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

Dengue virus infection and neurological manifestations: an update

Dengue virus is a flavivirus transmitted by the mosquitoes, Aedes aegypti and Aedes albopictus. Dengue infection by all four serotypes (DEN 1 to 4) is endemic globally in regions with tropical and subtropical climates, with an estimated 100-400 million infections annually. Among those hospitalized, the mortality is about 1%. Neurological involvement has been reported to be about 5%. The spectrum of neurological manifestations spans both the peripheral and central nervous systems. These manifestations could possibly be categorized into those directly related to dengue infection, i.e. acute and chronic encephalitis, indirect complications leading to dengue encephalopathy, and post-infectious syndrome due to immune-mediated reactions, and manifestations with uncertain mechanisms, such as acute transverse myelitis, acute cerebellitis and myositis. The rising trend in global dengue incidence calls for attention to a more explicit definition of each neurological manifestation for more accurate epidemiological data. The actual global burden of dengue infection with neurological manifestation is essential for future planning and execution of strategies, especially in the development of effective antivirals and vaccines against the dengue virus. In this article, we discuss the recent findings of different spectrums of neurological manifestations in dengue infection and provide an update on antiviral and vaccine development and their challenges.

Clinical, neuropathological, and immunological short- and long-term feature of a mouse model mimicking human herpes virus encephalitis

Herpes simplex encephalitis (HSE) is one of the most serious diseases of the nervous system in humans. However, its pathogenesis is still only poorly understood. Although several mouse models of predominantly herpes simplex virus 1 (HSV-1) infections mimic different crucial aspects of HSE, central questions remain unanswered. They comprise the specific temporofrontal tropism, viral spread within the central nervous system (CNS), as well as potential molecular and immunological barriers that drive virus into latency while only rarely resulting in severe HSE. We have recently proposed an alternative mouse model by using a pseudorabies virus (PrV) mutant that more faithfully represents the striking features of human HSE: temporofrontal meningoencephalitis with few severely, but generally only moderately to subclinically affected mice as well as characteristic behavioral abnormalities. Here, we characterized this animal model using 6- to 8-week-old female CD-1 mice in more detail. Long-term investigation over 6 months consistently revealed a biphasic course of infection accompanied by recurring clinical signs including behavioral alterations and mainly mild meningoencephalitis restricted to the temporal and frontal lobes. By histopathological and immunological analyses, we followed the kinetics and spatial distribution of inflammatory lesions as well as the underlying cytokine expression in the CNS over 21 days within the acute phase of infection. Affecting the temporal lobes, the inflammatory infiltrate was composed of lymphocytes and macrophages showing a predominantly lymphocytic shift 15 days after infection. A strong increase was observed in cytokines CXCL10, CCL2, CCL5, and CXCL1 recruiting inflammatory cells to the CNS. Unlike the majority of infected mice, strongly affected animals demonstrated extensive temporal lobe edema, which is typically present in severe human HSE cases. In summary, these results support the validity of our animal model for in-depth investigation of HSE pathogenesis.

An improved animal model for herpesvirus encephalitis in humans

Herpesviral encephalitis caused by Herpes Simplex Virus 1 (HSV-1) is one of the most devastating diseases in humans. Patients present with fever, mental status changes or seizures and when untreated, sequelae can be fatal. Herpes Simplex Encephalitis (HSE) is characterized by mainly unilateral necrotizing inflammation effacing the frontal and mesiotemporal lobes with rare involvement of the brainstem. HSV-1 is hypothesized to invade the CNS via the trigeminal or olfactory nerve, but viral tropism and the exact route of infection remain unclear. Several mouse models for HSE have been developed, but they mimic natural infection only inadequately. The porcine alphaherpesvirus Pseudorabies virus (PrV) is closely related to HSV-1 and Varicella Zoster Virus (VZV). While pigs can control productive infection, it is lethal in other susceptible animals associated with severe pruritus leading to automutilation. Here, we describe the first mutant PrV establishing productive infection in mice that the animals are able to control. After intranasal inoculation with a PrV mutant lacking tegument protein pUL21 and pUS3 kinase activity (PrV-ΔUL21/US3Δkin), nearly all mice survived despite extensive infection of the central nervous system. Neuroinvasion mainly occurred along the trigeminal pathway. Whereas trigeminal first and second order neurons and autonomic ganglia were positive early after intranasal infection, PrV-specific antigen was mainly detectable in the frontal, mesiotemporal and parietal lobes at later times, accompanied by a long lasting lymphohistiocytic meningoencephalitis. Despite this extensive infection, mice showed only mild to moderate clinical signs, developed alopecic skin lesions, or remained asymptomatic. Interestingly, most mice exhibited abnormalities in behavior and activity levels including slow movements, akinesia and stargazing. In summary, clinical signs, distribution of viral antigen and inflammatory pattern show striking analogies to human encephalitis caused by HSV-1 or VZV not observed in other animal models of disease.

