Focal perivascular alterations of white matter in herpes simplex encephalitis--a histological and immunocytochemical study

Several cases of human herpes simplex encephalitis treated with Vidarabin have been investigated with the histological and immunocytochemical techniques. Cases with a subacute evolution revealed areas of focal perivascular myelin destruction in the white matter. The distribution of herpes simplex antigen did not show any preferential localization of the virus in perivascular oligoglial cells. In contrast, a spatial and temporal relationship has been found between the appearance of immunoglobulin-bearing cells around the vessels and that of areas of focal perivascular myelin damage. Therefore, it is postulated that the areas of focal destruction of myelin are not related to the cytotoxic effect of the virus but are rather dependent on the immune response of the host.     

Early loss of astrocytes in herpes simplex virus-induced central nervous system demyelination

Immunohistochemistry was used to study herpes simplex virus type 1-induced central nervous system demyelination in the trigeminal root entry zone of mice inoculated with herpes simplex virus type 1 by the corneal route. There was no change in peripheral nervous system myelin as shown by immunostaining for P0 glycoprotein. Double immunoperoxidase staining for herpes simplex virus type 1 antigens and glial fibrillary acidic protein showed that most of the infected cells were astrocytes. Glial fibrillary acidic protein immunostaining was completely lost in the inferior medial portion of the trigeminal root entry zone at 6 days after herpes simplex virus type 1 inoculation, a time when central nervous system myelin was preserved as indicated by immunostaining for myelin basic protein. The pattern of glial fibrillary acidic protein staining did not change and herpes simplex virus type 1 antigens were no longer detected after day 8. There was a progressive loss of myelin basic protein staining within the area unstained by glial fibrillary acidic protein antisera on days 8 to 14. This pattern of astrocyte loss before central nervous system demyelination is strikingly different from the reactive astrocytosis seen in other demyelinating lesions, such as acute experimental allergic encephalomyelitis, progressive multifocal leukoencephalopathy, or acute multiple sclerosis. Herpes simplex virus type 1 infection in mice provides an unusual model of acute central nervous system demyelination preceded by a loss of astrocytes.     

Autopsy neuropathological findings in ''burnt out'' herpes simplex encephalitis and use of the polymerase chain reaction to detect viral DNA

We have conducted an autopsy study of the brains of three patients with 'burnt out' temporal and frontal lobe encephalitis, thought to be due to previous herpes simplex virus infection. The brains showed marked atrophy and yellow-brown discolouration predominantly involving the anterior part of both temporal lobes. Histology revealed destruction of grey and white matter, perivascular and leptomeningeal aggregates of lymphocytes and macrophages, and severe gliosis. Immunohistochemistry for herpesvirus antigens was negative but, by use of the polymerase chain reaction, a segment of the thymidine kinase gene of herpes simplex virus type 1 was detected in sections of temporal lobe from all three brains. These findings support the hypothesis that herpes simplex virus may persist within the central nervous system after acute herpes encephalitis, to cause latent or low-grade productive infection.     

Double encephalitis with herpes simplex virus and cytomegalovirus in an adult

A 51-year-old housewife developed symptoms of a cold followed by high fever, delirium, coma, rigidity of extremity muscles, positive Babinski sign and generalized convulsions, while complement-fixing antibody titre to herpes simplex virus in the sera raised over 128 X and declined to 8 X in the course. She finally expired of bronchopneumonia following status epilepticus after 94 days of illness. Severe necrosis with extensive hemorrhage in the white matter was predominant in the temporal, insular and orbitofrontal cortex, thalamus and globus pallidus. Focal rarefaction of the cerebral cortex with a very few eosinophilic intranuclear inclusions in the oligodendroglia and nerve cells, nerve cell destruction in the substantia nigra with glial nodules and perivascular inflammatory cell cuffs were observed. Abundant cytomegalic inclusion cells, originating from hypertrophic astrocytes, were present in the necrotic areas of cerebrum as well as in the rarefied tissue in the subependymal layers of the brainstem and cerebellum. Electron-microscopic study of the cytomegalic cells demonstrated the presence of numerous virions in both nucleus and cytoplasm. Fortuitour infection of the brain by cytomegalovirus with necrotizing encephalitis by herpes simplex virus is unique. The cause of double viral infections and severe lesions by less virulent strains is discussed.     

