Novel Flavivirus Attenuation Markers Identified in the Envelope Protein of Alfuy Virus

Alfuy (ALFV) is an attenuated flavivirus related to the Murray Valley encephalitis virus (MVEV). We previously identified markers of attenuation in the envelope (E) protein of the prototype strain (ALFV₃₉₂₉), including the hinge region (E273-277) and lack of glycosylation at E154-156. To further determine the mechanisms of attenuation we assessed ALFV₃₉₂₉ binding to glycosaminoglycans (GAG), a known mechanism of flaviviruses attenuation. Indeed, ALFV₃₉₂₉ exhibited reduced binding to GAG-rich cells in the presence of heparin; however, low-passage ALFV isolates were relatively unaffected. Sequence comparisons between ALFV strains and structural modelling incriminated a positively-charged residue (K327) in ALFV₃₉₂₉ as a GAG-binding motif. Substitution of this residue to the corresponding uncharged residue in MVEV (L), using a previously described chimeric virus containing the prM & E genes of ALFV₃₉₂₉ in the backbone of MVEV (MVEV/ALFV-prME), confirmed a role for K327 in enhanced GAG binding. When the wild type residues at E327, E273-277 and E154-156 of ALFV₃₉₂₉ were replaced with the corresponding residues from virulent MVEV, it revealed each motif contributed to attenuation of ALFV₃₉₂₉, with the E327/E273-277 combination most dominant. These data demonstrate that attenuation of ALFV₃₉₂₉ is multifactorial and provide new insights for the rational design of attenuated flavivirus vaccines.

Demonstration of Akabane virus antigen using immunohistochemistry in naturally infected newborn calves

Eight newborn calves showing ataxia were necropsied and examined histologically. Six of seven cerebrospinal fluid samples collected from these animals had neutralizing antibody for Akabane virus (AKV). All examined calves had nonsuppurative encephalomyelitis, localized mainly in the midbrain and spinal cord. Corresponding to the encephalitic lesion, AKV antigen was demonstrated in neuroglial cells in the brain stem and neuronal cells in the ventral horn of the spinal cord. This is the first study to demonstrate AKV antigen by immunohistochemistry in naturally infected newborn calves.

Morphological features of Murray Valley encephalitis virus infection in the central nervous system of Swiss mice

We have examined the histological and ultrastructural features of CNS infection with Murray Valley encephalitis (MVE) virus in mice inoculated with a virulent parental strain (BH3479). Light microscopic examination revealed neuronal necrosis in the olfactory bulb and hippocampus of MVE-infected brains by 5 days post-infection (pi). Electron microscopy of these regions showed endoplasmic reticulum membrane proliferation, and tubular and spherical structures in the cisternae of the endoplasmic reticulum, Golgi complex and nuclear envelope. At seven to eight days pi, infected neurones exhibited chromatin condensation and extrusion, nuclear fragmentation, loss of segments of the nuclear envelope, reduced surface contact with adjacent cells and loss of cytoplasmic organelles. This cell injury was particularly noticeable in the proximal CA3 and distal CA1 regions of the hippocampus. The inflammatory cell profile consisted of macrophages, lymphocytes and especially neutrophils, and many of these inflammatory cells were apoptotic. High mortality rates in the BH3479-infected population of mice correlated with the intense polymorphonuclear and mononuclear leucocyte inflammatory infiltrate in the CNS.

Characterization of infectious Murray Valley encephalitis virus derived from a stably cloned genome-length cDNA

An infectious cDNA clone of Murray Valley encephalitis virus prototype strain 1-51 (MVE-1-51) was constructed by stably inserting genome-length cDNA into the low-copy-number plasmid vector pMC18. Designated pMVE-1-51, the clone consisted of genome-length cDNA of MVE-1-51 under the control of a T7 RNA polymerase promoter. The clone was constructed by using existing components of a cDNA library, in addition to cDNA of the 3' terminus derived by RT-PCR of poly(A)-tailed viral RNA. Upon comparison with other flavivirus sequences, the previously undetermined sequence of the 3' UTR was found to contain elements conserved throughout the genus FLAVIVIRUS: RNA transcribed from pMVE-1-51 and subsequently transfected into BHK-21 cells generated infectious virus. The plaque morphology, replication kinetics and antigenic profile of clone-derived virus (CDV-1-51) was similar to the parental virus in vitro. Furthermore, the virulence properties of CDV-1-51 and MVE-1-51 (LD(50) values and mortality profiles) were found to be identical in vivo in the mouse model. Through site-directed mutagenesis, the infectious clone should serve as a valuable tool for investigating the molecular determinants of virulence in MVE virus.

