sensitivity and specificity of the system were evaluated by testing 181 peripheral blood mononuclear cell (PBMCs) and plasma specimens obtained from 21 patients subjected to bone marrow transplantation, 70 HIV-seropositive subjects and 23 healthy controls. Patients affected by EBV-associated post-transplant lymphoprolipherative disorders had the highest frequency of EBV detection and the highest viral load. Persons infected with HIV had higher levels of EBV DNA load in PBMCs and a higher frequency of EBV plasma viremia compared to healthy controls. In conclusion, this new assay provides a reliable high-throughput method for the quantitation of EBV DNA in clinical samples.

Salivary shedding of Epstein-Barr virus and cytomegalovirus in people infected or not by human immunodeficiency virus 1

The purpose of this study is to determine the frequency of EBV and CMV DNA detection in saliva of HIV infected and non-HIV individuals and their siblings. The study group comprised 240 individuals. Group 1 comprised of 40 HIV-infected patients, group 2 40 non-HIV individuals, group 3 two siblings for each patient from group 1 (n = 80), and group 4 two siblings for each individual from group 2 (n = 80). Non-stimulated whole saliva was collected, DNA was extracted, and amplification was performed using a nested PCR protocol. EBV and CMV DNA was detected in 7/40 (17.5%) and 5/40 (12.5%) individuals from group 1, 8/40 (20%) and 3/40 (7.5%) from group 2, 11/80 (13.8%) and 2/80 (2.5%) from group 3, and 8/80 (10%) and 1/80 (1.3%) from group 4, respectively. Five (71.4%) out of seven HIV/EBV coinfected individuals of group 1 had a relative also infected with EBV (OR = 11.25, CI [1.75-72.5], p = 0.011). Regarding group 2, among the eight non-HIV and EBV-infected individuals, three (37.5%) had a relative also positive to EBV (p = 0.320). No individual HIV/CMV coinfected had a relative CMV infected (p = 1.00). Also, only one non-HIV and CMV-infected individual had a relative also positive to CMV (p = 0.075). EBV and CMV DNA was detected mainly in those who had HIV viral load counts <400/mL (71%, p = 0.2 and 100%, p = 1, respectively) and those who had CD4 T cells counts between 200 and 400/mm(3) (57%, p = 0.544 and 60%, p = 0.249, respectively). HIV-infected individuals and healthy controls showed a similar frequency of viral DNA detection. EBV DNA was significantly amplified in saliva of household members of HIV/EBV coinfected individuals.

Forensic application of Epstein-Barr virus genotype: Correlation between viral genotype and geographical area

Using 50 forensic blood samples, the latent membrane protein 2A (LMP-2A) gene of Epstein-Barr virus (EBV) DNA was amplified to find a geographic correlation among the EBV genotypes. EBV DNA was detected in nine samples. From a phylogenetic analysis using 18 reported sequences as a reference, six EBV subtypes (Ia, Ib, Ic IIa, IIb, and IIc) were found. Japanese isolates were included in subtypes Ia or IIa. All the Asian reference isolates, except isolate D6, were included in subtype Ia or IIa. Mediterranean, an Alaskan and other African isolates were included in types Ib, Ic, IIb and IIc. The EBV genotype in the LMP-2A gene was thus demonstrated as being correlated with the host's geographical location. Typing in the EBV-associated nuclear antigen 2 gene was not related to that in the LMP-2A gene. Detection of the EBV genotype in the LMP-2A gene may be useful for determining the geographical origins of unidentified cadavers.

High prevalence of multiple human herpesviruses in saliva from human immunodeficiency virus-infected persons in the era of highly active antiretroviral therapy

Human immunodeficiency virus (HIV) infection is associated with an increased risk for human herpesviruses (HHVs) and their related diseases. Methods for limiting the transmission of HHVs require a better understanding of the prevalence and infectiousness of oral HHVs in HIV-infected patients. We performed quantitative PCR to investigate the prevalence, quantity, risk, and correlates of salivary HHVs from 58 HIV-seropositive individuals in a case control study. HHVs were significantly more prevalent in the salivas of HIV-seropositive persons than in those of the controls (odds ratios [ORs], 4.2 to 26.2; P<or=0.008). In HIV-infected patients, Epstein-Barr virus (EBV), human herpesvirus 8 (HHV-8), cytomegalovirus (CMV), and herpes simplex virus type 1 (HSV-1) were detected in 90%, 57%, 31% and 16% of samples, respectively, compared with 48%, 24%, 2%, and 2%, respectively, of samples from controls. Multiple HHVs were observed in 71% of HIV-seropositive persons and only 16% of controls (OR, 13.0; 95% confidence interval, 5.29 to 32.56). HIV-positive patients had significantly higher EBV loads than HIV-negative persons (P<0.0001). HIV-infected patients with CD4 counts above 200 cells/microl had increased probability for having HHV-8 in saliva (P=0.009) compared with patients whose counts were less than 200. In contrast, HSV-1, EBV, and CMV were detected more often when CD4 counts were low. High salivary HHV loads were detected for those (n=7) with oral lesions. These findings suggest that saliva is a potential risk factor for the acquisition of multiple HHVs, and several host factors may function to accelerate HHV reactivation or replication in patients with HIV infection.