In developed countries, more than 50% of humans are seropositive for the neurotropic Herpes Simplex Virus 1 (HSV-1) and two to four million cases of Herpes simplex encephalitis (HSE) are reported per year worldwide. Primary infection with HSV-1 takes place via the skin or the oral mucosa followed by intraaxonal retrograde spread to sensory ganglia of the peripheral nervous system where HSV-1 usually establishes latency. Further spread to the central nervous system results in HSE, a necrotizing encephalitis effacing predominantly the temporal and frontal lobes of the brain. Mice infected with HSV-1 develop encephalitis, but do not show the typical lesions and exhibit high mortality rates. Here we demonstrate that mice infected with a mutant pseudorabies virus lacking the tegument protein pUL21 and an active viral kinase pUS3 were able to survive the productive infection but developed lymphohistiocytic encephalitis with viral antigen distribution, inflammation and associated behavioral changes comparable to HSE in humans. These striking analogies offer new perspectives to study herpesviral encephalitis in a suitable animal model.

Epilepsy: Asia versus Africa

Is epilepsy truly an "African ailment"? We aimed to determine this, since international health agencies often refer to epilepsy as an African disease and the scientific literature has spoken the same tone. Various published materials, mainly reports, articles, were used to gather Asian and African evidence on various aspects of epilepsy and many of its risk and associated factors. Our results suggest that in no way can epilepsy be considered as an African ailment and such characterization is most likely based on popular beliefs rather than scientific evidence. In comparison to Africa, Asia has a 5.0% greater burden from all diseases, and is 17.0% more affected from neuropsychiatric disorders (that include epilepsy). Given that more countries in Asia are transitioning, there may be large demographic and lifestyle changes in the near future. However these changes are nowhere close to those expected in Africa. Moreover, 23 million Asians have epilepsy in comparison to 3.3 million Africans and 1.2 million sub-Saharan Africans. In comparison to Africa, Asia has more untreated patients, 55.0% more additional epilepsy cases every year, because of its larger population, with greater treatment cost and possibly higher premature mortality. Of several associated factors discussed herein, many have more importance for Asia than Africa. The current state of epilepsy in Asia is far less than ideal and there is an urgent need to recognize and accept the importance of epilepsy in Asia. In no way can epilepsy be considered as an African ailment. This is most likely based on popular beliefs rather than scientific evidence. A PowerPoint slide summarizing this article is available for download in the Supporting Information section here.

Chronic active herpes simplex type 2 encephalitis in an asymptomatic immunocompetent child

A unique form of chronic, active, granulomatous herpes simplex type 2 encephalitis is described in an asymptomatic, immunocompetent 8-year-old girl who acquired the virus as a neonate. The extensive, bilateral cerebral parenchymal involvement was discovered incidentally. Diagnosis was confirmed by a combination of serial neuroimaging, brain biopsy, and quantitative polymerase chain reaction targeted to DNA sequences in the glycoprotein G gene, allowing differentiation between herpes simplex virus types 1 and 2. The clinical course over a 5-year period, treatment with intermittent intravenous steroids, and daily valacyclovir, diagnostic imaging, and laboratory studies are reviewed in detail. This form of herpes simplex virus type 2 encephalitis hasn't been described previously and is significant because of its prolonged indolent course, absence of neurological findings or suggestive history, and benign behavior in this child, who is now 14 years old. The authors believe this entity can be unsuspected and underdiagnosed in the general pediatric population, especially in those with a prior maternal history of herpes simplex virus type 2 infection.

