Incidence and pathogenesis of clinical relapse after herpes simplex encephalitis in adults

OBJECTIVES: To study the occurrence of relapse of herpes simplex encephalitis (HSE) and to find out whether soluble activity markers in cerebrospinal fluid (CSF) indicate direct viral or immune- mediated events. METHODS: A consecutive series of 32 adult survivors of HSE were followed to determine the incidence of clinical relapse of HSE. Four patients had neurological deterioration interpreted as relapsing HSE. Four non-relapsing HSE cases were selected as matched controls. Fifty nine batched, paired CSF and serum samples from the eight HSE patients were analysed for soluble activity markers, predominantly cytokines and mediators (interferon-gamma, soluble CD8, tumour necrosis factor-alpha, and interleukin-10), amount of HSV-DNA and markers of glial and neuronal destruction (neurofilament protein, glial fibrillary acidic protein, S-100-beta, and neuron specific enolase). RESULTS: Relapse of HSE was diagnosed in 3 of 26 (12 %) acyclovir-treated patients (5 episodes during 6.1 years of followup) and in 1 of 6 vidarabine-recipients. All relapses occurred from 1 to 4 months after acute HSE, except for a second relapse after 3.3 years in one patient. Computer tomography at relapses revealed few abnormalities apart from those found during the primary disease. Intravenous acyclovir and corticosteroids were given for 7-21 days in all the relapse patients. All relapse patients seemed to recover to the pre-relapse condition. HSV-DNA was demonstrated in CSF in all patients during the acute stage but not in any of 13 CSF samples taken during relapse phases. The HSV viral load during the acute stage of HSE was not higher or of longer duration in the relapsing patients than in the non-relapsing HSE controls. The levels of sCD8 were increased in nearly all CSF samples tested with peaks of sCD8 at one month of acute HSE. In all episodes of relapse, sCD8 peaks were detected during the first week at high levels. CSF levels of neuron-specific enolase, S-100 and glial fibrillary acidic protein were markedly lower at relapse than at the acute stage of HSV-1 encephalitis. CONCLUSION: The lack of demonstrable HSV DNA in CSF, the lack of acute CSF signs and the lack of signs of neural and glia cells destruction indicate that a direct viral cytotoxicity is not the major pathogenic mechanism in relapse. Instead, the pronounced CSF proinflammatory immunological response and the relative lack of CSF anti-inflammatory cytokine IL-10 response suggest immunologically-mediated pathogenicity.     

Serum and cerebrospinal fluid brain damage markers neurofilament light and glial fibrillary acidic protein correlate with tick-borne encephalitis disease severity—a multicentre study on Lithuanian and Swedish patients

Background and purpose

Our aim was to examine the correlation between biomarkers of neuronal and glial cell damage and severity of disease in patients with tick-borne encephalitis.

Methods

One hundred and fifteen patients with tick-borne encephalitis diagnosed in Lithuania and Sweden were prospectively included, and cerebrospinal fluid (CSF) and serum samples were obtained shortly after hospitalization. Using pre-defined criteria, cases were classified as mild, moderate or severe tick-borne encephalitis. Additionally, the presence of spinal nerve paralysis (myelitis) and/or cranial nerve affection were noted. Concentrations of the brain cell biomarkers glial fibrillary acidic protein (GFAP), YKL-40, S100B, neurogranin, neurofilament light (NfL) and tau were analysed in CSF and, in addition, NfL, GFAP and S100B levels were measured in serum. The Jonckheere-Terpstra test was used for group comparisons of continuous variables and Spearman's partial correlation test was used to adjust for age.

Results

Cerebrospinal fluid and serum concentrations of GFAP and NfL correlated with disease severity, independent of age, and with the presence of nerve paralysis. The markers neurogranin, YKL-40, tau and S100B in CSF and S100B in serum were detected, but their concentrations did not correlate with disease severity.

Conclusions

Neuronal cell damage and astroglial cell activation with increased NfL and GFAP in CSF and serum were associated with a more severe disease, independent of age. Increased GFAP and NfL concentrations in CSF and NfL in serum were also indicative of spinal and/or cranial nerve damage. NfL and GFAP are promising prognostic biomarkers in tick-borne encephalitis, and future studies should focus on determining the association between these biomarkers and long-term sequelae.     

