INHIBITION OF PHOSPHORYLATION OF GLUCOSE IN MOUSE BRAINS BY VIRUSES AND ITS PREVENTION BY PREPARATIONS OF DIPHOSPHOPYRIDINE NUCLEOTIDE

1. Inhibition of glucose utilization in homogenates of brains of mice infected with poliomyelitis virus (Lansing strain) is reported. The inhibition occurs with glucose, or fructose-6-phosphate as substrate. No inhibition occurs in the presence of hexosediphosphate. 2. Brain homogenates of mice infected with the Theiler FA strain of mouse encephalomyelitis virus show inhibition ranging between 45 and 85 per cent (average 73 per cent). 3. Purified preparations of the Lansing and the Theiler FA strain invariably inhibit glycolysis when added to homogenates of normal mouse brain. A similar, but much less consistent inhibition is provoked by adding high concentrations of non-neurotropic viruses (influenza A and tobacco mosaic virus) to normal mouse brains. 4. The magnitude of inhibition caused by the purified virus is a function of the virus concentration and depends on temperature and time of incubation of the virus-brain mixture. 5. The inhibition of glycolysis in the brains of mice infected with Theiler FA virus and in normal brain-Theiler FA virus mixtures is prevented by the addition of preparations of DPN and glucose.     

Lanoconazole, a new imidazole antimycotic compound, protects MAIDS mice against encephalitis caused by Cryptococcus neoformans

The protective effect of a new antifungal compound, lanoconazole, against Cryptococcus neoformans infection in C57BL/6 mice exposed to LP-BM5 murine leukaemia virus (MuLV) (MAIDS mice) was investigated. Mice were infected intratracheally with C. neoformans, strain 613D, 40 days after infection with LP-BM5 MuLV. They were treated orally with various doses of lanoconazole or with fluconazole 10 mg/kg (a positive control) once daily beginning 1 day after the fungal infection and continuing until the end of the experimental period. The number of C. neoformans cells in the lungs and brains of infected mice was determined. Lanoconazole and fluconazole had a similar inhibitory effect on the growth of C. neoformans in the brains and lungs of normal mice. Whereas lanoconazole inhibited the growth of C. neoformans in the brains and lungs of MAIDS mice, the pathogen grew in the brains of MAIDS mice treated with fluconazole. Lanoconazole reduced the number of C. neoformans in the brains of normal mice treated with a type 2 cytokine mixture, whereas fluconazole did not. A predominance of type 2 T-cell responses was demonstrated in MAIDS mice. Splenic T cells from MAIDS mice, but not those from normal mice, released interleukins 4 and 10 into the culture medium when they were stimulated with an anti-CD3 monoclonal antibody. These results suggest that lanoconazole may have the potential to inhibit the growth of C. neoformans in AIDS patients with a predominance of type 2 T-cell responses.     

Morphological and quantitative comparison between infectious and non-infectious forms of influenza virus

Electron microscopic study has revealed the morphological entity responsible for the rise in viral hemagglutinin observed in brains of mice after intracerebral inoculation of non-neurotropic strains of influenza virus. This rise in hemagglutinin, although dependent on inoculation of fully infectious virus, is not associated with an increase in infectious titer. The hemagglutinating principle is functionally similar to the "incomplete" influenza virus which can be obtained from chick embryos by serial egg-to-egg transfer of undiluted, infected allantoic fluid according to the method of von Magnus. A method has been described which facilitates selective adsorption of viral particles recovered from organ extracts on saponine-lysed ghosts of fowl erythrocytes. This procedure has been utilized in studying the morphology of non-infectious, hemagglutinating virus from chorio-allantoic membranes or mouse brains and in comparing these two forms with each other and with ordinary, infectious (standard) influenza virus. Standard virus isolated from allantoic fluids or membranes of infected eggs was found to contain uniform particles of predominantly spherical shape with smooth surface and even density, resembling those described by others. The appearance of such particles was not affected by the procedure of extraction and concentration used. In contrast, non-infectious, hemagglutinating virus obtained either from allantoic sacs ("undiluted passages") or from mouse brain was pleomorphic and seemed to consist of disintegrating particles. The majority appeared flattened and bag-like and had a rough, granular surface and reduced, uneven density. 37 per cent of the non-infectious particles isolated from mouse brain infected with the non-neurotropic strain WS had diameters in excess of 170 mµ, as compared with only 2 per cent of the particles of the parent strain itself. Regardless of whether or not the contrast in appearance of standard and of non-infectious particles was due to differing resistance to the preparatory treatment, it indicated the existence of basic structural differences between the two types of virus. Correlation of particle counts with hemagglutinin titers has shown that the non-infectious virus obtained from mouse brain is, unit for unit, an equivalent counterpart of standard virus derived from infected eggs. The end-point of hemagglutination in a pattern test corresponds for both forms to that dilution at which the ratio virus particles/red cells approaches one. The quantitative data based on particle counts support the assumption that non-infectious virus arises in mouse brain as a product of viral multiplication.     

