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In the Kurgan region, the Siberian subtype of the tick-borne encephalitis virus (TBEV) is dominant. The vaccines prepared from Far-Eastern TBEV subtype are used in this area. Among TBE patients in 2007-2011, 23.79% were vaccinated according to complete or incomplete course. 76.9% of persons were vaccinated with Encevir vaccine, Tomsk. An unusual focal form of TBE with fulminant disease with lethal outcome was developed in a patient who was vaccinated 6 times with heterotype vaccines produced using the strains of the Far-Eastern TBE subtype. Inoculation of immunoglobulin in hospital produced aggravation of clinical symptoms, development of convulsions, brain oedema, and respiratory distress syndrome. The disease continues only 55 hours from first symptoms to fatal outcome. Siberian subtype of TBEV was isolated from patient spinal cord (Kurgan-118-2010 strain). Possible mechanisms of this disease are discussed.

The review deals with the basic characteristics of prion diseases of man and animals. It details the studies of some little known aspects of the pathogenesis of prion diseases and their lifetime diagnosis, conducted at the M. P. Chumakov Institute of Poliomyelitis and Viral Encephalitides, Russian Academy of Medical Sciences, in the past decades.

Effect of gentamicin, an aminoglycoside antibiotic, on the persistence of tick-borne encephalitis (TBE) virus in Syrian hamsters and Macaca iris in remote periods (70-434 days) after inoculation is studied. Attempts at virus isolation from animals treated with gentamicin failed. Unlike other aminoglycosides, e.g. streptomycin, gentamicin exerted no immunodepressive effect; moreover, immunocorrection was observed in some experiments on monkeys and hamsters. None of the 10 previously tested antibiotics elicited such an effect or inhibited the persisting TBE virus. Morphological study of the central nervous system in hamsters and monkeys showed that injection of gentamicin did not cause an exacerbation of chronic encephalitis. The mechanism of immunocorrecting effect of gentamicin is to be further investigated.

Morphological changes in the thymus, spleen, and brain are analyzed in white mice injected 16-component oligonucleotide (ON) pE16 complementary to the NS3 protein gene sequences of tickborne encephalitis (TBE) virus in doses of 1 to 0.001 nM. ON stimulated thymic and splenic cells. Besides the stimulating effect, injection of ON to mice infected with TBE enhanced the destruction of lymphocytes and boosted the macrophagal activity, which was paralleled by a decrease in the intensity of virus-specific injuries in the brain. Thus, the antiviral activity of ON may be due to not only the fact that it is complementary to the TBE virus genome, but to stimulation of the immune system, specifically, the thymus and T-related elements, as well.

The involvement of the thymus in the infectious process was established in Syrian hamsters inoculated intracerebrally with tick-borne encephalitis (TBE) virus of different degrees of virulence. Active virus reproduction, amplification of virus antigen, massive evacuation of thymocytes, morphological lesions in the epithelial stroma and Hassall's bodies were observed. The lesions were more marked after inoculation of the highly virulent Sophyin strain. The unusually high plasmatization of lymph nodes adjacent to the thymus observed after inoculation with the low-virulent 41/65 strain is described. The results indicate that the involvement of the thymus is an important factor in the pathogenesis of TBE.

The model of Chinese hamster (Cricetulus griseus) cell line infected with Sindbus virus was used to show that the presence in the maintenance medium of 0.01-0.1 micrograms/ml of colcemide inhibited the development of cytopathic changes, accumulation of viral antigens, and virus-specific complement-dependent cytolysis without affecting infectious virus production. The addition to the medium of 0.5% immune serum to Sindbis virus resulted not only in a similar inhibition but in a decrease of infectious virus titres. The latter effect was observed upon the addition of both colcemide and antiserum. Possible mechanisms of inhibition are discussed.

The Si strain isolated from a patient with subacute sclerosing panencephalitis like reference measles virus strains was shown to induce in cell cultures formation of symplasts and spindle-shaped cells, cytoplasmic and intranuclear inclusions, pathology of mitosis, appearance of intracellular and surface virus-induced antigens. The presence of the latter caused cell cytolysis under the effect of measles immune sera and complement.

Virus-specified immune cytolysis has been shown in mouse cell cultures infected with vesicular stomatitis virus under the action of specific virus antibody and active complement. The exogenous mouse interferon failed to enhance the cellular plasmalemma permeability or to inhibit cellular adsorption of infectious and inactivated virus as well as the lysis of the cells in the presence of the antiviral serum and complement. The interferon localization was studied by the method of fluorescent antibodies. In vital preparations the exogenous species-specific interferon was revealed on the surface of most cells in the treated cultures; in the fixed preparations of the same cultures the interferon was found only in the form of small lumps in the cytoplasm of few cells. A decrease in immune cytolysis was observed in the cultures treated with the interferon 20-24 hours before the infection, that can be accounted for by the inhibitory action of the interferon on the viral replication and the reduction of the number of the virus-inducing antigens in the cellular plasmalemma.