Lymphocyte subset numbers in cerebrospinal fluid: comparison of tick-borne encephalitis and neuroborreliosis

OBJECTIVE: The aim of this study was to analyze lymphocyte subset numbers in cerebrospinal fluid (CSF) from patients with tick-borne encephalitis (TBE) and acute neuroborreliosis. METHODS: CSF lymphocyte subsets were enumerated in 42 TBE and nine neuroborreliosis patients using flow cytometry. RESULTS: The CSF numbers of CD4+, CD8+, HLA-DR+ and total-T lymphocytes, B lymphocytes, and NK cells were all greater in neuroborreliosis patients than in TBE patients. Neuroborreliosis patients showed positive correlation of CSF protein levels with the numbers of CD4+, HLA-DR+ and total-T lymphocytes. Also, the numbers of CSF B lymphocytes correlated positively with intrathecal Borrelia burgdorferi-specific IgG antibodies. Conversely, TBE patients demonstrated intrathecal protein levels that correlated positively with all investigated CSF lymphocyte subsets. CONCLUSION: These results suggest an intensive recruitment of lymphocyte subsets into the central nervous system (CNS) during acute neuroborreliosis, whereas TBE is characterized by a lower accumulation of lymphocyte subsets in the CSF.     

Chemokines CXCL10 and CXCL11 in the cerebrospinal fluid of patients with tick-borne encephalitis

OBJECTIVES: The aim of our study was to determine whether cerebrospinal fluid (CSF) of patients with tick-borne encephalitis (TBE) contains CXCL10, CXCL11, p40 subunit of interleukin-12 (IL-12)/IL-23, IL-18 and IL-15. We compared serum and CSF concentrations of CXCL10 and analysed the possible concentration gradient of this chemokine between the periphery and central nervous system. MATERIALS AND METHODS: The study enrolled 19 TBE patients and 10 patients with non-inflammatory neurological diseases. RESULTS: CSF of TBE patients contained CXCL10 (median 217 pg/ml), CXCL11 (8.3 pg/ml), p40 subunit of IL-12/IL-23 (38.9 pg/ml), IL-18 (30.1 pg/ml) and IL-15 (5.9 pg/ml). CXCL10 in the CSF of TBE patients was higher compared with serum (median 62 pg/ml, P < 0.001). CONCLUSION: CSF of TBE patients contains CXCL10, CXCL11, p40 subunit of IL-12/IL-23, IL-18 and IL-15. Increased CXCL10 concentration in CSF suggests a role for this chemokine in the recruitment of CXCR3-expressing T-cells into the CSF of TBE patients.     

Intrathecal immune activation is associated with cerebrospinal fluid markers of neuronal destruction in AIDS patients

We analysed the relationship between cerebrospinal fluid (CSF) concentrations of the light subunit of the neurofilament protein (NFL, a marker of neurons, mainly axons), neopterin (a marker of immune activation), and quantitative HIV RNA levels in 47 patients with HIV-1 infection, 25 of whom had AIDS. In the AIDS patients, the mean levels of CSF NFL were high indicating neuronal destruction. The CSF NFL and the CSF neopterin concentrations were correlated in the subgroup of patients without CNS opportunistic infection (p < 0.05). There was no significant correlation between NFL and HIV RNA levels in CSF. In HIV seropositive patients without AIDS, only 3/22 had CSF NFL concentrations above the upper normal reference value. The results suggest that CNS neuronal destruction occurs frequently in patients with AIDS but rarely in those without AIDS, and that immune activation rather than the HIV viral load is associated with neurochemical signs of axonal destruction.     