Effect of 1-beta-D-arabinofuranosyl-E-5-(2-bromovinyl)uracil (brovavir) on experimental infections in mice with herpes simplex virus type 1 strains of different degrees of virulence.

In vivo antiherpesvirus effects of 1-beta-D-arabinofuranosyl-E-5-(2-bromovinyl)uracil (brovavir) were tested in two mouse model infections with herpes simplex virus type 1 (HSV-1) strains which showed different degrees of virulence in mice. Successful efficacies of oral and intraperitoneal (i.p.) treatments with brovavir were demonstrated in both intracerebral and i.p. infections with the HSV-1 WT-51 strain of moderate virulence. However, only weak or modest effects of brovavir were observed against the two model infections with a highly virulent strain, HSV-1 VR-3. Brovavir was not effective in reducing mortality of mice infected i.p. with HSV-1 KOS, which exhibited the highest virulence in mice among HSV-1 strains used when inoculated i.p. However, the drug had a significant effect on intracerebral infection with the KOS strain. Efficacies of oral treatment with brovavir were almost equal to those of i.p. administration in the model infections. After intracerebral inoculation, the VR-3 strain grew in brains of mice at a higher rate than the WT-51 strain. By oral treatment with 50 mg of brovavir per kg twice daily, replication of the WT-51 strain in the brains was markedly suppressed and was eliminated after transient elevation of the titer. Growth of the VR-3 strain in the brains was simply delayed by the drug treatment. Thus, the antiviral efficacy of brovavir in mice was affected by the degree of virulence of the challenge virus strain used for infection.     

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.     

STUDIES IN RODENT POLIOMYELITIS : V. INTERFERENCE BETWEEN MURINE AND MONKEY POLIOMYELITIS VIRUS

1. The murine strain of SK poliomyelitis virus interferes with the propagation in rhesus monkeys of SK, Aycock, and RMV poliomyelitis monkey virus. 2. This interference is demonstrable by intracerebral injection of mixtures of murine and monkey virus prepared in vitro as well as by separate injection of the two viruses by diverse routes. 3. Mixture tests carried out with graded doses of murine and monkey virus show that 0.5 cc. of a 10 per cent suspension prepared from the brains of paralyzed mice is capable of counteracting at least 100 minimal paralyzing doses of two strains of monkey virus. 4. No interference was demonstrable with suspensions of brains infected with murine virus which had been inactivated by heating for ½ hour at 75°C., or with suspensions prepared from normal mice, or with brain suspensions prepared from mice infected with herpes virus. 5. When murine virus is introduced into monkeys by the intravenous route, before or after intracerebral infection with monkey virus, distinct prophylactic or therapeutic results may be obtained. 6. Analysis of the figures shows that the success of interference depends upon (a) the size of the infecting dose of monkey virus, (b) the amount of murine virus injected, and (c) the choice of proper intervals between the injection of monkey and murine virus. 7. The mechanism of the interference phenomenon here described is discussed in the light of the available data.     

