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At least 73 records · Page 4Linked to original sources
PubMed1987

Standardization of a plaque assay for Lassa virus.

The plaque reduction neutralization test (PRNT) has been used routinely in serological studies with such arenaviruses as Junin, Machupo, and Parana. However, difficulties have been encountered in using the PRNT for LCM virus, while conflicting views have been expressed about the reliability and efficacy of the test with Lassa virus. We have therefore investigated and evaluated the plaque assay for Lassa virus. In addition, the suitability of the PRNT for determining the potency of a serum and its efficacy in passive immunization for the treatment of Lassa fever was also investigated. The Lassa virus plaque assay satisfied the criteria proposed by Cooper [1961] for determining satisfactory plaque technique. Lassa virus plaques appear within 3 days of inoculating Vero cell cultures. By day 5, the plaques are clearly defined, discrete, and measure 1.5 to 2.0 mm. In the plaque reduction neutralization test, the use of native non-inactivated serum was required for a reliable and reproducible determination of serum antibody titer. The potency and suitability of a serum for Lassa fever serotherapy was determined by the use of a constant serum-varying virus (CS-VV) and/or a constant virus-varying serum (CV-VS) PRN technique.

Animals↗
PubMedDate not supplied

[Serological evidence of Lassa virus circulation in the Republic of Guinea].

Seroepidemiological investigations in Guinea were carried out to estimate the areas of Lassa virus circulation. The recombinant protein of Lassa virus nucleocapsid was used as the antigen to analyse blood sera by ELISA. In some regions, from 30 to 54.9% of the population had antibodies to Lassa virus, but in others only 6-7%.

Adolescent↗
PubMedDate not supplied

[The cultivation and physicochemical properties of the Josiah strain of the Lassa virus].

Data on the stability of Lassa virus, Josia strain, isolated from man to the effect of physicochemical factors (heating at 50 degrees C, solutions of urea and formalin of various concentrations, UV irradiation) as well as on the time course of this strain reproduction in cell lines of different origins are presented. Recommendations for lowering of reactogenicity of the virus-containing material are given. The experimental results must be taken into consideration in the development and manufacture of diagnostic and therapeutic-prophylactic preparations for Lassa fever.

Animals↗
PubMed1990

Lassa virus glycoproteins: antigenic and immunogenic properties of synthetic peptides to GP1.

Synthetic peptides corresponding to predicted Lassa virus GP1 glycoprotein B-epitopes were used to study the antigenicity and immunogenicity of the protein. ELISA results showed that guinea pig polyclonal anti-Lassa virus serum bound effectively to peptides corresponding to amino acid residues 119-133 and 164-176 of the GP1 protein. Essentially it did not react to a peptide corresponding to GP1 amino acid residues 234-256. Sera obtained against peptides representing amino acid residues 119-133 and 164-176 reacted with inactivated purified Lassa virus.

Amino Acid Sequence↗
PubMedDate not supplied

[Immunization of rabbits with Lassa virus].

The parameters of humoral and cell-mediated immunity after inoculation of the infectious and inactivated antigen of Lassa virus to rabbits which are insusceptible to this infection were studied. Lassa virus antigen was demonstrated to induce synthesis of specific antibodies in rabbits the level of which was proportional to the dose of inoculation and the time of immunization. The results of leukocyte blastogenesis test and delayed type hypersensitivity test confirm the development of sensitization to inactivated Lassa virus in immune rabbits.

Animals↗
PubMed1993

Cross-protection against lymphocytic choriomeningitis virus mediated by a CD4+ T-cell clone specific for an envelope glycoprotein epitope of Lassa virus.

