Viral encephalitis

Viral Encephalitis in Adults: A Narrative Review

Viral infections of the central nervous system cause frequent hospitalization. The pathogenesis of viral encephalitis involves both the direct action of invading pathogens and the damage generated by the inflammatory reaction they trigger. The type of signs and symptoms presented by the patient depends on the severity and location of the ongoing inflammatory process. Most of the viral encephalitides are characterized by an acute development, fever, variable alterations in consciousness (confusion, lethargy, even coma), seizures (focal and generalized) and focal neurologic signs. The specific diagnosis of encephalitis is usually based on lumbar puncture. Cerebrospinal fluid examination should be performed in all patients unless absolutely contraindicated. Also, electroencephalogram and neuroimaging play a prominent role in diagnosis. Airway protection, ventilatory support, the management of raised intracranial pressure and correction of electrolyte disorders must be immediately considered in a patient with altered mental status. The only therapy strictly recommended is acyclovir in HSV encephalitis. The use of adjunctive glucocorticoids has poor-quality evidence in HSV, EBV, or VZV encephalitis. The role of antiviral therapy in other types of viral encephalitis is not well defined.

Effective Antiviral Medicinal Plants and Biological Compounds Against Central Nervous System Infections: A Mechanistic Review

BACKGROUND AND OBJECTIVE

Infectious diseases are amongst the leading causes of death in the world and central nervous system infections produced by viruses may either be fatal or generate a wide range of symptoms that affect global human health. Most antiviral plants contain active phytoconstituents such as alkaloids, flavonoids, and polyphenols, some of which play an important antiviral role. Herein, we present a background to viral central nervous system (CNS) infections, followed by a review of medicinal plants and bioactive compounds that are effective against viral pathogens in CNS infections.

METHODS

A comprehensive literature search was conducted on scientific databases including: PubMed, Scopus, Google Scholar, and Web of Science. The relevant keywords used as search terms were: "myelitis", "encephalitis", "meningitis", "meningoencephalitis", "encephalomyelitis", "central nervous system", "brain", "spinal cord", "infection", "virus", "medicinal plants", and "biological compounds".

RESULTS

The most significant viruses involved in central nervous system infections are: Herpes Simplex Virus (HSV), Varicella Zoster Virus (VZV), West Nile Virus (WNV), Enterovirus 71 (EV71), Japanese Encephalitis Virus (JEV), and Dengue Virus (DENV). The inhibitory activity of medicinal plants against CNS viruses is mostly active through prevention of viral binding to cell membranes, blocking viral genome replication, prevention of viral protein expression, scavenging reactive Oxygen Species (ROS), and reduction of plaque formation.

CONCLUSION

Due to the increased resistance of microorganisms (bacteria, viruses, and parasites) to antimicrobial therapies, alternative treatments, especially using plant sources and their bioactive constituents, appear to be more fruitful.

Prevalence of herpes simplex virus-1 in hospitalized adult patients with clinical diagnosis of meningoencephalitis using real-time polymerase chain reaction: A single-center, cross-sectional study

Background

Early diagnosis of herpes simplex virus-1 (HSV-1) meningoencephalitis is very important because antiviral therapy significantly decreases mortality and morbidity. Polymerase chain reaction (PCR) is a reliable method with high sensitivity and specificity in detection of HSV-1. The aim of this study is to determine the prevalence of HSV-1 in patients with diagnosis of meningoencephalitis using real-time PCR.

Materials and Methods

The cerebrospinal fluid samples were collected from 126 patients with clinical diagnosis of HSV-1 meningoencephalitis in Alzahra Referral Hospital in Isfahan, Iran. After deoxyribonucleic acid (DNA) extraction, real-time PCR was performed by fluorescence resonance energy transfer assay and participants underwent brain magnetic resonance imaging, as well.

Results

Among 126 patients, 68.3% were male and 31.7% were female. The mean age of the participants was 41.96 ± 22.36 years. Most of the participants were in the age group of 20-29 years. Three patients (2.4%) had positive and 123 patients (97.6%) had negative HSV-1 DNA test. Among three positive cases, two were in the age group of 20-29 years and one in the age group of ≥80 years. No HSV-2 DNA was detected.

