Human herpesvirus-6 and -7 infections in children: agents of roseola and other syndromes

Roseola Infantum: An Updated Review

BACKGROUND

Roseola infantum is a common viral disease that occurs during childhood worldwide.

OBJECTIVE

The purpose of this article is to familiarize pediatricians with the clinical manifestations, evaluation, diagnosis, and management of roseola infantum.

METHODS

A search was conducted in April, 2022, in PubMed Clinical Queries using the key terms "roseola infantum" OR "exanthem subitum" OR "sixth disease". The search strategy included all clinical trials, observational studies, and reviews published within the past 10 years. Only papers published in the English literature were included in this review. The information retrieved from the above search was used in the compilation of the present article.

RESULTS

Roseola infantum is a viral illness characterized by high fever that lasts 3 to 4 days, followed by the sudden appearance of rash at defervescence. The disease occurs most frequently in children between 6 months and 2 years of age. Human herpesvirus-6 (HHV-6) is the major cause of roseola infantum, followed by HHV-7. Transmission of the infection most likely results from the asymptomatic shedding of the virus in the saliva of the caregivers or other close contacts. Characteristically, the rash is discrete, rose-pink in color, circular or elliptical, macular or maculopapular, measuring 2 to 3 mm in diameter. The eruption is first seen on the trunk. It then spreads to the neck and proximal extremities. Typically, the rash blanches on pressure and subsides in 2 to 4 days without sequelae. Most children look well otherwise and appear to be happy, active, alert, and playful. The diagnosis is mainly clinical. Febrile seizures occur in 10 to 15 % of children with roseola infantum during the febrile period. In general, serious complications are rare and occur more often in individuals who are immunocompromised. There is no specific treatment. An antipyretic may be used to reduce fever and discomfort.

CONCLUSION

Roseola infantum is generally a benign and self-limited disease. Failure to recognize this condition may result in undue parental fear, unnecessary investigations, delay in treatment for conditions that mimic roseola infantum and complications from roseola infantum, unnecessary treatment of roseola infantum per se, and misuse of healthcare expenditure.

Toll-like receptor-mediated innate immunity against herpesviridae infection: a current perspective on viral infection signaling pathways

Background

In the past decades, researchers have demonstrated the critical role of Toll-like receptors (TLRs) in the innate immune system. They recognize viral components and trigger immune signal cascades to subsequently promote the activation of the immune system.

Main body

Herpesviridae family members trigger TLRs to elicit cytokines in the process of infection to activate antiviral innate immune responses in host cells. This review aims to clarify the role of TLRs in the innate immunity defense against herpesviridae, and systematically describes the processes of TLR actions and herpesviridae recognition as well as the signal transduction pathways involved.

Conclusions

Future studies of the interactions between TLRs and herpesviridae infections, especially the subsequent signaling pathways, will not only contribute to the planning of effective antiviral therapies but also provide new molecular targets for the development of antiviral drugs.

Febrile seizures and primary human herpesvirus 6 infection

Primary human herpesvirus 6 infection is acquired mainly during the first two years of life and is often associated with febrile seizures. The aim of the present study was to investigate in Greece the frequency and clinical characteristics of primary human herpesvirus 6 (HHV-6) infection in hospitalized children with febrile seizures. Children aged from 6 months to 5 years without known neurologic disease were examined for primary HHV-6 infection, by real-time polymerase chain reaction in acute-phase plasma and by indirect immunofluorescent assay for antibody titers in acute and convalescent serum. Of 65 children included in the analysis, 55 experienced the first febrile episode of seizures and 10 the second. Primary HHV-6 infection was verified in 10 of 55 children with a first febrile episode (18%), whereas none of the 10 children with a second episode of seizures had primary HHV-6 infection. Eight children were infected with HHV-6 type B and two with type A. None of the 85 control subjects had primary HHV-6 infection, but 49% had immunoglobulin G antibodies against the virus. These findings suggest that primary HHV-6 infection is frequently associated with febrile seizures in children in this geographic region and should be considered, especially for a first episode of febrile seizures.

Childhood viral exanthems

Many viral infections exhibit cutaneous lesions. Recognition of the exanthems associated with these infections and the broader clinical scenarios in which they occur can lead to more rapid diagnosis and appropriate treatment for affected patients.

Therapy of other viral infections: herpes to hepatitis

Over the past several years, there has been an increase in knowledge pertaining to the diagnosis and management strategies for the herpes family (Types 1-8), the pox viruses, mumps, measles, rubella, and parvovirus B19 as well as the viral etiologies of hepatitis. Various antiviral treatments, such as nucleoside analogs and interferon therapy, have been available to reduce the signs and symptoms of these common viral infections. This article summarizes the preferred treatment strategies to be employed for each of the viruses for reducing severity, duration, recurrences (notably in the herpes family), transmission rates, as well as preventive alternatives. The majority of the therapeutic options attenuate the course of disease. Treatment decisions are driven by knowledge of the natural history and often are tailored to incorporate clinical circumstances for individual patients. Promotion of community awareness and the development of vaccines should be emphasized in the battle against these common viruses, particularly the herpes simplex viruses, the pox viruses, and hepatitis B.