Recombinant vaccinia virus expressing the Lassa virus (LV) envelope glycoprotein precursor, V-LSGPC, was used to study the basis of LV-induced cross-protective immunity against the closely related arenavirus lymphocytic choriomeningitis virus (LCMV). C3H/HeJ mice primed with V-LSGPC developed neither circulating antibodies nor CD8+ cytotoxic T cells specific for LCMV, yet they resisted a normally lethal LCMV challenge. Spleen cells from such mice gave a proliferative response to LCMV in vitro that was inhibitable by anti-CD4 antibody. Synthetic peptides corresponding to predicted T-cell sites common to the envelope glycoprotein precursor (GP-C) of LV and that of LCMV were used to map the specificity of the proliferative response to an epitope located between amino acids 403 and 417 of LV GP-C. Several CD4+ T-cell clones specific for the 403-417 peptide were isolated and found to produce gamma interferon in response to both the peptide and LCMV. One of these clones, C9, was selected for further study. C9 lysed I-AK-bearing target cells, and when adoptively transferred to C3H/HeJ mice, it was capable of mediating both a peptide-specific delayed hypersensitivity reaction and resistance to lethal LCMV challenge. These collective findings demonstrate, for the first time, that CD4+ T cells can play a major role in arenavirus-specific cross-protective immunity.

Amino Acid Sequence↗
PubMedDate not supplied

[Experimental evaluation of the pathogenicity of Lassa virus variants].

Pathogenicity for guinea pigs and white mice of various Lassa virus variants: native, having had 1 passage in Vero cell culture and 4 passages in newborn white mouse brain; a virus having gone through 10 passages in Vero cells and 8 mouse brain passages (variant No. 10); a small-plaque clone derived from variant No. 10 by the method of plaque-to-plaque cloning (variant No. 11k), was studied. Both the native virus and variant No. 10 were found to be similarly pathogenic for susceptible laboratory animals, while the small-plaque variant of Lassa virus became non-fatal for guinea pigs and white mice. The decline of pathogenic properties in variant No. 11k was shown not to be associated with the presence of temperature-sensitive mutants or defective interfering particles.

Animals↗
PubMedDate not supplied

Imported lassa fever in Germany: molecular characterization of a new lassa virus strain.

We describe the isolation and characterization of a new Lassa virus strain imported into Germany by a traveler who had visited Ghana, Côte D'Ivoire, and Burkina Faso. This strain, designated "AV," originated from a region in West Africa where Lassa fever has not been reported. Viral S RNA isolated from the patient's serum was amplified and sequenced. A long-range reverse transcription polymerase chain reaction allowed amplification of the full-length (3.4 kb) S RNA. The coding sequences of strain AV differed from those of all known Lassa prototype strains (Josiah, Nigeria, and LP) by approximately 20%, mainly at third codon positions. Phylogenetically, strain AV appears to be most closely related to strain Josiah from Sierra Leone. Lassa viruses comprise a group of genetically highly diverse strains, which has implications for vaccine development. The new method for full-length S RNA amplification may facilitate identification and molecular analysis of new arenaviruses or arenavirus strains.

Adult↗
PubMed1974

Lassa virus isolation from Mastomys natalensis rodents during an epidemic in Sierra Leone.

Lassa fever is a severe febrile illness of man, first recognized in West Africa in 1969. During an epidemic in Sierra Leone, Lassa virus was isolated for the first time from wild rodents of Mastomys natalensis. A high prevalence of infected Mastomys was found in houses occupied by patients with Lassa fever. The data presented provide the first demonstration of an extra-human cycle of Lassa virus transmission and suggest that rodent control may be an effective method of limiting the disease.

Animals↗
PubMed1993

Evaluation of the polymerase chain reaction for diagnosis of Lassa virus infection.