Peripheral nervous system demyelination with herpes simplex virus

Inoculation of the cornea or footpad with herpes simplex virus Type I (HSV) has been shown to produce subsequent encephalitis or myelitis respectively. Although Schwann cells become infected, there is no destruction or demyelination in the peripheral nervous system (PNS). Demyelination only occurs in the central nervous system. Previous studies have shown that the Schwann cells infected with HSV do not produce enveloped viral particles. The studies presented here demonstrate that microinjection of HSV into the sciatic nerve of mice causes focal mononuclear cell infiltration and demyelination seven days after injection. The Schwann cells in this model produced enveloped virus. These studies demonstrate that when HSV is introduced into the extracellular space of the PNS, demyelination occurs.     

Infiltration of immune T cells in the brain of mice with herpes simplex virus-induced encephalitis

Herpes simplex virus (HSV) infection of mice can induce viral encephalitis. Using two-fluorochrome immunofluorescence, our present study shows that though there is extensive myelin loss and necrosis in the brain stem of mice with HSV encephalitis, only some oligodendrocytes, astrocytes and microglial cells are infected. T cells that express CD4 or CD8 and a large number of CD4+, F4/80+ macrophages are present in perivascular infiltrates close to and in contact with HSV-infected cells in areas of massive myelin loss. These findings suggest that the resultant infiltration of immune cells into the brain during HSV-1 infection may cause as much damage as the virus itself.     

A CLINICO–PATHOLOGICAL STUDY OF HERPES SIMPLEX ENCEPHALITIS

A retrospective clinical and pathological analysis has been performed of 24 cases of herpes simplex virus encephalitis (HSE) seen at the Institute of Neurological Sciences, Glasgow, between 1972 and 1985. All patients had been diagnosed on the basis of isolation of herpes simplex virus (HSV) from, and/or the demonstration of characteristic histological changes of acute necrotizing encephalitis (ANE) in brain biopsy and/or autopsy tissue. Clinical presentation on admission included a prodromal influenza-like illness (46%), sudden onset of headache and confusion (54%), meningism (38%), deep coma (42%), aphasia (54%) and focal neurological signs (79%). Seizures occurred in 46% of cases during the course of the illness. Of the 24 cases, 14 (58%) died and 10 (42%) survived. Intravenous acyclovir treatment was associated with the best prognosis. Cerebral biopsy of one temporal lobe was performed in 22 cases and in 19 of these a positive histological diagnosis of HSE could be made. HSV was isolated from 15 of the 19 (79%) biopsied cases in whom virus isolation was attempted. Only seven out of the 15 cases (47%) in which immunofluorescence assays for HSV antigens were performed were unequivocally positive. Herpes simplex virus was isolated in culture from all cases which were negative by immunofluorescence. Immunocytochemical analysis on tissue sections of five representative brain biopsies demonstrated the presence of HSV antigens in some astrocytes, neurons and macrophages especially within areas of inflammatory infiltration. In situ hybridization experiments with a cloned HSV DNA probe demonstrated viral RNA in astrocytes, neurons and macrophages in two human biopsies and mouse brains in areas broadly corresponding to the distribution of viral antigen labelling. The combined immunocytochemical and in situ hybridization procedure showed that many but not all of the cells containing viral RNA also contained HSV antigens, indicating a productive infection in these double-labelled cells.     

Relapse of herpes simplex encephalitis

This report describes a child with herpes simplex virus (HSV) encephalitis who improved dramatically while being treated with acyclovir but subsequently had neurological deterioration and died. A severe necrotizing process was present in the brain at autopsy but there were no focal areas of demyelination and poor inflammatory response. HSV was not cultured from brain biopsy during relapse or autopsy. Fourteen previous cases of relapsing herpes encephalitis are reviewed and treatment regime and mechanisms of relapse are discussed.     

