Effect of tacaribe virus infection on host cell protein and nucleic acid synthesis. (41/73)

Tacaribe virus stocks were prepared which induced definite lytic responses in Vero cells infected at multiplicities giving synchronous infection. Under these conditions, the first signs of cytopathic effect (c.p.e.) appeared at about 30 h post-infection and cell lysis occurred after 40 h. Before the onset of cytopathic changes, the virus induced inhibition of host cell protein, DNA and RNA (primarily rRNA) synthesis. These were designated c.p.e. (+) virus stocks. The effect of virus on host cell macromolecular synthesis and development of c.p.e. were not related to the virus isolate, but to the conditions under which the virus was produced. Thus, from a single virus clone, working stocks were derived which could or could not induce inhibition of host cell functions and c.p.e. development. The virus stocks that did not induce inhibition are defined as c.p.e. (-). Analysis of [3H]leucine-labelled proteins from Vero cells infected with either the c.p.e. (+) or the c.p.e. (-) virus stocks revealed synthesis of two virus-specific polypeptides migrating with mobilities corresponding to mol. wt. 68 000 and 79000. These are presumed to correspond, respectively, to the nucleoprotein and to the minor polypeptide p79. In cells infected with the c.p.e. (+) virus stock, the virus-specific polypeptides were synthesized at times when there was a drastic inhibition of host cell protein synthesis. The yield of infectious progeny during the first 24 h of infection is similar in Vero cells infected with either the c.p.e. (+) or the c.p.e. (-) virus stocks. The proportion of defective interfering particles was much higher in the c.p.e. (-) than in the c.p.e. (+) virus stocks. The results presented here are the first demonstration that an arenavirus affects the biosynthetic machinery of the host cell.  (+info)

Isolation of an arenavirus closely related to Lassa virus from Mastomys natalensis in south-east Africa. (42/73)

Five unidentified virus strains were recovered from the multimammate mouse ,Mastomys natalensis, during the course of studies on arbovirus infections in Mozambique. These agents were found to be morphologically and immunologically related to Lassa virus. Four of 19 sera from Mastomys captured in the study area had antibodies to both Lassa virus and one of the unidentified strains. Although not definitive, the differences noted in results of complement fixation and indirect immunofluorescent tests suggest that these viruses from south-east Africa are not identical to West African Lassa virus.  (+info)

Characterization of temperature-sensitive mutants of Pichinde virus. (43/73)

The synthesis of viral proteins and S RNAs in cells infected with 12 temperature-sensitive (ts) mutants of Pichinde virus was characterized. The mutants could be divided into five groups on the basis of the patterns of radiolabeled proteins immunoprecipitated from infected-cell lysates. Markedly reduced nucleoprotein levels and undetectable amounts of glycoprotein precursor and L protein were synthesized at the nonpermissive temperature in cells infected with five of the mutants. Reduced but detectable amounts of the viral proteins were synthesized at the nonpermissive temperature in cells infected with a single mutant. Two mutants were associated with the intracellular accumulation of glycoprotein precursor, which was apparently not transported across the cell membrane in cells incubated at the nonpermissive temperature. The synthesis of viral proteins in cells infected with two mutants was indistinguishable from those produced by wild-type virus. Two additional mutants were associated with markedly reduced amounts of immunoprecipitable proteins in infected cells incubated at both the permissive and nonpermissive temperatures. Analysis of viral RNA with radiolabeled single-stranded cDNA probes representing complementary and genomic-sense sequences corresponding to the 3' region of S RNA revealed two basic patterns of viral RNA synthesis. At the nonpermissive temperature, the synthesis of complementary- and genomic-sense sequences and mRNA of the S RNA segment was markedly reduced in cells infected with representative members of these mutant groups, suggesting the presence of mutations altering transcriptase activity. Viral-complementary- and genomic-sense sequence and RNA synthesis, as well as nucleoprotein mRNA in cells, was detected in reduced amounts for mutants associated with reduced levels of proteins at both temperatures. Interestingly, RNA species larger than the S RNA segment were detected in cells infected with some of the mutants, especially those with putative transcriptase lesions. These molecules suggest a possible oligomeric intermediate in the synthesis of S RNA of Pichinde virus.  (+info)

Immune serum increases arenavirus replication in monocytes. (44/73)