Biomechanical muscle properties and angiotensin-converting enzyme gene polymorphism: a model-based study

Previous studies reported an association of angiotensin-converting enzyme (ACE) I/D gene polymorphism with physical performance. The study was based on the hypothesis that certain individual biomechanical muscle properties could be associated with ACE genotype and that they could influence athletes' physical performance. Movement-independent individual biomechanical muscle properties of 62 sports students were determined by applying a mathematical model to experimental data. Subjects exerted concentric and isometric contractions at a leg-press. The model was based on a Hill-type muscle model, a function describing the geometrical arrangement of human leg extensor muscles, and an exponential function describing muscle activation. Mouthwash samples were taken to determine the ACE genotypes. Several combinations of experimentally determined biomechanical properties served as input variables for a discriminant analysis. We were able to show that individual biomechanical muscle properties correlated with ACE I/D gene polymorphism. With a combination of certain individual muscle parameters based on a Hill-type muscle model, we were able to separate three individual ACE genotypes (II, ID, DD) in a significant way (P<0.03) and correctly classify 89% of the cases using a discriminant analysis. We conclude that local biomechanical muscle properties are influenced by ACE genotype.

Distribution of Epstein-Barr virus genotypes in throat washings, sera, peripheral blood lymphocytes and in EBV positive tumor biopsies from Slovenian patients with nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a malignancy closely associated with Epstein-Barr virus (EBV). It is prevalent among the Chinese of Southern China, whereas outside China, the position seems to be different. The aim of this study was to determine the distribution of EBV genotypes in the patients with NPC in Slovenia, which is a nonendemic area. Detection of EBV was undertaken by testing the throat washes, sera, peripheral blood lymphocytes (PBLs), and biopsies of primary tumors of 48 patients with NPC in Slovenia. The sera of 20 patients with serologically confirmed primary EBV infection served as a control clinical material. The analysis of genotypes was carried out on three regions of EBV genome; BamHI WYH, BamHI I, and BamHI F, using the polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP). The results show that, in Slovenia, the predominant combination of EBV genotypes based on the differences in the three genomic regions is ADF. This combination was found in 56 out of 103 different EBV positive clinical samples (throat washes, sera, PBLs, and tumor biopsies) of patients with NPC and in 15 out of 17 sera of patients with primary EBV infection. Very low number of genotypes C and f were detected, in spite of the fact that these two genotypes were considered to be associated with the development and/or maintenance of NPC in Southern China. Genotype f was found in only two tumor biopsies; in all other clinical samples (throat washes, sera and PBLs), genotype F was detected. Genotype C was proven in 31/103 clinical samples, with the highest percentage in tumor biopsies (37.5%). As in the NPC patients from other countries (Alaska is an exception), genotype A was predominant and was detected in 86/103 clinical samples. Genotype B was found in 15 clinical samples of patients with NPC and in 3 the two genotypes A and B were found. In comparison to China, these results show different EBV genotypes distribution. It seems that the genetic disposition of human population is an important factor that may contribute to different susceptibility for specific EBV genotypes.

A Cohort Study among University Students: Identification of Risk Factors for Epstein‐Barr Virus Seroconversion and Infectious Mononucleosis

BACKGROUND

A vaccine against Epstein-Barr virus (EBV) infection is in clinical trials. Up-to-date information on risk factors for EBV infection and infectious mononucleosis (IM) among young adults is required to inform a vaccination strategy.

METHODS

We carried out a prospective study on a cohort of university students. All EBV-seronegative students were asked to report symptoms of IM and were followed up 3 years later to undergo repeat EBV testing and to complete a lifestyle questionnaire. EBV typing was performed for these subjects, as well as for students who were EBV seropositive at enrollment and for additional students with IM.

