Ultrastructural studies on the pathogenesis of poliomyelitis in monkeys infected with polivirus

Summary Poliovirus was inoculated intraspinally into cynomolgus monkeys to determine whether nerve cell damage in the central nervous system (CNS) is due primarily to virus multiplication in the neuron or to secondary effects of virus multiplication in the supporting cells. Electron-microscopically, the development of cytopathogenesis and of membrane-bound vesicles and virus particles in the neurons of the CNS in monkeys infected with poliovirus was compared with that of infected cultured cynomolgus monkey kidney (CMK) cells. The structure of membrane-bound vesicles in cytoplasm of damaged motoneuron was examined and found to be similar to the vesicles in infected cultured CMK cells. Virus-like particles were detected occasionally around or within membrane-bound vesicles in the cytoplasm of degenerating motoneurons as well as cultured CMK cells, although intracytoplasmic crystals were not detected in the neuron. No virus particles or membrane-bound vesicles were found in astrocyte foot plates, microglia, oligodendrocytes, axons, vascular endothelial, and inflammatory cells. In addition, poliovirus antigen was detected only in the nerve cells of the CNS by the immunoperoxidase technique, although specific staining was never found in the supporting tissues. From the present results we suggest that membrane-bound vesicles in the cytoplasm of the motoneuron are closely correlated with virus multiplication and that damage of the nerve cell is due to the direct action of the poliovirus.     

Comparative studies on the neurovirulence of temperature-sensitive and temperature-resistant viruses of enterovirus 71 in monkeys

The neurovirulence of strain BrCr of enterovirus 71 (E71) was compared in monkeys between temperature-sensitive (ts) and temperature-resistant (tr) viruses. Comparisons are made relative to clinical disease, pathologic findings, serum neutralizing antibody titers, CNS virus replication as measured by infectivity titrations and immunofluorescence. Clinically, ts virus did not produce a clinical disease. The tr virus, however, produced paralysis. Pathologically, little or no nerve cell damage was found in the CNS of monkeys inoculated with ts virus, although mild to moderate interstitial changes occurred. In monkeys inoculated with tr virus, marked nerve cell damage and inflammatory reaction were found in the CNS. Serum neutralizing antibody titers in monkeys inoculated with ts virus rose on day 25. No virus was detected in the CNS of monkeys inoculated with ts virus, while a high virus titer was detected in the CNS of monkeys inoculated with tr virus. No specific immunofluorescence was detected in the nerve cells of the CNS in monkeys inoculated with ts virus, but specific fluorescence was detected in the nerve cells of the CNS in monkeys inoculated with tr virus. Virus growth in the CNS correlated well with the severity of clinical and pathologic findings, and immunofluorescent studies. The results show that ts virus was much less neurovirulent than tr virus, indicating that ts virus resembles the attenuated poliovirus which could not grow at a higher temperature. It is inferred that the genetic factors which influence the reproductive capacity of E71 at a higher temperature are very closely correlated with the neurovirulence.     

Pathologic characterization of a murine model of human enterovirus 71 encephalomyelitis

We describe a model of Enterovirus 71 encephalomyelitis in 2-week-old mice that shares many features with the human central nervous system (CNS) disease. Mice were infected via oral and parenteral routes with a murine-adapted virus strain originally from a fatal human case. The mice succumbed to infection after 2 to 5 days. Vacuolated and normal-appearing CNS neurons showed viral RNA and antigens and virions by in situ hybridization, immunohistochemistry, and electron microscopy; inflammation was minimal. The most numerous infected neurons were in anterior horns, motor trigeminal nuclei, and brainstem reticular formation; fewer neurons in the red nucleus, lateral cerebellar nucleus, other cranial nerve nuclei, motor cortex, hypothalamus, and thalamus were infected. Other CNS regions, dorsal root, and autonomic ganglia were spared. Intramuscular-inoculated mice killed 24 to 36 hours postinfection had viral RNA and antigens in ipsilateral lumbar anterior horn cells and adjacent axons. Upper cord motor neurons, brainstem, and contralateral motor cortex neurons were infected from 48-72 hours. Viral RNA and antigens were abundant in skeletal muscle and adjacent tissues but not in other organs. The distinct, stereotypic viral distribution in this model suggests that the virus enters the CNS via peripheral motor nerves after skeletal muscle infection, and spread within the CNS involves motor and other neural pathways. This model may be useful for further studies on pathogenesis and for testing therapies.     