Encephalopathy in pediatric patients after allogeneic hematopoietic stem cell transplantation is associated with a poor prognosis

Encephalopathy is a poorly characterized complication of hematopoietic stem cell transplantation (HSCT). No comprehensive report of encephalopathy exists for children, and the literature contains only a few for adults. We analyzed a large cohort of 405 pediatric patients who underwent allogeneic HSCT during a 10-year period and identified 26 patients (6.4%) who experienced encephalopathy. Identifiable causes of encephalopathy included infection (n=5), single or multiorgan failure (n=4), medication-related complications (n=3), nonconvulsive seizures (n=4), acute disseminated encephalomyelitis (n=2), thrombotic thrombocytopenic purpura (n=2), and stroke (n=1). We were unable to identify the etiology of encephalopathy in five (19%) patients. The prognosis for pediatric patients with encephalopathy was poor: only four (15%) experienced complete neurologic recovery, and 10 (38%) patients experienced partial recovery with residual neurologic deficits. Nine (35%) patients with complete or partial recovery survive long term. A total of 17 patients died; one died of progressive encephalopathy, and 16 died of either relapse of primary disease or toxicity. MRI, CSF analysis including molecular testing for infectious pathogens, and brain biopsy were helpful in obtaining a diagnosis in most of our patients. However, a standardized approach to accurate and timely diagnosis and treatment is needed to improve outcome in these patients.

Human herpesviruses 6 and 7

Human herpesviruses 6 and 7 are newly discovered viruses that belong to the genus Roseolavirus within the subfamily Betaherpesvirinae. These ubiquitous viruses may cause primary or chronic persistent infection or remain in a state of latency for many years, until a decrease in the immunologic state of the host leads to reactivation of infection. Several diseases have been linked with HHV-6 and HHV-7. In the dermatologic arena, a definite association has been proven only for HHV-6 and exanthema subitum (roseola infantum), whereas the role of HHV-7 in the pathogenesis of pityriasis rosea remains a matter of debate.

Influenza encephalopathy associated with infection with human herpesvirus 6 and/or human herpesvirus 7

Influenza-associated encephalopathy is often reported in young Japanese children, but its pathogenesis is unknown. Although influenza virus can be demonstrated by throat culture for patients with encephalopathy, cultures of samples of cerebrospinal fluids (CSF) do not yield the virus. Eight patients with encephalopathy or complicated febrile convulsions had influenza virus infection diagnosed by means of culture, polymerase chain reaction (PCR), or rapid diagnosis using throat swabs. In all 8 cases, the results of PCR testing of CSF specimens for influenza virus were negative. On the other hand, human herpesvirus 6 (HHV-6) DNA was demonstrated in CSF specimens obtained from 2 of 8 patients. In 3 of 8 patients, the presence of human herpesvirus 7 (HHV-7) DNA was demonstrated in CSF specimens. Some cases of influenza-associated encephalopathy reported in Japan may be attributable to a dual infection with influenza virus and HHV-6, -7, or both. Another possibility is that latent HHV-6 or HHV-7 in the brain is reactivated by influenza, causing encephalopathy or febrile convulsions.

Human herpesvirus 7 induces the functional up-regulation of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) coupled to TRAIL-R1 down-modulation in CD4(+) T cells

Human herpesvirus 7 (HHV-7) is endemic in the adult human population. Although HHV-7 preferentially infects activated CD4(+) T lymphocytes, the consequence of T-cell infection for viral pathogenesis and immunity are still largely unknown. HHV-7 infection induces apoptosis mostly in uninfected bystander cells but not in productively infected CD4(+) T cells. To dissect the underlying molecular events, the role of death-inducing ligands belonging to the tumor necrosis factor (TNF) cytokine superfamily was investigated. HHV-7 selectively up-regulated the expression of TNF-related apoptosis-inducing ligand (TRAIL), but not that of CD95 ligand or TNF-alpha in lymphoblastoid (SupT1) or primary activated CD4(+) T cells. Moreover, in a cell-to-cell-contact assay, HHV-7-infected CD4(+) T lymphocytes were cytotoxic for bystander uninfected CD4(+) T cells through the TRAIL pathway. By contrast, HHV-7 infection caused a marked decrease of surface TRAIL-R1, but not of TRAIL-R2, CD95, TNF-R1, or TNF-R2. Of note, the down-regulation of TRAIL-R1 selectively occurred in cells coexpressing HHV-7 antigens that became resistant to TRAIL-mediated cytotoxicity. These findings suggest that the TRAIL-mediated induction of T-cell death may represent an important immune evasion mechanism of HHV-7, helping the virus to persist in the host organism throughout its lifetime.

Emerging viral infections

The past decade has witnessed the emergence of several significant viral pathogens and the further evolution of additional viral pathogens. Transmitted by a variety of differing routes, these organisms have presented substantial intellectual challenges to medicine of the 20th and 21st centuries. As perhaps the benchmark pathogen of the past decade, HIV has provided medicine and society with a most formidable opponent, and one that has yet to be fully conquered. Nonetheless, a variety of additional viral pathogens have also perplexed medicine over the past 10-15 years.