Genus Arenavirus

Type Species	Lymphocytic choriomeningitis virus	(LCMV)

Virion Properties

Morphology

Virions are spherical to pleomorphic, 50-300  nm in diameter (mean 110-130  nm), with a dense lipid envelope and a surface layer covered by club-shaped projections, 8-10  nm in length. A variable number of electron dense, 20-25  nm ribosomes are generally present within virus particles. Isolated nucleocapsids, free of contaminating host ribosomes, are organized in closed circles of varying length (450-1300  nm) which have been shown to assume supercoiled forms, and display a linear array of nucleosomal subunits (Fig. 1).

Physicochemical and Physical Properties

Virion Mr has not been determined. The S_20w is 325-500S. The buoyant density in sucrose is about 1.17-1.18  g/cm³, in CsCl it is about 1.19-1.20  g/cm³, in amidotrizoate compounds it is about 1.14  g/cm³. Virions are relatively unstable in vitro, and are rapidly inactivated below pH 5.5 and above pH 8.5. Virus infectivity is inactivated at 56°C, by treatment with organic solvents, or by exposure to UV- and gamma-irradiation.

Nucleic Acid

The genome consists of two ambisense ssRNA molecules, L and S, of length about 7.5  kb and 3.5  kb respectively. There are no poly(A) tracts at the 3-termini. The 3 terminal sequences (19-30  nts) are similar between the two RNAs and between different arenaviruses. Overall, they are largely complementary to the 5-end sequences. Although the RNA genomic species are thought to be present in virions in the form of circular nucleocapsids, the genomic RNA is not covalently closed. Variable amounts of full-length viral-complementary RNAs (predominantly S) and viral subgenomic mRNA species have been reported in virus preparations. Preparations of purified virus may also contain RNAs of cellular origin with sedimentation coefficients of 28S, 18S and 4-6S. These include ribosomal RNAs. The viral mRNA species are presumably associated with encapsidated ribosomes. The ratios of the S to L RNA species are not equimolar, apparently due to the packaging of multiple RNA species per virion.

Proteins

The most abundant structural protein is the nucleoprotein (N or NP), a non-glycosylated polypeptide (Mr about 63 10³) found tightly associated with the virus genomic RNA in the form of a ribonucleoprotein complex or nucleocapsid structure. A minor component is the L protein, an RNA polymerase (Mr about 200 10³). A putative zinc binding protein (Z or p11; Mr 10-14 10³) is also a structural component of the virus. Two glycosylated proteins (GP1 or G1, GP2 or G2; Mr 34-44 10³) are found in all members of the family and are derived by post-translational cleavage from an intracellular precursor, GPC (Mr about 75-76 10³). Other minor proteins and enzymatic activities have been described associated with virions including poly(U) and poly(A) polymerases, and a protein kinase that can phosphorylate N. It is thought unlikely that these are virally encoded.

Lipids

Lipids represent about 20% of virion dry weight and are similar in composition to those of the host plasma membrane.

Carbohydrates

Carbohydrates in the form of complex glycans on GP1 (5 or 6 sites in LCMV) and GP2 (2 sites in LCMV) represent about 8% of virion dry weight.

Genome Organization and Replication

The L and S RNAs of arenaviruses each have an ambisense coding arrangement (Fig. 2). The L RNA encodes in its viral-complementary sequence the L protein, and in the viral-sense 5-end sequence the Z protein. The Z mRNA is small (<0.5  kb). The N protein is encoded in the viral-complementary sequence corresponding to the 3-half of the S RNA, while the viral glycoprotein precursor (GPC) is encoded in the viral-sense sequence corresponding to the 5-half of S. The two proteins are made from subgenomic mRNA species transcribed from the viral (for N mRNA) or full-length viral-complementary S RNA species (for GPC mRNA). The intergenic regions of both S and L RNAs contain nucleotide sequences with the potential of forming one or more hairpin configurations. These secondary structural features may function to terminate mRNA transcription from the viral and viral-complementary S RNAs. The mRNAs are capped and contain 1-5 non-templated nucleotides of heterogeneous sequence at their 5-ends. The mRNAs are not polyadenylated. The transcription mechanism is not fully elucidated. Initiation of transcription may involve cap-snatching. The 3-termini of the mRNAs have been mapped to locations in the intergenic regions.