Herpes simplex virus types 1 and 2 in organotypic cultures of mouse central and peripheral nervous system. I. Light microscopic observations of myelin degeneration.

Mature mouse spinal cord-ganglion cultures, which contain both peripheral and central nervous system as one unit, were infected with herpes simplex virus type 1 (HSV 1) or type 2 (HSV 2) and observed by bright field microscopy for up to 72 hours. There was degeneration of both central and peripheral myelin in cultures infected with either virus, but the pattern of peripheral myelin degeneration associated with HSV 1-infected cultures was differrnt from that in HSV 2-infected cultures. Type 1 was charcterized by focal dilatations; type 2 by "sausage-shaped" swellings, and the cytopathic effect of HSV 2 both began (6 hours p.i.) and was completed (36 hours p.i.) earlier than in cultures infected with HSV 1 (12 hours and 48 hours p.i. respectively). In central nervous tissue, the apperance of degenerating myelin after infection with HSV 1 was indistinguishable from that in HSV 2-infected cultures, but the rate of myelin loss was greater in cultures infected with the type 2 virus. Evidence is presented which suggests that, at least in the peripheral nervous system,myelin degeneration did not appear to be dependent on neuronal or axonal dysfunction or death, but was a direct result of virus infection.     

Herpes simplex virus latency in the nervous system – a new model

Permissive herpes simplex virus (HSV) infection in tissue culture results in host cell destruction. Latent HSV infection in vivo occurs in neurons of peripheral sensory ganglia (PSG) and it therefore can not take place in neurons in which the virus has completed a lytic replication cycle similar to that present in vitro. Our hypothesis, based on experimental data and observations in humans, suggests that establishment of latent infection and reactivation of HSV-1 does not involve neuronal cell loss. Latency is established in neurons in which the virus does not replicate and is determined, in part, by the tissue levels of a herpes transactivating protein (Vmw65) that is a component of the viral tegument. We also suggest that reactivation of latent infection does not involve destruction of neurons and is due to replication of virus at the peripheral mucocutaneous tissues to where virus or viral DNA have been transported from the nervous tissue. Alternatively, reactivation is initiated in the PSG using a replication cycle which does not involve irreversible damage to neurons. This model explains the lack of damage to neurons which continue to serve as permanent reservoirs of latent virus for the entire life of the host.     

Neurovirulence in an experimental focal herpes encephalitis: relationship to observed seizures

An animal model of focal herpes simplex encephalitis was used to study several strains of type-1 herpes simplex virus. Rabbits were inoculated in the olfactory bulb by a standardized technique. Virus strains resulting in mortality of greater than 70% produced seizures of 3 types, and all animals that seized became moribund or died. In contrast, a virus strain resulting in a 20% mortality produced no seizures. Administration of 60 mg phenobarbital intramuscularly daily reduced mortality significantly in animals given the epileptogenic viruses. Cultures from temporal and frontal lobes showed viral growth more frequently than did cultures of other brain areas. Microscopic examination of routine and immunoperoxidase-stained brain sections confirmed the focal nature of the infection. Clinical syndromes such as seizures arising from viral brain disease may influence mortality in animal model systems.     

Herpes simplex encephalitis: an autopsy case with isolation of type 1 herpes simplex virus

Summary An adult case of herpes simplex encephalitis was studied after autopsy. Postmortem examination revealed necrotizing encephalitis associated with Cowdry type A intranuclear inclusion bodies in glial cells. Herper simplex virus type 1 was isolated from the removed brain. Herpes simplex virus antigens were detected diffusely in wide areas of the brain by immunofluorescent test and viral particles characteristic to herpes simplex virus were demonstrated by electron microscopy. There was an apparent discrepancy between severity of histological changes and distribution of virus antigen.     

Atypical herpes type 2 encephalitis associated with normal MRI imaging

We describe a case of chronic atypical herpes simplex type 2 encephalitis in an immunocompromised 68 year old man presenting with headache and cognitive changes without focal neurological or MRI findings. To our knowledge this is the first described case of herpes simplex encephalitis associated with normal MRI brain imaging and non-focal neurological examination. This further expands the range of clinical presentations that may be associated with herpes simplex encephalitis and emphasises the value of PCR for herpes simplex virus in the investigation of encephalitis regardless of imaging findings.     