STUDIES ON THE BIOCHEMICAL,BIOPHYSICAL, AND IMMUNOGENIC PROPERTIES OF JAPANESE B TYPE ENCEPHALITIS VIRUS AND VACCINES

Studies on the biochemical, biophysical, and immunogenic properties of Japanese B type encephalitis virus and vaccines have been made in order to determine whether a purified vaccine suitable for human use could be obtained by means of differential centrifugation of extracts of infected mouse brains. Studies were also made on extracts of normal mouse brains, it was found that extracts of normal as well as of infected mouse brains contained fairly large amounts of several components of high molecular weight. Components having sedimentation constants near 5 and 40 Svedberg units were found in extracts of infected brains. However the rates of sedimentation of the different components were so similar that it was found impossible, from a practical standpoint, to secure a vaccine consisting largely of virus by means of differential centrifugation. It was also found that a considerable portion of virus was lost or destroyed in the centrifugation process so that it was impossible to secure an effective degree of concentration of immunogenic potency. Although vaccines possessing about twice the immunogenic potency of the starting material were obtained, it was concluded that it was not practical to purify and concentrate Japanese B type encephalitis virus in infected mouse brain extracts by means of differential centrifugation for the production of a vaccine on a large scale. The optimum pH stability range of Japanese B type encephalitis virus activity was found to be near pH 8.5. The virus is inactivated fairly rapidly at pH 7 and very rapidly at more acid reactions. The virus is inactivated rapidly near pH 10. Extracts of infected mouse brains with buffers near pH 8 containing disodium phosphate were found to possess slightly higher titers than saline extracts near pH 7. However vaccines prepared from such extracts were found to possess essentially the same immunogenic potency, hence, although extraction at the more alkaline reaction may perhaps remove more active virus, there was no indication that more immunogenic material was removed at the more alkaline reaction. The use of different diluents in the titration of virus activity and the use of different agents in the preparation and storage of virus suspensions were investigated. It was found that low titers were obtained when Ringer''s solution, phosphate buffer at pH 7, or saline-phosphate buffer at pH 8.2 were used as diluents but that high titers were obtained when 10 per cent rabbit serum in saline or in phosphate buffer, 10 per cent skim milk in saline or in phosphate buffer, or 1 per cent arginine at pH 8.3 were used. Undiluted skim milk adjusted to pH 8.4 was found to be as satisfactory as undiluted rabbit serum for the preparation of infected brain suspensions for storage at –70° C. A satisfactory neutralization test was conducted with virus stored in undiluted skim milk at –70° C. and subsequently diluted with 10 per cent skim milk in saline. The demonstration that skim milk can be substituted for rabbit serum in the storage, titration, and neutralization tests of Japanese B type encephalitis virus is of practical importance, for skim milk is more convenient to prepare and more readily available in many localities.     

Monoclonal antibody to Theiler''s murine encephalomyelitis virus defines a determinant on myelin and oligodendrocytes, and augments demyelination in experimental allergic encephalomyelitis

Theiler's murine encephalomyelitis virus (TMEV) causes a chronic demyelinating disease in mice. The mechanisms underlying the demyelination have not been fully elucidated. We have raised a mAb to TMEV (DA strain), H8, that reacts both with TMEV VP-1 and galactocerebroside (GC). In mouse brain cultures, cells positive for the mAb H8 epitope were double labeled with antibody to myelin basic protein, indicating that those cells were oligodendrocytes. Further, mAb H8 could immunostain myelin structures in frozen sections from mouse brains. When injected intravenously into mice with acute allergic encephalomyelitis, mAb H8 increased by 10-fold the size of demyelinated areas within the spinal cords. This is the first report demonstrating that an antibody to virus can enhance demyelination of a central nervous system disease. Ig fractions from the sera of mice with chronic TMEV infection had antibody(s) to GC, as well as to TMEV, as determined by ELISA. Furthermore, a competition ELISA for TMEV or GC antigen revealed that sera from these infected mice contained antibody(s) with the same specificity as mAb H8. Our results indicate that antibodies generated by immune response to TMEV can react with myelin and oligodendrocytes, and contribute to demyelination through an immune process.     

Effect of ribavirin and tributylribavirin on argentine hemorrhagic fever (Junin virus) in guinea pigs.