PATHOGENICITY OF A POLIOMYELITIS-LIKE DISEASE IN MONKEYS INFECTED ORALLY WITH ENTEROVIRUS 71: A MODEL FOR HUMAN INFECTION

Hashimoto I. & Hagiwara A. (1982) Neuropathology and Applied Neurobiology 8, 149–156
Pathogenicity of a poliomyelitis-like disease in monkeys infected orally with enterovirus 71: a model for human infection
Ten cynomolgus monkeys were given enterovirus 71 (E71) by mouth. Clinically, only one monkey showed weakness of the lower extremities. Histopathologically, vascular lesions of variable intensity, perivascular cuffing, degeneration and necrosis of the neurons and neuronophagia were observed in the CNS of 7 monkeys. E71 was recovered from the CNS and specific immunofluorescence was detected in the neurons and in associated macrophages in the CNS. Serum neutralizing antibody titres rose from 14 to 21 days. These monkeys are as susceptible to E71 infection by the oral route as by the subcutaneous route as previously shown, and its neuronal virulence was confirmed by its producing CNS lesions after oral infection. The orally infected monkey with E71 appears to provide an excellent model for infection by this agent in man.     

The onset and development of descending pathways to the spinal cord in the chick embryo

The ontogenetic development of afferent (supraspinal and propriospinal) as well as efferent (ascending) fiber connections of the spinal cord was examined following the injection of horseradish peroxidase (HRP) or wheat germ agglutinin HRP (WGA-HRP) into the cervical and lumbar spinal cords (or brains) of embryos ranging in age from 4 to 14 days of incubation. A few cells were first reliably retrogradely labelled in the pontine reticular formation on embryonic day (E) 4 and E5 following the injection of WGA-HRP into the cervical and lumbar spinal cord, respectively. Propriospinal projections to the lumbar spinal cord, originating from brachial spinal cord, were found by E5, and from the cervical spinal cord by E5.5. Ascending fibers arising from neurons in the lumbar spinal cord could be followed to rostral mesencephalic levels in E5 embryos. Thus, the earliest supraspinal, propriospinal, and ascending fiber connections appear to be formed almost simultaneously. Retrogradely labelled cells were found in the raphe, reticular, vestibular, interstitial, and hypothalamic nuclei in E5.5 embryos following lumbar injections of WGA-HRP. Except for neurons in cerebellar nuclei, all the cell groups of origin that project to the cervical spinal cord of posthatching chicks were also retrogradely labelled by E8. There was a delay in the time of appearance of the projections from various regions of the brain stem to the lumbar versus the cervical spinal cord, ranging from 0.5 to 7 days, but typically of about 3 days duration. A large number of cells located in the ventral hypothalamic region, just dorsal to the optic chiasma, were found to be labelled following cervical HRP injection between E6 and E10. These cells may represent transient projections that are present only during embryonic stages since no labelled cells were found in this region in the newly-hatched chick.     

Immunopathological reactions in viral infections of the central nervous system

Viral infections of the central nervous system (CNS), as of any other organ, evoke humoral and cellular immune responses which enable the host to eliminate the pathogen. However, effective responses may themselves produce tissue damage sometimes exceeding that caused by the virus itself. The relative contribution of the various immunopathological mechanisms in human viral encephalitides remains mostly ill defined. Most of our understanding of the immunopathogenesis in viral CNS infections comes from studies on experimentally infected animals. The prototype model of a virus-induced, cell-mediated, immunopathological CNS disease is the neurological illness of mice that follows intracerebral inoculation with lymphocytic choriomeningitis virus. Virus-specific cytotoxic T cells are crucial to the pathogenesis but death of the animals only results when these cells are targeted into functionally essential brain structures like the circumventricular organs or the medulla oblongata and cervical spinal cord.     