Measles neuroinfection was studied in 3-week Syrian hamsters inoculated intracerebrally with the neurovirulent Edmonston-42 strain of measles virus. The infectious virus was shown to be recoverable from the animals' brains both early after infection (up to 16 days) and at later intervals (28--63 days). At the same intervals (up to 69 days), measles antigen was demonstrated in brain impressions. All the animals under study had RNA-containing inclusions in some cells, slight cellular infiltrates and some oedema. Brains of a number of animals showed moderate inflammatory changes, dystrophic lesions in neurons, and microglial proliferation. The influence of the age and general resistance to the pattern of the course of measles neuroinfection in Syrian hamsters was demonstrated.

Pathomorphology of the infection caused by Powassan virus strains isolated in the Primorsky Kray was studied in white mice. The central nervous system of the animals sacrificed in the time course of the infectious process was studied by light and luminescent microscopy. Severe diffuse inflammatory-degenerative changes were found in the brain and spinal cord. Immunofluorescence revealed cytoplasmic localization of the virus antigen in neurons, glial and connective tissue cells.

The properties of the Vasilchenko strain of tick-borne encephalitis (TBE) virus and its 3 variants isolated at various stages of persistent infection (383, 453, and 535 days) in Macaca rhesus monkeys and Syrian hamsters with different forms of the chronic TBE were studied. The process characterized by chronic focal inflammatory-degenerative changes in the brains of hamsters without the disturbance of motor functions was associated with persistence of different kinds of virus-specific antigens without virulent virus production. Brain explants of this group of hamsters yielded a virus with cytopathogenic properties but not pathogenic for mice. In a chronic disease developing without the initial acute period, a virus was recovered from hamsters which proved to be virulent for mice and to possess the hemagglutinating and high invasive activity. The most virulent strain was isolated from monkeys with continuously progressive chronic encephalitis with steady paralysis of the extremities. This isolate differed from the parental Vasilchenko strain by a high pathogenicity for hamsters by intracerebral and subcutaneous routes, and thermostability at 50 degrees C.

Infection of random-bred mice with Sindbis virus at various intervals of pregnancy results in increased resistance of their offsprings to infection with this virus in the first days after birth. Antibodies present in the colostrum and milk of immunized females play an important role in decreasing the susceptibility of sucklings to alphavirus infection.

Four cell lines derived from tumors induced by adenovirus SA7, its DNA (intact and fragmented with restrictase Sal-1), as well as isolated C-Sal-1 fragment (19.5% of genome) containing oncogene were studied. All the cell lines had the phenotypic markers of tumor cells, similar tumorigenicity, and produced T- and S-antigens. The line derived from the tumor induced by intact DNA contained the smallest adenovirus SA7 genome region (12%) which suggests that the information required for the synthesis of T and S antigens of adenovirus SA7 lies within the limits of this genome region.

Inoculation of random-bred mice with Sindbis virus at various periods of pregnancy resulted in the development of marked changes and loss of 24.7% of fetuses when mice were infected at the stage of placentation. Retardation in the development and death of progeny in females infected at later stages of pregnancy were observed. Antibody production was shown to be enhanced in pregnant mice as compared with non-pregnant. Possible mechanisms of increased susceptibility to alphaviruses during pregnancy and in early stages of ontogenesis are discussed. A potential danger of development of embryo- and fetopathies in humans is considered on the basis of the above studies and the data on equivalent stages of prenatal development of mice and human beings.

Studies of cell lines obtained as a result of in vitro transformation by bovine adenovirus type 3 at low multiplicities of infection: BHK-21/13-780 and BHK-21/13-782 (8 X 10(-5) TCD50/cell) and hamster embryo tissue HET-1 and HET-2 (2 X 10(-3) TCD50/cell) showed them to possess some oncologic characteristics typical of spontaneous neoplasia such as low degree of differentiation, high rate of cell growth, reduced adhesiveness, high tumorigenicity. In hamster embryo tissue cells (HET) transformed in vitro virus-specific transplantation antigen and S-antigen were found. In transformed cells of the initial BHK-21/13S culture possessing the capacity of transforming spontaneously and under the effect of oncogenic viruses no transplantation antigen coded for by bovine adenovirus type 3 were detected. It is suggested that the above-described transformed cell lines be used as experimental models for investigation of the processes of transformation and tumour progression.

In the first few hours after inoculation of Chinese hamster cells with western equine encephalomyelitis virus the mitotic activity of the cells did not change significantly but mitoses stopped mainly in the stage of metaphase and had all signs of pathological mitoses. Treatment of the cells for 1 hour with the homologous antiviral immune serum and complement resulted in destruction and death of practically all cells except those in the state of mitosis. In the latter specific fluorescence of virus antigen was demonstrated by the fluorescent antibody technique same as before treatment with the homologous immune serum and complement. Resistance of mitoses to immune cytolysis is probably conducive to virus persistence.