Cerebrospinal fluid biomarkers in patients with varicella-zoster virus CNS infections

Varicella-zoster virus (VZV) is one of our most common viruses causing central nervous system (CNS) infection with sometimes severe neurological complications. Glial fibrillary acidic protein (GFAp), light subunit of neurofilament protein (NFL) and S-100β protein are cerebrospinal fluid (CSF) biomarkers that have been used to estimate the severity of brain damage and outcome in various CNS diseases. So far, these biomarkers have not been utilised to investigate glial pathology and neuronal damage in patients with VZV CNS infections. In this prospective study, we measured CSF GFAp, NFL and S-100β as markers of brain damage in 24 patients with acute neurological manifestations and VZV DNA detected in CSF by PCR and compared with a control group (n = 14). Concentrations of CSF NFL and GFAp were increased in patients with VZV CNS infection compared with controls (p = 0.002 and p = 0.03) while levels of S-100β were reduced. In patients with VZV encephalitis the elevations of CSF NFL and GFAp were more pronounced compared with patients with other VZV CNS syndromes. No correlations between the levels of biomarkers and viral load, neurological sequels or clinical outcome were found in this limited number of patients. These results indicate that VZV induces neuronal damage and astrogliosis with more severe brain damage in patients with VZV encephalitis than in patients with other neurological complications caused by this virus.     

Herpes-simplex-related antigen in human demyelinative disease and encephalitis

Summary Using immunohistochemical methods optimized to detect herpes simplex virus type 2 (HSV-2) antigen, paraffin sections from human central nervous system tissues from 31 cases pathologically diagnosed as multiple sclerosis (MS), 34 cases of other neurological diseases, 4 adult cases of HSV encephalitis, and mouse brains infected with various HSV strains were examined. Two distinct patterns of immunoreactivity with HSV antisera were seen. In typical acute human and experimental encephalitis, antigen was readily detected using high dilutions of antisera to both HSV types –1 and –2, and was found nonselectiviely in both neurons and glia. Lesions were destructive, with necrosis of all neural cell types, and inflammation was a mixture of polymorphonuclear and mononuclear cells. By contrast, immunoreactivity in lesions in each of three MS cases and in one case of brain stem encephalitis was found only with HSV-2 antisera, and relatively high antiserum concentrations were required to detect it. Reactivity appeared to be largely restricted to glial cell nuclei within and near lesions that were selectively demyelinated. Only mononuclear inflammation was present. These experiments suggest that HSV-related antigen may be found in a broader spectrum of human CNS lesions than has previously been recognized, and that HSV or a related agent may be associated with a selective infection of glial cells and with CNS demyelination.     

Selective neuronal vulnerability in HIV encephalitis.

Recent studies of human immunodeficiency virus type 1 (HIV-1) encephalitis have shown that in addition to well established white matter damage, the neocortex shows thinning, loss of large neurons and dendritic damage. In order to identify neuronal populations affected in HIV encephalitis and to determine how neuronal damage relates to the severity of HIV infection within the nervous system, we quantified parvalbumin (PV+) and neurofilament (NF+) immunoreactive neurons in the frontal cortex and hippocampus. We found that in the neocortex, the density of NF+ and PV+ neurons was independent of severity of HIV encephalitis, and therefore changes in these neuronal subsets did not account for previously reported neuronal loss. However, neuritic processes of PV+ neurons were fragmented, atrophic and in some cases distended. In contrast to the frontal cortex, there was a trend toward decreased density of PV+ neurons in the hippocampus which only reached significance in the CA3 layer where there was a 50-90% decrease in PV+ neurons. This decrease was closely correlated with the severity of HIV encephalitis. Double-label immunocytochemical analysis confirmed neuritic damage to interneurons. These results suggest that HIV encephalitis differentially involves specific subpopulations of neurons. Since direct HIV infection of neuronal cells was not detected, damage to PV+ cells and fibers may be indirectly mediated by cytokines released by HIV-infected microglia.     

Apoptotic neurons in brains from paediatric patients with HIV-I encephalitis and progressive encephalopathy