Pursuit of the origin of the large myelinated fibers of the anterolateral funiculus in the spinal cord in humans in relation to the pathomechanism in amyotrophic lateral sclerosis

To determine the origin of the large myelinated fibers in the anterolateral funiculus (ALF) in the spinal cord of humans, myelinated fibers in the ALF of the mid-cervical spinal cord were examined quantitatively. Five groups of subjects were examined, consisting of control subjects, patients with cerebral lesions and showing complete degeneration of the unilateral/bilateral pyramis of the medulla oblongata, those with lesions of the pontine tegmentum, those with lesions of the lower cervical spinal cord, and those with thoracic/lumbar lesions. The results indicate that the large myelinated fibers in the ALF of the mid-cervical spinal cord of humans originate from the tegmentum of the brain stem and the lower cervical spinal cord, and not from the cerebrum, or the thoracic or lumbar spinal cord. Thus, they are descending fibers from the brain stem tegmentum and ascending fibers from the lower cervical cord, and not corticospinal tracts or long-ascending fibers from the thoracic or lumbar spinal cord. The origin of the large myelinated fibers in the ALF of the spinal cord in humans, the number of which was severely decreased in patients with amyotrophic lateral sclerosis, is considered to be the long-descending neurons in the brain stem tegmentum and the propriospinal neurons in the spinal cord. Received: 23 December 1998 / Revised, accepted: 29 March 1999     

Virus spread and initial pathological changes in the nervous system in genital herpes simplex virus type 2 infection in mice

Summary Mice were infected by the vaginal route with the MS strain of herpes simplex virus type 2 (HSV-2). Serial vaginal cultures were used to confirm infection and to select mice for this study. Two mice were killed by perfusion on days 2–6 post infection (p.i.) and lumbar and sacral cord with cauda were fixed and embedded for electron microscopy. Semithin Epon-sections were stained for viral antigen using a rabbit anti-HSV-2 antiserum and the Avidin-Biotin (ABC) method. Thin sections from antigen-positive blocks were examined by electron microscopy, and the number and types of infected cells detected by these two methods were compared. A good correlation was found between detection of infected cells by these methods. Infected cells included neurons of dorsal root ganglia and spinal cord, satellite cells of dorsal root ganglia, non-myelinating Schwann cells, astrocytes, oligodendrocytes and arachnoidal cells. Infected cells were first detected in the cauda on day 3 p.i. and in the spinal cord on day 5 p.i. The temporal and spatial distribution of infected cells was consistent with neural spread to and within the CNS. The pathological lesions showed a good correlation with the distribution and number of infected cells and are probably due to a direct virus effect. The similar sensitivity of the Epon-ABC method to electron microscopy in detecting infected cells indicates that this method may have useful applications in both experimental and diagnostic work.     

The distribution of inflammation and virus in human enterovirus 71 encephalomyelitis suggests possible viral spread by neural pathways