Conditions of activation of persistent infection caused by subcutaneous inoculation of Syrian hamsters with the B-383 and Vasilchenko strains of tick-borne encephalitis virus (TBE) were studied. After 2 administrations of cyclophosphane (CP) on day 170 of infection clinically manifest disease developed in some animals with increasingly severe pathomorphological lesions in the CNS. Several variants of activated TBE virus were isolated from brains and spleens of CP-treated hamsters. The activation of persistent infection was observed in the presence of marked decreased of humoral immunity level, weight of the thymus, and values of spontaneous rosette-formation.

On the model of Syrian hamsters inoculated intracerebrally with 9 tick-borne encephalitis (TBE) virus strains varying in virulence, the specific involvement of the organs of the immune system (spleen and lymph nodes) was established and morphological features of the process described. The most severe destructive changes of these organs were found in the hamsters inoculated with highly virulent strains which appeared to be one of the factors leading to 100% death of the animals. In hamsters inoculated with strains of low virulence, the destructive changes in immunogenesis organs were less marked, but active migration and proliferative processes developed in them. The above-described differences in the involvement of the immune system organs should be taken into consideration in the interpretation of TBE pathogenesis and evaluation of the degree of virulence of the virus strains.

The features of pathogenesis of infection caused in adult Balb/c mice intraperitoneally infected with Sindbis virus, virulent or attenuated strains of West Nile (WN) virus, individually or in combination with Rauscher leukemia virus (RLV) were studied. The influence of the latter on the course of togavirus infections was characterized by 3 features: (a) different effects on the visceral and neural phases of the pathogenesis (increased period of viremia and virus reproduction in the viscera did not lead to stimulation of virus reproduction in the CNS); (b) changes in the time of togavirus persistence in the infectious form; (c) the dependence of the observed effect on the togavirus properties.

The effect of streptomycin (C) on persistence of tick-borne encephalitis (TBE) virus in Syrian hamsters infected with 3 strains of the virus (41/65, Aina/1448, Vasilchenko ) intracerebrally or subcutaneously was studied. In the animals not given C the infectious virus could be detected in the brain for 8-14 days but not later although their organs (mostly brains and spleens) contained the hemagglutinating antigen and viral antigen detectable by immunofluorescence. Intramuscularly C was given twice daily for 13-35 days in a daily dose of 200 mg/kg. The C-treated hamsters yielded 7 virulent TBE virus strains: 3 from the brain, 3 from the spleen, and one from the blood. No virus could be isolated from the liver, kidneys, or lungs despite the use of various methods for isolation including tissue explantation. The activating effect of C was observed against the background of 4-fold decrease in the titre of complement-fixing and antihemagglutinating antibodies. C exerted its activating effect both at early (70 days) and late (9 months) stages of TBE virus persistence. The activating effect of C appears to be due to its immunosuppressive properties and neurotoxic action on the CNS.

Reciprocal stimulation or inhibition are observed in double infection of mice with Rauscher leukemia virus (RLV) and togaviruses Sindbis or West Nile (WN). Stimulation of togavirus infections is manifested by the enhancement of the visceral phase of pathogenesis without subsequent activation of togarivus reproduction in the CNS. This effect is accompanied by enhanced togavirus replication in splenocytes, a decrease in the number of antibody-producing cells in the spleen, a decrease of antihemagglutinins titer in the blood without any significant change in the virus-neutralizing antibody and interferon titers. RLV-induced immunosuppression is termporary and of varying intensity with regard to individual parameters of immune response and to different variants of WN virus (highly virulent, poorly virulent). It is assumed that the differentiated and temporary nature of the immunosupressive effect of RLV is conducive to selective stimulation of the visceral phase of togavirus reproduction followed by inhibition of the neural phase under the influence of restored immune mechanisms and interferon. Because of the defects of humoral and cellular immunity, however, no complete elimination of togavirus occurs and conditions for its long-term persistence are created.

The results of a comparative study of different routes of inoculation of simian hemorrhagic fever (SHF) virus to Macaca monkeys are presented as well as the results of virological examinations of sick animals. Only the parenteral route of inoculation has been found to be effective. After virus penetration, a long-term viremia and generalization of the infection are observed. The virus is found in the brain, the spinal cord and bone marrow, the spleen, the liver, the kidneys, the cerebrospinal fluid, the urine and nasopharyngeal washings. By the fluorescent antibody technique the virus-specific antigen is demonstrated in the capillary endothelium, neurons and glial cells of the brain, and in the reticulo-endothelial and macrophagal elements of parenchymatous organs.

The method of fluorescent antibody (MFA) has first been used for the study of regularities of human interferon biosynthesis in superinduced cells. The dynamics of the appearance and accumulation of interferon in individual cells and the dependence of these processes upon the time elapsing since the termination of superinduction were determined. Clear-cut inverse relationship between the interferon content in cells (MFA) and the interferon content in the culture fluid (titrations of biological activity) was established.