RESULTS

A total of 510 students (25%) who took part in the study were EBV seronegative when they entered the university; of the 241 who donated a second blood sample 3 years later, 110 (46%) had seroconverted to EBV, 27 (25%) of whom developed IM [corrected] Penetrative sexual intercourse was a risk factor for EBV seroconversion (P = .004), but neither condom use nor oral sex significantly altered the rate of seroconversion. EBV type 1 was significantly overrepresented in IM, compared with silent seroconversion (P = .001).

CONCLUSIONS

Our findings suggest that acquisition of EBV is enhanced by penetrative sexual intercourse, although transmission could occur through related sexual behaviors, such as "deep kissing." We also found that EBV type 1 infection is significantly more likely to result in IM. Overall, the results suggest that a large EBV type 1 load acquired during sexual intercourse can rapidly colonize the B cell population and induce the exaggerated T cell response that causes IM. Thus, IM could, perhaps, be prevented with a vaccine that reduces the viral load without necessarily inducing sterile immunity.

Prevalence of some herpesviruses in gingival crevicular fluid

BACKGROUND

The herpesviruses, ancient pathogens which have co-evoluted with human, are etiologically associated with a number of diseases, from asymptomatic to oncogenic and mortal diseases. It seems that some of them have also an important role in the pathogenesis of human periodontal disease.

OBJECTIVE

This study aimed to determine the prevalence of Epstein-Barr virus (EBV), human herpesvirus 6 (HHV-6), human herpesvirus 8 (HHV-8) and human cytomegalovirus (HCMV) in gingival crevicular fluid (GCF) and, eventually, to find the correlation between specific virus types and clinical parameters which are important in periodontitis, like plaque index (PI), gingival index (GI) and probing depth (PD).

STUDY DESIGN

A polymerase chain reaction (PCR) and digestion of PCR products with restriction endonuclease were employed to identify the presence of EBV, HHV-6, HHV-8 and HCMV.

RESULTS

Out of 66 samples of GCF taken from the patients with periodontal disease, EBV was found in 29 (43.9%), HHV-6 in 16 (24.2%) and HCMV in 2 (3%) samples, while in the samples of healthy persons, these viruses were not found. HHV-8 was detected neither in the patients with periodontitis nor in healthy control group. More positive results were found in clinical samples taken from people with higher PI and GI and in the samples taken from the patients with medium PD (PD=3-6mm). In all HHV-6 positive samples, we found only variant A; as for EBV positive samples, type A and type B were identified and also co-infection with the two types. It seems that there is a correlation between PI, PD and EBV types, but no correlation was found between EBV types and GI or HHV-6 types and PI, PD, GI.

CONCLUSIONS

The present findings confirm some association between herpesviruses and human periodontitis.

Epstein-barr virus (EBV) in healthy carriers: Distribution of genotypes and 30 bp deletion in latent membrane protein-1 (LMP-1) oncogene

There are two types of Epstein Barr virus (EBV): EBV-1 and EBV-2, distinguished by genomic polymorphism in the genes encoding the nuclear antigens (EBNA-2, -3A, -3B, -3C). Latent membrane protein 1 (LMP-1) is an EBV protein with known oncogenic properties. Different variants had been described; among them, a 30 base pair (bp) deletion (del-LMP-1) had been reported in benign and malignant pathologies, but there is little information about its frequency in healthy populations. The aim of this study was to determine the distribution of the EBV genotypes and the 30 bp deletion frequency, in EBV healthy carriers from Argentina. Analysis of EBNA-3C and LMP-1 genes were done by polymerase chain reaction (PCR) followed by Southern blot hybridization on DNA of peripheral blood mononuclear cells (PBMCs) from blood bank donors. EBV-1 was present in 75.9% of samples, EBV-2 in 14.6%, and co-infections with both types in 6.5%. The deleted LMP-1 variant was found in 7.4% of analyzed samples, corresponding 3.2% to deleted variant alone and 4.2% to co-infections with non-deleted form. The non-deleted variant was found in 64.6% whereas in the remaining 28%, no PCR product was detected. These results showed that EBV-1 was the more prevalent type in healthy carriers of Argentina, similar to reports from others countries. A predominance of the non-deleted LMP-1 variant was observed. The presence of co-infections with both types and variants demonstrated that healthy individuals may also harbor multiple EBV infections.