Conclusion

According to the estimated prevalence of HSV-1 meningoencephalitis in the current study, it seems that the prevalence of HSV-1 meningoencephalitis is not too high in our community; therefore, initial empiric acyclovir therapy is frequently overused.

Encephalitis

Encephalitis is a serious and potentially treatable infection of the central nervous system. A pathogen is identified in less than 50% of cases. The differential diagnosis includes acute infection, immune-mediated causes, and other central nervous system processes. Emergent investigations include blood work, cerebrospinal fluid analysis, and neuroimaging. Empiric acyclovir and antibiotics should be started immediately to maximize the child's chance of neurologic recovery.

Viral CNS infections: role of glial pattern recognition receptors in neuroinflammation

Viruses are the major causative agents of central nervous system (CNS) infection worldwide. RNA and DNA viruses trigger broad activation of glial cells including microglia and astrocytes, eliciting the release of an array of mediators that can promote innate and adaptive immune responses. Such responses can limit viral replication and dissemination leading to infection resolution. However, a defining feature of viral CNS infection is the rapid onset of severe neuroinflammation and overzealous glial responses are associated with significant neurological damage or even death. The mechanisms by which microglia and astrocytes perceive neurotropic RNA and DNA viruses are only now becoming apparent with the discovery of a variety of cell surface and cytosolic molecules that serve as sensors for viral components. In this review we discuss the role played by members of the Toll-like family of pattern recognition receptors (PRRs) in the inflammatory responses of glial cells to the principle causative agents of viral encephalitis. Importantly, we also describe the evidence for the involvement of a number of newly described intracellular PRRs, including retinoic acid-inducible gene I and DNA-dependent activator of IFN regulatory factors, that are thought to function as intracellular sensors of RNA and DNA viruses, respectively. Finally, we explore the possibility that cross-talk exists between these disparate viral sensors and their signaling pathways, and describe how glial cytosolic and cell surface/endosomal PRRs could act in a cooperative manner to promote the fulminant inflammation associated with acute neurotropic viral infection.

Malingering or expected deficits? A case of herpes simplex encephalitis

This study describes a patient with herpes simplex encephalitis. Brain MRI showed the expected finding of medial temporal damage. Neuropsychological assessment results were consistent with the location of damage, with profound memory impairment and mildly impaired naming, but normal visuospatial and executive skills. The patient also showed a typical testing pattern of insufficient effort and possible malingering, which was concerning as she was seeking disability compensation. In spite of this, we chose to place greatest weight on the finding of deficits consistent with the type, location, and severity of brain damage, considering this to be true cognitive impairment.

The correlation between neurological evaluations and neurological outcome in acute encephalitis: a hospital-based study

Acute encephalitis is a common CNS infectious disease in children. However, there are limited studies concerning about the correlation between the clinical evaluations and neurological outcome. To investigate the value of neurological evaluations, and the correlation between these evaluations and neurological outcomes of acute encephalitis, in the present study we retrospectively evaluated the neurological outcome of 0- to 16-year-old children with encephalitis or meningoencephalitis between 1999 and 2000. Of 101 children enrolled, 4 died and 25 had other neurological sequelae, including epilepsy, headache, developmental delay, and emotional or behavioral changes during the 5 years of follow-up. The causative organisms in patients with neurological sequelae were herpes virus (HSV) 2/2 (100%), influenza 2/3 (67%), mycoplasma 5/12 (42%), and enterovirus 71 2/7 (29%). The important predictors for adverse outcomes were focal neurological signs, multiple seizures or status epilepticus on admission, leukopenia, focal slow waves or continuous generalized delta waves in electroencephalography (EEG), and focal cortical parenchymal hyperintensity in the magnetic resonance imaging (MRI) (p<0.05). Patients with initial presentations of focal neurological signs, papilledema, myoclonic jerks, and status epilepticus tended to have higher incidence of abnormal findings in brain MRI, although not achieving statistic significances. In addition, children with focal spikes or continuous generalized delta waves in EEG also had higher incidence of MRI abnormalities. We conclude that brain MRI studies may be indicated in patients with focal neurological signs, intractable seizure, and focal spikes, focal delta waves, or continuous generalized delta waves in EEG. For those with MRI examinations, focal cortical hyperintensity suggests poorer neurological outcomes.