The spectrum of herpes simplex encephalitis in children

Clinical and basic science research carried out in recent years into herpes simplex encephalitis (HSE) have shown that the concept of a "classical" picture of HSE in children is now outdated and that our current knowledge of the disease is probably only the tip of an iceberg. Indeed, increasing evidence supports the existence of a wider range of pathophysiological mechanisms, clinical presentations and disease progressions in paediatric HSE. This paper reviews the clinical, biological and radiological data available and redefines the spectrum of HSE in children. Full understanding of the condition should improve the management of suspected cases and decrease the morbidity and the mortality associated with this disease.

T-cells in human encephalitis

Encephalitis literally means inflammation of the brain. In general, this inflammation can result from a viral or bacterial infection in the brain itself or alternatively from a secondary autoimmune reaction against an infection or a tumor in the rest of the body. Besides this, encephalitis is present in (believed autoimmune) diseases with unknown etiology, such as multiple sclerosis or Rasmussen encephalitis (RE). This article summarizes the existing data on the role of T-cells in the pathogenesis of three types of human encephalitis: RE, paraneoplastic encephalomyelitis, and virus encephalitis. In all of them, T-cells play a major role in disease pathogenesis, mainly mediated by major histocompatiblity complex class I-restricted CD8⁺ T-lymphocytes.

Acute and long-term alteration of chemokine mRNA expression after anti-viral and anti-inflammatory treatment in herpes simplex virus encephalitis

Mortality and morbidity rates remain high among patients with herpes simplex virus encephalitis (HSVE). Chemokine-mediated recruitment and activation of leukocytes to focal areas of viral CNS infection are crucial steps in antiviral response and clearance. However, the inflammatory reaction and cellular antiviral response may enhance collateral damage to neurons and account for chronic progressive brain damage. We identified a specific mRNA expression of the interferon-gamma-inducible chemokines (CXCL9, CXCL10 and CXCL11), and RANTES (CCL5) in the acute course and long-term of experimental HSVE. This pattern was substantially altered by anti-viral and anti-inflammatory treatment. Our findings indicate a pivotal role of these chemokines in the immunopathogenesis of HSVE.

Chronic Granulomatous Herpes Simplex Encephalitis in Children

Herpes simplex encephalitis is usually a monophasic acute illness but can cause chronic disease, particularly in children. Little information is available as to the histological substrate. We report the findings in 3 children. In 2 children, herpes encephalitis had occurred during the first 2 years, but both later developed intractable epilepsy that led to neurosurgery. The biopsies showed chronic granulomatous inflammation with foci of mineralization. One child made a good post-operative recovery. The other was found post-operatively to have herpes simplex virus type 1 (HSV-1) DNA and elevated titers of HSV IgM antibodies in the CSE He was given acyclovir but after initial improvement developed hemiparesis, with extensive signal change on MRI. Repeat biopsy revealed florid granulomatous inflammation with necrosis. The third patient was an infant who had had a cutaneous facial HSV-2 eruption soon after birth. This was treated with topical acyclovir, after which she remained well until 2 months, when she presented with a relatively non-specific illness, developed blisters of the right hand and foot, and died a few days later. Necropsy revealed severe granulomatous encephalitis, most extensive in the temporal lobe and insula, and associated with mineralization. Our findings indicate that herpes simplex encephalitis in children can be complicated by chronic granulomatous inflammation with mineralization. This pattern of disease may be an under-recognized complication of herpes simplex infection during the first few years of life.

Molecular mimicry in infectious encephalitis and neuritis: binding of antibodies against infectious agents on Western blots of human nervous tissue

OBJECTIVES

To study the occurrence of cross-reactivities of antibodies against infectious agents with human nervous tissue.