Subcutaneous injections of ribavirin into guinea pigs infected intraperitoneally or intracerebrally with Junin virus significantly increased the mean time to death but did not enhance survival of the animals. We found similar results with tributylribavirin. Virus replication was delayed, but not prevented, in ribavirin-treated infected guinea pigs. The animals usually died with high virus titers in their brains and frequently were paralyzed.     

EXPERIMENTAL TRANSMISSION OF INFLUENZA VIRUS INFECTION IN MICE : IV. RELATIONSHIP OF TRANSMISSIBILITY OF DIFFERENT STRAINS OF VIRUS AND RECOVERY OF AIRBORNE VIRUS IN THE ENVIRONMENT OF INFECTOR MICE

A mouse-adapted Jap. 305 strain of influenza A₂ virus was found to be much more readily transmitted from one mouse to another than the NWS strain of influenza A₀ virus although the two viruses were equally pathogenic for mice as judged by pulmonary virus titers and lung lesions. The survival of artificially created aerosols of virus and the quantity of airborne virus required to initiate infection in mice were identical for the two viruses. The difference in transmissibility was associated with the recovery of infectious airborne virus in the environment of mice infected with the Jap. 305 strain during the period of their maximum infectiousness, but not in the environment of mice infected with the NWS strain.     

Magnetic resonance spectroscopy reveals that activated monocytes contribute to neuronal injury in SIV neuroAIDS

Difficulties in understanding the mechanisms of HIV neuropathogenesis include the inability to study dynamic processes of infection, cumulative effects of the virus, and contributing host immune responses. We used H magnetic resonance spectroscopy and studied monocyte activation and progression of CNS neuronal injury in a CD8 lymphocyte depletion model of neuroAIDS in SIV-infected rhesus macaque monkeys. We found early, consistent neuronal injury coincident with viremia and SIV infection/activation of monocyte subsets and sought to define the role of plasma virus and monocytes in contributing to CNS disease. Antiretroviral therapy with essentially non-CNS-penetrating agents resulted in slightly decreased levels of plasma virus, a significant reduction in the number of activated and infected monocytes, and rapid, near-complete reversal of neuronal injury. Robust macrophage accumulation and productive virus replication were found in brains of infected and CD8 lymphocyte-depleted animals, but no detectable virus and few scattered infiltrating macrophages were observed in CD8 lymphocyte-depleted animals compared with animals not receiving antiretroviruses that were sacrificed at the same time after infection. These results underscore the role of activated monocytes and monocyte infection outside of the brain in driving CNS disease.     

Organ-specific selection of viral variants during chronic infection [published erratum appears in J Exp Med 1988 Jul 1;168(1):457]

This study demonstrates organ specific selection of viral variants during chronic lymphocytic choriomeningitis virus (LCMV) infection in its natural host. Isolates with different biological properties were present in the central nervous system (CNS) and lymphoid tissues of carrier mice infected at birth with the wt Armstrong strain of LCMV. Viral isolates from the CNS were similar to the wt Armstrong strain and induced potent virus-specific cytotoxic T lymphocyte (CTL) responses in adult mice and the infection was cleared within 2 wk. In contrast, LCMV isolates derived from the lymphoid tissues caused a chronic infection in adult mice associated with suppressed CTL responses. Revertants with wt Armstrong phenotype were present in the CNS of mice infected with a spleen isolate showing unequivocally the importance of host tissues in the selection of viral variants. These results provide a possible mechanism by which viral variants emerge in nature and suggest that tissue- and cell-specific selection is an important aspect of virus evolution.     

Evidence of ssDNA in tubulofilamentous particles: their relationship to scrapie-associated fibrils.

Abnormal tubulofilamentous particles were identified by electron microscopy using a simple touch negative staining technique from brains of mice infected with four strains of the scrapie agent. Treatment by three proteolytic enzymes and subsequent treatment with DNase and mung bean nuclease of grids prepared from the infected animals confirmed previous observations that the tubulofilamentous particles observed in scrapie-effected brains are complex structures. The core of the tubulofilamentous particle scrapie-associated fibrils was revealed by treatment with SDS. Treatment with proteolytic enzymes and subsequent treatment with DNase or mung bean nuclease or S1 nuclease also revealed typical and transitional stages of scrapie-associated fibrils. However, treatment with RNase A had no effect. The data suggest that nucleic acid is a single-stranded DNA protected by a protein coat.     