Spatiotemporal changes of the herpes simplex virus entry receptor nectin-1 in murine brain during postnatal development

Herpes simplex virus (HSV) is known to replicate within the limbic system and to alter behavior in both humans and experimental animals. However, the reason why the virus selectively damages this anatomical, developmental, and functional neural unit remains a mystery. Nor is it known why herpes simplex encephalitis fails to respect these neuroanatomical boundaries in newborns. In the present study, the authors determined the spatiotemporal changes in the distribution of the major neural entry receptor for HSV (nectin-1) in postnatal mouse and rat brains. Discrete nectin-1 immunopositivity was observed in regions susceptible to HSV infection in specific developmental phases of central nervous system. The authors also describe nectin-1-related pathways controlling neuronal cell migration/brain morphogenesis, the disruption of which might lead to the emergence of mental disorders with a rapid cognitive decline.

[18F]FHPG positron emission tomography for detection of herpes simplex virus (HSV) in experimental HSV encephalitis

Herpes simplex virus type 1 (HSV-1) is one of the most common causes of sporadic encephalitis. The initial clinical course of HSV encephalitis (HSE) is highly variable, and the infection may be rapidly fatal. For effective treatment with antiviral medication, an early diagnosis of HSE is crucial. Subtle brain infections with HSV may be causally related to neuropsychiatric disorders such as Alzheimer's dementia. We investigated the feasibility of a noninvasive positron emission tomography (PET) imaging technique using [(18)F]FHPG as a tracer for the detection of HSE. For this purpose, rats received HSV-1 (infected group) or phosphate-buffered saline (control group) by intranasal application, and dynamic PET scans were acquired. In addition, the distribution of tracer accumulation in specific brain areas was studied with phosphor storage imaging. The PET images revealed that the overall brain uptake of [(18)F]FHPG was significantly higher for the infected group than for control animals. Phosphor storage images showed an enhanced accumulation of [(18)F]FHPG in regions known to be affected after intranasal infection with HSV. High-performance liquid chromatography metabolite analysis showed phosphorylated metabolites of [(18)F]FHPG in infected brains, proving that the increased [(18)F]FHPG uptake in infected brains was due to HSV thymidine kinase-mediated trapping. Freeze lesion experiments showed that damage to the blood-brain barrier could in principle induce elevated [(18)F]FHPG uptake, but this nonspecific tracer uptake could easily be discriminated from HSE-derived uptake by differences in the tracer kinetics. Our results show that [(18)F]FHPG PET is a promising tool for the detection of HSV encephalitis.

Molecular methods for diagnosis of viral encephalitis

Hundreds of viruses cause central nervous system (CNS) disease, including meningoencephalitis and postinfectious encephalomyelitis, in humans. The cerebrospinal fluid (CSF) is abnormal in >90% of cases; however, routine CSF studies only rarely lead to identification of a specific etiologic agent. Diagnosis of viral infections of the CNS has been revolutionized by the advent of new molecular diagnostic technologies to amplify viral nucleic acid from CSF, including PCR, nucleic acid sequence-based amplification, and branched-DNA assay. PCR is ideally suited for identifying fastidious organisms that may be difficult or impossible to culture and has been widely applied for detection of both DNA and RNA viruses in CSF. The technique can be performed rapidly and inexpensively and has become an integral component of diagnostic medical practice in the United States and other developed countries. In addition to its use for identification of etiologic agents of CNS disease in the clinical setting, PCR has also been used to quantitate viral load and monitor duration and adequacy of antiviral drug therapy. PCR has also been applied in the research setting to help discriminate active versus postinfectious immune-mediate disease, identify determinants of drug resistance, and investigate the etiology of neurologic disease of uncertain cause. This review discusses general principles of PCR and reverse transcription-PCR, including qualitative, quantitative, and multiplex techniques, with comment on issues of sensitivity, specificity, and positive and negative predictive values. The application of molecular diagnostic methods for diagnosis of specific infectious entities is reviewed in detail, including viruses for which PCR is of proven efficacy and is widely available, viruses for which PCR is less widely available or for which PCR has unproven sensitivity and specificity, and nonviral entities which can mimic viral CNS disease.