METHODS

Binding of 25 antibodies against 17 neurotropic pathogens comprising Borrelia burgdorferi, Toxoplasma gondii, and various DNA and RNA viruses to Western blots of human cortex and myelin from central and peripheral nervous system was investigated.

RESULTS

Fourteen of the 25 antibodies tested showed binding to Western blots of human nervous tissue, suggesting the presence of shared epitopes. Binding of 11 antibodies against 10 pathogens to cortex and/or myelin correlated with the tissue targeted by neuropathological lesions. Three antibodies did not show such correlation; 11 antibodies did not bind at all.

CONCLUSIONS

Our results suggest that shared epitopes between infectious agents and human nervous tissues are more common than previously expected. Thus, molecular mimicry should be considered more frequently as a possible pathogenetic mechanism, among others, inducing tissue damage in encephalitis and neuritis caused by various pathogens.

Immunocytochemical characterization of long-term persistent immune activation in human brain after herpes simplex encephalitis

The clinical, virological and immunocytochemical features of three children who recovered from acute herpes simplex encephalitis (HSE) before the age of 2 years, and who developed secondary severe focal epilepsy after a symptom-free period, leading to neurosurgery 3-10 years later are described. In one child, relapse of HSE occurred immediately after surgery. In all three patients, brain sample biopsies showed abundant CD3-positive T lymphocytes with a majority of CD8 cells, and abundant activated macrophage-microglial cells, a pattern similar to that found in acute HSE. Herpes simplex virus DNA was retrieved from the tissue biopsy in one case. The long-term persistent cerebral inflammatory process observed after HSE differed from that observed in another chronic viral disease, subacute sclerosing panencephalitis. This inflammatory reaction may be a result either of low-grade viral expression or self-induced immune activation. The role of inflammation in triggering epilepsy remains hypothetical. Solving these issues should have major therapeutic implications. Herpes simplex virus DNA latency in brain may be the source of replicative HSE relapse.

Neonatal herpes simplex virus type 1 brain infection affects the development of sensorimotor gating in rats

The effect of neonatal brain infection of herpes simplex virus type 1 (HSV-1) on the development of sensorimotor function in the rat was investigated using an acoustic startle paradigm. Intracerebral inoculation of HSV-1 at day 2 after birth, but not at day 4, caused a significant delay in the development of prepulse inhibition of acoustic startle. A decrease in prepulse inhibition was shown at 37, 46 and 58 days of age in these rats compared to control rats. No evidence was obtained for other behavioural dysfunctions such as differences in sensorimotor reactivity, sensorimotor response habituation, spontaneous locomotor activity, rearing activity or stereotyped behaviour. Prepulse inhibition of acoustic startle is an accepted model of sensorimotor gating in the CNS, a function which has been shown diminished in schizophrenic persons. The present results suggest that early viral infections during a neurone-susceptible period may contribute to the development of this deficit.

Herpes simplex virus type 1 and Alzheimer's disease

Until recently, the only risk factors implicated in noninherited cases of Alzheimer's disease were increasing age, Down's syndrome, and probably, head injury. Having found that herpes simplex type 1 virus (HSV1) is present in the brain of many elderly people, we discovered that it is a risk factor for Alzheimer's disease when in the central nervous system of APOE-epsilon4 allele carriers. On the basis of this result and our finding that apoE-epsilon4 is a risk factor for herpes labialis, we suggested that the combination of virus and genetic factor is particularly damaging in the nervous system. The present review describes 1) the search for HSV1 in human brain; 2) HSV1 infection of the peripheral nervous system; 3) HSV1 infection of the central nervous system; 4) how APOE genotype might influence HSV1 infection; 5) possible APOE genotype effect on viral latency and its reactivation; 6) interactions of viruses with lipoproteins, their components, and lipoprotein receptors; 7) the role of APOE in repair; 8) pathological processes in AD and their relationship to prior damage; and 9) implications for the prevention or treatment of Alzheimer's disease.