The process of infection involves attachment to cell receptors (undefined), entry via the endosomal route, uncoating and mRNA transcription in the cytoplasm of infected cells. Because of the ambisense coding arrangement, only N and L mRNAs can be synthesized from the genomic RNAs by the virion polymerase prior to translation. The products of these mRNAs are presumed to be involved in the synthesis of full-length viral complementary species which serve as templates for the synthesis of GPC and Z mRNAs and the synthesis of full-length viral RNAs. The process of RNA replication, which may involve a slippage mechanism during initiation, and read-through of transcription termination signals, has not been fully elucidated. However, the presence of full-length viral-complementary genomic RNAs and viral subgenomic mRNA species in virus preparations may affect this perceived temporal order of RNA and protein synthesis.

The viral envelope glycoproteins are synthesized in cells as a single mannose-rich precursor molecule which is proteolytically cleaved and processed to contain complex glycans during transport to the plasma membrane. Virions mature by budding at sites on the surface of cells. Ribosomes are also observed at such sites.

Interstrain reassortant progeny can be formed, including diploid (or multiploid) species with respect to the genomic RNA segments. Some evidence for interspecies reassortment between Lassa virus (LASV) and Mopeia virus (MOPV) has been obtained.

The replication in vitro of a number of arenaviruses is inhibited by a variety of antiviral agents, including amantadine, alpha-amanitin, glucosamine, and thiosemicarbazones. Ribavirin inhibits the replication of several arenaviruses in vitro and is effective in the therapy of humans and primates infected with LASV.

Antigenic Properties

Viruses possess a number of distinct antigenic determinants as shown by monoclonal and polyclonal antibody analyses. Antigens on the 44 10³ GP1 of Lymphocytic choriomeningitis virus (LCMV) are involved in virus neutralization. These are type-specific, although cross-neutralization tests have demonstrated partially shared antigens between Tacaribe virus (TCRV) and Junín virus (JUNV). Also cross-protection has been demonstrated against JUNV following prior infection by TCRV, or against LASV following infection by MOPV. Major complement-fixing antigens are associated with the viral N proteins, which were used to define the Tacaribe complex of arenaviruses. Monoclonal antibodies react with common epitopes on the N proteins of all arenaviruses and a single highly conserved epitope has also been described in the transmembrane GP2 glycoprotein.

By monoclonal and polyclonal antibody analyses, the African arenaviruses are distinguishable from the New World arenaviruses. Fluorescent antibody studies show that antisera against New World viruses, as well as those against African viruses, react with LCMV. Cytotoxic T-lymphocyte epitopes have been identified on the nucleoprotein and glycoproteins of LCMV. The number and location of epitopes varies depending on the virus strain and host MHC class I molecules. No hemagglutinin has been identified.