Viral encephalitis. Experiences with 53 patients in Middle Hessia

Clinical symptoms, course of disease, cerebrospinal fluid (CSF) and cranial CT of 53 patients suffering from acute or subacute encephalitis were evaluated retrospectively. The virus could be identified in 21 (39%) patients. Nine of them had herpes simplex virus-encephalitis. 16 patients, eight with herpes simplex virus-encephalitis, died due to the disease. Complete restitution could be observed in 73% of survivors. Disturbance of consciousness and severe focal neurological deficit worsened prognosis towards letality and functional recovery. Most patients had initially elevated number of cellular elements and/or pathological protein concentration in CSF. CSF protein profile showed disturbance of blood-CSF-barrier function in a great number of patients during the first week of the disease whereas autochthonous production of immunoglobulin G was observed predominantly during the second and third week. Elevated concentration of CSF-lactate was seen in herpes simplex virus-encephalitis and in letal cases. 28 (53%) patients had pathological CT-findings. Generalized brain edema, focal hypodensities, focal and cortical contrast enhancement and hemorrhagic imbibation were observed. With one exception patients with herpes simplex virus-encephalitis had hypodense lesions in the temporal lobe. Besides this CT-findings did not allow conclusions regarding the etiology of encephalitis. Prognosis of encephalitis caused by other than herpes simplex virus was worse in case of pathological CT.     

Intraocular herpes simplex virus injection in neonatal rats induces sympathetic nerve cell destruction: effect of nerve growth factor

The effect of herpes simplex virus (HSV) injection on the sympathetic nerve system of newborn rats was studied at structural, ultrastructural, and immunohistochemical levels. It was found that HSV injected into the anterior eye chamber is retrogradely transported and reaches the nerve cell bodies of the ipsilateral superior cervical ganglion (SCG) after 18-24 hr, causing complete cell destruction within 3-4 days. In subsequent days, nerve cells of the contralateral SCG, spinal sensory ganglia, chromaffin cells and brain cells also become infected and are eventually killed by the virus. Pretreatment with nerve growth factor (NGF) produces an initial protection from viral cell destruction, but does not block the final, lethal effect of the virus. These investigations demonstrate that sympathetic nerve cell destruction can be induced in newborn rodents by HSV, and that NGF treatment renders the cells, for a time-limited period, more resistant to the virus.     

The limbic system and the localisation of herpes simplex encephalitis.

The selective destruction of temporal and frontal lobe structures by herpes simplex encephalitis has been explained as a consequence of the proximity of those regions to the point of entry of the virus in the encephalon, through olfactory pathways or meningeal branches of the trigeminal nerves. An alternative hypothesis is presented: that the encephalitis is due to a special affinity of the herpes simplex Type 1 virus for the limbic cortices, that is, that distinctive neuroanatomical, neurochemical and neuroimmunological properties of those cortices permit the virus to manifest its destructive behaviour, regardless of the route of entry to the CNS, possibly during altered immunological states. The study of the neurochemical and neuroimmunological properties of the limbic cortices may be a useful approach to the enigma of why and when herpes simplex Type 1 causes encephalitis.     

ARREST OF MYELINATION AND DEMYELINATION IN RABBIT RETINA INDUCED BY HERPES SIMPLEX VIRUS INFECTION

Herpes simplex virus was injected into the vitreous of suckling and adult rabbits. In the suckling rabbits the infection caused an arrested myelination of the strip. Further, the infected strips showed degenerative changes with splitting and distension of myelin sheaths which then disintegrated. Ultrastructurally, herpes simplex virus particles were found in both oligodendroglial cells and in astrocytes in the bundles. No increase in intraocular pressure was recorded during the inflammation. The infection spread along optic pathways to the opposite side. Inflammatory cells appeared at the surface and infiltrated the degenerating strip. Especially in the contralateral eye, an extensive inflammatory cell infiltration was seen among bundles of nerve fibres which showed partly well-preserved myelin and partly with signs of demyelination reminiscent of the picture of experimental allergic encephalomyelitis in the epiretinal strip.     

