Family: Filoviridae

Genus: Dianlovirus

Distinguishing features

Měnglà virus (MLAV) is the only currently classified dianlovirus. Like cuevaviruses, orthomarburgviruses, and Bombali virus (BOMV) and possibly other orthoebolaviruses, dianloviruses infect bats. Dianlovirus genomes are highly reminiscent in organization of orthomarburgvirus genomes but contain four rather than only one gene overlap (Yang et al., 2019, Makenov et al., 2023).

Nucleic acid

The dianlovirus genomes is a linear non-segmented RNA molecule of negative polarity. Genomic RNA is about 18.5 kb (Yang et al., 2019) and is likely uncapped and not polyadenylated.

Proteins

Dianloviruses express seven structural proteins, all of which are homologous to those of cuevaviruses, orthoebolaviruses, and orthomarburgviruses (Table 1.Dianlovirus). After VP40, the second most abundant structural protein in virions is assumed to be the nucleoprotein (NP), which encapsidates the dianlovirus genome. The least abundant protein is assumed to be the large protein (L), which mediates dianlovirus genome replication and transcription via its RNA-directed RNA polymerase (RdRP) domain. The dianlovirus ribonucleoprotein (RNP) complex likely consists of NP, RNP complex-associated protein (VP24), polymerase cofactor (VP35), transcriptional activator (VP30), and L. These RNP complexes associate with the matrix protein (VP40), which lines the inner side of the virion membrane and GP₁ and GP₂, which form globular spikes on the outside of the virion membrane (Yang et al., 2019).

Table 1.Dianlovirus. Location and functions of dianlovirus structural proteins.

IFNA1, interferon alpha 1; IFNB1, interferon beta 1; IRF3, interferon regulatory factor 3; MX1, MX dynamin like GTPAse 1 (formerly MxA); NEDD4, NEDD4 E3 ubiquitin protein ligase; NPC1, NPC intracellular cholesterol transporter 1; PRKRA, protein activator of interferon induced protein kinase EIF2AK2 (formerly PACT); RNP, ribonucleoprotein; STAT1, signal transducer and activator of transcription 1; TSG101, tumor susceptibility 101; VP, virus protein

Genome organization and replication

The dianlovirus genome has the gene order 3′-NP-VP35-VP40-GP-VP30-VP24-L-5′ (Figure 1.Dianlovirus). The undetermined extragenic sequences at the extreme 3′-end (leader) and 5′-end (trailer) of the genome are assumed to be conserved and to be partially complementary. Genes are flanked by conserved transcriptional initiation and termination (polyadenylation) sites. Four dianlovirus genes overlap (Yang et al., 2019).

Figure 1.Dianlovirus. Schematic representation of dianlovirus genome organization. Genome is drawn to scale. Wavy lines indicate incomplete genome ends.

The replication strategy of dianloviruses remains to be studied but is assumed to be highly similar to that of orthomarburgviruses and reminiscent of that of cuevaviruses and orthoebolaviruses. Dianlovirions are assumed to associate with attachment factors at the plasma membrane that mediate infection by endocytosis. Dianlovirus GP₁ and GP₂ are assumed to mediate cell surface C-type lectin binding and subsequent low-pH-dependent fusion into endosomes, followed by GP₁ and GP₂ binding to the endosomal receptor NPC intracellular cholesterol transporter 1 (NPC1), which is also used by cuevaviruses, orthoebolaviruses, and orthomarburgviruses. Uncoating is presumed to occur in a manner analogous to that of other mononegaviruses. Dianlovirus transcription and genome replication likely take place in the cytoplasm and, in general, follow the models for other members of the Filoviridae family. Transcription starts at the conserved transcriptional initiation site, and polyadenylation occurs at a stretch of uridine residues within the transcriptional termination site. The 5′-terminal non-coding sequences favor hairpin like structures for all mRNAs. Replication involves the synthesis of full-length positive-sense copies (antigenomes). During infection, it is assumed that massive amounts of nucleocapsids accumulate intracellularly and form intracytoplasmic inclusion bodies. Virions are likely released via budding from plasma membranes (Figure 3.Filoviridae) (Yang et al., 2019).

Biology

Dianloviruses were discovered in 2019 by high-throughput sequencing of samples taken from an apparently healthy Rousettus sp. bat in China (Yang et al., 2017, Yang et al., 2019, Makenov et al., 2023).

Antigenicity

Initial studies indicate that MLAV is antigenically distinct from other filovirids, but more closely related to orthomarburgviruses than to orthoebolaviruses (Sherwood and Hayhurst 2019).

Species demarcation criteria

The genus currently includes only a single species.

Related, unclassified viruses

Virus names, the choice of exemplar isolates, and virus abbreviations, are not official ICTV designations.