We evaluated the polymerase chain reaction (PCR) and hybridization procedures for diagnosis of Lassa fever. Primers were derived from a region of the small RNA segment of Lassa virus coding for the glycoprotein. Serum samples stored for a 14-year period from patients in Sierra Leone, West Africa were examined retrospectively. Blinded samples were then tested prospectively. Eighty-eight virus isolation-negative control sera were negative by PCR and hybridization. In the retrospective study, virus was isolated from 51 of 98 specimens from patients with Lassa fever, and 33 of these were positive for Lassa virus RNA by PCR, and 42 by PCR and hybridization. Fifteen were positive by PCR and hybridization but isolation-negative, and nine were positive by isolation but PCR/hybridization-negative. Thirty-two were negative by all methods (sensitivity by PCR/hybridization compared with virus isolation 0.82, specificity 0.68). In a prospective blinded study of 195 patient sera, 51 were positive by PCR and virus isolation, and 24 were PCR positive but virus isolation-negative (sensitivity 0.66, specificity 0.71). After hybridization, 66 virus isolation-positive sera were positive. The sensitivity was 0.86 and the specificity was 0.59, and the probability of false-positive results compared with virus isolation was 32%, (chi 2 = 21.9, by McNemar's test). Since some specimens may not have contained viable virus, we re-analyzed the data of individual patients using laboratory-confirmed case definitions for Lassa fever. All specimens from patients in whom Lassa fever was excluded by serologic tests were negative by PCR/hybridization.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMedDate not supplied

[Electron microscopic study of Lassa virus].

Ultrafiltration through hollow fibrous filters followed by purification in interrupted and linear urografin gradients yielded a Lassa virus suspension of high concentration. The use of gamma-irradiation for inactivation of the frozen virus suspension (-70 degrees C) caused no apparent structural changes of virions and made it possible to examine Lassa virus in electron microscope by negative staining. The observed virus particles in their morphology and sizes did not differ from previously described particles of other members of the Arenaviridae family. In ultrathin sections of Lassa virus-infected Vero cells, atypical virions were sometimes visible alongside with typical particles. Within one type of such particles no ribosome-like granules could be detected. Such "hollow" particles may possibly be defective virions. Another kind of atypical particles contained homogeneous electron-dense core and resembled mycoplasma. Of greatest interest are the particles with heterogeneous core in which "sandy" granules can be distinguished. The presence of greater amounts of uranophilic material than usually may be explained by getting into the virion in the process of its formation of a greater amount of genetic material than that present in typical virions.

Animals↗
PubMed2006

The role of myristoylation in the membrane association of the Lassa virus matrix protein Z.

The Z protein is the matrix protein of arenaviruses and has been identified as the main driving force for budding. Both LCMV and Lassa virus Z proteins bud from cells in the absence of other viral proteins as enveloped virus-like particles. Z accumulates near the inner surface of the plasma membrane where budding takes place. Furthermore, biochemical data have shown that Z is strongly membrane associated. The primary sequence of Z lacks a typical transmembrane domain and until now it is not understood by which mechanism Z is able to interact with cellular membranes. In this report, we analyzed the role of N-terminal myristoylation for the membrane binding of Lassa virus Z. We show that disruption of the N-terminal myristoylation signal by substituting the N-terminal glycine with alanine (Z-G2A mutant) resulted in a significant reduction of Z protein association with cellular membranes. Furthermore, removal of the myristoylation site resulted in a relocalization of Z from a punctuate distribution to a more diffuse cellular distribution pattern. Finally, treatment of Lassa virus-infected cells with various myristoylation inhibitors drastically reduced efficient Lassa virus replication. Our data indicate that myristoylation of Z is critical for its binding ability to lipid membranes and thus, for effective virus budding.

Amino Acid Sequence↗
PubMedDate not supplied

[Production of immune mediators, induced by Lassa virus, in a human mononuclear cell culture].

Infection of human mononuclear cells with Lassa virus leads to production of inflammatory cytokines (tumor necrosis factor and interleukin-1). These cytokines cause expression of adhesion receptors ICAM-1 and VCAM-1 by human endothelial cells. Mitogen-induced cell proliferation was not suppressed 1 h after infection of human mononuclear cells with Lassa virus in a dose of 0.01 PFU/cell. The capacity of cells to proliferation in response to mitogen stimulation decreased significantly only 4 h after infection.