Viral encephalopathy and retinopathy of farmed marine fish species in Italy

Viral encephalopathy and retinopathy, otherwise known as fish encephalitis or viral nervous necrosis (VNN), is an emerging problem in several farmed marine fish species in various geographic areas all over the world. Since summer 1995, heavy losses affecting mainly juvenile and adult sea bass (Dicentrarchus labrax) have been observed in several on-growing facilities in Italy. Dying fish show abnormal swimming behaviour and, at temperatures higher than 20-22 degrees C, mortality rates range between 15 and 50%. Neither significant external nor internal gross pathological signs, except frequent abnormal swim bladder hyperinflation, were detected. Histological investigations reveal vacuolations in the grey matter of the brain and spinal cord and in the granular layers of the retina. Serial tissue sections examined by an immunohistochemical method carried out with antisera against fish nodaviruses showed a positive reaction. Additionally, spherical virus-like particles 22-25 nm in diameter were detected by electron microscopy in negative stained preparations of brain tissues, and the same samples gave a positive reverse transcription-polymerase chain reaction (RT-PCR) for the T4 region of the fish nodavirus gene. These results indicate that both juvenile and adult sea bass subject to mass mortality in Italy since summer 1995 are infected with a fish nodavirus and strongly suggest that the identified virus is the cause of the observed mortality.

Induction of nodavirus disease in seabass, Dicentrarchus labrax, using different infection models

The aim of this study was to investigate the susceptibility of juvenile and adult seabass, which are generally thought to be refractory to nodavirus. Moreover, preliminary immunological studies were performed to examine the immune response of adult seabass. Successful transmission of the disease was experimentally demonstrated in juvenile and adult seabass as ascertained by the presence of the clinical signs of the disease, re-isolation of the virus in the SSN-1 cell line and subsequent confirmation by histopathology and immunohistochemistry. Bigger seabass not only developed the clinical disease but also suffered mortalities. Serum neutralisation titres were considered low in this study.

Murray valley encephalitis virus envelope protein antigenic variants with altered hemagglutination properties and reduced neuroinvasiveness in mice

Neutralization escape variants of Murray Valley encephalitis virus were selected using a type-specific, neutralizing, and passively protective anti-envelope protein (E) monoclonal antibody (4B6C-2) which defines epitope E-1c. Nucleotide sequence analysis revealed single nucleotide changes in the E genes of 15 variants resulting in nonconservative amino acid substitutions in all cases. One variant had a three-nucleotide deletion in the E gene which resulted in loss of serine at residue 277. Changes were clustered into two separate regions of the E polypeptide (residues 126-128 and 274-277), indicating that E-1c is a discontinuous epitope. One variant (BHv1), altered at residue 277 (Ser-->Ile), failed to hemagglutinate across the pH range 5.5-7.5, in contrast to parental virus and the other escape variants which hemagglutinated at an optimal pH of 6.6. BHv1 was also of reduced neuroinvasiveness in 21-day-old mice following intraperitoneal inoculation compared to the other viruses. Parental virus and the neutralization escape variants grew equally well in both vertebrate and invertebrate cell cultures, indicating that the reduced neuroinvasiveness of BHv1 was not due to a major abnormality of replication.

Astrogliosis in von Economo's and postencephalitic Parkinson's diseases supports probable viral etiology

A marked generalized astrogliosis was observed in the frontal and temporal white matter from a case of von Economo's disease and another of postencephalitic Parkinson's disease, which areas were otherwise devoid of any other demonstrable microscopic lesions. No similar astrocytic reaction of any severity was observed in the same areas in a number of other brain diseases or controls, except when other kinds of lesions were present in the same section, with reactive astrocytes being present within the primary or defining lesion or immediately close by. The marked astrogliosis in von Economo's and postencephalitic Parkinson's diseases in areas "distant" from the primary lesions seeming to indicate extensive pathological involvement, added to the strong qualitative and quantitative similarity of this reaction to that observed in concurrently studied cases of encephalitides caused by the human immunodeficiency virus, lend further factual support to the hypothesis of a viral etiology, albeit unspecified, in both von Economo's and postencephalitic Parkinson's diseases.

[A case of brain infarction associated with viral encephalitis: MRI and pathological findings]

A 10-year-old girl had an infarction in the left brain during an acute viral meningoencephalitis. She initially showed seizure, unconsciousness and fever, and right hemiplegia gradually developed. She died at the 48th day of disease from respiratory disturbance and renal failure. Cranial MRI during the acute phase of the disease, when there was no clinical sign of right hemiplegia, showed a high intensity lesion in the left parietal and occipital areas on T-2 weight image. Autopsy disclosed the findings suggesting viral encephalitis, including multiple focal necrosis, perivascular round cell infiltration, proliferation of glial cells and spongy degeneration with some intranuclear inclusion bodies, and infarction in the left hemisphere. These findings suggest that T-2 high intensity lesion on MRI reflected infarction.

