Human herpesvirus-6: clinical implications of a recently discovered, ubiquitous agent

HHV-6 and seizure: A systematic review and meta-analysis

Human herpesvirus-6 (HHV-6) is a common infection in childhood. This systematic review aims to assess the relationship between HHV-6 infection and seizure disorders based on available literature. MEDLINE database was searched using a search strategy. We included studies that were published after 1993 in English, and described patients with HHV-6 infection and accompanying seizure or status epilepticus. We identified 503 articles, and included 147 studies. Meta-analysis results showed a 0.21 detection rate of HHV-6 in febrile seizure patients. In the febrile seizure group (110 cases), 76 patients had simple and 34 had complex febrile seizures. Patients with "HHV-6 infection and status epilepticus" had a mean age of 16.24 months. In children with febrile illnesses, a higher index of clinical suspicion for HHV-6 infection may be required. Further studies including CSF and brain tissue may be needed to validate relationships between HHV6 infection and epilepsy. J. Med. Virol. 89:161-169, 2017. © 2016 Wiley Periodicals, Inc.

HHV-6 encephalitis in umbilical cord blood transplantation: a systematic review and meta-analysis

Reactivation of human herpesvirus-6 (HHV-6) frequently occurs following hematopoietic SCT (HSCT), and has been associated with clinical consequences in many patient populations. HHV-6 reactivation and HHV-6 encephalitis seem to occur more frequently in patients undergoing HSCT with cord blood (CB) as the stem cell source. We have conducted a systematic literature review and meta-analysis to investigate the clinical significance of this correlation. A systematic review of publications indexed in PubMed was performed for HSCT studies published over the past 10 years that fit inclusion criteria. Data on prevalences of HHV-6 reactivation and HHV-6 encephalitis post HSCT were abstracted from 19 papers. Meta-analyses were conducted to calculate combined prevalence estimates. The prevalences of HHV-6 reactivation and encephalitis were compared among CB vs non-CB HSCT. Prevalences of HHV-6 reactivation and HHV-6 encephalitis were significantly higher in patients receiving CB as the stem cell source than in patients receiving another stem cell source (72.0% vs 37.4%, P<0.0001; 8.3% vs 0.50%, P<0.0001, respectively). HHV-6 reactivation and HHV-6 encephalitis are significant complications in the post-HSCT setting, particularly in patients receiving CB as the stem cell source. Thus, patients undergoing umbilical CB transplantation should be closely monitored for HHV-6 reactivation.

Seroprevalence of 13 common pathogens in a rapidly growing U.S. minority population: Mexican Americans from San Antonio, TX

Background

Infection risks vary among individuals and between populations. Here we present information on the seroprevalence of 13 common infectious agents in a San Antonio-based sample of Mexican Americans. Mexican Americans represent the largest and most rapidly growing minority population in the U.S., and they are also considered a health disparities population.

Methods

We analyzed 1227 individuals for antibody titer to Chlamydophila pneumoniae, Helicobacter pylori, Toxoplasma gondii, cytomegalovirus, Epstein-Barr virus, herpes simplex virus-1, herpes simplex virus-2 (HSV-2), human herpesvirus-6 (HHV-6), varicella zoster virus (VZV), adenovirus-36, hepatitis A virus, and influenza A and B. Seroprevalence was examined as a function of sex, age, household income, and education.

Results

Seroprevalence estimates ranged from 9% for T. gondii to 92% for VZV, and were similar in both sexes except for HSV-2, which was more prevalent in women. Many pathogens exhibited a significant seroprevalence change over the examined age range (15-94 years), with 7 pathogens increasing and HHV-6 decreasing with age. Socioeconomic status significantly correlated with serostatus for some pathogens.

Conclusions

Our findings demonstrate substantial seroprevalence rates of these common infections in this sample of Mexican Americans from San Antonio, Texas that suffers from high rates of chronic diseases including obesity and type-2 diabetes.

Herpes viruses in transplant recipients: HSV, VZV, human herpes viruses, and EBV

The herpes viruses are responsible for a wide range of diseases in patients following transplant, resulting from direct viral effects and indirect effects, including tumor promotion. Effective treatments and prophylaxis exist for the neurotropic herpes viruses HSV-1, HSV-2, varicella zoster virus, and possibly HHV-6. Antivirals seem to be less effective at prevention of the tumor-promoting effects of Epstein-Barr virus and HHV-8. Reduction in immunosuppression is the cornerstone to treatment of many diseases associated with herpes virus infections.