Biological Properties

The reservoir hosts of almost all the arenaviruses are species of rodents. LCMV is found in Mus and the African viruses mainly in the rodents Mastomys and Praomys, in the sub-family Murinae. The New World viruses are mostly found in the Sigmodontine rodents Calomys, Neacomys, Neotoma, Oryzomys and Sigmodon. Exceptionally, TCRV was isolated from fruit-eating bats (Artibeus spp.), but subsequent attempts to recover it from bats or from other potential hosts have been unsuccessful. It is notable that the geographic range of an arenavirus is generally much more restricted than that of its cognate rodent host. Most of the viruses induce a persistent, frequently asymptomatic infection in their reservoir hosts, in which chronic viremia and viruria occur. Such infections are known or suspected to be caused by a slow and/or insufficient host immune response. Most arenaviruses do not normally infect other mammals or humans. However, LASV is the cause of widespread human infection (Lassa fever) in West Africa (Nigeria, Sierra Leone, Liberia, Guinea), and JUNV causes Argentine hemorrhagic fever in agricultural workers in an increasingly large area of that country. Machupo virus (MACV) has caused isolated outbreaks of similar disease in Bolivia, and Guanarito virus (GOTV) (is associated with human disease in Venezuela. Sabiá virus (SABV) was isolated from a fatal human case in Brazil. Human infection with LCMV may occur in some rural and urban areas with high rodent populations, and has been acquired from pet hamsters. LCMV acquired from mice has also caused a highly fatal hepatitis in captive Callitrichid primates. Severe laboratory-acquired infections have occurred with LCMV, LASV, JUNV, MACV, SABV and Flexal virus (FLEV). Asymptomatic infections with Pichinde virus (PICV) have been reported.

Experimental infection in laboratory animals (mouse, hamster, guinea pig, rhesus monkey, marmoset, rat) varies with the animal species and the virus. In general, New World viruses are pathogenic for suckling but not weaned mice; LCMV and LASV produce the opposite effect. Viruses grow moderately well in many mammalian cells. LCMV can grow in murine T-lymphocytes.

Vertical, venereal and horizontal transmission occurs in the natural hosts, including transuterine, transovarian and post-partum, and by milk-, saliva- or urine-borne routes. Horizontal transmission within and between species occur by contamination and aerosol routes. No arthropod vectors are thought to be involved in the normal transmission process.

List of Species Demarcation Criteria in the Genus

The parameters used to define a species in the genus are (1) an association with a specific host species or group of species; (2) presence in a defined geographical area; (3) etiological agent (or not) of disease in humans; (4) significant differences in antigenic cross-reactivity, including lack of cross-neutralization activity where applicable; (5) significant amino acid sequence difference from other species in the genus. For example, although both Pirital virus (PIRV) and GTOV circulate in the same region of Venezuela, they are distinguished by their isolation from different rodent hosts (Sigmodon alstoni and Zygodontomys brevicauda respectively). Additionally in ELISA with hyperimmune mouse ascitic fluids, titers differ by at least 64-fold, and sequence analysis shows less than 55% amino acid identity in partial nucleocapsid protein sequences. In another example, both LASV and MOPV share a common rodent host (Mastomys) at the genus level. However, they are distinguished by their different geographical range, different profiles of reactivity with panels of monoclonal antibodies, and by N protein amino acid sequence divergencies of about 26%. Also, LASV is the cause of hemorrhagic fever in humans and other primates, while MOPV is not associated with human disease and does not cause disease in experimentally infected primates.

List of Species in the Genus

Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus names, natural hosts, geographic location, sequence information, accession numbers [ ] and assigned abbreviations ( ) are:

Species in the Genus

Old World Arenaviruses
Ippy virus	Arvicanthis sp., Central African Republic			(IPPYV)
Dak AN B 188d virus		N gene (partial)	[U80003]
Lassa virus	Mastomys sp., West Africa			(LASV)
GA391 virus		S segment	[X52400]
LP virus		N gene (partial)	[U80004]
Josiah virus		S segment	[J04324]
		L segment	[U73034]
Lymphocytic choriomeningitis virus
	Mus musculus, Europe, Americas			(LCMV)
Armstrong virus		S segment	[M20869]
		L segment	[J04331, M27693]
WE virus		S segment	[M22138]
Mobala virus	Praomys sp., Central African Republic			(MOBV)
3099 virus		N gene (partial)	[U80007, U80008]
3076 virus		N gene (partial)	[AF012530]
Mopeia virus	Mastomys natalensis, Mozambique, Zimbabwe			(MOPV)
AN 21366 virus, also referred to as 800150		S segment	[M33879]
AN 20410 virus		N gene (partial)	[U80005]
New World Arenaviruses
Amapari virus	Oryzomys capito, Neacomys guianae, Brazil			(AMAV)
BeAn 70563 virus		N gene (partial)	[U43685]
Flexal virus	Oryzomys spp., Brazil			(FLEV)
BeAn 293022 virus		N gene (partial)		[U43687]
Guanarito virus	Zygodontomys brevicauda, Venezuela			(GTOV)
INH-95551 virus		N gene (partial)	[L42001]
		N gene (partial)	[U43686]
Junín virus	Calomys musculinus, Argentina			(JUNV)
MC2 virus		S segment	[D10072]
XJ virus		GPC gene	[U70799]
		N gene	[U70802]
Latino virus	Calomys callosus, Bolivia			(LATV)
10924 virus		N gene (partial)	[U43688]
Machupo virus	Calomys callosus, Bolivia		(MACV)
AA288-77 virus		N gene	[X62616]
Oliveros virus	Bolomys obscurus, Argentina			(OLVV)
RIID 3229 virus		S segment	[U34248]
Paraná virus	Oryzomys buccinatus, Paraguay			(PARV)
12056 virus		N gene (partial)	[U43689]
Pichinde virus	Oryzomys albigularis, Colombia			(PICV)
3739 virus		S segment	[K02734]
Pirital virus	Sigmodon alstoni, Venezuela			(PIRV)
VAV-488 virus		N gene (partial)	[U62561]
VAV-499 virus		N gene (partial)	[U62562]
Sabiá virus	Natural host unknown, Brazil			(SABV)
SPH114202 virus		S segment	[U41071]
Tacaribe virus	Artibeus spp., Trinidad			(TCRV)
p2b-2 virus		S segment	[M20304]
T.RVL.II 573 virus		L segment	[M65834, J04340, M33513]
Tamiami virus	Sigmodon hispidus, Florida, U.S.A.			(TAMV)
W10777 virus		N gene (partial)	[U43690]
Whitewater Arroyo virus	Neotoma albigula, New Mexico, U.S.A.			(WWAV)
AV 9310135 virus		N gene (partial)	[U52180]

Tentative Species in the Genus

Pampa virus	Bolomys sp., Argentina			(PAMV)
PAn 18400 virus		N gene (partial)	[U66898]

List of Unassigned Viruses in the Family

None reported.

Phylogenetic Relationships within the Family

Nucleic acid sequences from the N genes of all the known arenaviruses have provided the basis for phylogenetic analysis which supports previously defined antigenic groupings and further defines virus relationships within them (Fig. 3). Sequence data derived from other regions of the genome, where available, are largely consistent with this analysis. Among the Old World viruses, LASV, MOPV and Mobala virus (MOBV) are monophyletic, while Ippy virus (IPPYV) and LCMV are more distantly related. The New World viruses can be divided into three groups on the basis of the sequence data. In group A are PIRV, PICV, Paraná virus (PARV) and FLEV from South America, together with Tamiami virus (TAMV) and Whitewater Arroyo virus (WWAV) from North America. Group B contains the human pathogenic viruses MACV, JUNV, GTOV, and SABV and the non-pathogenic TCRV and Amapari virus (AMAV). Latino virus (LATV) and Oliveros virus (OLVV) form a small separate group of viruses (group C). The division of the arenaviruses into Old World and New World groups, as well as the subdivision of New World arenaviruses into three groups, is strongly supported by bootstrap resampling analysis (Fig. 3). It is important to note that the trait of human pathogenicity appears to have arisen on at least two independent occasions during arenavirus evolution.

Similarity with Other Taxa

None reported.

Derivation of Names

Arena: from Latin arenosus, “sandy” and arena, “sand”, in recognition of the sand-like ribosomal contents of particles in thin section. The name originally proposed was arenovirus, but was subsequently changed to avoid possible confusion with adenovirus.