Previous neuropathologic studies of Enterovirus 71 encephalomyelitis have not investigated the anatomic distribution of inflammation and viral localization in the central nervous system (CNS) in detail. We analyzed CNS and non-CNS tissues from 7 autopsy cases from Malaysia and found CNS inflammation patterns to be distinct and stereotyped. Inflammation was most marked in spinal cord gray matter, brainstem, hypothalamus, and subthalamic and dentate nuclei; it was focal in the cerebrum, mainly in the motor cortex, and was rare in dorsal root ganglia. Inflammation was absent in the cerebellar cortex, thalamus, basal ganglia, peripheral nerves, and autonomic ganglia. The parenchymal inflammatory response consisted of perivascular cuffs, variable edema, neuronophagia, and microglial nodules. Inflammatory cells were predominantly CD68-positive macrophage/microglia, but there were a few CD8-positive lymphocytes. There were no viral inclusions; viral antigens and RNA were localized only in the somata and processes of small numbers of neurons and in phagocytic cells. There was no evidence of virus in other CNS cells, peripheral nerves, dorsal root autonomic ganglia, or non-CNS organs. The results indicate that Enterovirus 71 is neuronotropic, and that, although hematogenous spread cannot be excluded, viral spread into the CNS could be via neural pathways, likely the motor but not peripheral sensory or autonomic pathways. Viral spread within the CNS seems to involve motor and possibly other pathways.     

Electrophysiological response properties of spinoreticular neurons in the monkey

Extracellular recordings were made from 29 spinoreticular cells in the spinal cords of anesthetized monkeys. The cells were in either the cervicalor the lumbar enlargement, and they were identified by antidromic activation from the medial part of the pontomedullary reticular formation. More spinoreticular neurons were sampled in the cervical than in the lumbar cord. Most of the cells were contralateral to the side from which antidromic activation was observed, but a higher proportion of the spinoreticular neurons inthe cervical enlargement than in the lumbar enlargement was ipsilateral to the antidromic stimulus. Three cells in the lumbar cord were antidromicallyactivated not only from the reticular formation but also from the contralateral thalamus, confirming that some spinoreticular projections are formed by collaterals from spinothalamic cells. Most of the spinoreticular neurons were in the ventral horn in laminae VII and VIII, although a few were in laminae IV-VI. Nearly half of the spinoreticular cells in the sample could not be activated by any form of peripheral stimulation tested. The other cells could be activated by stimulation of receptive fields that varied from small to large, that were sometimes bilateral regions of the skin or of deep tissues. Although some spinoreticular cells could be classified as low threshold or wide dynamic range, the largest proportion were high threshold, requiring noxious stimulation for their activation. Descending volleys resulting from stimulation in the reticular formation could often be shown to inhibit or to excite spinoreticular neurons. It can be concluded that at leastsome spinoreticular neurons may play a role in nociception.     

Nerve fibre regeneration across the PNS-CNS interface at the root-spinal cord junction

Root-spinal cord regeneration was investigated in immature and adult rats. The elongation in the dorsal root of regrowing dorsal root axons, rerouted ventral root nerve fibres (cholinergic neurons) or hypogastric nerve fibres (catecholaminergic neurons) is impeded as they meet the astrocyte dominated CNS tissue of the root. The establishment of synaptoid nerve terminals as the regrowing axons encounter astrocytes indicates a mechanism for growth inhibition other than a physical impediment in the CNS environment. The glial cells of the CNS segment in the root are influenced by the type of regenerating nerve fibres in terms of maintenance, multiplication and phenotypic expression. After a dorsal root lesion in the neonatal rat several root axons may reinnervate the spinal cord. In these rats, the normal establishment of a CNS root segment has been disrupted and the PNS-CNS border is situated central to the root-spinal cord junction. Implantation of cut dorsal roots into the spinal cord of adult rats results in the extension of processes from intrinsic spinal cord neurons out into the root. After implantation of avulsed ventral roots into the ventro-lateral aspect of the cord, axonal regrowth and functional restitution of alpha-motoneurons could be demonstrated by intracellular recordings and injections with horseradish peroxidase. These results show that regeneration can occur across a PNS-CNS interface that has been established secondary to a trauma in the mature animal and in the immature animal before the astrocyte-rich CNS root segment has been developed.     

Lacrimal preganglionic neurons form a subdivision of the superior salivatory nucleus of rat: transneuronal labelling by pseudorabies virus.