Human herpesvirus 6 infection and transient acquired myelodysplasia in children

BACKGROUND

To demonstrate that primary human herpesvirus 6 (HHV-6) infection in childhood can cause hematopoietic dysplasia that mimics a myelodysplastic syndrome (MDS) in severe cases.

PROCEDURE

Seven immunocompetent children, who presented at admission with concomitant cytopenias in blood and morphologic features of dysplasia in bone marrow, were evaluated. Diagnosis of acute HHV-6 infection was secondary made by detection of HHV-6 DNA in plasma, bone marrow, or cerebrospinal fluid and measurement of plasma antibody titers. Peripheral blood and bone marrow aspirate smears were examined at diagnosis and during follow-up. Morphologic recognition of myelodysplasia was made according to the recommendations of the Third MIC Cooperative Group.

RESULTS

Anemia was the most frequent cytopenia (five of seven cases). Bi- or tri-lineage dysplasia was observed in the marrow samples. Granulocytic and erythroid cells were always affected with dysgranulopoiesis and dyserythropoiesis scores equal to or higher than 3. Myelodysplasia was not due to a clonal disorder and disappeared gradually within 1 or 2 months.

CONCLUSIONS

Our results indicate that severe HHV-6 infection may induce reversible myelodysplastic changes. These findings contribute to elucidate the pathogenicity of HHV-6 and furthermore suggest that HHV-6 infection must also be considered as a cause of dysplasia in the differential diagnosis of MDS.

Transient erythroblastopenia of childhood: prospective study of 10 patients with special reference to viral infections

PURPOSE

It has been proposed that human parvovirus B19 or human herpesvirus 6 (HHV-6) causes transient erythroblastopenia of childhood (TEC). This study was performed prospectively and accurately in a sufficiently large population to confirm or reject these suggestions, or possibly to find another causative agent for TEC.

PATIENTS AND METHODS

The authors studied prospectively the causative aspects of 10 consecutive children with TEC presenting at five Swedish pediatric clinics from 1994 to 1998 using serologic assays and polymerase chain reaction assays for B19, HHV-6, cytomegalovirus, and Epstein-Barr virus (EBV). The authors also performed isolation investigations of virus from bone marrow, stools, and aspirate from the nasopharynx.

RESULTS

The authors found acute EBV infection in one child. There were no other instances of IgM positivity for any viruses at presentation, but a few children did show IgG positivity to HHV-6 (n = 2), EBV (n = 1), and cytomegalovirus (n = 1). No children were positive with respect to IgG for B19. However, it could not be determined when these children had been infected, and thus, a connection to TEC cannot be proved or excluded. No child showed B19 or HHV-6 DNA in serum or bone marrow collected at presentation. Isolation of virus from bone marrow, stools, and aspirate from nasopharynx culture was negative in all children but one, who had rotavirus in stool.

CONCLUSIONS

HHV-6, B19, EBV, and cytomegalovirus are not common causative agents of TEC. The authors found no proof of any single agent causing TEC.

Human herpesviruses and neurological disorders of childhood

The human herpesviruses, a group of DNA viruses that includes herpes simplex viruses types 1 and 2, varicella zoster virus, cytomegalovirus, Epstein-Barr virus, and human herpes viruses types 6, 7, and 8, cause substantial neurological morbidity among infants and children. This review describes the biology of these viruses and summarizes the clinical manifestations and therapy of the diseases that result from childhood infection with these important pathogens.

Serological association of measles virus and human herpesvirus-6 with brain autoantibodies in autism

Considering an autoimmunity and autism connection, brain autoantibodies to myelin basic protein (anti-MBP) and neuron-axon filament protein (anti-NAFP) have been found in autistic children. In this current study, we examined associations between virus serology and autoantibody by simultaneous analysis of measles virus antibody (measles-IgG), human herpesvirus-6 antibody (HHV-6-IgG), anti-MBP, and anti-NAFP. We found that measles-IgG and HHV-6-IgG titers were moderately higher in autistic children but they did not significantly differ from normal controls. Moreover, we found that a vast majority of virus serology-positive autistic sera was also positive for brain autoantibody: (i) 90% of measles-IgG-positive autistic sera was also positive for anti-MBP; (ii) 73% of measles-IgG-positive autistic sera was also positive for anti-NAFP; (iii) 84% of HHV-6-IgG-positive autistic sera was also positive for anti-MBP; and (iv) 72% of HHV-6-IgG-positive autistic sera was also positive for anti-NAFP. This study is the first to report an association between virus serology and brain autoantibody in autism; it supports the hypothesis that a virus-induced autoimmune response may play a causal role in autism.

