Studies in tissue culture on pH-stability of rinderpest virus

The pH-stability of three strains of rinderpest virus, propagated in tissue cultures, was investigated at 4°C. in veronal-acetate buffers (Michaelis) of pH 3·0–10·7.

An attenuated laboratory strain, in its 95th culture passage (RBOK), showed maximal stability in the pH range 7·2–8·0, the half-life being about 3·7 days. It was relatively stable from pH 4·0 to 10·2, the half-life at the extremes of this range being over 2 hr. At pH 3·0 the infectivity declined very rapidly, the half-life period being 24·0 sec.

One virulent strain (RGK/1) showed a significantly lower resistance than strain RBOK at pH 3/0, probably also at pH 5·0. The inactivation rates for these two strains were, however, not greatly different at pH 10·7. The other virulent strain (RBT/1) was even less stable than RGK/1 at pH 4·0 or 5·0 but of a comparable stability at pH 9·0 and 10·2.

These findings are discussed in comparison with published data on the related viruses of measles and canine distemper. The importance of strain differences in studies of this kind is stressed.

We are grateful to Mr C. S. Rampton, A.I.M.L.T., and Mr L. W. Rowe, F.I.M.L.T., for help in the preparation of the diagrams. This paper is published with the permission of Mr H. R. Binns, C.M.G., O.B.E., Director, E.A.V.R.O.

The propagation of the virus of epizootic hemorrhagic disease of deer in newborn mice and HeLa cells

The New Jersey strain of EHD virus has been propagated in newborn Swiss mice by the intracerebral route and is regularly lethal beyond the first serial mouse passage. A complement-fixing antigen prepared from the brains of infected mice reacts positively with the sera of deer recovered from infection with either the New Jersey or South Dakota strain of virus, but not with the serum of normal deer. The mouse-passaged virus induced an inapparent infection in an experimental deer. The virus can also be grown serially in HeLa cell culture and induces a characteristic cytopathic effect. It is neutralizable in such cultures to high titer by the sera of deer recovered from EHD (New Jersey strain) and to lower titer by the serum of a deer recovered from EHD (South Dakota strain). Normal deer serum does not neutralize the virus in tissue culture. The HeLa cell-passaged virus induced typical lethal EHD in an experimental deer and virus could be recovered from most of the tissues of this animal in HeLa cell culture. An unexplained prozone of inhibition of cytopathogenicity at low dilutions was observed in cultures of some of the organs. The fact that EHD virus exhibited a limited sensitivity to sodium desoxycholate suggests that it may belong in the arbor virus group.

Electron microscopic studies on the development of vesicular stomatitis virus in KB cells

The development of vesicular stomatitis virus in KB cells was studied by electron microscopy. Sections of infected cells were made 1, 4, 7, 10, and 20 hours after inoculation of the cell cultures, and at the same intervals the supernatant fluid was assayed for virus titer by the plaque test in chick embryo cells. At 10, 14, and 20 hours after inoculation, virus rods were observed attached to cytoplasmic membranes, inside cytoplasmic vacuoles, and attached to the membranes delimiting these vacuoles; they were also found on the surface membrane of the cells. Besides the rods, spherical particles of different sizes and shapes were seen. The possibility that these structures are related to the development of virus rods is discussed. A similarity was noted between the site of maturation of vesicular stomatitis virus rods and that of some other arbor viruses.

An electron microscope study of the development of SV40 virus

Kidney cells, predominantly from Cercopithecus monkeys but also from baboons, were infected in vitro with the SV40 virus. The infectious cycle was studied with the electron microscope by means of thin sections of cells fixed from 3 hours up to 11 days after infection. The frequency of virus formation and various nuclear and cytoplasmic lesions in relation to the infection are described. The virus particles appear in the nucleus in close contact with the chromatin. In a small number of cells they have been observed as early as 10 to 12 hours after infection, but most often they appear 24 to 48 hours afterward. Their mean diameter is 33 mµ. They have no membrane and are frequently arranged as crystal-like structures. In addition to the appearance of virus, one observes various lesions in the nucleoplasm and particularly in the nucleolus, which shows an early hypertrophy and produces unusual, dense condensations in contact with the nucleolonema. The importance of these nucleolar lesions and the relationship between the SV40 virus and the polyoma, common wart, and Shope papilloma viruses are discussed.

The uptake and development of vaccinia virus in strain L cells followed with labeled viral deoxyribonucleic acid

Vaccinia virus which had its DNA labeled with thymidine-H³ was purified and used as inoculum for L cells growing in suspension. Samples taken over an 8-hour period after infection were studied by light and electron microscopic autoradiography. Within 20 minutes of its being taken up at the cell membrane in phagocytic vesicles, the outer coat of vaccinia becomes disrupted and the virus core containing the labeled DNA passes into the cytoplasmic matrix. Within 1 hour after inoculation the labeled material passes out of the cores into zones of viroplasm, where cores or remnants of cores are gathered and the label becomes more concentrated by 3 hours after inoculation. Most of the label is conserved in the viroplasm areas during the remainder of the experiment. However, 6 hours after inoculation a very small proportion of progeny virus in the cytoplasm, morphologically distinct from the cores of the inoculum, has associated with it labeled material, perhaps derived from the DNA of the inoculum.

PLAQUE ASSAY FOR PSITTACOSIS VIRUS IN MONOLAYERS OF CHICK EMBRYO FIBROBLASTS

Piraino, F. (City of Milwaukee Health Department, Milwaukee, Wis.), and C. Abel. Plaque assay for psittacosis virus in monolayers of chick embryo fibroblasts. J. Bacteriol. 87:1503-1511. 1964.-A tissue culture system for the assay of 6BC psittacosis virus by plaque production on chick embryo fibroblast cells is described. Experiments are given which characterize the specificity of the reaction and identify factors found to cause variations in plaque counts. The statistical data obtained indicate this assay to be a precise and highly reliable procedure for the detection of 6BC virus and antibody.

COMPARISON OF THE ELUTION AND ADSORPTION OF PICORNAVIRUSES BY COTTON AND CALCIUM ALGINATE WOOL SWABS

The recovery of picornaviruses by cotton and calcium alginate wool swabs was studied by use of prototype strains of poliovirus 1, echovirus 1, coxsackievirus A9, and rhinovirus 16/60. No significant differences in recovery of viruses by the two types of swabs could be demonstrated. It is suggested that use of cotton swabs in the virus laboratory be continued, since wool swabs may favor the recovery of undesirable bacterial contaminants. Adsorption of viruses by cotton and wool swabs was similar from virus-buffer mixtures at pH 4.0, 7.0, and 8.0 at 24 and 37 C. Elution of virus from cotton and wool swabs was also studied. There was no significant difference in the amount of virus eluted at pH 5.5, 7.1, or 8.4.