Comparative evaluation of colorimetric microtiter plate systems for detection of herpes simplex virus in cerebrospinal fluid

In the past few years, application of the PCR to the detection of herpes simplex virus (HSV) DNA in the cerebrospinal fluid (CSF) from patients with encephalitis and meningitis has become standard laboratory practice. However, from an operational perspective, the true diagnostic value of PCR in this setting is yet to be realized because most laboratories subject the amplification products to lengthy probe hybridization procedures by Southern blotting. As alternatives to Southern blotting, we evaluated colorimetric microtiter plate (MTP) systems from ViroMed Laboratories, Inc. (PrimeCapture), CPG, Inc. (Quanti-PATH), and Incstar Corp. (GEN-ETI-K), in addition to a system developed at the Mayo Clinic with the PCR ELISA system (Boehringer Mannheim Corp.). We tested PCR products from 86 clinical CSF specimens submitted to our Molecular Microbiology Laboratory. The CSF specimens used had to have sufficient volume for comparative analysis. By conventional Southern blotting methods, 54 were positive and 32 were negative for HSV DNA. Compared with Southern blotting, the sensitivity and specificity were 63.0 and 100.0%, respectively, for the PrimeCapture system, 98. 2 and 96.9%, respectively, for the Quanti-PATH system, 98.2 and 100. 0%, respectively, for the GEN-ETI-K system, and 100.0 and 96.9%, respectively, for the Mayo system. All four MTP systems had turnaround times 12 to 24 h less than that for Southern blotting. There were no significant differences in costs or technologist time between the Mayo system and Southern blotting. Other features of the Mayo system include type-specific genotypic identification of HSV and the potential for determination of drug resistance by DNA sequencing. Overall, we found that colorimetric MTP systems were likely to improve test turnaround times and patient care at no additional cost.

In situ polymerase chain reaction demonstration of JC virus in progressive multifocal leukoencephalopathy, including an index case

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease that is caused by JC papovavirus. The virus can be demonstrated in brains with PML using a variety of techniques. In situ polymerase chain reaction (PCR) is a new method that combines the sensitivity of PCR with the histological localization of in situ hybridization. We here show that in situ PCR can detect JC virus in archival tissue sections of 3 cases of PML, including 1 of the original cases described in 1958 and 1 case that was fixed in formalin for 7 weeks. JC virus DNA was amplified directly on tissue and demonstrated in the characteristic enlarged oligodendrocytes and bizarre astrocytes. These data illustrate the utility of the in situ PCR technique in detecting JC virus in archival sections, including those fixed for prolonged periods, and provide a historical footnote to the original report of PML.

Autopsy findings in two cases of neonatal herpes simplex virus infection: detection of virus by immunohistochemistry, in situ hybridization and the polymerase chain reaction

We describe the pathological findings in two fatal cases of neonatal infection with herpes simplex virus. One had an encephalitis caused by herpes simplex virus type 2 (HSV-2); the other had a disseminated infection with herpes simplex virus type 1 (HSV-1). Confirmation of the diagnosis was obtained by use of the polymerase chain reaction to amplify viral DNA from paraffin sections of autopsy tissues. By using primers which amplify fragments of the HSV-1 thymidine kinase gene and HSV-2 glycoprotein gene respectively it was possible to discriminate between infection with HSV-1 and HSV-2. In contrast, immunohistochemistry and in situ hybridization using commercially available reagents did not distinguish between HSV-1 and HSV-2 infection. However, immunohistochemistry and in situ hybridization are probably more reliable than the polymerase chain reaction for assessment of the distribution of virus in different tissues.

In situ polymerase chain reaction: localization of HSV-2 DNA sequences in infections of the nervous system

