Family: Arenaviridae

Genus: Hartmanivirus

Distinguishing features

Like reptarenaviruses, hartmaniviruses infect captive snakes. In contrast to mammarenaviruses and reptarenaviruses, but similar to antennaviruses, hartmaniviruses lack the gene encoding the zinc-binding matrix protein (Z) (Hepojoki et al., 2018). 

Virion

Morphology

Virions are spherical or pleomorphic in shape, 120–150 nm in diameter, with dense lipid envelopes (Figure 1. Hartmanivirus). The virion surface layer is covered with club-shaped projections. These projections are made of trimeric spike structures of two virus-encoded membrane glycoprotein (GP) subunits (GP1 and GP2) and a stable signal peptide (SSP) (Hepojoki et al., 2018). 

Figure 1. Hartmanivirus.  Hartmanivirus particles. A) Cryo-electron micrograph of Hartmaan Institute snake virus 1 (HISV-1). Courtesy of Pasi Laurinmäki and Sarah Butcher, Cryo-EM Core Facility, Biocenter Finland, University of Helsinki, Finland. B) Negative-stain electron micrograph of HISV-1. Courtesy of Andrea Laimbacher and Elisabeth M. Schraner, Institute of Veterinary Anatomy and Virology, Vetsuisse Faculty, University of Zurich, Switzerland.

Physicochemical and physical properties

Not reported. 

Nucleic acid

Virions contain 1 ambisense and 1 negative-sense single-stranded RNA segment that are encapsidated independently. The termini of the RNAs contain inverted complementary sequences encoding transcription and replication initiation signals (Hepojoki et al., 2018). 

Proteins

Viruses express 3 structural proteins. The most abundant structural protein in virions is nucleoprotein (NP), which encapsidates the genomic segments. The least abundant protein is the RNA-directed RNA polymerase (L), which mediates virus genome replication and transcription. Glycoproteins (GP1 and GP2) are derived by post-translational cleavage from an intracellular glycoprotein precursor, GPC. A third GPC cleavage product, the stable signal peptide (SSP), stays attached to the GP complex (Hepojoki et al., 2018). 

Lipids

Not reported. SSP is likely myristoylated (Hepojoki et al., 2018). 

Carbohydrates

Not reported. 

Genome organization and replication

The S RNA of hartmaniviruses encodes two proteins in non-overlapping open reading frames (ORFs) of opposite polarities (ambisense coding arrangement) that are separated by non-coding intergenic regions (IGRs) (Figure 2. Hartmanivirus): NP in the virus genome-complementary sequence, and GPC in the virus genome-sense sequence. The L RNA encodes L in the virus genome-complementary sequence. The IGR forms one or more energetically stable stem-loop (hairpin) structures and functions in structure-dependent transcription termination and in virion assembly and budding (Hepojoki et al., 2018). 

Figure 2. Hartmanivirus.  Schematic representation of the bisegmented hartmanivirus genome organization. The 5'-and 3'-ends of both segments (S and L) are complementary at their termini, likely promoting the formation of circular ribonucleoprotein complexes within the virion. GPC, glycoprotein precursor; L, RNA-directed RNA polymerase; NP, nucleoprotein. Intergenic regions (IGRs), which form hairpin structures (not shown), separate open reading frames.

Biology

Hartmaniviruses were first discovered in Helsinki, Finland, in a captive boa constrictor (Squamata: Boidae: Boa constrictor Linnaeus, 1758) that was co-infected with a reptarenavirus and had boid inclusion body disease (BIBD) (Hepojoki et al., 2015). Several distinct hartmaniviruses were since isolated in boa constrictor I/1Ki cells. Whether hartmaniviruses cause disease in snakes remains to be determined (Hepojoki et al., 2018). 

Derivation of names

Hartmanivirus: from Haartman Institute, located at the University of Helsinki in Finland, the place where Hartmaan Institute snake virus 1 was first discovered (Hepojoki et al., 2015). 

Species demarcation criteria

Not applicable. 

Relationships within the genus

Phylogenetic relationships across the genus have been established from maximum likelihood trees generated from complete of NP and L proteins (Figure 3. Hartmanivirus). 

Related, unclassified viruses

Virus names and abbreviations are not official ICTV designations.