Isolation of brain parenchymal lymphocytes for flow cytometric analysis. Application to acute viral encephalitis

A strategy for the isolation of mononuclear cells from the brain parenchyma of mice with ongoing central nervous system (CNS) inflammation has been developed in order to permit flow cytometric (FCM) analysis of these cell populations. Sindbis virus (SV) encephalitis in mice is characterized morphologically by an infiltration of mononuclear cells into both brain parenchyma and cerebrospinal fluid (CSF). Perfused brain tissue from infected animals is collected, homogenized, and subjected to a mild enzymatic digestion. A sedimentation at unit gravity is performed to remove any large particulate debris, and the remaining tissue is then centrifuged over a modified density gradient which separates intact cells from smaller tissue fragments. Cells collected directly from these gradients can be stained with monoclonal antibodies and analyzed by FCM without further manipulation. Data generated by this method correlates with previous studies of SV encephalitis using immunohistochemical analysis of brain tissue sections to quantify mononuclear cell types. This suggests that representative samples of the cellular infiltrate are obtained using this technique. The approach however, offers the possibility of more sophisticated and quantitative analyses of CNS inflammatory cells which is unobtainable by tissue section staining.

Replication and plaque formation of swine hemagglutinating encephalomyelitis virus (67N) in swine cell line, SK-K culture

Swine hemagglutinating encephalomyelitis virus (HEV), 67N strain, adapted to suckling mouse brain, grew readily in a porcine cell line, SK-K cell culture with cytopathic effect (CPE) consisting of syncytium formation and detachment of fused cells and round cells from glass surface. After further passages in SK-K cell monolayers with undiluted culture fluid, CPE developed earlier and became complete within 48 h postinoculation (p.i.). Viral specific antigen was detected in the cytoplasm of the infected SK-K cells by indirect immunofluorescence using rabbit antiserum against the mouse-passaged virus. The SK-K-passaged virus as well as the original mouse-passaged virus formed clear plaques on SK-K cell monolayers under simple overlay medium. The plaque assay system for HEV 67N was established by studying various factors influencing the plaque formation in the SK-K cell cultures. By this system more than 10(6) PFU/0.2 ml of the virus yield was detected in the fluid phase of the infected cultures at 48 h p.i. The SK-K-passaged virus caused fatal infection in 4-week-old mice by intracerebral inoculation, but was inhibited by rabbit antiserum against the mouse-passaged virus. Plaque formation and hemagglutinating activity of the virus were specifically inhibited by antisera against the mouse-passaged and SK-K-passaged 67N virus.

[Personality change following encephalitis lethargica in childhood. Eventual fate of a patient]

An account is given of a patient who died at the age of sixty. He had no recollection of having had encephalitis as a child. In his schooldays, the patient was subject to severe behavioral disorders which were not susceptible to outside influence. During his military service he was frequently punished for conduct prejudicial to discipline and good order, and at the front he was even sentenced to death, but reprieved. His later life brought him no tranquility, ever new conflicts driving him from one job after another. Breaking into uncontrollable fits of rage, he would psychically attack the people around him, threatening to kill them. He was incapable of controlling his impulses. He spent the second half of his life in institutional care, his extrems impulsiveness being the cause of considerable disruption. Post mortem examination confirmed the encephalitis lethargica he was assumed to have suffered as a child, which was responsible for the typical change of character. It is evident how encephalitis lethargica in childhood sets a lifelong mark on the conduct, with appalling consequences.

Encephalitis lethargica. A report of four recent cases

Four patients are described with an encephalitic illness identical to that described by von Economo. Electroencephalographic, evoked potential and autopsy data suggest that involvement of the cerebral cortex is more extensive than has been generally recognized. Serological tests and viral cultures failed to reveal the infectious agent but the presence of oligoclonal IgG banding in the cerebrospinal fluid in 3 of the patients during the acute phase of the illness would be in keeping with a viral aetiology.

An outbreak of encephalitis in pigeons (Columba livia) in the Canary Islands (Spain)

An encephalitic disease in pigeons, characterized by paralysis of extremities, torticollis, head tremor, and diarrhea, is described. The negative titers in the hemagglutination tests, the presence of Feulgen-positive intranuclear inclusions in the cells of the granular layer of the cerebellum and the fibroblast culture, and the presence of viral particles with an icosahedral-herpetic morphology and a diameter of 100-170 nm all indicate that the etiology of this outbreak may be related to the encephalitis caused by herpesvirus, at present diagnosed only in Iraq and some African countries.