In vitro and in vivo activities of the hydroxynaphthoquinone 566C80 against the cyst form of Toxoplasma gondii.

The in vitro and in vivo activities of the hydroxynaphthoquinone 566C80 against the cyst form of Toxoplasma gondii were evaluated. In vitro treatment (100 micrograms of 566C80 per ml for 3 days) of cysts isolated from brains of mice infected for 1, 2, 3, 4, or 9 months resulted in loss of viability of the cysts and did not reveal any influence of the duration of in vivo infection on sensitivity to the drug. In vivo experiments to determine the effect of prolonged treatment with 200 mg of 566C80 per kg of body weight per day on cysts in brains of CBA/Ca mice infected with strain ME49 revealed a steady and significant decline in the numbers of cysts compared with the numbers in untreated controls. Histopathology of brains from control mice revealed inflammatory infiltrates around capillaries and in the parenchymas and meninges which were consistently less evident in the brains of treated mice. In addition, cysts were rarely observed in treated mice, whereas extensive inflammation and large numbers of cysts were found throughout the entire brain in control mice infected for the same period. The reduction in the numbers of cysts was evident as early as day 5 of treatment but was more marked at 8 weeks of treatment. The numbers of cysts in the brains of Swiss Webster mice infected for 3 or 6 months also significantly decreased following treatment for 15 or 30 days with the same dose of 566C80. Our results indicate that 566C80 has excellent activity against cysts of T. gondii both in vivo and in vitro and that sensitivity of the cysts to 566C80 is not affected by the duration of the infection in vivo.     

Dengue carrier culture and antigen production in human lymphoblastoid lines.

Replication of dengue type 2 (D2) viruses was studied in four lymphoblastoid cell lines; Raji, HR1, EB3 and RPMI 6410. The HR1 cell line failed to support D2 growth while the other cell lines showed varying susceptibility. Both D2 strain 16681 and strain New Guinea C (NGC) passaged in LLC-MK2 cells replicated readily in Raji cells, while a high mouse-brain-passaged NGC strain did not. A soluble complement-fixing (SCF) antigen from D2-infected Raji cells showed lines of identity with a D2SCF antigen prepared from infected suckling mouse brains. Electron microscopic studies of a D2 Raji carrier culture showed that virions were located in a membrane-vesicle complex in the cytoplasm of the cells. Precursors of viral particles were more frequently observed in the parts of the vesicle which had rough endoplasmic reticular membranes. Mature virus particles were observed often at the boundary of the other part of the vesicle, which consisted of smooth endoplasmic reticulum. Occasionally, a large crystalloid structure consisting of incomplete viral particles was seen in degenerative cells. Dengue carrier cultures in human lymphoblastoid lines may provide a convenient in vitro system for study of aspects of dengue virus-leukocyte interactions.     

Mixed infection with two tobamoviruses: the formation of particles containing the coat protein messenger RNAs of either virus.

Plants mixedly infected with the U2 strain of tobacco mosaic virus (T2MV) and sunnhemp mosaic virus (SHMV) and grown at 35 degrees, yield particles of the same modal lengths (300 and 40 nm) as those found in plants singly infected with SHMV, but not in plants infected with T2MV, which yield only the long particles. At least some of the particles produced in mixedly infected plants contain coat proteins of both viruses. When RNAs from these particles are translated in vitro the coat proteins of both viruses are produced, although when a mixture of RNAs from particles of SHMV and T2MV, grown separately, are translated in vitro only SHMV protein is produced. These and other results suggest that the short particles produced in mixedly infected plants contain both coat protein messengers.     

Adenovirus fiber protein produces synthesis of interferon in mouse spleen and macrophage cultures

The possibility of complementation between herpesvirus papio (HVP) and Epstein-Barr virus (EBV) was investigated. Strain 594S-F9 of HVP, unlike strain P3HR-1 of EBV, is not capable of inducing virus antigen synthesis in the EBV genome-carrying, nonproducer lymphoma cell line Raji. The effects of dual infection with these viruses were studied. With untreated viruses, the percentage of cells positive for viral antigens was equal to or slightly less than that in cultures infected with P3HR-1 virus only. However, if UV-irradiated P3HR-1 virus was employed in the dual infection, the relative number of virus antigen-positive cells was enhanced over cultures infected with P3HR-1 virus alone. These results suggest functional complementation between EBV and HVP.     