Cell Division↗
PubMed1977

Isolation of an arenavirus closely related to Lassa virus from Mastomys natalensis in south-east Africa.

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.

Africa, Northern↗
PubMed2006

Mutational analysis of the lassa virus promoter.

The promoter sequences directing viral gene expression and genome replication of arenaviruses reside within the 3' and 5' termini of each RNA segment. The terminal 19 nucleotides at both ends are highly conserved among all arenavirus species and are almost completely complementary to each other. This study aimed at characterizing the Lassa virus promoter in detail. The relevance of each position in the promoter was studied by site-directed mutagenesis using the Lassa virus minireplicon system. The data indicate that the Lassa virus promoter functions as a duplex, regulates transcription and replication in a coordinated manner, and is composed of two functional elements, a sequence-specific region from residue 1 to 12 and a variable complementary region from residue 13 to 19. The first region appears to interact with the replication complex mainly via base-specific interactions, while in the second region solely base pairing between 3' and 5' promoter ends is important for promoter function.

Base Pairing↗
PubMed2006

Role of interferons in the control of Lassa virus replication in human dendritic cells and macrophages.

Lassa fever is a hemorrhagic fever caused by Lassa virus (LV), which primarily targets human dendritic cells (DC) and macrophages (MP). Massive numbers of viral particles are released with no effect on the viability, activation or maturation of these cells. LV does not inhibit the activation of cells induced by sCD40L or LPS. We report here the consequences of exogenous activation of LV-infected human DC and MP for viral replication. The activation of cells with lipopolysaccharide or exogenous poly(I-C) and the transfection of cells with poly(I-C) strongly inhibited LV replication, at least partly by inducing type I interferon (IFN) synthesis. In contrast, cell stimulation with sCD40L did not induce type I IFN responses or inhibit LV release. Recombinant type I IFNs strongly inhibited LV replication in both cell types, whereas IFNgamma and IFNlambda did not. The modest type I IFN production observed in LV-infected MP, but not in DC, was involved in controlling LV replication in MP. These results provide an explanation for the slower replication of LV in MP than in DC, and suggest that type I IFNs are crucial in the control of LV.

Animals↗
PubMed1975

Lassa virus hepatitis. Observations on a fatal case from the 1972 Sierra Leone epidemic.

During a recent outbreak of Lassa fever in Sierre Leone, a 20-year-old woman developed an acute febrile disease with tonsillar exudates and hemorrhagic manifestations. Lassa virus was isolated in cell cultures from pharyngeal secretions and pleural fluid and was identified by complement fixation. Typical arenavirus particles were observed in these infected cell cultures. In a liver biopsy specimen, diffuse hepatocellular damage and focal necroses were evident, with a spectrum of liver cell change, ranging from slight vacuolizaiton to frank lysis. Virus was frequently observed in nearby extracellular spaces and was clearly associated with hepatocytes rather than sinusoidal cells. The demonstration for the first time of Lassa virus particules in human tissue provides direct evidence that the virus is responsible for the observed pathologic changes.

Disease Outbreaks↗
PubMed1982

Pathology of Lassa virus infection in the rhesus monkey.

The clinical signs and gross and microscopic lesions of Lassa virus infection in the rhesus monkey are described. Of 17 monkeys infected with Lassa virus, nine died or were killed when moribund. The clinical signs were lethargy, aphagia, constipation, fever, conjunctivitis, and skin rash. Pulmonary congestion, pleural effusion, pericardial edema, hydropericardium, and a few visceral hemorrhages were present grossly. Major microscopic lesions were necrotizing hepatitis and interstitial pneumonia. Other microscopic changes were present in the heart, small intestine, spleen, lymph nodes, kidney, urinary bladder, adrenal glands, and central nervous system; however, most of these lesions were mild. In fact, death could not always be attributed to the morphologic changes; therefore, function alterations must be examined.

Animals↗