Pathological findings of adenine arabinoside (ARA-A) and cytarabine (ARA-C) in the treatment of herpes simplex encephalitis in rabbit model

The injection of herpes simplex virus type 1 (HSV-1) into the vitreous body of the eye in the 18 day old albino rabbits consistently induced herpes encephalitis with 90% survival. In the untreated rabbits the lesions follow a defined anatomical pathway producing a progressive disease not dissimilar to the natural human disease in that HSV travels slowly by cell-to-cell infection of neuroglia. The effects of adenine arabinoside (ara-A) and cytarabine (ara-C) on HSV encephalitis in rabbit model were studied by starting the treatment on 4th day post-inoculation of HSV. Deaths due to toxic side effects were caused by ara-A and ara-C in 30% and 50% of animals respectively, compared with 10% in untreated animals. Neurological signs, such as head jerking, ataxia and frequent epileptiform fits, occurred in ara-A, and ara-C and untreated rabbits. Comparative histological studies of optic nerves and brains showed that ara-A and ara-C had no beneficial effect, but surprisingly enhanced the disease.

Ocular bobbing in encephalitis

Abnormal eye movements described as ocular bobbing are most often encountered in the setting of pontine vascular disease. This report deals wih the onset and course of ocular bobbing in a young woman who had encephalitis confirmed by biopsy. Unusual eye movements developed during progressive deterioration of brain and brain stem function which led to coma. The eye movements occurred spontaneously and could also be triggered by cutaneous stimulation of the face, head, extremities, and auditory canals. The patient recovered fully over a period of several months.

Acute viral encephalitis: its diagnosis and outcome

Sixty patients with acute viral encephalitis admitted to The London Hospital in the last fifteen years have been reviewed. These consisted of 12 patients with known viral infection, 29 patients with acute viral infection of undetermined type, and 19 patients in whom an encephalitic illness followed a viral infection (post-infection encephalitis). The patients with primary viral encephalitis presented with an inflammatory brain disorder, including headaches and fever, and developed focal or diffuse neurological signs. Patients with post-infection encephalitis, usually following a 'flu'-like illness, presented with an acute neurological disturbance. The results of investigations, including virological studies, CSF examination, electroencephalography and neuroradiology, are described. Biopsy or autopsy material was available in 11 patients and these pathological findings supported the clinical classification of these patients. The mortality was highest in patients with herpes simplex virus encephalitis and lowest in patients with post-infection encephalitis. A considerable morbidity was found, not only in patients with primary viral encephalitis, but also in patients with encephalitis of unknown aetiology and post-infection encephalitis.

Neuropathology of S. Paulo south coast epidemic encephalitis (Rocio flavivurus)

The neuropathology of 8 cases of S. Paulo south coast epidemic encephalitis (Rocio flavivirus), a new arbo B virus encephalitis, is described. The topographic pattern of the lesions appears to be almost specific. The gray matter is predominantly affected. Interstitial mononuclear infiltration, microglial proliferation and perivascular lymphocytic cuffing were seen. Neuronophagia was seldom seen except during the acute phases of the disease. Throughout the neuraxis, the gray matter was affected to a greater degree than white matter. The more damaged structures, in descending order, were as follows: thalamus, dentate nucleus, substantia inominata, brain stem, spinal cord and basal nuclei. Most of the cases exhibited thalamic inflammatory necrosis. Electron microscopy disclosed in one case virus-like particles, resembling those described in other arbo B viruses in the cytoplasm of thalamic neurons. In this case, virus was isolated from the brain and an immunofluorescence test also showed antigenic material in the thalamic neurons.

A hamster-attenuated, temperature-sensitive mutant of Venezuelan encephalitis virus

Pathogenicities of 10 temperature-sensitive mutants of Venezuelan encephalitis virus were studied using the hamster model of human virulence. The parental strain and nine of the temperature-sensitive mutants produced lethal infections in hamsters. Strain ts 126 showed reduced hamster virulence. Deaths with the lethal mutants usually occurred 1 to 3 days later than with parental virus. Nine mutants produced lower levels of viremia than parental virus. Attenuation of ts 126 was related to restriction of viral growth in spleen and probably bone marrow and to absence of the usual pathological lesions in hemopoietic tissues and brain, but was functionally unrelated to temperature sensitivity since temperatures of both normal and infected hamsters remained within the permissive range of the mutant. Deaths did not correlate with titers of the 10 mutants in blood at permissive temperatures or with reversions of four temperature-sensitive mutants to non-temperature-sensitive virus in hamsters.