The pathogenesis of human immunodeficiency virus type 1 (HIV-1) associated dementia in adults involves neuronal loss from discrete areas of the neocortex and subcortical regions, but the mechanism for neuronal death is poorly understood. Gene-directed cell death resulting in apoptosis is thought to be a normal feature of neuronal development, but little is known about neuronal apoptosis in disease states. We investigated whether HIV-1 infection of the central nervous system is spatially associated with apoptosis of neurons. Using an in situ technique to identify newly cleaved 3'-OH ends of DNA as a marker for apoptosis, we demonstrate the presence of apoptotic neurons in cerebral cortex and basal ganglia of children that had HIV-1 encephalitis with progressive encephalopathy. Furthermore, an association was observed between the localization of apoptotic neurons and perivascular inflammatory cell infiltrates containing HIV-1 infected macrophages and multinucleated giant cells. Apoptotic neurons and p24–positive macrophages were observed infrequently in cerebral cortex and basal ganglia in children with HIV-1 infection without encephalitis or clinical encephalopathy. In nine control (HIV-1 negative) brains, ranging from the first post-natal month of life to 16.5 years of age, infrequent neuronal apoptosis was observed in three cases. These findings suggest that neuronal apoptosis is unlikely to be associated with post-natal development except in early post-natal germinal matrix, and that it may instead represent the end result of specific pathological processes, such as HIV-1 encephalitis.     

Characterisation of a syndrome of autoimmune adult onset focal epilepsy and encephalitis

We report a series of patients with a clinical syndrome characterised by the explosive onset in adulthood of recurrent focal seizures of frontotemporal onset and features suggestive of autoimmune encephalitis. We propose that this presentation of “autoimmune adult onset focal epilepsy and encephalitis” is a recognisable clinical syndrome, and provide evidence it may be associated with heterogeneous immunological targets. Between 2008 and 2011 we encountered six patients with new-onset epilepsy in whom we suspected an autoimmune aetiology. We first characterised the clinical, electroencephalographic, cerebrospinal fluid (CSF), imaging, and pathological findings of this syndrome. We subsequently tested them for antibodies against both intracellular and neuronal cell surface antigens. All patients presented with recurrent seizures with focal frontotemporal onset, refractory to multiple anticonvulsants. Four had focal T2-weighted hyperintensities on MRI. CSF mononuclear cells were variably elevated with positive oligoclonal bands in four. Brain biopsy in one patient demonstrated perivascular lymphocytic infiltration. Two were treated with immunosuppression and went on to achieve complete seizure control and return to baseline cognition. Three of four patients who received only pulsed steroids or no treatment had ongoing frequent seizures, with two dying of sudden unexpected death in epilepsy. Subsequently, three had antibodies identified against neuronal cell surface antigens including N-methyl-d-aspartate receptor and leucine-rich glioma inactivated 1. We suggest that patients with such a presentation should be carefully evaluated for a suspected autoimmune aetiology targeting cell surface antigens and have a therapeutic trial of immunosuppression as this may improve their long-term outcome.     

Flow cytometric analysis of lymphocytes in cerebrospinal fluid in patients with tick-borne encephalitis

Introduction – Cerebrospinal fluid (CSF) lymphocyte subsets were examined by flow cytometry in 33 patients with tick-borne encephalitis (TBE) in order to determine their values. Patients and methods – Lymphocytes were isolated from CSF and lymphocyte subsets were determined: lymphocytes T (CD3+), lymphocytes B (CD19+), NK cells (CD3-CD56+), helper T cells (CD3+CD4+) and cytotoxic T cells (CD3+CD8+). The expression of IL-2 receptors (CD25+) and transferrin receptors (CD71+) on T cells and HLA-DR molecules on T cell subsets was examined. Furthermore, possible relationships among different TBE patient population variables (gender, age, severity of disease, duration of meningitis) were considered. Results – The analyses of the CSF lymphocyte population subsets are presented. Lymphocytes T (CD3+) were significantly higher in the CSF than in the peripheral blood as was the case with the T cells that expressed transferrin receptors (CD71). Lymphocytes B (CD19+) and NK cells (CD3-CD56+) prevailed in the peripheral blood. In the early course of the disease, a higher expression of HLA-DR molecules on T lymphocytes was observed, while later a higher expression of IL-2 receptors (CD25+) was observed. Discussion – Significant differences in lymphocyte subsets between the CSF and the peripheral blood were found. Significant time-dependent changes of CSF lymphocyte subsets during course of infection were observed. The results of the present study give us deeper insight into CNS cellular immunopathogenic mechanisms in patients with TBE.     

