ICTV Virus Taxonomy Profile: Arenaviridae.

Members of the family Arenaviridae produce enveloped virions containing genomes consisting of two or three single-stranded RNA segments totalling about 10.5 kb. Arenaviruses can infect mammals, including humans and other primates, snakes, and fish. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the family Arenaviridae, which is available at www.ictv.global/report/arenaviridae.

Cell culture and electron microscopy for identifying viruses in diseases of unknown cause.

During outbreaks of infectious diseases or in cases of severely ill patients, it is imperative to identify the causative agent. This report describes several events in which virus isolation and identification by electron microscopy were critical to initial recognition of the etiologic agent, which was further analyzed by additional laboratory diagnostic assays. Examples include severe acute respiratory syndrome coronavirus, and Nipah, lymphocytic choriomeningitis, West Nile, Cache Valley, and Heartland viruses. These cases illustrate the importance of the techniques of cell culture and electron microscopy in pathogen identification and recognition of emerging diseases.

Isolation of an arenavirus from a marmoset with callitrichid hepatitis and its serologic association with disease.

Callitrichid hepatitis (CH) is an acute, often fatal viral infection of New World primates from the family Callitrichidae. The etiologic agent of CH is unknown. We report here the isolation of an arenavirus from a common marmoset (Callithrix jacchus) with CH by using in vitro cultures of marmoset hepatocytes and Vero-E6 cells. Enveloped virions 67 to 133 nm in diameter with ribosomelike internal structures were seen in infected cultures. Immunofluorescence and Western immunoblot analysis using CH-specific antisera (principally from animals exposed to CH during zoo outbreaks) revealed three antigens in cells infected with this CH-associated virus (CHV). These antigens had the same electrophoretic mobilities on sodium dodecyl sulfate-polyacrylamide gels as did the nucleocapsid, GP2, and GPC proteins of lymphocytic choriomeningitis virus (LCMV). Monoclonal antibodies specific for these arenavirus proteins also reacted with the three CHV antigens. Conversely, the CH-specific antisera reacted with the nucleocapsid, GP2, and GPC proteins of LCMV. CHV thus appears to be a close antigenic relative of LCMV. The serologic association of CHV with several CH outbreaks implicate it as the etiologic agent of this disease.

The 3' end termini of the Tacaribe arenavirus subgenomic RNAs.

Tacaribe virus (TV), a member of the Arenaviridae family, contains two single-stranded RNA genome segments called S and L. Two proteins, in an ambisense coding strategy, are encoded in both the S RNA and the L RNA. The 3' ends of the TV four putative mRNAs have been characterized using S1 nuclease mapping. The experiments revealed that the transcripts terminate within the intergenic region in each RNA segment. No special sequences that might function as termination signals were evident. The 3' end sequences of the four putative mRNAs can be predicted to adopt GC-rich stable hairpin configurations (delta G greater than or equal to -25 kcal). These observations suggest that the transcript structure rather than particular sequences might be the signal involved in the termination of arenavirus transcription.

Infection and coding strategies of arenaviruses, phleboviruses, and nairoviruses.

The infection and coding strategies of three groups of negative-stranded RNA viruses (arena viruses, phleboviruses, and nairoviruses) that include the etiologic agents of hemorrhagic disease in humans have been studied. Arenaviruses have two viral RNA species. The smaller RNA species (S) codes for the viral nucleoprotein (N protein) and for the viral glycoprotein species (G1 and G2, which are derived from a precursor glycoprotein, GPC). The S RNA has an ambisense arrangement. The proteins are translated from subgenomic mRNA species (viz., N protein from a viral-complementary mRNA and glycoprotein from a viral-sense mRNA). The larger arenavirus RNA species (L) is presumed to code for the viral transcriptase/replicase. Phleboviruses and nairoviruses are members of the Bunyaviridae. They both have three species of viral RNA. Other than the sizes of the viral proteins and the viral RNA species, virtually nothing is known about the coding strategy of nairoviruses. Phleboviruses have an ambisense coding arrangement to their smallest (S) RNA species. This S RNA codes for the viral N protein (translated from a viral-complementary mRNA) and a nonstructural protein (translated from a viral-sense mRNA). The middle-size (M) RNA of phleboviruses codes for a precursor to the viral glycoproteins (translated from a viral-complementary mRNA). The largest viral RNA (L) is presumed to code for the viral transcriptase/replicase.

Electron microscopy and antigenic studies of uncharacterized viruses. I. Evidence suggesting the placement of viruses in families Arenaviridae, Paramyxoviridae, or Poxviridae.

During approximately 35 years, investigators in various laboratories studying arbovirus ecology and epidemiology accumulated many virus isolates, more than 60 of which were not characterized or placed in taxa. By a combination of electron microscopic and antigenic studies we collected information sufficient to provisionally classify 60 isolates. Electron microscopic observations suggest that 20 are members of the virus family Bunyaviridae, 20 Rhabdoviridae, 14 Reoviridae, one Togaviridae, one Paramyxoviridae (Mapuera virus, from a bat), and one Poxviridae (Yoka virus, from mosquitoes). Serologic studies provided evidence sufficient to place some of these viruses in recognized antigenic groups, within families and genera, and to establish new antigenic groups and taxa for others. Three viruses were found to have morphologic and morphogenetic characteristics consistent with those of members of the family Arenaviridae: Quaranfil virus, a human pathogen, Johnston Atoll virus, isolated from birds and ticks, and Araguari virus, isolated from an opossum. This, the first in a series of three papers, described methods used for these investigations and also presents descriptions of viruses provisionally placed in the families Arenaviridae, Paramyxoviridae, or Poxviridae. Descriptions of viruses provisionally placed in families Bunyaviridae and Reoviridae are published in the second and third papers, respectively. Viruses of the family Rhabdoviridae have been described separately.

[Electron microscopic study of Lassa virus]. / Elektronno-mikroskopicheskoe izuchenie virusa Lassa.

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.

Localization of an arenavirus protein in the nuclei of infected cells.

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.

Fine structure analysis of Pichinde virus nucleocapsids.

The structure and organization of the ribonucleoprotein (RNP) complex of an arenavirus, Pichinde virus, was investigated. The basic configuration of the RNP was found to be a linear array of globular subunits or nucleosomes, 4 to 5 nm in diameter, that represent individual molecules of the major N polypeptide. This filament appears to fold progressively through a number of intermediate helical structures, 12 to 15 nm in diameter, that reveal an increasing number of nucleosomes associated with each turn of the helix. They range from a fragile configuration of two or three nucleosomes per turn to a more stable fibre in which the nucleosomes cannot be resolved. The strands were shown to form closed circles and it appeared that the twisting of these circular forms resulted in the formation of 20 nm-thick fibres which were seen in isolated viral core structures. The association of these RNP structures with other viral components is discussed.