A study of the evolution of viral infection in experimental herpes simplex encephalitis and rabies by means of fluorescent antibody

Virus spread and initial pathological changes in the nervous system in genital herpes simplex virus type 2 infection in mice. A correlative immunohistochemical, light and electron microscopic study

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.

Histological study of the progression of herpes simplex virus in mice

The progress of an experimental infection with Herpesvirus hominis type 1 was studied in newborn mice inoculated into the foot pad of the hind leg. To trace the viral antigen, the unlabeled antibody enzyme PAP (peroxidase/antiperoxidase) method was employed. The virus antigen appeared first in the epidermal and connective tissue cells of the inoculation site, and then progressed along the sciatic nerve. This nerve was studied by electron microscopy and showed active multiplication within the Schwann cells, with the production of virions, some of which were found in the intercellular spaces. No intra-axonal particles were observed. The infection then spread to the spinal ganglia and to the spinal cord. In this progression, the pia mater appeared to play an important role. From the spinal cord, the infection spread to the encephalon. The present study supports a mixed route for the neural transport of herpes simplex virus: a) by cell-to-cell transmission (Schwann and connective tissue cells in the sciatic nerve; meningeal cells, neurons and glial cells in the CNS); b) by a passive motion of the virions along the intercellular spaces. The inoculated virus also gave rise to viremia with viral multiplication in several viscera.

Infection of cultivated CNS tissue with herpes virus, HSVII. A reappraisal

Organized cultures of newborn rat and hamster cerebellum were infected with herpes virus type II, after 7 and 14 days "in vitro". 48 h after the infection, electron microscopic examination of the cultures showed that astrocytes contained numerous intranuclear and intracytoplasmic viral particles, while neurons remained apparently intact. The specificity of the infection for a given cell type is discussed.

Pathogenesis of herpetic neuritis and ganglionitis in mice: evidence for intra-axonal transport of infection

The pathogenesis of acute herpetic infection in the nervous system has been studied following rear footpad inoculation of mice. Viral assays performed on appropriate tissues at various time intervals indicated that the infection progressed sequentially from peripheral to the central nervous system, with infectious virus reaching the sacrosciatic spinal ganglia in 20 to 24 hr. The infection also progressed to ganglia in mice given high levels of anti-viral antibody. Immunofluorescent techniques demonstrated that both neurons and supporting cells produced virus-specific antigens. By electron microscopy, neurons were found to produce morphologically complete virions, but supporting cells replicated principally nucleocapsids. These results are discussed in the context of possible mechanisms by which herpes simplex virus might travel in nerve trunks. They are considered to offer strong support for centripetal transport in axons.

Immunosuppression and experimental virus infection of the nervous system

This chapter describes the current views of the pathogenesis of virus infections of the nervous system, with particular attention to certain aspects of virus-host interactions. Following invasion of the central nervous system, infection can follow a variety of patterns, as to number and distribution of neuronal and non-neuronal cells involved. There is a corresponding diversity in the pathological lesions of the central nervous system (CNS) produced by acute virus infection. Infection can be pictured as a race between virus and host defenses, where many factors, acting through different mechanisms, can influence the outcome. Outcome is always determined by multiple virus and host variables, although single variables can be independently studied under experimentally controlled conditions in the laboratory. The chapter demonstrates that in many virus-host combinations, the immune response plays an important role in recovery from primary infections. It mentions that an immunopathological process mediates the disease which follows certain CNS virus infections.

Rabiesvirus neuronitis

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Herpes simplex virus-host cell relationships in organized cultures of mammalian nerve tissues

Studies on the replication of herpes simplex virus in organized cultures of rat central nervous system (CNS) and peripheral nervous system (PNS) tissue demonstrated synthesis of intra- and extracellular virus, as determined by plaque assay on HEp-2 cells. Newly synthesized intracellular virus appeared 12 to 14 hr after inoculation of CNS, followed 10 hr later by the appearance of extracellular virus. In PNS cultures, where higher inputs of virus were introduced, intracellular virus appeared 6 to 8 hr after inoculation, followed by extracellular virus 12 hr later. Polykaryocyte formation was observed in CNS and PNS tissue involving neuroglial, meningeal, or Schwann cells. Neuron somas did not participate in polykaryocyte formation, but they underwent progressive morphological changes starting with increased cytoplasmic granularity followed by nucleolar distortions and disintegration, margination of nuclear chromatin, and the appearance of intranuclear inclusions. Finally, all recognizable cellular detail was lost. Immune serum globulin failed to inhibit both the progressive nature of the cytopathic effect and the synthesis of intracellular virus. These findings are discussed in relation to other in vitro systems, as well as to disease processes in man and animals.

Acute necrotizing encephalitis: a problem in diagnosis

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[Investigations on the pathomorphology and pathogenesis of Aujeszky's disease. I. On the histopathology of the spinal ganglia, spinal nerve roots and the spinal cords in rabbits after experimental infection]

Lumbo-intramuscular or naso-oral infection of 15 rabbits with Aujeszky's virus consistently produced alterations in the nerve cells of the spinal ganglia, the spinal nerve roots and the spinal cord, viz. nuclear inclusions of Cowdry types A and B. Lumbar infection produced neural lesions extending continuously from the site of infection via the spinal nerve roots and spinal ganglia as far as the dorsal and ventral nuclear regions of the spinal cord. The viral lesions following nasooral infection involved electively the sympathetic centers of the spinal cord with severe alterations of the sympathetic trunk ganglia. Despite this demonstration of viral propagation along neural routes, one should not disregard the possibility of hematogenous-lymphogenic propagation.

Comparative studies between pathogenesis of street and fixed rabies infection

Comparative neuropathology of Ammon's horn caused by both the street and fixed rabies infection was studied by combined light and electron microscopy. Neurons containing Negri bodies appeared comparatively little damaged. In striking contrast, in the case of fixed virus infection, neurons showed the following variety of degeneration. Lightly damaged neurons showed an increase in the number of small vesicles throughout the cytoplasm. A considerable number of lysosomes were also encountered within these nerve cells. Severe necrotic alteration involving the nucleus as well as the cytoplasm was found in the nerve cell band. The characteristic homogeneous foci (matrices) were discernible within these neurons. It appears that the matrix is morphologically identical with the ground substance of the Negri body, though its size is smaller than that of the Negri body. This evidence suggests a possibility that fixed virus injures neurons so extensively that they cannot bring about the full development of the characteristic matrix of the Negri body recognizable by the light microscope. Selective vulnerability was demonstrated among different groups of neurons in respect of cytopathogenesis of both street and fixed virus infection.