Suppression of synaptic plasticity by cerebrospinal fluid from anti-NMDA receptor encephalitis patients

The functional effects of cerebrospinal fluid (CSF) from patients with anti-NMDA receptor (NMDAR) encephalitis on the NMDAR-mediated synaptic plasticity were evaluated by using mouse hippocampus slices. Anti-NMDAR antibody detection system was established by immunostaining recombinant NMDAR heteromers expressed in HEK cell culture as well as native NMDARs in cultured hippocampal neurons. Under a complete blind manner for the clinical information, CSF and sera collected from 36 pre-diagnosed patients were tested for anti-NMDAR antibodies. With this test, thirteen patients were diagnosed as anti-NMDAR encephalitis. CSF positive for anti-NMDAR antibodies suppressed induction of long-term potentiation (LTP) at Schaffer collateral-CA1 synapses in mouse hippocampal slices. LTP induction was not suppressed by CSF collected from herpes simplex virus (HSV) encephalitis or non-encephalitis control patients. Antibody absorption with NMDAR-expressing HEK cell culture reversed the suppression of LTP by anti-NMDAR encephalitis patients' CSF, confirming that anti-NMDAR antibodies suppressed LTP. The present experiments firmly support the proposal that the anti-NMDAR encephalitis autoantibody is responsible for cognitive disorders like amnesia accompanying this disease.     

Damage and repair of DNA in HIV encephalitis

Neuronal damage and dementia are common sequelae of HIV encephalitis. The mechanism by which HIV infection of CNS macrophages results in neuronal damage is not known. We examined the brains from 15 AIDS autopsies (8 with HIV encephalitis and 7 without) and 4 non-infected control autopsies for the presence of DNA strand breaks, for associated changes in the expression of the DNA repair enzymes KU80 and Poly (ADP-ribose) polymerase (PARP), and for accumulation of amyloid precursor protein (APP). Abundant DNA damage was observed with terminal transferase-mediated dUTP nick end-labeling (TUNEL), however, there was no morphologic evidence of significant neuroglial apoptosis. The DNA repair enzyme KU80 was immunocytochemically detectable in neuronal and glial cells in autopsy brains from patients with and without HIV encephalitis; however, in cases with HIV encephalitis the staining was more prominent than in the infected or non-infected controls without encephalitis. There was no difference in KU80 immunostaining in oligodendroglia from autopsies with and without encephalitis. Immunostaining for PARP was more intense in gray and white matter of cases with HIV encephalitis. No clear spatial relationship existed between expression of DNA repair enzymes and the spatial proximity of microglial nodules or HIV-infected macrophages. The cytoplasm of cortical and subcortical neurons immunostained for APP Stronger cortical neuronal APP staining was observed in cases without HIV encephalitis. Staining of deep gray matter neurons was similar, irrespective of the presence or absence of encephalitis. While foci of intense APP staining were noted in white matter not related to HIV infection, they were associated with foci of opportunistic infections (e.g. due to CMV or PML). We conclude that damaged DNA and altered patterns of expression of DNA repair proteins and APP are common findings in the brains of AIDS patients at autopsy, but do not have a spatial relationship to HIV-infected macrophages.     

Tick-borne encephalitis in Sweden in relation to aseptic meningo-encephalitis of other etiology: a prospective study of clinical course and outcome

A total of 149 patients with clinical symptoms of acute viral meningo-encephalitis were enrolled in this study from June 1991 to December 1993. Tick-borne encephalitis (TBE) was diagnosed in 85 of the 149 patients (males 54%, median age 42 years (range 15–78)). The initial clinical appearance of TBE was classified as mild (mainly meningeal; (n = 47), moderate (n = 31) or severe (n = 7), more or less encephalitic. The most common acute symptoms of encephalitis were ataxia (26%), altered consciousness (20%), decreased concentration or memory (9%), irritable response to light and sound (28%), tremor (9%) and dysphasia (9%). Spinal nerve paralysis (11%) occurred in all three clinical stages and did not correlate with the severity or duration of encephalitis. The duration of hospitalisation, the time on the sick-list and the time to recovery were significantly longer in TBE patients. All patients survived, but many patients with TBE suffered an extended period of neurological dysfunction. Of patients with TBE 80% (68/85) showed persisting symptoms of CNS dysfunction on follow-up at week 6, compared with 55% (35/64) of the patients with aseptic meningitis of other aetiology. The corresponding figures after 1 year were 40% (33/83) and 20% (13/ 64). One year after TBE 13 (28%) patients with initially mild, meningeal symptoms had decreased memory and decreased concentration capacity, dysphasia or ataxia. Spinal nerve paralysis persisted after 1 year in 5 of 9 patients with TBE. In conclusion, TBE in Sweden is associated with a significant morbidity and a post-TBE syndrome existed after 1 year in more than one third of the patients. Received: 15 February 1996 Received in revised form: 6 September 1996 Accepted: 22 November 1996     