Global identification of three major genotypes of varicella-zoster virus: longitudinal clustering and strategies for genotyping

By analysis of a single, variable, and short DNA sequence of 447 bp located within open reading frame 22 (ORF22), we discriminated three major varicella-zoster virus (VZV) genotypes. VZV isolates from all six inhabited continents that showed nearly complete homology to ORF22 of the European reference strain Dumas were assigned to the European (E) genotype. All Japanese isolates, defined as the Japanese (J) genotype, were identical in the respective genomic region and proved the most divergent from the E strains, carrying four distinct variations. The remaining isolates carried a combination of E- and J-specific variations in the target sequence and thus were collectively termed the mosaic (M) genotype. Three hundred twenty-six isolates collected in 27 countries were genotyped. A distinctive longitudinal distribution of VZV genotypes supports this approach. Among 111 isolates collected from European patients, 96.4% were genotype E. Consistent with this observation, approximately 80% of the VZV strains from the United States were also genotype E. Similarly, genotype E viruses were dominant in the Asian part of Russia and in eastern Australia. M genotype viruses were strongly dominant in tropical regions of Africa, Indochina, and Central America, and they were common in western Australia. However, genotype M viruses were also identified as a minority in several countries worldwide. Two major intertypic variations of genotype M strains were identified, suggesting that the M genotype can be further differentiated into subgenotypes. These data highlight the direction for future VZV genotyping efforts. This approach provides the first simple genotyping method for VZV strains in clinical samples.

Detection of Epstein-Barr virus in saliva by real-time PCR

The purpose of this investigation was to assess the salivary levels of Epstein-Barr virus (EBV) in patients with periodontitis using real-time PCR. EBV was detected in 16 out of 33 (48.5%) periodontitis patients and in 3 out of 20(15%) healthy subjects. The baseline mean values for bleeding on probing in EBV-positive patients were significantly higher than those in EBV-negative patients. A significant decrease in EBV levels was observed after initial periodontal treatment. Our findings indicate that levels of EBV in saliva may reflect the status of periodontal inflammation.

Biclonal expansion of T cells infected with monoclonal Epstein-Barr virus (EBV) in a patient with chronic, active EBV infection

Recent studies have suggested that a high percentage of Epstein-Barr virus (EBV)-infected lymphocytes in peripheral blood of patients with chronic, active EBV infection (CAEBV) is of T cell origin. Although T cells are expanded oligoclonally in CAEBV, it is not clear whether the restricted diversity of T cells arise from immune reaction against EBV-related antigens or from proliferation of EBV-infected cells. We experienced a patient with CAEBV who had biclonal expansion of peripheral blood T cells. We identified clonotypes of these two T cell clones in detail and purified the T cell clones. EBV infected mainly the two T cell clones, whereas the viral loads in peripheral blood cells other than these T cell clones were low or undetectable. The EBV strains infecting the two T cells clones were indistinguishable from each other by a series of genotype analyses of the virus. These results suggest that the two T cell clones infected with the same monoclonal EBV proliferated in peripheral blood of the patient.

Multiple Epstein-Barr virus infections in healthy individuals

We employed a newly developed genotyping technique with direct representational detection of LMP-1 gene sequences to study the molecular epidemiology of Epstein-Barr virus (EBV) infection in healthy individuals. Infections with up to five different EBV genotypes were found in two of nine individuals studied. These results support the hypothesis that multiple EBV infections of healthy individuals are common. The implications for the development of an EBV vaccine are discussed.

Detection of Epstein-Barr Virus, but not Human Herpesvirus 8, DNA in Cervical Secretions From Swedish Women by Real-Time Polymerase Chain Reaction

BACKGROUND

Epstein-Barr virus (EBV) and human herpesvirus 8 (HHV-8) are two related herpesviruses that may be sexually transmitted.

GOAL

To examine the presence of HHV-8 and EBV DNA in the female genital tract.

STUDY DESIGN

Real-time polymerase chain reaction systems for quantification of DNA from HHV-8, EBV, and herpes simplex virus type 2 were developed and used for examination of cervical secretions from 112 Swedish women. HHV-8, EBV, and herpes simplex virus type 2 serology was also performed on samples from all subjects.

RESULTS

EBV DNA was found in 10 cervical secretion samples, sometimes in high amounts. No cervical secretion or leukocyte sample contained detectable HHV-8 DNA. Antibodies to HHV-8-latent and -lytic antigens were found in 2.7 % and 24% of serum samples, respectively.

CONCLUSION

This study supports a possible sexual route of transmission for EBV but not for HHV-8. The new real-time polymerase chain reaction systems could be valuable in future studies of relations between virus load and disease.