Specificity, Ly phenotype, and H-2 compatibility requirements of effector cells in delayed-type hypersensitivity responses to murine influenza virus infection

Delayed-type hypersensitivity (DTH) to infectious and to noninfectious (UV-irradiated) influenza A viral preparations was measured in mice by the increase in footpad swelling 24 h after injection of the eliciting virus. DTH mice sensitized with noninfectious virus was elicited only by virus that shared hemagglutinin specificity with the sensitizing virus, whereas footpad injection of a given A-strain virus (A/WSN) could elicit DTH in mice sensitized with a variety of infectious A- strain viruses, including some not sharing hemagglutinin or neuraminidase specificities. The effector T cells generated in mice sensitized with either form of virus were sensitive to anti-Ly 1.1 serum and complement, but not to anti-Ly 2.1 serum and complement. Adoptive transfer of DTH was H-2 restricted. With spleen cells from mice sensitized subcutaneously with either infectious or noninfectious virus, sharing of the IA region was both necessary and sufficient for successful transfer to occur. Cells recovered from infected mouse lungs, and secondary effector cells generated in vitro transferred DTH if injected into the footpad with the eliciting virus. The effector cells had the Ly 1 phenotype, and, in both cases, the cells were I restricted. These results contrast with earlier findings that transfer of DTH to lymphocytic choriomeningitis virus infection required K- or D- region sharing between donor and recipient. Thus, the earlier hypothesis that multiplying infectious agents such as viruses would "alter" K- or D-coded, rather than I-coded, structures is not generally correct.     

Electron microscopy of salivary gland viruses

A human and a mouse strain of the salivary gland virus have been examined by electron microscopy. The human strain was transmitted, prior to examination, to tissue cultures derived from human myometrial cells, while the mouse strain was examined in mice inoculated intraperitoneally. The nuclear forms associated with both strains of virus were morphologically similar. Nuclear inclusions, composed of particles interspersed with dense clumped chromatin, were a striking feature of infected cells. The cytoplasmic forms were of 2 types—one a 300 to 500 mµ homogeneous dense spherical form, and the other a target-like form composed of a central dense dot in a pale zone surrounded by a dense shell—the entire configuration measuring 100 to 180 mµ. The target-like particle appeared to be identical in both strains. The spherical cytoplasmic forms in cells infected with the human strain appeared to be solid, while in cells infected with the mouse strain there was evidence of formation of target-like forms within the spheres. Possible mechanisms by which infection of the cell may occur, as well as possible mechanisms and sites of multiplication of virus, are discussed.     

Serological relationships between the nucleocapsids of some planthopper-borne rhabdoviruses of cereals

Leaves infected with barley yellow striate mosaic virus (BYSMV) from Italy, wheat chlorotic streak virus (WCSV) from France, northern cereal mosaic virus (NCMV) from Japan, maize sterile stunt virus (MSSV) from Australia or Shiraz maize rhabdovirus (SMRV) from Iran were homogenized in buffered 1% Nonidet P-40, releasing intact nucleocapsids. These (except SMRV) were trapped on electron microscope grids using appropriate antisera and tested by decoration with serial dilutions of antisera to BYSMV, NCMV, MSSV, Moroccan wheat rhabdovirus (MWRV), wheat rosette stunt virus (WRSV) from China, and maize mosaic virus (MMV) from Venezuela. The results suggest that BYSMV and NCMV, though related, are distinct viruses; MWRV and WCSV are strains of BYSMV; MSSV is intermediate between BYSMV and NCMV but may be considered a strain of BYSMV; WRSV is a strain of NCMV; and MMV and SMRV are unrelated to each other and to the other viruses tested. SMRV was morphologically quite different from BYSMV, NCMV, WCSV and MSSV, all of which had the same morphology.