No evident neuronal damage after electroconvulsive therapy

Electroconvulsive therapy (ECT) is regarded as one of the most effective treatments for major depressive disorder but has also been associated with cognitive deficits possibly reflecting brain damage. The aim of this study was therefore to evaluate whether ECT induces cerebral damage as reflected by different biochemical measures. The concentrations in the cerebrospinal fluid (CSF) of three established markers of neuronal/glial degeneration, tau protein (tau), neurofilament (NFL) and S-100 beta protein, were determined in nine patients who fulfilled DSM-IV criteria for major depression. CSF samples were collected before and after a course of six ECT sessions. The CSF/serum (S) albumin ratio reflecting potential blood-brain barrier (BBB) dysfunction was also determined at these time points. The treatment was clinically successful with a significant decline of depressive symptoms in all patients as assessed by the Montgomery-Asberg Rating Scale for Depression. Several patients had signs of BBB dysfunction and/or neuronal damage before the start of treatment. Levels of CSF-tau, CSF-NFL and CSF-S-100 beta levels were not significantly changed by ECT. Also the CSF/S albumin ratio was found to be unchanged after the course of ECT. In conclusion, no biochemical evidence of neuronal/glial damage or BBB dysfunction could be demonstrated following a therapeutic course of ECT.     

20例抗N-甲基-D-天冬氨酸受体脑炎患者临床特点分析

目的回顾性分析总结20例抗N-甲基-D-天冬氨酸受体(NMDAR)脑炎患者的临床特点,增强对抗NMDAR脑炎的认识。方法对90例临床疑似脑炎患者的血清和脑脊液进行抗NMDAR-IgG检测,分析确诊为抗NMDAR脑炎的20例患者的临床表现、实验室检查、治疗及预后。结果抗NMDAR脑炎患者男女比例为6:14,中位年龄24岁,首发症状及主要精神症状多有不同。20例抗NMDAR脑炎患者中有12例患者血清和脑脊液中抗NMDAR-IgG抗体均阳性,其他8例仅在血清或脑脊液中检测到抗NMDAR-IgG抗体。5例盆腔检查异常,其中1例病理确诊为成熟囊性畸胎瘤。6例患者脑电图异常,7例头颅MRI异常。除1例患者未接受免疫治疗死亡外,其余患者接受免疫治疗后症状均有不同程度的缓解,其中3例未伴畸胎瘤的患者用二线免疫治疗后复检血清和脑脊液中抗NMDAR-IgG抗体水平下降。结论抗NMDAR脑炎患者中年轻女性发病率较高。二线免疫治疗可能对不伴有畸胎瘤患者的疗效更好。CSF中的抗NMDAR-IgG抗体的阳性率高于血清,同时检测血清和脑脊液中抗NMDAR抗体可以提高疾病的诊断效率。     

Serum S-100B protein levels in patients with herpes simplex encephalitis and tick-borne encephalitis — A marker of CNS damage during the initial stage of disease