Transneuronal viral tracing was applied to localize preganglionic parasympathetic neurons in the brainstem which innervate the extraorbital lacrimal gland in the rat. The Bartha strain of pseudorabies virus was injected into the lacrimal gland, and after different survival times, the superior cervical and Gasserian ganglia, the upper thoracic spinal cords and the brainstems were immunostained by antiviral antiserum. Virus-labelled neurons appeared in the ganglia and in the ventrolateral part of the ipsilateral brainstem at the pontomedullary junction 45 h after inoculation. The virus-labelled brainstem neurons comprised a subgroup of the superior salivatory nucleus (SSN) located between the root fibers of the facial nerve and the nuclei of the superior olive, and were clearly distinguished from the tyrosine hydroxylase (TH)-immunopositive, A5 catecholaminergic neurons by double immunostaining. The number of infected cells in the ipsilateral SSN was increased by 72 h, and labelled neurons appeared in the intermediolateral cell column (IML) of the ipsilateral thoracic spinal cord. In rats with cervical ganglionectomy prior to the virus injection in the lacrimal gland, virus-infected cells appeared in the SSN, but not in the thoracic spinal cord, indicating that preganglionic SSN cells were infected via parasympathetic axons of the facial nerve. A double-virus tracer labelling technique was applied to determine the topographical relationship between the preganglionic parasympathetic neurons of the lacrimal gland and those of the submandibular gland within the SSN. Simultaneous injection of Bartha strain of pseudorabies virus into the submandibular gland, and a lacZ gene-containing Bartha-derived virus strain into the lacrimal gland (and vice versa) demarcated a ventral lacrimal and a dorsal submandibular subgroup in the SSN.     

Astrocytes and Schwann cells are virus-host cells in the nervous system of rats with Borna disease

Borna disease virus (BDV) replicates only in cells in the central (CNS) and peripheral (PNS) nervous system in adult rats. Infection of the nervous system is associated with a transient, intense mononuclear meningoencephalitis and immunemediated loss of BDV-infected neurons. The identification of BDV antigen in neurons and the accompanying immunologically-specific lysis of these cells led to the prediction that the CNS would be virus-free after the animal had recovered from encephalitis. However, BDV infectivity and antigen persist for the lifetime of the animal. It appeared, therefore, that other neural cells might be hosts for viral replication and provide a reservoir for the virus. Morphological criteria were used to identify astrocytes and Schwann cells which expressed BDV antigens in vivo. Borna disease virus (BDV) infected astrocytes were identified by double labeling tissue sections with combined cell-specific and BDV-specific antibodies in an avidin-biotin immunocytochemical assay. Examination of serial I micrometer-thick cryosections of hippocampus and sciatic nerve preparations revealed several cells that expressed both glial and BDV antigens. Infectious virus was recovered from cultures of Schwann cells from infected rats. Borna disease virus-infected glial elements persisted beyond the period of inflammation and massive neuronal destruction, and represented a major class of infected cells during chronic disease.     

Cortical neurons projecting to the cervical and lumbar enlargements of the spinal cord in young and adult rhesus monkeys

Cortical neurons projecting to cervical and lumbar segments of the spinal cord in five young and one adult monkeys were identified using the retrograde transport method following multiple unilateral injections of horseradish peroxidase (HRP) into the anterior horn at cervical and lumbar levels of the spinal cord. Somatotopically organized labeled neurons were found in the precentral and postcentral gyri, the rostral half of both the medial and dorsal aspects of area 5, the cingulate sulcus within the medial aspect of area 6, and the second somatosensory area within the lateral sulcus. All HRP-positive neurons were confined to cortical layer V or to a depth corresponding to the fifth layer in regions where delineation of cortical layers was obscured due to freezing or sectioning artifacts. Although cross-sectional areas of labeled neurons varied widely within each field, more large labeled neurons were present in the leg than in the arm subdivision of the precentral gyrus. HRP-positive neurons in the first and second somatosensory areas as well as those in the medial aspect of area 5 were of medium size, and those in the primary and supplementary motor areas as well as those within the dorsal aspect of area 5 were of medium or larger size.     