Simultaneous in situ detection of viral antigens and RNA in brain tissues from a patient with herpes simplex encephalitis by immunocytochemistry and in situ hybridization

In order to elucidate the correlation between herpes simplex virus (HSV-1) and the central nervous system tissue, we performed the simultaneous detection of viral antigens and RNA in the brain tissue sections from a patient with herpes simplex virus (HSV) encephalitis using immunocytochemistry and in situ hybridization. In the present study the hybridization protocol reported by Brahic M et al. in 1984 were applied for the simultaneous detection of viral RNA and antigens with a few modification. The sections were first immunocytochemically stained to detect HSV-1 antigens by ABC method, and then hybridized with 3H-labelled HSV-1 cDNA probe for the detection of RNA after the acetylation of slides for the prevention of nonspecific bindings of isotope to slides. In the present study, viral antigens were immunocytochemically stained to brown-colored deposits located in the cytoplasm and nucleus whereas viral RNA were detected as the accumulation of many silver grains over the nuclei or cytoplasm. In this case the light microscopic findings in a part of temporal lobe showed multiple areas of necrosis mainly involving the gray matter and a few inflammatory changes such as perivascular cell cuffings. HSV-1 infected Vero cells as positive control demonstrated both antigens and RNA as shown in Fig.1 a. However, no hybridization signals and color deposits were observed in uninfected Vero cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

THE DEVELOPMENT OF RETINITIS IN MICE WITH NONFATAL HERPES SIMPLEX ENCEPHALITIS

Anderson J.R. & Field H.J. 1982 Neuropathology and Applied Neurobiology 8, 277–287
The development of retinitis in mice with non-fatal herpes simplex encephalitis
A mutant strain of herpes simplex virus, type 1 (HSVl), selected for high resistance to acyclovir (ACV) was inoculated intracerebrally into mice. The mice survived with no obvious neurological signs but developed cataracts within 4–8 weeks of inoculation. Histological examination revealed only a mild encephalitis, but around 7 days after injection a florid, necrotizing, viral retinitis developed. There was almost simultaneous involvement of both eyes. Inflammatory cell infiltration and early myelin degeneration along the course of the optic nerve suggested cell to cell spread of virus to the retinal nerve cell bodies. Although virus could only be recovered from the eye in the early stages of retinitis, destruction of the neural retina was frequently complete and subsequently the optic nerves showed Wallerian type degeneration. Visible cataracts were a late complication, but changes in the lens were initiated during the phase of acute retinitis. This experiment shows that antiviral agents may induce mutant forms which cannot reproduce classical disease, but are capable of permissive infection in unexpected sites. Herpes retinitis is occasionally recognized as a complication of fatal HSV encephalitis in man. Theoretically, more effective treatment of encephalitis with nucleoside analogues, for example with acyclovir, could reveal the development of retinitis in survivors.     

Latent herpes simplex virus trigeminal ganglionic infection in mice and demyelination in the central nervous system.

Mice were inoculated with herpes simplex virus (HSV) type 1 by gently scraping the skin of the nose with a fine needle. About 80% of the animals developed latent inapparent HSV infections in trigeminal ganglia. Virus was demonstrable for at least 6 months post inoculation (p.i.) by cocultivation of ganglionic tissue with GMK cells. Histologically, trigeminal ganglia revealed infiltrations of inflammatory cells even 6 months p.i. In addition, lesions occurred in the brainstem corresponding to the entry of trigeminal roots, trigeminal tracts and nuclei. Inflammatory cell infiltration, disruption of myelin sheaths and macrophages laden with myelin degradation products were observed 7 days p.i. Fourteen to 30 days p.i. electron microscopy demonstrated completely naked axons. In the transitional region of the trigeminal root denuded axons occurred in the central part of the region while the peripheral myelin, bordering the demyelinated central segments, was intact. Small areas of demyelination were still detectable 3 and 6 months p.i. but there were then also signs of remyelination. Possible mechanisms causing the demyelinations are discussed.