Prevalence of human herpesvirus 6 antibody in the population of Belém, Pará, northern Brazil

A total of 497 serum samples obtained from residents of 2 neighbourhoods (Terra-Firme and Guamá) in Belém, Pará, Brazil was tested for the presence of antibody to human herpesvirus 6 (HHV6), using an indirect immunofluorescence assay. The overall seroprevalence was 90%, with seropositivity rates ranging from 75% to 100% in the different age groups and sexes. There was a significant difference between the antibody prevalences in Terra-Firme and Guamá, 94% and 87%, respectively (P = 0.01). The geometric mean titres (GMT) of antibody to HHV6 declined from the first (< or = 2 years) to the sixth (31-40 years) age groups, and slightly increased (GMT > 50) among individuals older than 40 years.

Human herpesvirus-6 (HHV-6)-associated hemophagocytic syndrome

Virus-associated hemophagocytic syndrome (VAHS) is characterized by histiocytic proliferation and phagocytosis triggered by virus infections. Viruses in the herpes group, especially the Epstein-Barr virus (EBV), are well known to cause VAHS; however, the relationship between this syndrome and human herpesvirus-6 (HHV-6) infection has rarely been reported. In this study, we describe a 23-month-old girl who exhibited typical manifestations of VAHS associated with HHV-6 infection. To the best of our knowledge, this case is the fifth reported case in the English literature.

Human herpesvirus-6 infections

HHV-6 is ubiquitous in the community, appears to be acquired early in life, and has been proved to cause the clinical syndrome of exanthem subitum, and rarely to cause encephalitis. Like other herpesviruses, HHV-6 is capable of establishing latent infection and reactivating under a variety of stimuli. Improved diagnostic techniques have led to increased recognition of HHV-6 in the presence of many diseases, but much of the evidence for an aetiological role is inconclusive. There is accruing evidence for possible pathological roles in the immunocompromised host, but the evidence is less convincing for the range of associations otherwise listed for the normal host at the present time.

Association of human herpesvirus 6 infection with exanthem subitum in Belem, Brazil

Recent human herpesvirus 6 (HHV-6) infection was detected in cases of exanthem subitum (ES) involving four children, aged 10 to 24 months, between April and August 1994, in Belém, Brazil. By using the indirect immunofluorescence antibody assay (IFA), significant increases (at least eight times) in antibody concentrations were noted from the acute to the convalescent serum samples, with titers ranging from < 1:10/1:80 to < 1:10/1:640 (patients 3 and 2, respectively). All children had high fever (over 39 degrees C) for three days, followed by generalized, maculo-papular skin rash. A physical examination of the children also revealed concomitant, cervical lymph node swelling and tonsillar pharyngitis in two of them.

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.

Herpesviruses in chronic encephalitis associated with intractable childhood epilepsy

Herpesviruses (especially cytomegalovirus [CMV] and Epstein-Barr virus [EBV]) have been implicated in the pathogenesis of chronic (Rasmussen) encephalitis associated with epilepsy. To assess the presence of herpesvirus genes in brain tissue from epileptic children with chronic (usually Rasmussen type) encephalitis, DNA was extracted from surgically resected brain tissue and studied by the polymerase chain reaction using primers specific for CMV, varicella zoster virus, herpes simplex virus, EBV, and human herpesvirus 6 genes. By this technique evidence for the presence of low levels of CMV and EBV genes was detected in most brain specimens from encephalitis patients and in several brain specimens from patients without encephalitis (eg, cortical dysplasia, gliosis, or encephalomalacia) who also had intractable epilepsy. Occasionally, both EBV and CMV genes were found in the same brain. Signal strength for both CMV and EBV was much lower in epileptic brains than in the brains of acquired immunodeficiency syndrome patients with CMV encephalitis or brain lymphoma. We found evidence for infection of the brain by human herpesvirus 6 in only one patient with encephalitis. Polymerase chain reaction technology applied to resected brain tissue from epileptic patients may provide evidence for or against viral-mediated pathogenesis of Rasmussen encephalitis or other types of encephalitis. The small amounts of EBV and CMV genes found suggest that herpesvirus infection of the brain does not directly cause Rasmussen encephalitis.