[Cellular fusion induced in vitro by the mouse scrapie agent]

A method is described to demonstrate and measure the cell-fusion in vitro induced by viruses. This technique has been established using Sendai virus. It has been used to study the fusing ability of the Scrapie agent which is responsible of a slowly progressing spongiform encephalopathy in Mice. In Vero cells, the Scrapie agent induces a fusion which appears slowly and remains moderate. This test can help to detect the human spongiform encephalopathies.

Herpes simplex retinitis

Fatal encephalitis with accompanying retinitis developed in a previously healthy 18-month-old infant. Clinically the disease appeared as whitish-yellow punctate lesions, perivascular cuffing, and hemorrhage. The antibody titer to herpes simplex rose from 1:8 on the day of admission to 1:256 on the day of death. Postmortem, intranuclear inclusion bodies that were typical of those found with herpesvirus were seen in the brain and retina. Viral particles consistent with those of herpesvirus were found by electron microscopy in the brain and in the inner-nuclear and ganglion-nerve fiber layers of the retina. This demonstrates the direct infectious nature of herpetic retinitis. Hematogenous spread of the virus to the retina is presumed.

Vascular and neuroglial changes in experimental herpes simplex encephalitis enzyme histochemical study

An enzyme histochemical study of experimental herpes simplex encephalitis of the mouse has revealed a decrease in the number of capillaries displaying alkaline phosphatase activity. Glial cells showed increased Inosine 5 diphosphatase and ATPase activity. These enzyme histochemical changes were distributed throughout the nervous parenchyma while the lesions, seen by light microscopy, are localized to well defined areas. Mice inoculated with a pure culture of irradiated HSV failed to show the above mentioned modifications.

[Sulphated glycosaminoglycans as virus inhibitors. 3rd communication: therapy of viral diseases by means of glycoasaminoglycanpolysulphates. Establishment of fundamentals in experiments with laboratory animals (author's transl)]

Following the in vitro and in vivo demonstration of their inhibitory effect upon 17 D yellow fever virus (Comm. I and II) it has been tried to demonstrate the therapeutic effect of three GAGPS (L1, L5, L8)1 in experimental animals. It had been found that L1 possessed the strongest inhibitory action and L5 the lowest toxicity. L8 served as control substance with different chemical structure. Mice that had been intracerebrally infected with 50 to 100 LD50 yellow fever virus were subsequently treated with L1, L5 and L8 by i.v., i.p., i.m., and oral routes. At first it was found by cytophotometric measurements that the i.c. applicated substances accumulated in the nerve cells of the hippocampus major, the cerebellum (Purkinje cells) and the cortex; the uptake was nearly doubled if a mixture with virus was used (Table 1). Following preliminary experiments to determine the adequate quantity of virus, five experiments were performed in the order mentioned. In the first series were treated groups of 30 animals after intracerebral infection with 100 mug/0.02 ml L1 by the i.m. and i.p. routes respectively, beginning from the first day p.i. for a period of seven days (Table 2). A certain difference of the rate of deaths and surfivals was seen between the treated and untreated groups. Among the treated mice delayed death was a prominent occurrence (Fig. 1). A second experiment involving a double dose of L1a (200 mug/0.02 ml) from another batch of GAGPS showed no better effect (Table 3). An explanation was given by the fact that L1a demonstrated a moderate toxicity with high doses about 5000 mug/ml in the i.c. control (Table 4 and 5). A graphic representation of both experiments can be found in Figs. 2a and 2b. The relative low virus input in the third series as shown in the virus control impedes additionly clearcut results. In the fourth experiment the infected mice were treated with GAGPS doses between 250 and 2500 mug/ml; L1 was administered by the oral, L5 and L8 by the intraveneous route. The death rate of the animals treated with low doses of L1 (250-1000 mug/ml) is diminished clearly and there was a significant difference between treated and untreated mice when L5 and L8 were applied (Table 6). Fig. 3 shows the graphic representation of experiment four. The good results of treatment were confirmed by histopathological findings (Table 7). There was a clear difference in the kind and quantal distribution of cerebral lesions in treated and untreated mice. In the last series L1 was administered by the i.v., L5 and L8 by the oral route (Table 8). Although the virus dose given in this series was rather low a protective effect was seen with low doses of L1 (312 mug/ml) and L5 )500 and 1000 mug/ml). Also these results were confirmed by histopathological examination. In summary, the GAGPS L1, L5 and L8 were found to have a clear therapeutic effect upon the experimental encephalitis of mice caused by infection with 17 D yellow fever virus, in the case of experiment four with statistical significance.