Targeting apoptosis in neurological disease using the herpes simplex virus

Herpes Simplex Viruses type 1 (HSV-1) and 2 (HSV-2) cause central nervous system (CNS) disease ranging from benign aseptic meningitis to fatal encephalitis. In adults, CNS infection with HSV-2 is most often associated with aseptic meningitis while HSV-1 frequently produces severe, focal encephalitis associated with high mortality and morbidity. Recent studies suggested that the distinct neurological outcome of CNS infection with the two viruses may be due to their distinct modulation of apoptotic cell death: HSV-1 triggers neuronal apoptosis, while HSV-2 is neuroprotective. Apoptosis also occurs in the etiology of neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease and Down's syndrome, and determines the loss of specific neuronal populations and the decline in cognitive functions. Notwithstanding, the therapy of these disorders may rely on the use of replication-defective HSV-1 vectors to deliver anti-apoptotic transgenes to the CNS. However, the recent discovery of a neuroprotective activity innate to the HSV-2 genome (the ICP10 PK gene) suggests that: i) ICP10 PK may constitute a novel therapeutic approach by targeting both the apoptotic cell death and the cognitive decline, and ii) HSV-2 may be more suitable than HSV-1 as a vector for targeting neuronal disease.

Detection and subtyping of Herpes simplex virus in clinical samples by LightCycler PCR, enzyme immunoassay and cell culture

BACKGROUND

Prompt laboratory diagnosis of Herpes simplex virus (HSV) infection facilitates patient management and possible initiation of antiviral therapy. In our laboratory, which receives various specimen types for detection of HSV, we use enzyme immunoassay (EIA) for rapid detection and culture of this virus. The culture of HSV has traditionally been accepted as the diagnostic 'gold standard'. In this study, we compared the use of real time PCR (LightCycler) for amplification, detection and subtyping of specific DNA with our in-house developed rapid and culture tests for HSV.

RESULTS

The LightCycler PCR (LC-PCR) detected and subtyped HSV in 99% (66/67) of HSV positive specimens, compared to 81% (54/67) by rapid antigen EIA or 57% (36/63) by culture. A specimen was considered positive when two or more tests yielded HSV identifications or was culture positive. Discordant results were confirmed with an in-house developed PCR-ELISA or DNA sequence analysis. The typing results obtained with the LC-PCR and by culture amplified test were completely concordant.

CONCLUSIONS

This study showed that the LC-PCR provided a highly sensitive test for simultaneous detection and subtyping of HSV in a single reaction tube. In addition to increased sensitivity, the LightCycler PCR provided reduced turn-around-times (2 hours) when compared to enzyme immunoassay (4 hours) or culture (4 days).

Intravenous infusion of cereport increases uptake and efficacy of acyclovir in herpes simplex virus-infected rat brains

The outcome of herpes simplex virus (HSV) infections manifesting as encephalitis in healthy or immunocompromised individuals is generally very poor with mortality rates of about 8 to 28% with treatment. The long-term prognosis of survivors is often problematic, posing the need for alternative treatments that may decrease the mortality and morbidity associated with herpes encephalitis. This study addresses one such approach that includes a temporary permeabilization of the blood-brain barrier during treatment with acyclovir (ACV). In these studies we utilized a synthetic bradykinin analog, Cereport (RMP-7), in conjunction with ACV to treat HSV infection of the brain in a rat model. Cereport, infused intravenously via the jugular vein, was shown to increase [(14)C]ACV uptake in both the HSV-1-infected and -uninfected rat brain by approximately two- to threefold, correlating with enhanced efficacy of ACV in various brain compartments. In another series of experiments to determine efficacy, various doses of unlabeled ACV were administered during infusion with RMP-7. The decrease in viral titers in the temporal regions of the brain after 5 days of treatment suggested that this approach enhanced the efficacy of ACV treatment. These data indicated that Cereport infused with ACV enhances both the penetration and efficacy of this drug in the treatment of an experimental HSV-1 infection of the rat brain.