To detect and localize a herpes simplex virus type 2 (HSV-2) thymidine kinase gene sequence in paraffin sections of brains and trigeminal ganglia of infected mice, an in situ polymerase chain reaction (ISPCR) protocol was developed. Using a single pair of primers, a 110 base pair DNA target sequence, and incorporation of a digoxigenin-labelled nucleotide during amplification, this procedure permitted rapid, specific, reproducible detection of infected cells. During acute brain infection, cells labelled by ISPCR were in the same infected foci that, in adjacent sections, contained viral antigen. This, together with controls, gave evidence of method specificity. In mice surviving acute infection, latently infected cells were labelled by ISPCR. In brains, focal areas contained labelled cell nuclei, and in trigeminal ganglia, neuronal nuclei were likewise labelled. Latent infection was confirmed by several methods, including identification of an HSV-specific sequence in DNA extracts of brains and ganglia, virus isolation from explanted ganglia, and HSV-2 latency-associated transcript (LAT) RNA localization in ganglionic neurons by in situ hybridization. Evidence in brains of ISPCR-labelled cells in regions where HSV-2 LAT-positive cells were not detected, and in ganglia of more ISPCR-labelled neurons than were LAT-positive, indicated that ISPCR is more sensitive in detecting latently infected cells than previous methods.

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.

Distribution of herpes simplex virus DNA in the brains of human long-term survivors of encephalitis

We have examined the distribution of type 1 herpes simplex virus (HSV-1) DNA in the brains of 8 humans surviving for between 4 months and 17 years after acute encephalitis. Histological examination showed neuronal loss and gliosis largely confined to the temporal and frontal lobes, typical of HSV-1 encephalitis. There was a widespread persistent inflammatory infiltrate, present in both the cerebrum and brainstem. Viral DNA was detected in paraffin sections of formalin-fixed paraffin-embedded autopsy brain by use of the polymerase chain reaction to amplify a fragment of the HSV-1 thymidine kinase gene. HSV-1 DNA was amplified from the cerebrum in 6/8 cases and from the brainstem in 4/8 cases. These findings suggest the possibility that HSV-1 may persist within the human central nervous system after acute herpes simplex encephalitis. The distribution of the viral DNA correlates better with that of the persistent inflammatory infiltrate than with the destructive lesions of the acute encephalitis.

Detection of viral DNA in neonatal herpes encephalitis autopsy tissues by solution-phase PCR: comparison with pathology and immunohistochemistry

To detect DNA sequences of herpes simplex virus (HSV) in neural and non-neural tissue sections in disseminated human neonatal HSV infection, a solution polymerase chain reaction (PCR) protocol was developed which amplified HSV thymidine kinase and host genomic DNA sequences that were hybridized with sequence-specific probes in Southern blots. Serial sections of formalin-fixed, paraffin embedded autopsy tissues were tested by PCR and compared to histology and HSV antigen detection. The sensitivity, specificity and reproducibility of this PCR protocol were determined on uninfected and HSV-infected mouse tissues and on HSV DNA from infected tissue culture cells. Samples estimated to contain as few as 60 copies of preserved HSV DNA target sequence gave a positive PCR result. In nine neonates that died during acute HSV infection, all non-neural tissues and a minority of neural tissues with histological lesions had HSV antigen; when DNA could be amplified, HSV DNA sequences were detected by PCR. Together, these findings indicate a direct role for virus in the pathogenesis of these lesions. In the same cases, some or all brain samples were negative for HSV antigen, but nevertheless had HSV DNA sequences detected by PCR. The possible explanations for this finding are discussed. In one neonate dying seven weeks after birth, HSV sequences were found in brain lesions in the absence of HSV antigen; neither HSV DNA nor antigen were found in non-neural tissues, suggesting a latent HSV infection in brain. It is practical to apply PCR methods to detect minute quantities of viral DNA in formalin-fixed, paraffin embedded autopsy tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Sequencing and quantitative assessment of mutant and wild-type mitochondrial DNA in paraffin sections from cases of MELAS

MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes) is a clinically devastating disease of children and young adults. The cause of the stroke-like episodes is not known. We have sequenced the mitochondrial DNA (mtDNA) in archival paraffin-embedded material from two cases. In only one of these did the mitochondrial tRNA(Leu(UUR) gene contain the nucleotide 3243 A-to-G mutation that is most commonly responsible for MELAS. In this case, we determined the relative proportion of mutant:wild-type mtDNA in sections of the central nervous system and other tissues by PCR amplification, PalI digestion, DNA electrophoresis, and scanning densitometry of the ethidium bromide-stained gels. The technique allowed the proportion of mitochondria that contain the mutant genome to be compared with the histological findings in immediately adjacent sections of tissue. The mutant mtDNA was detectable in most tissues, the percentage of mtDNA ranging from barely detectable levels to 78 per cent. The relative amount of mutant mtDNA correlated poorly with the distribution of histological lesions, both within the central nervous system and in other tissues examined. The proportion was high in tissues such as liver, kidney, adrenal, and pancreas that appeared histologically normal. Relatively low levels were present in some regions of the central nervous system, such as the occipital lobe, which contained many of the characteristic infarct-like lesions. These observations do not support previous speculation that the distribution of these lesions reflects that of the defective mitochondria. The results emphasize the usefulness of the polymerase chain reaction in correlative histogenetic studies.

PCR-mediated search for herpes simplex virus DNA in sections of brain from patients with multiple sclerosis and other neurological disorders

Herpes simplex virus (HSV) has been shown to cause central nervous system demyelination in experimental animals and several studies have implicated HSV in the aetiology of multiple sclerosis (MS). We have used the polymerase chain reaction to look for DNA of both type 1 HSV (HSV-1) and type 2 HSV (HSV-2) in formalin-fixed paraffin-embedded brain tissues from patients with MS and other neurological diseases. Primers which amplify a fragment of the normal cellular gene c-myc were included in the reactions to assess the preservation of DNA in the tissue samples. 77 plaques of demyelination from 23 patients with MS were examined. HSV-1 DNA was amplified from only one plaque. This plaque involved the trigeminal root entry zone in the pons and it is suggested that the presence of viral DNA was related to the site examined rather than to the demyelination per se. HSV-2 DNA was amplified from none of the plaques. As expected, HSV-1 DNA was detected in the brains of 6 patients who died of HSV-1 encephalitis and HSV-2 DNA was amplified from the brain of a neonate with congenital HSV-2 infection. In sections of brain from 39 patients with a wide range of other neurological diseases HSV-1 DNA was detected in the pons of only 1 patient, who had AIDS associated with cytomegalovirus ventriculitis; subsequent investigation confirmed the presence of concomitant HSV-1 brain stem infection.(ABSTRACT TRUNCATED AT 250 WORDS)

A prospective study of the polymerase chain reaction for detection of herpes simplex virus in cerebrospinal fluid submitted to the clinical virology laboratory

Polymerase chain reaction (PCR) was prospectively performed with cerebrospinal fluid (CSF) from 51 patients whose CSF was available for analysis and was submitted for viral culture and/or herpes simplex virus (HSV) serology and 20 patients whose CSF was submitted exclusively to the Clinical Biochemistry Laboratory. Primers were used that flanked a 92 bp segment of the HSV DNA polymerase gene (35 cycles). Amplified products were electrophoresed on agarose gel, blotted onto nylon membrane, and probed with a 32P-labelled sequence internal to the primers. For nested PCR, 1 microliter of PCR product was amplified for an additional 35 cycles before electrophoresis and Southern blot analysis. Review of the clinical records revealed that 15 patients had central nervous system (CNS) infections. Specific HSV DNA sequences were detected in CSF specimens of three of the individuals [PCR(2), nested PCR(1)]. Two of these patients had disseminated HSV infection including encephalitis and one patient had aseptic meningitis. The diagnoses of the 12 patients with CNS infection who did not have HSV DNA detected in CSF included encephalitis [varicella-zoster virus (1), cytomegalovirus (1), Mycoplasma pneumoniae (1)], meningitis [Neisseria meningitidis (1), Coccidioides immitis (1), Enterovirus (1), aseptic meningitis (1)], varicella-zoster radiculitis (2), human immunodeficiency virus dementia (2), and transverse myelitis due to Epstein-Barr virus (1). Importantly, HSV DNA was also not detected in the CSF of the 36 patients who did not have CNS infection and 20 samples submitted exclusively to the Clinical Biochemistry Laboratory. Our findings demonstrate the utility of PCR as a rapid, non-invasive method for the routine laboratory diagnosis of CNS infection due to HSV.