The U937 monocytic cell line was used to determine whether antibodies could facilitate infection and replication of the arenaviruses, Pichinde virus (PV) and Lassa fever virus (LFV). When high dilutions of PV-immune serum were added to cultures simultaneously with PV inoculum, virus replication was dramatically (1000-fold) increased. Low dilutions of this antiserum neutralized the virus. LFV also replicated in U937 cells. The presence of LFV-specific immune serum in the growth medium increased the viral titre as much as 10,000-fold. Addition of heat-aggregated IgG partially inhibited antibody-mediated enhancement, probably by inhibiting the binding of immune complexes to the monocytic cells.  (+info)

Localization of an arenavirus protein in the nuclei of infected cells. (45/73)

Host cell nuclear involvement in an arenavirus infection was examined by immunofluorescence. Both polyclonal antisera and monoclonal antibodies specific for the major nucleocapsid (N) polypeptide revealed virus-specific nuclear inclusions in Pichinde virus-infected Vero cells. Immunoprecipitation of infected cell extracts with the anti-N monoclonal antibodies and subsequent analysis by SDS-PAGE, identified two N-related proteins with mol. wt. of 36,000 (p36) and 28,000 (p28) in addition to the N polypeptide. Only those monoclonal antibodies which precipitated p28 as well as N and p36 were found to produce nuclear as well as cytoplasmic fluorescence. These findings suggest that either the p28 protein itself or a conformational variant of N was the nuclear antigen detected.  (+info)

Synergistic antiviral effects of ribavirin and the C-nucleoside analogs tiazofurin and selenazofurin against togaviruses, bunyaviruses, and arenaviruses. (46/73)

Binary combinations of the N-nucleoside ribavirin (1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide) and the C-nucleoside analog selenazofurin (2-beta-D-ribofuranosylselenazole-4-carboxamide) or tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide) were tested in vitro for activity against Venezuelan equine encephalomyelitis, Japanese encephalitis, yellow fever, Rift Valley fever, Korean hemorrhagic fever, and Pichinde viruses. The 50% effective dose for each compound alone or in a series of combinations was determined with a plaque reduction assay. Combinations of ribavirin and selenazofurin were synergistic against Venezuelan equine encephalomyelitis, Japanese encephalitis, yellow fever, and Pichinde viruses, with fractional inhibitory concentrations of 0.1, 0.2, 0.4, 0.4, respectively, but showed additive effects against Korean hemorrhagic fever and Rift Valley fever viruses. Combinations of ribavirin and tiazofurin were synergistic against yellow fever and Japanese encephalitis (fractional inhibitory concentrations, 0.41 and 0.48, respectively) but showed additive effects against Korean hemorrhagic fever virus. Combinations of selenazofurin and tiazofurin had additive effects against Japanese encephalitis, yellow fever, and Korean hemorrhagic fever viruses. The effect of combinations on cell toxicity was additive, both in monolayers of nondividing cells incubated under agar for the same period as the plaque assay and for rapidly dividing cells given short-term exposure (4 h), followed by determination of the proportion of surviving cells with a colony forming assay.  (+info)

Exotic viral diseases. (47/73)

Marburg virus disease, Lassa fever, monkeypox, and Ebola virus diseases of humans have all been recognized since 1967. These are examples of some of the exotic virus diseases which through importation may present a potential public health problem in the United States. Some of these viruses are also highly hazardous to laboratory and medical personnel. This paper is a review of the general characteristics, the epidemiology, and laboratory diagnosis of the exotic viruses which have been described during the last 25 years.  (+info)

Characterization of polypeptides immunoprecipitable from Pichinde virus-infected BHK-21 cells. (48/73)

Using hamster anti-Pichinde virus serum, we immunoprecipitated polypeptides from BHK-21 cells infected with Pichinde virus. Seven immunoprecipitable polypeptides exhibited a time- and multiplicity of infection-dependent appearance when the cultures were pulse-labeled with L-[35S]methionine for 1 h. The predominant polypeptide was a nucleoprotein (NP) of 64,000 daltons. Components of 48,000, 38,000, and 28,000 daltons, when analyzed by two-dimensional tryptic peptide mapping, were found to be derived from NP. After a 3-h chase period, polypeptides of 17,000, 16,500, and 14,000 daltons were evident, and peptide mapping revealed that these three polypeptides were also related to NP. During a series of pulse-chase experiments, a 79,000-dalton glycoprotein (GPC) was cleaved to glycoproteins of 52,000 and 36,000 daltons. Radiolabel in a polypeptide of approximately 200,000 daltons (L) did not chase into smaller cleavage products. L, GPC, and NP were found to be unique by two-dimensional tryptic peptide mapping. Comparison of polypeptides immunoprecipitated from infected cells with structural components of purified virus revealed that L protein was evident in both. This is the first report of a high-molecular-weight polypeptide in Pichinde virus particles and infected cells.  (+info)