Pathology of roots, spinal cord and brainstem in syringomyelia-like syndrome of Tangier disease.

We report here a post-mortem examination of a 46-year-old patient who died after a 23-year-long syringomyelia-like syndrome of Tangier disease. The L5 dorsal root and the superficial peroneal nerve showed fiber loss and lipid vacuole accumulation in Schwann cell cytoplasm. The L5 ventral root had moderate fiber loss without lipid vacuoles. In the cervical roots, fiber loss was intense and there were no foamy Schwann cells. Motor neuron loss was severe in the cervical spinal cord and the facial nerve nucleus and slight at the lumbar level. Under electron microscopy, some neurons of the lower spinal cord showed atypical inclusions. These data suggest that an unknown metabolic defect is responsible for a primary neuronopathy. Lipid accumulation in Schwann cells, resulting from fiber degeneration is probably transient, accounting for the absence of foamy cells in regions with longstanding involvement.     

HSV (Type 1) infection of the trigeminal complex

Following corneal inoculation with herpes simplex virus (Type 1) (HSV), virus spreads to the CNS by axonal transport in the central branches of trigeminal ganglion cell neurons. Although this mode of viral entry to the CNS is rare for humans, it appears to be the principal route of entry into the CNS in animal models of herpetic corneal disease. In this study, the corneas of BALB/c mice were unilaterally inoculated with HSV, and the distribution of HSV-immunoreactive label was studied to identify the central branches of the axons of infected trigeminal ganglion cells. Virus was first noted in the brainstem trigeminal complex 4 days after corneal inoculation, when HSV-labeled afferents were found throughout the course of the descending tract of V as well as in interstitial neurons in the tract. By 5 days labeled neurons were also found not only in the n. caudalis and portions of the n. interpolaris of the trigeminal complex but also in laminae I–IV of the dorsal horn of the upper cervical levels of the spinal cord. No immunoreactivity was seen in other regions of the complex, including the n. oralis or the main sensory n. of V. By 6 days, however, the infection had spread to the main sensory division of V.     

Central motor and sensory conduction in X-linked recessive bulbospinal neuronopathy.

Central conduction was studied in 12 patients with X-linked recessive bulbospinal neuronopathy (XBSN) using percutaneous electrical cortical, cervical and lumbar stimulation and somatosensory evoked potentials (SEPs). The central motor conduction time from the motor cortex to the cervical and lumbar segments of the spinal cord was normal in XBSN. SEPs, however, were abnormal or central sensory conduction time was prolonged in patients with XBSN. These results are consistent with the clinicopathological findings of XBSN in which the primary sensory neurons are involved as well as the lower motor neurons in the CNS, whereas the upper motor neurons are well preserved.     

Ultrastructural observations of spinal cord lesions and blood-brain barrier changes in scrapie-infected mice

Summary Spinal cord samples from IM or VM mice injected intracerebrally with the 87V scrapie agent were examined ultrastructurally at the clinical stage of disease for changes in blood vessel permeability and for pathological alterations. In several animals, (3 of 16), massive changes were noted in the cervical spinal cords in the subependymal area of the cortical gray matter immediately surrounding the central canal including ependymal cell changes, the presence of amyloid plaque in close association with microglial cells, extensive neuropil vacuolation, the appearance of reactive astrocytes, degenerating neurites and vacuolated neurons. In those regions showing structural damage, localized increased permeability to horseradish peroxidase across the blood-brain barrier was noticed along with the appearance of numerous vesiculo-canalicular profiles in micro-blood vessel endothelial cells with extravasation of the tracer to the neuropil. Some damaged neurons appeared flooded with this tracer. These changes were not observed in either the thoracic or lumbar spinal cord regions. The occurrence of pathological changes in the spinal cords of a small percentage of intracerebrally injected mice was probably due to a high concentration of the scrapie agent which localized in the cervical spinal cord, presumably after entering the spinal fluid via the lateral ventricle at the time of injection.Supported in part by a grant from the NINCDS No. 18079     