Background and purpose   This study was mainly aimed at the comparative analysis of serum S-100B protein in patients with herpes simplex encephalitis (HSE) and tick-borne encephalitis (TBE). S-100B protein is an established biochemical marker of astroglial damage in central nervous system (CNS) injury. Methods   Serum levels of S-100B were measured using a commercial immunolumino-metric assay (LIA). Results   Patients with HSE (n = 17) had significantly higher levels of S-100B with median 0.351 μg/l (range 0.017–0.636) compared to patients with TBE (n = 15), who had 0.04 μg/l (range 0.001–0.542) (p < 0.001), as well as controls (n = 17) 0.054 (range 0.004–0.214) (p < 0.001). 11/17 patients with HSE had serum S-100B levels above 0.2 μg/l, in contrast to 1/15 patients with TBE and 1/17 of the control patients. The patients with HSE with serum levels below 0.2 μg/l had a mean 3.2 days disease duration, while patients with levels above 0.2 μg/l had 6 days disease duration. Conclusions   The serum levels of S-100B in the acute stage of disease were significantly higher in patients with HSE than in patients with TBE or controls. A role for the use of serum S-100B in monitoring CNS damage during initial stage of disease in HSE is suggested.     

Tick-borne encephalitis in dogs: neuropathological findings and distribution of antigen

Eight dogs originating from different regions of Austria [all of them known as tick-borne encephalitis (TBE) areas] with severe neurological signs were either euthanatized or died spontaneously. Tick-borne encephalitis virus (TBEV) antigen was detected in the brains of five of these dogs by immunohistology, but not in the others. All of the dogs, however, had identical neuropathological changes. There were moderate lymphohistiocytic meningitis, widespread neuronal necroses, karyorrhexis of glial cells, numerous neuronophagic nodules, and extensive microgliosis. In the cerebellum, loss of Purkinje cells and proliferation of microglial cells in the molecular layer were found. All brain regions showed numerous perivascular cuffs consisting of lymphocytes, macrophages, plasma cells and, occasionally, red blood cells. The blood-derived cells were not restricted to the perivascular spaces but diffusely infiltrated the neuropil. The most severe changes were localized in the neuroparenchyma surrounding the fourth ventricle. Lesions were less severe in basal ganglia, thalamus, mesencephalon, nuclei of pons and medulla oblongata. Moderate lesions were found in the gray matter of neocortex and allocortex, hippocampus and molecular and Purkinje cell layers of the cerebellum. White matter was slightly to moderately affected. The choroid plexus was free of inflammation. Due to rapid virus clearance mechanisms in this disease, antigen was not detectable in all cases. Neuropathological changes identical with those of immunohistologically proven cases justified the diagnosis TBE in these cases. In addition, the neuropathological diagnosis was supported by the origin of the affected dogs from endemic areas, the seasonal occurrence of the disease and a clinical history of a highly febrile neurological disease with short duration. Received: 25 July 1997 / Revised: 16 October 1997 / Accepted: 20 October 1997     

Visualization of Central European tick-borne encephalitis infection in fatal human cases

Central European tick-borne encephalitis (TBE) is caused by a flavivirus vectored by the Ixodes ricinus tick. In severe infections, TBE presents as (myelo)meningoencephalitis with considerable mortality. Characteristic neuropathologic changes feature a multinodular to patchy polioencephalomyelitis accentuated in spinal cord, brainstem, and cerebellum. Visualization of viral infection by immunohistochemistry has not yet been achieved. We analyzed immunohistochemically the distribution of viral antigens and its correlation with neuropathologic changes, serological data, and disease duration in 28 brains of cases with a clinical diagnosis of TBE and neuropathologically confirmed (meningo)encephalomyelitis. In 20 brains (including 10 seropositives), viral antigens were detectable. These cases were characterized by relatively short clinical duration ranging from 4 to 35 days. Immunoreactivity was most prominent in perikarya and processes of Purkinje cells and large neurons of dentate nucleus, inferior olives, and anterior horns. In addition, immunoreactivity was detected in neurons of other brainstem nuclei, isocortex, and basal ganglia. There was an inverse topographical association of severe inflammatory changes with presence of viral antigens. Some cytotoxic T cells were in direct contact with tick-borne encephalitis virus (TBEV)-infected neurons. We conclude that 1) TBE viral antigens are immunohistochemically detectable in brains of fatal cases with relatively short natural clinical course; 2) TBE virus neurotropism preferentially targets large neurons of anterior horns, medulla oblongata, pons, dentate nucleus, Purkinje cells, and striatum; 3) topographical correlation between inflammatory changes and distribution of viral antigens is poor; and 4) immunologic mechanisms may contribute to nerve cell destruction in human TBE.