A Re-Evaluation of the Frequency of CD8+ T Cells Specific for EBV in Healthy Virus Carriers

EBV is a gammaherpesvirus that can establish both nonproductive (latent) and productive (lytic) infections within the cells of its host. Although T cell responses to EBV latent proteins have been well characterized, little is known about the importance of responses to lytic proteins in long term virus carriers. Here we have compared the frequencies of CD8+ T cells specific for EBV latent and lytic Ags in healthy virus carriers, using three techniques: limiting dilution analysis, enzyme-linked immunospot assay, and FACS staining with tetrameric MHC-peptide complexes. T cells specific for EBV lytic protein epitopes were readily detectable in all donors and were usually more abundant than those specific for latent epitopes. We infer that direct T cell control of viral replicative lesions is maintained in long term carriers of EBV and is an important component of the immune response to this virus. Estimates of CD8+ T cell frequencies varied considerably according to methodology; values obtained from MHC-peptide tetramer staining were, on the average, 4.4-fold higher than those obtained from enzyme-linked immunospot assays, which were, in turn, on the average, 5.3-fold higher than those obtained from limiting dilution analysis. Tetramer staining showed that as many as 5.5% circulating CD8+ T cells in a virus carrier were specific for a single EBV lytic protein epitope. Such values are much greater than previously imagined and illustrate how antigenic challenge from a persistent herpesvirus can influence the composition of the host’s CD8+ T cell pool.

A single subtype of Epstein-Barr virus in members of multiple sclerosis clusters

OBJECTIVES

Epidemiological studies strongly indicate an infectious involvement in multiple sclerosis (MS). Epstein-Barr virus (EBV), to which all multiple sclerosis patients are seropositive, is also interesting from an epidemiological point of view. We have reported a cluster of MS patients with 8 members from a small Danish community called Fjelsø. To further evaluate the role of EBV in MS we have investigated the distribution of EBV subtypes in cluster members and in control cohorts.

MATERIALS AND METHODS

Blood mononuclear cells were isolated from cluster members, unrelated MS patients, healthy controls, including healthy schoolmates to the Fjelsø cluster patients and finally from persons with autoimmune diseases in order to investigate the number of 39 bp repeats in the EBNA 6-coding region in the EBV seropositive individuals.

RESULTS

We observed a preponderance of the subtype with 3 39 bp repeats in the EBNA 6-coding region both in the MS patients and the healthy controls. In the Fjels cluster all 8 cluster members were harbouring this subtype, which is significantly different from the finding in healthy controls (n = 16), which include 8 schoolmates to the cluster members and 8 randomly selected healthy persons (Fischer's exact test P = 0.0047), and also compared to all non-clustered individuals studied (P = 0.017).

CONCLUSION

Infection with the same subtype of EBV links together the 8 persons from the Fjelsø cluster who later developed MS. This finding adds to the possibility that development of MS is linked to infection with EBV.

Definition and distribution analysis of glycoprotein B gene alleles of human herpesvirus 7

As for other herpesviruses, glycoprotein B (gB) of human herpesvirus 7 (HHV-7) is believed to play a major role in virus infection and as a target of the host immunogenic response. Using nested PCR, we amplified the whole HHV-7 gB gene from 108 human peripheral blood mononuclear cell samples and studied its variability. By means of restriction fragment length polymorphism (RFLP) analysis, three distinct patterns, designated I, II, and III, were defined and detected at frequencies of 93, 5, and 2%, respectively. Determination of the nucleotide sequence allowed us to recognize five critical positions in the gB gene with six specific combinations of point changes at these positions. These combinations were gB alleles A, B, C, D, E, and F. Alleles D and E corresponded to RFLP patterns II and III, respectively, while the other four alleles corresponded to RFLP pattern I. Identical gB alleles were detected in serial samples as well as in paired samples of blood and saliva from the same individuals, except for one case. In contrast, the distribution of gB alleles differed according to the geographical origin of the human samples: C was the most frequent allele in both African and Caribbean samples, whereas F was the most frequent allele in European ones. Although none of the allele-specific nucleotide changes induced any modification at the protein level, the definition of gB alleles provided convenient viral markers for the study of both HHV-7 infections and human population genetics.

Epstein-Barr virus strain characterization

The Epstein-Barr virus (EBV), a ubiquitous human herpesvirus originally described in cultured lymphoblasts from African Burkitt's lymphoma, is the causative agent of infectious mononucleosis, but appears to be involved in the pathogenesis of a variety of diseases. EBV has the ability to establish lifelong persistent infection, where only a restricted pattern of the viral proteins is expressed. Periodic reactivation of EBV occurs, where mature EBV particles are produced. Strain variation is potentially important in the biology and epidemiology of EBV, and in attempts to relate EBV to associated diseases. Analysis of the EBV genomes isolated from patients with EBV-associated diseases and from various parts of the world has so far failed to identify conclusive disease-specific viral subtypes. This review focuses on the different strategies which have been used for strain characterization or subtyping of EBV.