Nerve growth factor stimulates development of substance P in the embryonic spinal cord

Development of the putative neurotransmitter, substance P (SP), in the embryonic rat dorsal root ganglion (DRG) and spinal cord was defined in vivo. SP was not detectable by radioimmunoassay before day 17 of gestation (E17). On E17, cervical sensory ganglia contained 4 pg SP/ganglion, rising to 49 pg/ganglion at birth. The dorsal cervical spinal cord contained 0.75 ng SP/mg protein on E17, rising to 6 ng SP/mg protein on postnatal day 3. The ventral spinal cord contained approximately 20% of the SP content in the dorsal cord at each gestational age. Intrauterine forelimb amputation partially prevented the normal development increase of SP in sensory ganglia destined to innervate that limb, suggesting that target structures regulate the development of peptidergic neruons. Conversely, treatment with nerve growth factor (NGF) stimulated development of SP in the DRG. Moreover, NGF treatment increased SP in the dorsal spinal cord, suggesting that NGF can modulate development within the CNS, as well as peripheral structures. It is likely that the CNS effect reflects NGF peptidergic neruons. Conversely, treatment with nerve growth factor (NGF) stimulated development of SP in the DRG. Moreover, NGF treatment increased SP in the dorsal spinal cord, suggesting that NGF can modulate development within the CNS, as well as peripheral structures. It is likely that the CNS effect reflects NGF peptidergic neruons. Conversely, treatment with nerve growth factor (NGF) stimulated development of SP in the DRG. Moreover, NGF treatment increased SP in the dorsal spinal cord, suggesting that NGF can modulate development within the CNS, as well as peripheral structures. It is likely that the CNS effect reflects NGF action on peripheral ganglia, but a direct effect on the spinal cord has not been excluded. However, treatment with antiserum to NGF failed to significantly inhibit development of ganglion SP. The system of SP-containing neurons in the DRG may provide a convenient model for defining events regulating peptidergic maturation.     

Attempts to reproduce amyotrophic lateral sclerosis in laboratory animals by inoculation of Schu virus isolated from a patient with apparent amyotrophic lateral sclerosis

Summary A virus isolated from the CSF of a patient who had amyotrophic lateral sclerosis for 7 years, and prolonged pleocytosis in the CSF, was adapted to suckling mouse brain by subsequent serial blind passages. This Schu virus belongs to the tick-borne encephalitis complex of the genus Flavivirus (Togaviridae). Suckling mouse brain homogenate of the 13th passage was used for transmission experiments in various species of laboratory animals. Golden hamsters infected subcutaneously fell ill after a number of months, lost weight, and had paresis of the legs. Histologically they had petechial hemorrhages in different parts of the CNS and inflammatory changes in the gray substance of the spinal cord.Pilot studies with repeated inoculations of small doses of different flavivirus strains suggest a course of the disease in experimental animals which resembles slow-virus infections insofar as no encephalitis is produced and degenerative changes of the anterior horn cells prevail over inflammatory signs in the spinal cord.After intracerebral application of Schu virus, cynomolgus monkeys developed the typical lesions of togavirus panencephalitis with epileptic seizures, ataxia, and paresis. After subcutaneous application, the virus seems to spread along peripheral nerves to anterior spinal roots and spinal cord, where mainly motor neurons of the anterior horn are damaged, and from there to the brain.The histological findings are such that one may assume the disease of the patient was due to the infection with the virus isolated from his CSF. Therefore, the hypothesis may be advanced that at least some of the cases diagnosed as amyotrophic lateral sclerosis are due to a togavirus infection.This paper was presented at the Symposium on Chronic Virus Diseases in Smolenice, October 1977 and at the meeting of the German Neuropathological Society in Tübingen, October 1977