- Volume 15, Issue 3, 1972

The cytopathology of Pelargonium leaf tissues infected by an Italian isolate of the leaf curl virus (PLCV) was studied with the electron microscope. Virus particles were found in both parenchyma cells and conducting elements either irregularly scattered or in crystalline arrays. Clusters of virus particles were often seen within vesicle-like cytoplasmic extrusions protruding into the central vacuole. Cellular organelles were much damaged and internally disorganized. A peculiar budding condition of chloroplasts was observed. Virus particles were associated with nuclei and chloroplasts. In the latter, groups of particles not surrounded by visible membranes occurred apparently free in the plastidial stroma and in the buds developing from chloroplasts. The significance of the various pathological features is discussed.

Defined virulent and avirulent strains of Semliki Forest virus were used to infect young and old Porton mice by respiratory or intraperitoneal routes. The infectivity of the blood, brain and spleen from individual mice showed very wide variations; levels of infectivity in blood were apparently unrelated to those which developed later in brain.

Initial patterns of infection in brain and blood following avirulent or virulent infection were indistinguishable. By 24 to 36 hr after virulent infection the fastest responding mice showed higher incidence and level of infectivity in brain and spleen. By 48 hr after respiratory infection or 72 hr after intraperitoneal infection virus replication was suppressed in the brains of avirulent infected mice but not in those of virulent infected mice. For young adult mice of 25 to 32 days old, virulent and avirulent infections were further distinguished at 72 hr by the levels of infectivity in brain and spleen. Virulent infections leading to death were associated with brain infectivities above a critical level and spleen infectivities below a critical level. Avirulent infections were associated with the reversed condition.

These results are discussed in terms of the differential triggering of distinct lethal and protective responses.

Infection of chick embryo and baby hamster kidney cells with the virulent Newcastle disease virus (NDV) strains herts, texas and warwick and the mesogenic strain beaudette c produced a significant reduction in the thickness of the cell coat material. There was a temporal relationship between the reduction in coat thickness, the formation of polykaryocytes by cell fusion, and the release of lysosomal enzymes in cells infected with these strains. No reduction in coat thickness was found in cells infected with the avirulent strains, queensland and ulster, which did not produce cell fusion. Little lysosomal enzyme release was found in cells infected with these strains. Cell fusion and the reduction in coat thickness in cells infected with the virulent strains were inhibited by treatment of infected cells with anti-NDV serum without impairment of virus replication.

The morphology of Sendai virus envelope is described in detail. The interaction of the virus envelope and erythrocytes is examined by negative staining and ultrathin sectioning.

In this morphological study haemolysis is seen to progress in the following sequence: attachment of virus to cell membrane; dissolution of cell membrane at the site of attachment; dissolution of spikes opposite the dissolved cell membrane; fusion of the innermost virus (nanogranular) layer with the cell membrane proper; extension of this fused area with annular formation and extrusion of the virus internal components into the lumen of the cell; finally integration of the virus envelope into the cell envelope and detachment of the spikes. This stage could then lead to haemolysis and fusion. Haemolysis could occur through breaks in the unstable virus part of the integrated membrane and cell fusion could occur when this area is stabilized. Cell fusion of two or more cells is achieved by bridging with interspersed virus envelopes.

The inactivation of Escherichia coli bacteriophage T1 was determined after formation of aerosols from solutions in NaCl, NaBr, NaNO3 and Na2SO4. In all cases, survival varied rapidly with relative humidity, with a minimum near the relative humidity corresponding to a saturated solution of the salt. Survival was better when the aerosol was formed at low initial salt concentrations. Broth protected against aerosol-inactivation. Phage particles surviving surface-inactivation by shaking in solution were resistant to aerosol-inactivation.

The inactivation process in the range of humidities where the aerosol particles are fluid seems mainly to be due to surface-inactivation.

In two previous papers, Rubio-Huertos et al. (1968a), Fujisawa, Rubio-Huertos & Matsui (1971), inclusion bodies induced by carnation etched ring virus (CERV) were studied by light and electron microscopy. The inclusion bodies were composed of a dense matrix and virus particles. They were not limited by membranes and their general appearance, both in the light and electron microscopes, was very similar to that described for cauliflower mosaic virus (CAMV) Rubio (1956), Rubio-Huertos et al. (1968a) to which CEMV is serologically related, Hollings & Stone (1969).

In this paper, we describe the formation of these intracellular inclusions, and the presence of CERV virus particles in the nuclei of Dianthus barbatus infected cells.

Several small plants of Dianthus barbatus were inoculated mechanically with crude sap. of Dianthus caryophyllus L. infected with CERV. Samples were taken at intervals from the infected plants and fixed and embedded in Durcupan, as described previously, Rubio-Huertos et al. (1968b).