Genetic determinants of Sindbis virus neuroinvasiveness.

After peripheral inoculation of mice, Sindbis virus replicates in a variety of tissues, leading to viremia. In some cases, the virus can enter the central nervous system (CNS) and cause lethal encephalitis. The outcome of infection is age and virus strain dependent.

Loss of active neuroinvasiveness in attenuated strains of West Nile virus: pathogenicity in immunocompetent and SCID mice.

The neuropathogenicity of West Nile virus (WNV) and two derived attenuated strains WN25 and WN25A, was studied in young adult ICR mice and in severe combined immunodeficient (SCID) mice. Similarity in serology and RNA fingerprints were found between WNV and WN25. The viral envelope proteins of the attenuates differed from WNV in their slower mobility in SDS-PAGE due probably to the presence of N-linked glycan.

A novel variant of Sindbis virus is both neurovirulent and neuroinvasive in adult mice.

A strain of Sindbis virus (SV), recently isolated from mosquitoes in Israel, was used as a source for variants which differ in neuroinvasiveness and virulence that were generated by serial passage of SV in suckling and weanling mouse brain. At the 15th passage a neurovirulent variant was observed and designated SVN (neurovirulent). After 7 more passages in weanling mouse brains, another variant was observed and designated SVNI (neuroinvasive) and both were isolated and purified.

Spinal cord slices with attached dorsal root ganglia: a culture model for the study of pathogenicity of encephalitic viruses.

We describe here a culture system for long-term growth of organotypic slices of spinal cord, with attached dorsal root ganglia (DRG) derived from 13-14 day mouse fetuses. This is a unique in vitro tool in which both central and peripheral nervous tissue grow and differentiate in culture to become heavily myelinated. During cultivation the slices and the ganglia become flattened so as to allow microscopical and immunocytochemical staining.

West Nile virions aligned along myelin lamellae in organotypic spinal cord cultures.

Organotypic spinal cord cultures infected with West Nile Virus (WNV) exhibited a remarkable arrangement of virions among lamellae of the myelin sheath. Virions were first observed in neurons and only at day 4 after infection appeared within the myelin lamellae. Virions were observed only in the central myelin, aligned along the interperiod lines and therefore attached to the outer side of the oligodendrocyte membrane.

Different pathogenicity of encephalitic togaviruses in organotypic cultures of spinal cord slices.

The pathogenicity of two encephalitic Togaviruses, Sindbis virus (SV), an alphavirus, and West Nile virus (WNV), a flavivirus, was studied in organotypic cultures of fetal mouse spinal cord slices grown in roller tubes. After about 3 weeks in vitro, during which time the cultures became abundantly myelinated, they were infected either by 5 X 10(5) PFU SV or by 5 X 10(6) PFU WNV per culture. The viruses caused different patterns of cytopathogenicity: SV induced severe cytotoxicity in all glia cells and neurons with concomitant demyelination within 48 hr.

Sodium dodecylsulphate induces a breach in the blood-brain barrier and enables a West Nile virus variant to penetrate into mouse brain.

A novel and convenient assay was used to determine the effect of recombinant Interleukin-2 (IL-2) on the function of the blood-brain barrier (BBB). The assay is based on a variant of the West Nile virus, WN-25, which had lost its neuroinvasiveness but not its neurovirulence. WN-25, when injected intravenously, can cause the death of mice only if the function of the BBB is impaired.

Determination of human IgG and IgM class antibodies to West Nile virus by enzyme linked immunosorbent assay (ELISA).

An enzyme-linked immunosorbent assay (ELISA) was developed and used for the detection of IgG and IgM antibodies to West Nile virus in human sera. Thirteen paired sera of clinical cases and 24 control sera taken randomly from a blood bank repository were tested. The sera were reacted in microtiter plates coated with PEG-treated WNV antigen.

Ultrastructural and virological aspects of Langat virus-induced SSPE in suckling hamsters.

The morphology of subacute sclerosing panencephalitis (SSPE) lesions in hamsters following i.p. inoculation of Langat virus was studied by light microscopy and electron microscopy.

Assay of togavirus haemagglutination-inhibition antibodies by the micro method: loss of information and its rectification.

Haemagglutination inhibition (HI) activity was assayed by the micro and macro methods in immune sera prepared against four togaviruses. HI titres were always 4 to 8 times lower by the micro method, and coincided with 4 to 8 times lower haemagglutinin titres in micro method assays. Because of this phenomenon, positive sera with HI macro method titres lower than 1: 80 will be false negative for HI by the micro method when tests begin at a 1: 10 serum dilution.

Some properties of togavirus hemagglutinin studied with the aid of kaolin-adsorbed virus.

Acidification (at pH 5.75) of Semliki Forest virus and West Nile virus suspensions completely eliminated their hemagglutinating activity within several minutes, but did not affect their infectivity or change their ability to absorb homologous hemagglutination-inhibition antibodies. In order to assay antibody absorption it was necessary to remove all of the immune complex from the reaction mixture, because the immune complex inhibited additional hemagglutinin.

Prevalence of antibodies to arboviruses in various animals in Israel.

A serological survey of the prevalence of arbovirus antibodies in various mammals and birds was made in Israel during the years 1959-60, employing the haemagglutination-inhibition technique and using group-A and group-B antigens. High proportions of the animals of several species were found to be positive to group-B arboviruses. Most of these animals showed higher titres against the West Nile virus than against that of turkey meningoencephalitis, but in some cases there were higher titres against the latter virus.